Myxidium anatidum

The bile duct of a bird is probably the last place you'd expect to find a microscopic, parasitic relative of jellyfish, but that is exactly what the study featured in this post is all about. The parasite in question is a myxozoan, a type of single-celled parasites with complex life cycles which are found in a range of vertebrate animals. Evolutionary speaking, they're technically animals, but for whatever reason, over the course of their evolution, they had abandoned having bodies made of multiple cells to become the only known group of unicellular animals.

Left: Histology section show Myxidium anatidum spores in the bile duct, Centre: Myxidium anatidum myxospore under brightfield (top) and Nomarski Interference Contrast, Right: Photo of a bald eagle.
Photos from the paper (left), this paper (centre), and US Fish and Wildlife Service

There are over 2000 known species of myxozoan and most of them are usually found in fish, though there are also some species that infect amphibians and turtles. The myxozoan parasite being featured in this host was found in a rather unexpected host - a bald eagle, of all things. This eagle was found in Western Canada and was found in very poor condition prior to its death. The parasite's spores were found throughout the eagle's bile duct. While that may sound concerning, the parasite clearly played no role in the eagle's death. That's because based on the bird's condition when it was found and the toxicology findings, the eagle had died from lead poisoning. 

So why would a bald eagle be harbouring a type of parasite which is usually associated with fish and amphibians? While it is true that most myxozoan tend to be found in cold-blooded aquatic or semi-aquatic animals, some discoveries over the last decades have shown warm-blooded land-dwelling animals are not beyond the reach of these single-celled jellyfish cousins, and that includes the parasite found in the eagle's bile duct - Myxidium anatidum, a species that seems to specialise on our feathered friends

Myxidium anatidum was initially described back in 2008 from seven species of ducks (hence the "anatidum" species name) collected from across different parts of the United States. Much like with that bald eagle, the parasite resided in the bile duct and most of those infected ducks had died of other causes. This discovery overturned a lot of the previous assumptions about myxozoans and what they're capable of infecting, but since then there hasn't been any new findings about this peculiar parasite, which is still surrounded in mysteries. One such mysteries is the parasite's life cycle.

For other myxozoans, they have a complex life cycle which involves an asexual stage living in a vertebrate animal host, and the sexual stage living in either segmented worms or bryozoans (moss animals). But it is currently unknown how M. anatidum infects its feathery host, nor what invertebrate it infects for the sexual stage of its life cycle. 

When M. anatidum was initially discovered, researchers examined worms and fish from one of the ponds where an infected duck was collected, and while they did find some which were infected with myxozoans, none of them had M. anatidum. In nature, the prevalence of myxozoans in their worm hosts can be rather low, so it is possible that they had simply missed the infected worms, or the parasite was only present in worms during certain seasons, or perhaps the ducks have picked up the infection from elsewhere. Given what is known about myxozoan life cycles, since many ducks are dabblers, it is conceivable that they might have acquired the parasite through swallowing infected worms which had been hiding in the muck. 

But in that case, how did a bald eagle end up contracting this parasite? Bald eagles primarily eat fish, so it is possible that M. anatidum may have been using fish as a type of "paratenic host" - an animal that serves as an optional stopover that can potentially carry the parasite to its nominal host. It's kind of like going on a side quest which could help you complete the main goal. While the use of paratenic hosts is common among other parasites with complex life cycles, it has not been reported for myxozoans. But then again, myxozoans haven't been reported in bald eagles until now.

Since lead poisoning was what actually led to the infected eagle's death, there may be many other healthier bald eagles flying around with M. anatidum lurking in their bile duct. Between the eagles and the ducks, this humble parasite is clocking up some frequent flyer miles which its fish-infecting cousins could never hope to match. 

Reference:

Perdrizet, U. G., Lockerbie, B., & Bollinger, T. K. (2026). Myxidium anatidum in a Bald Eagle Haliaeetus leucocephalus from Western Canada. Journal of Wildlife Diseases 62: 257-259.

Forficuloecus pezopori

Parasites are a major part of biodiversity, but they spend most of their time hidden in plain sight. Even with some animals that have been known to science for centuries, their parasite fauna remains completely unknown. This can either be due to the lack of research interest into their parasites, or the host animal is just really rare, so there has been very little to no opportunities to study the parasites that live on or in them. In some cases, those rare animals are at risk of going extinct, which means their parasites and symbionts may also disappear before we even know they exist. This post is a story about a ground parrot and its hidden louse.

Left: Forficuloecus pezopori louse viewed under light microscope, Right: a western ground parrot (Pezoporus flaviventris).
Both photos from graphical abstract of the paper

The parasite being featured in this post is Forficuloecus pezopori, and it is the first known parasite from the western ground parrot (Pezoporus flaviventris), also known as Kyloring. Kyloring is one of the rarest parrots in the world and is considered critically endangered, which is bad news for F. pezopori, because we have barely gotten to know this little insect, and it may already be at risk of disappearing along with its feathered host. Lice are particularly vulnerable to co-extinction as they are completely helpless off the host's body and are often specifically adapted to living on just one particular host species.

Forficuloecus pezopori was found on some captive ground parrots at Perth Zoo, the lice were hanging around the feathers at the back of the birds' head and nape. As far we know, the western ground parrot is the only host for this parasite. There is a slim chance that it might also be found on the western ground parrot's closest relative, the eastern ground parrot (Pezoporus wallicus), but we can't verify that at this point, because we know so little about the parasites of ground parrots in Australia.

For example, a subspecies of eastern ground parrot in Tasmania was found to support a type of feather mite called Dubininia pezopori but it is uncertain whether that mite is unique to just that particular subspecies, or if it is also found on the mainland eastern ground parrots, since nothing is actually known about the parasites and symbionts of those birds. Given the eastern and western ground parrot have been separated since the Pleistocene about 2 million years ago, there would have been enough separation in time and space for the two species to develop their own distinct collection of parasites. So as far as we can tell, the Kyloring is the only host for F. pezopori.

Parasites on endangered hosts such as the Kyloring are in a precarious position, because not only are they at risk of dying out alongside their hosts, historically, there have been cases of parasites being wiped out in the process of people trying to conserve their hosts. For example, during the California condor breeding program, a unique species of condor louse was wiped out due to the pesticide-based delousing that the birds received when they were taken into captivity. And the California condor louse is not the only victim of extinction via conservation efforts. The Iberian lynx louse also suffered the same fate. 

Even more tragic is the case of Rallicola extinctus - a louse of the Huia, which was a species of New Zealand bird that became extinct early in the 20th century, with its last confirmed sighting in 1907. But the louse that it hosted was not even formally described until 1990 - many decades after the host had already gone extinct, hence the species name R. extinctus. Forficuloecus pezopori and many other lice species are at risk of such entangled fates, or become victims of well-meaning conservation efforts.

While a lot of people may not mourn the loss of parasites, it might be their hosts that end up missing them the most. The presence of parasites may help them develop a properly functioning immune system, and their absence could leave the host with a range of physiological disorders. And these parasites might be better off together with their hosts as they can tell us a lot about how the host animals live, and the ecosystem they exist in.

To rectify the mistakes of the past, the researchers suggested that any future studies on wild populations of ground parrots should incorporate a routine louse check to see how common F. pezopori are among those birds, but not to remove any of the lice that are found, and just let those little insects be. Especially since they don't seem to harm healthy, wild parrots. At the same time, lice infection on captive birds can serve as an opportunity to learn more about F. pezopori - saving the host along with its parasites at the same time

Living organisms are intertwined within a network of ecological interactions, if you pull on one loose thread you might trigger a series of co-extinctions and unravel the entire tapestry. Because of those connections, we could be losing more species than we realise.  Though they are often hidden out of sight, and thus out of minds, losing parasites and symbionts would leave us with emptier ecosystems and a lesser world.

Reference:

Martin, S. B., Keatley, S., Wallace, A., Vaughan-Higgins, R. J., & Ash, A. (2024). A critically co-endangered feather louse Forficuloecus pezopori n. sp.(Phthiraptera: Philopteridae) detected through conservation intervention for the western ground parrot Pezoporus flaviventris (Psittaculidae). International Journal for Parasitology: Parasites and Wildlife 24: 100931.

Prosthogonimus cuneatus

Prosthogonimus is a genus of flukes that live in a special part of a bird's anatomy. It is usually found either in the Bursa of Fabricius, an organ that only birds have, or in the oviduct, and it's this latter location which lend this parasite its common name, the oviduct fluke. This fluke is found all over the world in many different species of birds, and while it doesn't seem to cause much issues for wild birds, it presents a major problem for the poultry industry.

Left: Dragonflies Sympetrum vulgatum (top) and Sympetrum depressiusculum (bottom), Right: A metacercaria cyst of Prosthogonimus cuneatus. Photos from Fig. 2 and Fig. 3 of the paper

Since this fluke lives by clinging to and feeding on the surface of mucosal membranes, its activities can leave lesions and cause inflammations, and heavy infection of Prosthogonimus can lead to all kinds of oviduct disorders in chickens. This includes leaking milky discharges from the cloaca, laying soft-shelled or malformed eggs, or even egg peritonitis, where egg yolk material gets displaced into the hen's body cavity, leading to secondary infections and death. In some cases, the fluke can even end up getting bundled into the egg itself, which seems pretty mild compared with what I have mentioned above, but it would nevertheless be a nasty surprise for anyone looking to make an omelette. To make matters worse, there are currently no effective treatments available for getting rid of this fluke once a bird is infected.

So how do birds end up with this peculiar parasite? Prosthogonimus has a multi-host life cycle that takes it across three very different animals - freshwater snails, dragonflies, and birds. In the dragonfly, the larval Prosthogonimus lies in wait as a dormant cyst called a metacercaria, waiting for its host to get eaten by a bird. That is why this parasite is usually associated with free-range chickens, as they have more opportunity to feed on a variety of things. Most studies on Prosthogonimus have focused on the effects it has on the bird hosts, but surprisingly fewer studies have investigated the source of the infection - parasitised dragonflies.

To rectify this oversight, a group of researchers undertook a truly herculean effort to investigate the presence of Prosthogonimus in dragonflies from the Heilongjiang province, China. The researchers collected over TEN THOUSAND dragonflies, composed of 12 different species from 41 locations. They identified each of the dragonflies before dissecting them for Prosthogonimus metacercariae, which are usually located in the abdominal muscles. The researchers noticed that infected dragonflies tend to have softer abdominal muscles, possibly due to injuries caused by the presence of the Prosthogonimus cysts.

They found three different species of Prosthogonimus in those dragonflies, of which Prosthogonimus cuneatus was the most common. Overall, about 20% of the dragonflies they examined were infected by Prosthogonimus, but it was more common in some species than others. The spotted darter (Sympetrum depressiusculum) was most frequently infected (28.53% prevalence), followed closely by the vagrant darter (Sympetrum vulgatum) (27.86% prevalence) and the autumn darter (Sympetrum frequens) (20.99% prevalence). The highest number of fluke larvae in a single dragonfly goes to an unlucky Sympetrum kunckeli which was packed with 157 Prosthogonimus metacercariae in its abdomen.

But dragonflies are aerial predators - how do they end up being infected with fluke larvae which are shed from freshwater snails? Well, before becoming acrobatic flying hunters, dragonflies spend their early life as underwater predators. But this aquatic life also expose them to Prosthogonimus' waterborne larvae, which are drawn into the dragonfly nymph's body through its respiratory current - in other words, they get sucked through the dragonfly nymph's butt whenever it takes a breath. Even as the dragonflies metamorphose into airborne adults, they carry the legacy from their youth in the form of Prosthogonimus cysts

Overall, the study found that Prosthogonimus was most common in Heihe, which might be due to the presence of large wetlands in the area. Those wetlands are home to high levels of biodiversity which help support the life cycle of this parasite - they provide habitats for numerous snails that can host the asexual stage of Prosthogonimus, along with wild birds that would usually act as the final host for this parasite. Just add dragonflies, which are always common around water bodies, and the circle of life is complete for Prosthogonimus.

Studying and elucidating the life cycles and ecological role of parasites in their natural context is an important part of disease ecology research. Understanding what these parasites actually do in nature can help us prevent them from causing problems in the animals that we raise.

Reference:

Li, B., Lan, Z., Guo, X. R., Zhang, A. H., Wei, W., Li, Y., Jin, Z. H., Gao, Z. Y., Zhang, X. G., Li, B., Gao, J. F., & Wang, C. R. (2023). Survey of the Prosthogonimus spp. metacercariae infection in the second intermediate host dragonfly in Heilongjiang Province, China. Parasitology Research 122: 2859-2870.

Bothrigaster variolaris

Student guest post time! One of the assessments that I set for students in my ZOOL329 Evolutionary Parasitology class is for them to summarise and write about a paper that they have read in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) here on the Parasite of the Day blog. So from the class of 2023, here’s a post by Nikita Sheelah, about a bird of prey with too many flukes.

To dare to do what hasn’t been done before has been the driving force behind many advancements in society, such as the creation of vaccines, anime, or the ground-breaking Reese’s Peanut Butter Cups. Being the first in recorded history to do something different essentially immortalises people in the history books, which often carries incredible pride and achievement. This seems to be the case for a group of trematode flukes (Bothrigaster variolaris) which infected a snail kite (Rostrhamus sociabilis), and made their way into the bird’s air sacs, causing the snail kite’s fatal end. 

Left: Snail Kite, photo taken by Bernard DuPont, used under Creative Commons (CC BY-SA 2.0) license. 
Right: Bothrigaster variolaris fluke from Fig. 6 of the paper. Centre Insert: Bothrigaster variolaris fluke on the pericardium of the Snail kite's heart from Fig. 1 of the paper

“Big deal,” you say, “trematodes infect air sacs in birds all the time.” And you’re right! Death from trematodes infecting air sacs is fairly common,  but this has mostly been reported in Passeriformes; birds known to be more susceptible to these parasites. It has even been reported in snail kites themselves, but that was in Florida rather than South America. Every continent needs its own firsts, after all. 

So how did this even happen? Let me explain. Snail kites, as you might have ingenuously guessed from the name, eat snails! Apple snails (Pomacea spp.), to be precise. Trematodes in the Cyclocoelidae family use snails as their hosts for the larval stage, meaning when those snails are eaten, little baby trematodes get to grow up into a mature adult in the body of whatever ate the snail (usually birds). So, much like eating too many candy apples can rot your teeth with cavities, the snail kite indulged in too many infected apple snails and rotted their insides. With flukes. Not cavities. And the insides weren’t rotten, just parasitised. That wasn’t that great of an analogy, actually. 

A wildlife rehabilitation hospital brought this male adult snail kite into their care and did their best to help him, but he passed shortly after arrival. Immediately afterwards, a necropsy was performed to poke and prod at his insides, taking tissue samples and collecting the flukes. Not the most dignified funeral rites, but it’s all in the name of science, because over 200 flukes were counted in the bird! Thirty-five were collected for DNA analysis and were identified to be in a distinct clade within the Cyclocoelidae family. The physical characteristics of the flukes backed this up, especially the ventral sucker, which is characteristic to the genus Bothrigaster within that family.

Researchers concluded that the bird most likely died from suffocation due to the obstruction by the parasites, as well as lesions in the respiratory tissue. They also noted a mature trematode in one of the wing bones, which is a pretty uncommon spot for a parasitic flukes to be. What an adventurer!

So, these ambitious Cyclocoelidae made history by being the first reported trematodes to have caused death by air sac infection in snail kites in south America. Realistically, this may happen more than we think, and has probably been happening for quite some time, but being the first trematodes to be written about in this sense is a pretty big feat! Their mothers must be so proud. 

References: 

Díaz, E., Donoso, G., Mosquera, J. M., Ramírez-Villacís, D., González, G. T., Zapata, S. C., & Cisneros-Heredia, D. F. (2022). Death by massive air sac fluke (Trematoda: Bothriogaster variolaris) infection in a free-ranging snail kite (Rostrhamus sociabilis). International Journal for Parasitology. Parasites and Wildlife 19: 155–160.

This post was written by Nikita Sheelah

Leucochloridium passeri

Leucochloridium paradoxum is one of those parasites which is immediately recognisable on sight. Commonly known as the "zombie snail parasite", its habit of turning the eyestalks of snails into pulsating candy canes has also earned it the name "green-banded broodsac", and it has appeared in various forms of media, including the opening of the Chainsaw Man anime. But far from just being a bizarre one-of-a-kind oddity, L. paradoxum is just one out of ten known species in the Leucochloridium genus which infect amber snails and produce these "broodsacs" structures. And these colourful, pulsating sacs are the key for distinguishing different species of Leucochloridium.

Left: Snail infected with Leucochloridium passeri collected from Hemei Township (Changhua County) by Jui-An Lin, photo from Fig. 1 of the paper. Top right: Labelled L. passeri broodsac from Fig. 1 of the paper. Bottom right: A trio of L. passeri broodsacs with metacercariae removed from an infected snail, from Supplementary video 3 of the paper

The adult stage of Leucochloridium are found in birds where they dwell in the cloaca or a special organ called Bursa of Fabricius. While parasite identification is usually based upon the various anatomical features of the adult parasite, in the case of Leucochloridium, the adult flukes of different species all look rather similar to each other. In contrast, the broodsac stages come in a wide variety of colours and patterns that are extremely noticeable and unique to each species. So short of comparing their DNA sequences, the colours and stripes of the larval broodsacs are the most reliable way to tell apart the different species.

This blog post features a study on Leucochloridium passeri, a species that was first described as adult flukes from Eurasian tree sparrows in Guangdong, and has subsequently been found across the Indomalayan realm. It is one of five different Leucochloridium species found in Taiwan, but it is the only one for which their broodsac stage has been documented. While not as well known as L. paradoxum, its broodsacs nevertheless present an attention-grabbing sight. You might recognise it from this video, which has gone viral and been posted all over the internet, usually without credit or attribution of the original source.

It can be easily distinguished from L. paradoxum and other Leucochloridium species by a distinctive wide band of red-brown patches or longitudinal stripes in the mid-section of each mature broodsac. Many people who have some familiarity with this parasite would know about the pulsating sacs forcing their way into the snail's eye tentacles, but what they might not know is that those are only part of the entire parasite mass residing within the snails.

Those pulsating "broodsacs" are actually the parasite's asexual larvae. In addition to the very flamboyant mature broodsacs, there are also translucent immature broodsacs which are tucked away deeper in the snail's body. Digenean flukes have an asexual stage in their life cycle, and in most flukes they produce hundreds to thousands of sausage-shaped asexual larvae in the snail's body. Those wriggly sausages would then give birth to free-swimming larvae called cercariae that are release into the environment where they infect the next host in the life cycle. In the case of Leucochloridium, the cercariae stay in those wriggly sausages and develop into round, jelly-coated cysts within the snail. Each mature broodsac can contain up to two hundred cysts, so when a bird swallows one of these colourful wriggling sausages, they are inviting hundreds of flukes to take up residency in their cloaca.

The L. passeri broodsacs described in this study were found in Yilan County in Taiwan, and they look very similar to some Leucochloridium broodsacs which have been found in Okinawa, Japan. They both have the distinctive wide band of red-brown stripes and splotches, and when researchers compared their DNA sequences, they found that they both belong to the same species - Leucochloridium passeri.

Relatively little is known about the birds that can serve as the final hosts for L. passeri, but researchers have noticed that the distribution of various Leucochloridium species in different zoogeographical regions seems to be related to the distribution of birds and amber snails which are native to those particular regions. Since some of those birds are migratory, this provides Leucochloridium with the means to cross oceans while seated snugly in the butt of their feathery host, ready to settle down wherever there are amber snails to infect. 

Reference:

Chiu, M. C., Lin, Z. H., Hsu, P. W., & Chen, H. W. (2022). Molecular identification of the broodsacs from Leucochloridium passeri (Digenea: Leucochloridiidae) with a review of Leucochloridium species records in Taiwan. Parasitology International 102644.

P.S. Leucochloridium is a very distinctive parasite and has been subjected to numerous artistic depictions, here's my own artistic depiction of Leucochloridium in the form of a Parasite Monster Girl.

Guimaraesiella sp.

Quite a few years ago I wrote a blog post about a study on some bird lice that hitch-hike on louse flies as a way of reaching new hosts - this type of interaction whereby an organism attach itself to the body of another as a way of getting around is called "phoresy". And while it is a fascinating interaction with important ecological implications, this phenomenon is not particularly well-studied. Well, the paper that is being featured in this blog post revisited that field of research, and used multiple approaches to investigate this type of interaction. And the researchers behind it did so by combining literature review, traditional parasitology, DNA barcoding, and citizen science.

Left: Guimaraesiella lice found on from louse flies. Right: Louse fly with lice attached (indicated by red arrows). 
From Figure 3 of the paper.

The researchers of this study were trying to figure out how common phoresy is among bird lice, and who exactly is hitch-hiking on what. They conducted a review of the existing scientific literature on phoretic relationships between lice and louse flies, and found that many of the older records were unusable because they lack sufficient details regarding species identity of the lice involved. Furthermore, while phoretic behaviour in lice is most well-documented in North America and Europe, there are other parts of the world with much richer avian fauna (and thus more bird lice species), but phoretic behaviour of bird lice in those regions are not as well-studied.

To address this, the researchers came up with a way of collecting lice and louse flies from a large number of birds, and did so with some help from members of the public. As a part of long-term project to monitor bird mortality from vehicle and building collisions, ordinary citizens in Singapore were encouraged to report any dead birds that they come across. Through this, the researchers were able to track down and collect over a hundred recently deceased birds for this study. They then screened the dead birds for lice and louse flies, which were identified based on their morphology and their DNA.

In total, they screened 131 birds composed of 54 different species, and collected 603 lice and 32 louse flies. Of those, 22 birds had louse flies on them, but only three of the louse flies also happened to be carrying hitch-hiking lice, which were identified as belonging to the genus Guimaraesiella. Amidst all that, they found something unexpected - one of the birds, a Blue-winged pitta (Pitta moluccensis) was infected with louse flies carrying Guimaraesiella lice. This is the first time that Guimaraesiella lice has been found on pittas, as those birds are usually infected with lice in the Picicola genus.

It is likely that riding on louse flies is how Guimaraesiella ended up on the pitta. Indeed, lice in that genus appear to live on a wider range of birds compared with most bird lice, which are often confined to a single or handful of closely related host species, and its hitch-hiking habit may be the key to their success. While bird lice are very adept at climbing around and between their host's feathers, they are completely helpless off the host's body. This doesn't give them much opportunity to branch out and onto other bird species as they can only climb onto a new host through direct contact.

But since louse flies feed on a variety of different bird hosts, travelling on one of those flying blood-suckers can open up a whole new world of possibilities for lice that engage in phoresy. The species of Guimaraesiella lice they found on the pitta has also been found on at least 24 other species of birds, possibly more. Considering that the louse fly that Guimaraesiella rides on - Ornithophila metallica - feeds from over a hundred different bird genera, perhaps it is surprising that Guimaraesiella hasn't been found from even more bird species. So while the louse fly presents its hitch-hiker lice with many different species of birds, those well-travelled lice still stay fairly selective when it comes to where they settle on. These lice are like Goldilocks when it comes to picking a new feathery home - it needs to be just the right fit.

The approach taken by the researchers in this study to recover and screen large numbers of birds for louse flies and lice can also be applied to other parts of the world. This would help us obtain a more complete understanding of how widespread hitch-hiking lice actually are, and the role this behaviour has played in the evolution of these ectoparasitic insects.

Reference:
Lee, L., Tan, D. J., Oboňa, J., Gustafsson, D. R., Ang, Y., & Meier, R. (2022). Hitchhiking into the future on a fly: Toward a better understanding of phoresy and avian louse evolution (Phthiraptera) by screening bird carcasses for phoretic lice on hippoboscid flies (Diptera). Systematic Entomology 47: 420-429.

Parorchites zederi

Today, we are featuring a guest post from Marie Defraigne - she is an MSc student on the IMBRSea programme, and is currently working (albeit remotely) with Dr. Katie O’Dwyer at the Galway-Mayo Institute of Technology in Ireland, during her professional practice placement. This post is about a tapeworm which is commonly found among penguins of the Antarctic sea.  

Antarctica can be considered as a continent of extremes. It is so extreme that species like mosquitoes, which are found everywhere in the world, cannot survive in this bitter cold wilderness. However, there are some creatures that can persist in the Antarctic ecosystem. The most famous of these are the penguins. Penguins are a group of seabirds belonging to the family Spheniscidae, and there are many species within this family that share the same parasite: Parorchites zederi, a species of Cestoda, or tapeworm.

This parasite can mainly be found in Gentoo Penguins, Chinstrap Penguins, Adélie penguin and Emperor Penguins. The life cycle of the parasite involves multiple host animals, with krill being a known intermediate host. Since krill is an important part of the penguins’ diet, the parasite can use those crustaceans as a way of reaching their penguin hosts.

Macroscopic lesions on intestinal wall in penguins infected with Parorchites zederi, Antarctic Peninsula, 2006-2008.
(a) Intestine of adult Gentoo Penguin (Pygoscelis papua) with irregular raised nodules. (b) Heavy infection of tapeworms.
Photos from Figure 1 of Martin et al. (2016)

Tapeworm-infected penguins can end up with swellings that can be seen from the outside of the intestine, and the heaviest infections can produce yellowish-white nodules. This is a clear sign that this tapeworm negatively affects the health of the penguin. When looking more closely at the tissue, inflammation is visible with increased lymphocytes and macrophages, which are white blood cells, that form an integral part of the immune system. The presence of this tapeworm results in tissue damage and bleeding in the gut of infected penguins.

Not only do these changes lead to a reduction of normal gut functions, but the afflicted penguin probably has to endure a lot of pain when they have to digest their food in an already damaged intestine. Moreover, bacteria responsible for diarrhoea often find a cosy home in some of the tapeworm-induced lesions. No surprise then that Parorchites zederi, along with other helminths, is responsible for about 6% loss of body mass in Antarctic penguins. Losing weight is very risky business in Antarctica where insulation against the cold temperatures is vital.

Nonetheless, this tapeworm is quite common among Antarctic penguins. In some colonies of Gentoo Penguins,  parasite prevalence can even reach 100%. Given its ubiquity and the effect this parasite can have on penguin health, it is important to monitor their prevalence. Since infections with gastrointestinal parasites are closely related to foraging habits, changes in the host’s diet owing to climate change or anthropogenic impacts can lead to changes in parasite prevalence in Antarctic penguins.

In recent years there has been a decrease in sea ice cover, and because of this phenomenon, the amount of Antarctic krill has also decreased. Less krill means a lower prevalence of the tapeworms, but on the other hand it also means less food for the penguins. In this way, P. zederi can tell us more about how the Antarctic ecosystem is changing, while these penguins are faced with a constant challenge of feeding on krill and managing these problematic parasite infections.

References:

María A Martín, Juana M Ortiz, Juan Seva, Virginia Vidal, Francisco Valera, Jesús Benzal, José J Cuervo, Carlos de la Cruz, Josabel Belliure, Ana M Martínez, Julia I Díaz, Miguel Motas, Silvia Jerez, Verónica L D'Amico, Andrés Barbosa (2016) Mode of attachment and pathology caused by Parorchites zederi in three species of penguins: Pygoscelis papua, Pygoscelis adeliae, and Pygoscelis antarctica in Antarctica. Journal of Wildlife Diseases 52: 568-575.

S. Kleinertz, S. Christmann, L. M. R. Silva, J. Hirzmann, C. Hermosilla, A. Taubert (2014) Gastrointestinal parasite fauna of Emperor Penguins (Aptenodytes forsteri) at the Atka Bay, Antarctica. Parasitology Research 113: 4133–4139.

Simeon L. Hill, Tony Phillips and Angus Atkinson (2013) Potential climate change effects on the habitat of Antarctic Krill in the Weddell quadrant of the Southern Ocean. PLoS One 8: e72246.

post written by Marie Defraigne

Corynosoma australe

Most parasites are very picky about what host they infect. Even those that can infect a number of different host species usually parasitise a selected bunch from the same family or order. But sometimes circumstances can bring together unlikely parasite and host pairings. The parasite featured in this post is Corynosoma australe, and it is an acanthocephalan - a group of prickly parasites commonly called thorny-headed worms. Corynosoma australe usually infects pinnipeds, the group of marine mammals that includes seals and sea lions. But in the study featured in this blog post, researchers found this worm living in the gut of a decidedly non-mammalian host - specifically the Magellanic penguin. So how did penguins end up acquiring parasites that usually infect seals?

(A) Adult male Corynosoma australe, (B) Adult female C. australe, (C) spiny proboscis of an adult worm
Photos from Fig 4. of the paper

For this, we need to look at the life-cycle of this parasite. Like other acanthocephalans, C. australe infects an arthropod as their first host, in the case of Corynosoma, this is usually tiny shrimp-like crustaceans called amphipods. For other acanthocephalans, the life-cycle is complete when the infected arthropod is eaten by a vertebrate predator, which can be a mammal, fish, bird, reptile or an amphibian, depending on the species of acanthocephalan in question. But during the life-cycle of C. australe, it also infects what is known as a paratenic host - a host animal which is not vital to the completion of the parasite's life-cycle, but can act as a vehicle to get it to the final host. In this case, the paratenic host is a fish.

The reason why they need a paratenic host is that seals and sea lions do not usually go rummaging through the the mud for tiny thumbnail-size crustaceans. But there are fish that do, and it is those fish that seals and sea lions eat. By using fish as paratenic hosts, C. australe can bridge the ecological gap between tiny amphipods and seals. But having fish as paratenic hosts also open up other possibilities because pinnipeds are not the only marine animal with a taste for fish. This is where penguins enter the story.

Even though taxonomically, birds and mammals are on very different branches of the vertebrate animal tree, because seals and penguins lead comparable life-styles, sometimes they can also end up with similar (or in this case, the same) parasites. In this case, Magellanic penguins end up with what is usually a seal parasite because they have been eating the same fish that the seal usually feed on, and they are physiologically similar enough to seals and sea lions for C.australe to go "Eh, good enough.". In fact, C. australe seems to be a fairly versatile parasite - it has been reported from 16 different types of marine mammals and birds. However, those previous reports also indicate that the parasite can only produce viable eggs while living in pinnipeds, and in the evolutionary game it all comes to nothing if you can't reproduce. Which means while C. australe can stay alive in those non-pinniped hosts, those other hosts are effectively dead ends.

But, this study shows that not only can C. australe survive perfectly fine in penguins, they can also reproduce while living in a bird host. From the samples that the researchers examined, 19 out of the 20 seals and sea lions they looked at were infected with C. australe. In comparison, only 18 out of the 87 penguins they examined were infected. Female worms grew bigger in the gut of Magellanic penguins, yet at same time they did not produce as much eggs as those living in pinnipeds. Also for some currently unknown reason (s), the sex ratio of C. australe in penguins is highly skewed - whereas seals and sea lion have an almost one-to-one ratio of male versus female worms in their guts, females worms vastly outnumbered male worms in the gut of Magellanic penguins.

Judging from egg production and prevalence, Magellanic penguins are not exactly the most ideal or reliable hosts for C. australe. Pinnipeds remain the hosts with the most for C. australe, but at least penguins can serve as a viable (if not ideal) substitute. For C. australe living in penguins, this might be a case of ecological fitting, whereby an organism can survive and (and even thrive) in a habitat which different to the one that it usually live in because it just so happen to have the right set of adaptations that allows it to survive in this new and novel environment.

But there is another twist to this story. While most species of Corynosoma live in marine mammals, it seems that they had evolved from ancestors that originally lived in aquatic birds. So perhaps Corynosoma already has the latent ability to survive in the gut of a bird, and when circumstances brought them together, C. australe was ready. When it comes to this thorny worm, what is good enough for the sea lion is good enough for the penguin.

Reference:
Hernández-Orts, J. S., Brandão, M., Georgieva, S., Raga, J. A., Crespo, E. A., Luque, J. L., & Aznar, F. J. (2017). From mammals back to birds: Host-switch of the acanthocephalan Corynosoma australe from pinnipeds to the Magellanic penguin Spheniscus magellanicus. PloS One 12(10): e0183809.

Cardiocephaloides longicollis

Human activities are having very significant impacts on the ecosystems of this planet and it is affecting every organisms. Parasites are not exempted from that - indeed parasites with complex life-cycles which involve many different host animals are in prime position to have their usual way of life altered by human intervention. The study being featured here today is on a parasitic fluke - Cardiocephaloides longicollis - which has a life-cycle that involves a carnivorous scavenging whelks, a variety of fish, and gulls. The researchers behind this study set out to investigate how commercial fisheries is affect the transmission dynamics of this parasite.

Left: Stained specimens of C. longicollis under light microscopy from here
Right: SEM of a closely related species Cardiocephaloides physalis from here

The asexual stages of C. longicollis reside in the body of whelks which acts as a kind of clone factory for the parasite, producing a stream of swimming larvae call cercariae. These larvae then go in the water to infect a variety of different fish. While C. longicollis has previously been recorded in 19 fish species, in this study the researchers found a further 12 species which are also viable hosts for C. longicollis, making for a grand total of 31 species of fish. The final host for this parasite are gulls, which acquire the fluke when they eat parasitised fish.

When it comes to C. longicollis infections, fish that hang around near the sea floor or the coast are the most loaded, most likely because they are in close proximity to the whelks which are sources of infection. Furthermore practically all the fish above a certain size (about 14 cm in length) are infected.  Fish in those size range have on average 73 C. longicollis larvae in their brain, with one unlucky fish recorded to have 220. Ironically, while these larger fish are the motherlode when it comes to parasites as they have been accumulating parasites for longer, since they live in deeper waters they are out of the gulls' reach. So regardless of their heavy larval fluke burden, because gulls can't get to them, all those parasites are at a dead end, destined to die or end up in the stomach of another predator which is not a gull - at least not without human intervention.

Many of the 31 species of fish which C. longicollis infects are either targeted by commercial fishing operations, or end up as by-catch. Many of those by-catch fishes - some of which are loaded with parasites - are discarded at the port. This pile of of parasite-laden fish present opportunistic gulls with a rich and accessible feast. It is a similar situation at fish farms, where the researchers found over half the fish there are infected with C. longicollis. At these facilities, organic matter from left-over feedstock, fish poop, and dead fish would also attract hungry gulls. But they're not the only ones who are attending the seafood party - being opportunistic carnivores, the whelks also come along to scavenge - so you end up with a situation where two of the host for C. longicollis are hanging out at the same location.

As the gulls feed on the discarded fish, they also are also getting infected with C. longicollis. Meanwhile, the flukes which have already reached maturity in the gulls' gut from previous feeding bouts are laying eggs which get pooped out into the water, right next to the whelks which have come for the scraps. And as mentioned above, the whelks are next host in the parasite's life-cycle, and some of those attending the feast will end up serving as parasite factories for C. longicollis in the future. For these parasites, this entire arrangement is a blessing - whereas without the activities of commercial fishing many C. longicollis larvae would have been consigned to a dead end in a large, benthic-dwelling fish, never to reach their final host. Indeed, the researchers found the fluke to be more abundant in areas with intensive fishing activity and aquaculture.

Cardiocephaloides longicollis is not the only parasite benefiting from commercial fishing activities, a study published a few years ago showed that overfishing can also benefits the tongue-biter parasite. A more recent study shows that clams living at commercially harvested sites are more heavily infected with parasitic flukes. While this does not apply for all parasites, as many would actually be negatively affected by commercial harvesting as their host population dwindles, for some species like C. longicollis human activities provide them with a rich opportunity for expansion.

Reference:
Born-Torrijos, A., Poulin, R., Pérez-del-Olmo, A., Culurgioni, J., Raga, J. A., & Holzer, A. S. (2016). An optimised multi-host trematode life cycle: fishery discards enhance trophic parasite transmission to scavenging birds. International Journal for Parasitology 46: 745-753.

Confluaria podicipina

Most of the time, being infected with parasites is costly to the host in some way. But sometimes there might be circumstance when the presence of parasites might be a good thing. For brine shrimps (known to most as "sea monkeys"), it seems like tapeworm larvae might be a worthwhile accessory - admittedly one that turns you bright red and make you more likely to be eaten by a bird.

Photo of infected (red) and uninfected (transparent) brine shrimps
From Fig 1 of the paper

The study being featured today were based on a population of brine shrimps living at salt marshes in southwestern Spain which are infected by nine different species of tapeworm larvae. The most common species are Flamingolepis liguloides (which have previously been featured on this blog here) and Confluaria podicipina. At the site where the scientists conducted this study, about two-thirds of the brine shrimps were infected with either F. liguloides or C. podicipina, and about a third of them are unlucky enough to be simultaneous infected by both species (alongside a bunch of other less common species).

All these parasites are using the shrimps as a temporary vehicle for getting into final host where they can mature into adult worms, and for that to happen, the shrimp needs to be eaten by a bird. However, in the environment that these shrimps dwell in, tapeworms like C. podicipina can convey some unexpected benefits. It seems that shrimps infected with tapeworms are more resistant towards arsenic.

Previously, we have featured a study on how tapeworms can act as a sink for heavy metal in seabirds soaking up the toxin before they get absorbed into the host's tissue. But that study was on adult tapeworms living in the gut of a bird host. Though they are also tapeworms, the physiological interaction between an adult tapeworm in the gut of a vertebrate host is very different to that of a larval tapeworm residing inside a small arthropod.

Flamigolepis liguloides cysticerocoid (larger one on the left) and Confluaria podicipina cysticercoid (indicated by arrows)
From Fig 2 of the paper

In this case, the tapeworm larvae increased the level of various fatty substances - C. podicipina increases triglyceride level, while F. liguloides increase the amount of lipid in the host. Together, these fatty droplets help soak up any arsenic in the brine shrimp. Additionally, the tapeworms also help the shrimp sequester carotenoid which enhances the shrimp's capacity to produce antioxidant enzymes which mops up harmful free radicals, and help the shrimp deal with the presence of arsenic in their bodies.

Whereas F. liguloides seems to be present in high numbers all the time, C. podicipina only appear in April. This might be related to the seasonal movement of their final host - which are flamingos in the case of F. liguloides, but for C. podicipina, the final hosts are grebes, which only visit the lake during certain time of year. Indeed, that was the finding of a previous study which has been featured on this blog.

Additionally, it seems that the brine shrimps are better at handling arsenic in May when they are mostly only infected with F. liguloides. So why is that the case? Well, it could be that (1) C. podicipina is not as good at helping their host deal with arsenic, (2) it is harmful to the host in other ways that offset their detoxification effects, and (3) it only appears during the warmer months when the brine shrimp's overall resistance to arsenic is lower anyway, so it simply coincided with their appearance.

Of course, neither F. liguloides and C. podicipina are doing this as some kind of favour to the host - C. podicipina and its fellow tapeworm larvae are doing this for their own benefit. They are manipulating host physiology to make the host a more suitable shelter and vehicle for reaching the final host - increasing the fat content of the host makes it a cosier site for development, and increasing the carotenoid level makes the shrimp bright red and stand out more to the bird host. But it just so happens that all these changes also have a side effect of benefiting the shrimp, even if temporarily, before they end up between the beaks of a bird

Reference:
Sánchez, M. I., Pons, I., Martínez-Haro, M., Taggart, M. A., Lenormand, T., & Green, A. J. (2016). When Parasites are Good for Health: Cestode Parasitism Increases Resistance to Arsenic in Brine Shrimps. PLOS Pathogen 12(3): e1005459.

Trichobilharzia szidati

If you have ever gone for a swim in a lake and later found your arms and legs covered in red itchy welts resembling mosquito bites, it is quite likely that you have encounter parasites related to the one being featured today. Trichobilharzia szidati is an avian blood fluke, and it has relatives living all over the world in both freshwater and marine environments. While they usually infect waterbirds like duck, they are not very good at telling birds apart from humans. To them, any warm-blooded terrestrial vertebrate animal is fair game, which is rather unfortunate for both humans and flukes alike - more so for them than us. As a result of this encounter, we end up covered in intensely itchy spots, but getting under the skin of a human means immediate death for such flukes.

Cercaria of Trichobilharzia regenti, a species related to T. szidati
Scale bar = 200 μm. Photo from this paper

So why is that the case? Blood flukes are masterful molecular mimics - they are able to disguise themselves with proteins that resembles the host's own molecules, allowing them to stealthily sneak pass the host's immune system. But Trichobilharzia szidati and similar avian blood flukes have evolved to bypass the immune system of birds, and when it encounters a mammalian immune systems like ours - all bets are off. Our immune system takes immediate action against this intruder with extreme prejudice, which results in an inflammatory reaction that manifest itself as "duck itch" or "swimmer's itch".

But aside from getting inside the circulatory systems of ducks or giving us a nasty itch, it seems that trematode larvae like those of T.szidati are also making a contribution to the environment which usually get overlooked.

As a part of their lifecycle, parasitic flukes turn snails into parasite factories - churning out a continuous stream of free-swimming parasite larvae called cercariae, which in the case of T. szidati is the stage that infects birds and cause us temporary grief. But most of these cercariae don't actually end up infecting a bird or getting (and dying) under the skin of an unsuspecting human swimmer. The majority of them end up entering the food web as food for a range of other animals. To aquatic insects and fish, the swimming parasite larvae is simply another tasty morsel. Alternatively, the cercariae simply use up their limited energy reserves and expire, becoming food for all manner of scavengers and detritivores. So how much food is being provided by these tiny parasite larvae?

In the study being featured today, scientists collected some T. szidati-infected snails from a fish pond in Czech Republic and made daily observations on the amount of cercariae they were pumping into the environment. The noticed that most cercariae came streaming out upon first light in the morning, in order to coincide with the daily routine of the bird host, then dwindled as the day went by. But throughout the day, it adds to to hundreds and thousands of larvae.

When they conducted the first set of observations in April, they found that on average infected snails were releasing about 1000 cercariae per day, with a maximum of over 4500. However, when they made another series of observation again in September, the average daily output was ten times that of the snails they studied in April, with a maximum output of almost 30000 cercariae per snail per day. It is worth noting that while they made four sets of observations for the April sample, only one set was conducted during September, which means the sample could have be skewed by an unusual sample. Additionally, the snails in the September sample were larger than those from April, and larger hosts are usually able to produce more parasite larvae. But these are the kind of seasonal and individual variations which would have exist in the natural environment anyway.

Since each infect snails are releasing thousands of cercariae per day, though they are microscopic, those contributions really adds up. Based on the numbers they obtained from the study, the research estimated that over its lifetime, an infected snail produce as much as its own body mass (or more) in the form of T. szidati larvae. Therefore, in a large fish pond with a relatively low infection prevalence such as 5%, the infected snails would be contributing about a 500 kilograms of biomass per year in the form of T. szidati cercariae. But in some location where almost half the snails are infected at any given period, the yearly output of all these snails can add to to 4.65 tons of parasite larvae, which weighs as much as an Asian elephant.

Trichobilharzia szidati and other avian blood flukes do not exist in isolation - the snails they infect can also host an entire communities of other flukes species, some of which have been recorded to churn out even more cercariae than T. szidati. When you put them together, they provide quite a substantial food source for all the aquatic organisms that they share the environment with. These parasitic flukes are the unseen elephant(s) in the pond.

Reference:
Soldánová, M., Selbach, C., & Sures, B. (2016). The Early Worm Catches the Bird? Productivity and Patterns of Trichobilharzia szidati Cercarial Emission from Lymnaea stagnalis. PloS One 11: e0149678.

Trichomonas gypaetinii

What does the cause of pigeon canker, today's parasite, and the most common curable sexually transmitted infection in the world have in common? All of them are parasites from the genus Trichomonas. The species that causes pigeon canker is T. gallinae, a protozoan that lives in the upper gastrointestinal tract of pigeons, and it is currently posing a significant threat California's only native pigeon. While T. gallinae does not always cause disease, when the host is stressed, the parasite multiplies, causing lesions to develop in the throat and mouth of their host. The host eventually dies from starvation as the lesions makes it difficult for them to swallow anything. It is possible that a parasite like T. gallinae might have even brought down the occasional Tyrannosaurus rex over 65 million years ago - though the culprit is most likely to have been a different (but similar) species of parasite given how long ago that it all happened.

Photo composed from Fig. 5 & 6 of the paper

With T. rex being one of the most badass dinosaur of all time, it is appropriate that the species of Trichomonas that we are featuring today - T. gypaetinii - is found in some pretty badass living dinosaurs as well. This parasite was first isolated from a bearded vulture (Gypaetus barbatus) - which I am sure most would agree  is a very handsome and intimidating bird. When T. gypaetini was initially isolated, it was not fully described as a species, as there was insufficient material  to do so. However, this study reports on newer samples obtained from a wide epidemiological study of avian trichomonosis in Spain. The research team managed to obtain isolates of T. gypaetini from another two species of vultures - the Egyptian Vulture (Neophron percnopterus) and the Black Vulture (Aegypius monachus) - and now we have a formal description.

So what differentiates T. gypaetinii from canker-causing T. gallinae? There was nothing about their appearance which separates the two species, but when the research team did some genetic analysis on the parasite, they found that all the Trichomonas samples from vultures were perching on their own branch, far away from T. gallinae. When they search for previously published sequences of Trichomonas from vultures, they hit upon the previously undescribed isolate from the bearded vulture mentioned earlier.

So where does T. gypaetinii sit on the Trichomonas family tree? Genetically, T. gypaetinii is actually more similar to T. vaginalis - a sexually transmitted parasite that infects over 160 million people worldwide each year - most of the time without them being aware of it as most cases show no symptoms. Much like those cases of T. vaginalis infection, T. gypaetinii does not appear to cause any problems to their bird host either.

Furthermore, it seems that T. gypaetini is only found in carrion-feeding birds. Other birds of prey can get infected by T. galinae - the canker-causing species - through eating other birds, especially pigeons. But the vultures' comparatively specialised diet and digestion physiology (especially that of the bone-munching bearded vulture) means that  T. gypaetinii is the only Trichomonas that can successfully make vultures their hosts.

Reference:
Martínez-Díaz, R. A., Ponce-Gordo, F., Rodríguez-Arce, I., del Martínez-Herrero, M. C., González, F. G., Molina-López, R. Á., & Gómez-Muñoz, M. T. (2015). Trichomonas gypaetinii n. sp., a new trichomonad from the upper gastrointestinal tract of scavenging birds of prey. Parasitology Research 114: 101-112.

Oxyspirura petrowi

Photo by USFWS Endangered Species

The Lesser Prairie-Chicken (Tympanuchus pallindicintus) is a very distinctive bird. During breeding season, the males aggregate to put on an elaborate courtship display composed of raised feathers, a series of rapid stomping followed by "booming" and inflating a pair of bright orange air sacs on the side of their necks. But life as a prairie chicken is not so great these days, since the early 1900s, their population and range has shrunken by over 90 percent, mostly due to habitat loss and fragmentation from agriculture and industrial developments.

On top of that, they have to deal with Oxyspirura petrowi - a nematode (roundworm) parasite that lives in their eyes - on the front and/or behind the eyeballs. And these worms aren't small either, they can grow to more than 15 mm long and they feed on blood too, causing severe haemorrhaging and swelling around the eyes. So being infected with O. petrowi can cause a significant impairment to the host. Based on studies on a related species - Oxyspirura mansoni (which infects poultry) - it is most like that the prairie chicken are infected when they eat arthropods which contain the larval stage of the worm and research is still under way to try and figure out which arthropod is the carrier.

Photo of Oxyspirura petrowi from fig 1 of this paper

The lesser prairie-chicken is not the only bird that gets infected by O. petrowi, this worm also infects various game birds like pheasants and quails, as well as some migratory songbirds. If a bird cannot see properly, then it is not going be very good at flying without eventually hitting something. And some prairie-chickens have been reported to fly into vehicles or even the side of barns. Obviously such birds are not going to be very good at evading predators if they cannot even avoid flying into a barn. So is the worm also contributing to the prairie chicken's decline, or something else?

Mercury and lead are both metals that can contaminate the environment as by-products of burning fossil fuel, spent ammunition, and industrial activities. Both have well-documented toxicity effects on animals including neurological damage that results in sensory impairment, convulsions and behavioural disorders. Another common pollutant is organochloride. While organochloride pesticides have been banned or restricted for years, they can linger in the environment for a long time and accumulate up the food chain. In high enough dosage, such pesticides have been known to cause reproductive impairment as well as convulsion and emaciation in birds.

The researchers behind this study analysed the level of these chemical pollutants in the organs of some prairie chickens from Kansas, and while they found traces of all three in the prairie chicken's organs, they were all below the level at which they would being harmful. The level of organochloride was just as they had expected given the birds were from an area that used to be a farmland. As for the two metals, the lead levels lower than toxicity level and the levels of mercury were below detectable limits.

What they did find was a higher prevalence of O. petrowi than they had expected from the region, and some of the birds they examined had up to 16 worms in their eyes. It is worth noting that the birds these researchers sampled were donated by hunters, so it is likely that the eyeworms made them easier targets. So is O. petrowi playing a role in the prairie chicken's decline? It seems unlikely given that birds like bobwhites have been documented to be infected with even higher levels of this worm. But its presences is certainly not helping and may interfere with some conservation practices.

For example, one current conservation practice to put up signs and coloured marking tape around fence lines to reduce bird-fence collisions. The idea is that the fences are clearly marked out so the prairie chickens can avoid running into them. But if they are half-blind from having a bunch of worms in their eyes, they might instead end up using those markers as targets and fly headlong into the fence.

When trying to protect any species in a complex environment, it is important to also take their parasites into account, as their presence might confounds your expectations. To save the prairie chickens, you might first have to understand the eyeworm.

Reference:
Dunham, N. R., Peper, S. T., Baxter, C. E., & Kendall, R. J. (2014). The Parasitic Eyeworm Oxyspirura petrowi as a Possible Cause of Decline in the Threatened Lesser Prairie-Chicken (Tympanuchus pallidicinctus). PloS One 9, e108244.

P.S. You can read my article about other blinding parasites in The Conversation here.

Columbicola columbae

You would think that of all living things, parasites would have the least need to move around. After all, it is sitting in its ideal habitat and is already (in a way) surrounded by food. Why would it need to go anywhere else? But most parasites usually reside at a very specific part of the host's body - at some stage, it would have had to makes its way there somehow, even if it stays in one spot after that. Furthermore for some parasites, where they live on the host is not the same as where they eat, so they have to commute regularly in order to get their meal ticket.

Photo by Vince Smith at phthiraptera.info

One such parasite is the humble pigeon louse (Columbicola columbae), which is usually found hanging out on the wing feathers of pigeons. It has evolved a narrow body that allows it to fit snugly between the barbs of the flight feathers and safe from the preening beak of the host. But while wing feathers are a nice place to seek shelter, they do not make for such an appetising meal - they are far too tough for C. columbae to chew on. So when the pigeon louse gets hungry, it needs to make a move to the body region where the more palatable, downy feathers are found.

So how does C. columbae find its way from the wing to the body? It's not like it can just look up Google Pigeon or something like that and get directions. Well, based the study we are featuring today on this blog, they use temperature to find their way.

Like us, birds are homeotherms - which means they keep a consistent body temperature, regardless of the outside environment. But even for a homeothermic animal, the temperature is not consistent across the body. For example, the temperature at the wings and tail of a pigeon is about 32 °C (89.6 °F), whereas the body region temperature is approximately 36 °C (96.8 °F). So are the lice using temperature differentials across parts of the pigeon's body as a cue for navigation? To find out, a pair of researchers did a series of experiments to determine what temperature the lice preferred under different circumstances.

They did a choice experiment where they put some pigeon lice in a glass petri dish with one end resting on top of a heated metal block. They also did another experiment where they placed some lice on a piece of filter paper sit on a heating apparatus that they built to generate a radial temperature gradient. In both experiments, they recorded where the lice moved to and found while the lice did respond according to the temperature differences, it was also dependent on whether they were hungry or not.

Lice which had a full belly prefer to hang out at 32 °C (wing region temperature), but those that have been experimentally starved for 18-20 hours tend to move to where it is 36 °C (body region temperature). But if down feathers are so tasty, why don't they just hang out there all the time? While the pigeon's main body is covered in tastier feathers, it is also more exposed to the murderous beak of a preening host. Whereas on the wings, the skinny body of C. columbae allows it to tuck itself between the barbs of the pigeon's flight feathers, and stay safe and sound.

So some lice like it hot, but only if they are hungry.

Reference:
Harbison, C. W., & Boughton, R. M. (2014). Thermo-orientation and the movement of feather-feeding lice on hosts. Journal of Parasitology 100: 433-441.

Sarcocystis cernae

This is the fifth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Reece Dalais that he had titled "A fuzzy shuttle bus to a feathery airport" about what the parasite Sarcocystis does to its vole host (you can read the previous post about a midge that sucks blood from the belly of mosquitoes here).

Photo from here

Many protozoan parasites make use of one or more hosts before finally infecting the host species with suitable real estate for sexual reproduction (e.g. Sarcocystis dispersa and S. putorii). These ‘intermediate’ hosts act as temporary living quarters, in which the parasite accumulates resources, multiplies and then prepares for the trip to the next neighbourhood. In the Netherlands, the protozoan parasite Sarcocystis cernae, uses its intermediate host, the common vole (Microtus arvalis), to multiply itself and then as a vehicle to its honeymoon suite – the small intestine of the common kestrel (Falco tinnunculus). In the lining of the kestrel’s intestine, S. cernae lays its sporocysts, (which are equivalent to eggs) which leave the intestine with the stool of the bird.

Voles forage daily at regular intervals before scurrying back underground. During this time, they can accidentally consume kestrel faeces as they eat vegetation. Once inside the common vole, S. cernae develop in the rodent’s liver before entering its bloodstream and then declaring war on its muscles. In the vole’s musculature the parasite sits tight, and multiplies (asexually) to form large cysts – known as statocysts – which contain numerous bodies capable of sexual reproduction – or cystozoites. These cystozoites break free to reproduce (sexually) once the vole is torn apart and ingested by an adult kestrel or its young – which become the future protozoan distributors. In the mid to late 1980s, it was been discovered by a pair of scientists (Hoogenboom and Dijkstra) that infection with S. cernae makes the vole twice as likely to be taken in aerial attacks. The reason for this is still under question, and has oddly been ignored by researchers since 1987. Could it be due to some form of host manipulation whereby S. cernae forces a change in the behaviour in the vole? Or is it merely a helpful side effect caused by the protozoan running amuck inside the vole’s muscles?

Photo by Małgorzata Miłaszewska

The researchers collected vole samples by snap trapping and from nest boxes during the breeding season. Voles brought to the kestrel nestboxes for their young were taken and replaced them with lab mice of a similar weight – so feeding could continue as usual. Once these voles were dissected, the results revealed that 92% of infected voles had cysts present in the locomotory muscles (the biceps, triceps and quadriceps) – the muscles responsible for movement. Hence it is likely that infected voles were slower to escape the kestrels than their Sarcocystis-free pals. However, it was also proposed that once a vole becomes infected with S. cernae they may be forced to find food at dangerous times. Without infection, voles forage at the same time as other voles and, as a group, are more aware of predators. So if these inbuilt rhythms were to be interrupted by a parasite, the vole would become an easier target. This would be an example of host manipulation, as S. cernae, would be forcing the vole to change its foraging behaviour.

Although the effect of S. cernae on the common vole is not completely understood, it is without doubt that the cunning protozoan helps to drive its furry rodent host towards a feathery final destination.

Reference:
Hoogenboom, I., Dijkstra, C. (1987) Sarcocystis cernae: A parasite increasing the risk of predation of its intermediate host, Microtis arvalis. Oecologia 74: 86-92

This post was written by Reece Dalais