"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

July 24, 2014

Special Report: #ASP2014 (Australia) Part II: Something Fishy This Way Come

This is Part 2 of my report on the annual meeting of the Australian Society for Parasitology (ASP 2014) I attended earlier this month. If you had missed Part 1 of my report, you can read it here

Barramundi photo by Nick Thorne
At the end of the previous post about ASP 2014, I alluded to the abundance of fish and their parasites. In this post I cover research on fish parasites presented at the conference - and there was quite a bit of it. There were a quite a few talks and posters that were focused on the parasite of Barramundi / Asian seabass (Lates calcarifer), which is a prominent aquaculture species in Australia. Like many other production animal, they have their fair share of parasites and there were a number of presentations focused on those said parasites from the Hutson lab including their identification, tracking, and means of control.

 One of the most persistent and common parasites of barramundi in Australian aquaculture is a tiny parasitic flatworm call Neobenedenia. Though they can be quite numerous on an afflicted fish, they are also are tiny and transparent, making them difficult to spot and even harder to study in situ. However, Alejandro Gonzalez presented a method for making these otherwise near-invisible parasites visible by labelling the parasite larvae with a fluorescent dye. Under the sight of an epifluorescence microscope, these treated parasites stands out like glow sticks at a rave club. Gonzalez was able to track how they distribute themselves over the fish's body

But Neobenedenia is just one of many different parasite species clinging to barramundi, a poster presented by Soranot Chotnipat found that there are at least eight different species of parasitic flatworms from the Diplectanidae family alone which are found on the skin of farmed barramundi of Asia-Pacific. But with all these parasites, what can be done about them? Kate Hutson presented a poster with a number of methods being trialled for treating farmed barramundi, including garlic and seaweed extracts, but of which the most novel is the use of cleaner shrimp. She found that fish housed with these shrimps have half as many external parasites as those without, and those shrimps consume all stages of the parasites - including their eggs which the shrimps happily grind up like crunchy treats.

Cleaner shrimp photo by Chris Moody
While there is still much to be learned about the parasites of farmed fish, that is nothing in comparison with the diversity of fish parasite outside of captivity, where there is a wild world of parasites full of murky unknowns. A parasite which has captured the imagination of the public is the tongue-biters which are related to a plethora of parasitic crustaceans in the Cymothoidae family. This family encompasses 361 described species and they range in life-style from skin-clingers to face-huggers to gill-tuggers and belly-burrowers. So how are face-huggers like Anilocra related to belly-burrowers like Ourozuektes? Melissa Martin presented a poster on some preliminary results on their interrelationship which seems to show that they might have independently evolved their respective attachment sites.

For most fish parasites, we do not even know what is out there let alone how they are related to each other, especially on a site of rich biodiversity like the Great Barrier Reef (GBR). Thomas Cribb from University of Queensland has been studying and describing flukes for over 20 years and he presented an overview of the current sum of knowledge about parasitic flukes on the GBR. Currently 326 species of flukes are known from 505 species of fish on the GBR, yet that represent only a small fraction of the 16000 or so species of fish found the the GBR, most of which are yet to be examined for parasites. The fluke fauna on the GBR are also very picky about their host, sticking to just two or so host species on average, and about 45% of them are found exclusively on the GBR. Cribb estimated that at this rate, it will take another 150 years to describe all the flukes (not even counting the other groups parasites) inhabiting the fishes of the GBR.

It is clear that underneath the surface of a tropical reef like the GBR is an extensive network of parasite life-cycles and transmission. To get a glimpse into this hidden world, Abigail Downie examined over 700 fish from 191 species, finding a trove of fluke larvae that utilise those fish as a mean of reaching their final host. She found that one species of goby - Amblygobius phalaena - seems to be a parasite hotspot with 16 species of flukes infecting it. Seeing as all those flukes require their temporary fish host to be eaten to complete their life-cycle, it is not surprising that they have all homed in on a small fish which would be a tasty dish for a range of predators, many of which may serve as potential hosts. Indeed, comparatively small fish species also tend to harbour proportionately more larval parasites than adult stages.

Epaulette shark photo by Strobilomyces
Aside from diversity, Downie also found that the ecology of the fish can influence what families of flukes infect them. For example, flukes in the Heterophyidae family produce free-living larvae that are energetic swimmers that hang out near the water's surface. Accordingly they were mostly found in surface or shallow water fishes such as mullets and halfbeaks. In contrast, flukes from the Opecoelidae family have nub-like tails and move by crawling along the seafloor like microscopic leeches. There they encounter fish that spend most of their time near or resting on the seafloor such as damselfishes and gobies.

One of the surprising finds by Downie was an epaulette shark which was heavily infected with opecoelid cysts. The flukes larvae were lodged in the fins which, when viewed under a microscope, looked like a bag of (gross) marbles. While epaulette sharks do spend a lot of time resting on the sea floor, fluke larvae are not usually known to infect elasmobranchs. At this point, it is unknown if shark serves as a viable transmission pathway for the opecoelids or if it is simply a dead-end parasite sink?

On that note, that is it for for my reports on the ASP 2014 (Australia) conference. It was fun to catch up with some colleagues and see some new research on parasites being presented. Start from next month, it is back to the usual parasite blog posts. Well kind of - as I did last year, next month I will be posting the best student blog posts from the Evolutionary Parasitology class of 2014 - so be sure to keep an eye out for that! Until then, you can check out some of the student blog posts from last year here.

July 11, 2014

Special Report: #ASP2014 (Australia) Part I: The Wild World of Parasites

Photo by Lisa Jone
Recently I attended the annual meeting of the Australian Society for Parasitology (ASP) - it also happened to be the 50th anniversary of the Society, so it was kind of a big deal for the ASP. The first day featured an opening speech by Australian Chief Scientist Ian Chubb. In it, he discussed the many people of the world of dying and suffering from preventable infectious diseases which is the price of poverty, poor sanitation and ignorance. He also talked about how the political priorities of Australia's current government does a great disservice to science, and the lack of long range strategies regarding science, technology, and engineering is holding back Australia as a nation.

He likened it to scattering pieces of a jigsaw puzzle with no means of connecting them, and it is detrimental to Australia's future. Chubb also emphasised that science is vital to the future of Australia and the importance of engaging the public and the next generation with the importance and awe of science (which I hope that I am playing at least a tiny part in by writing this blog!). Speaking of science, as that is what you came to this blog for after all, what kind of parasitology research caught my attention at the conference? For this post I will mostly discuss the presentation on wildlife parasites I saw at the conference.

There was a very interesting plenary talk by Vanessa Ezenwa about how multiple parasites infecting the same animal can influence the resulting pathology inflicted by those parasites upon the host. She presented a case in African buffaloes whereby the removal of parasitic worms affected the disease severity of bovine tuberculosis (bovine TB). There appears to be a trade-off between being resistance to macroparasites (worms) and microparasites (TB bacteria), with buffaloes that are more resistant intestinal worms being less able to mount a response to invasion by the tuberculosis bacteria. It seems as if the worms are pre-occupying the host immune budget, thus allowing the TB bacteria to slip by. However, if the buffaloes are treated with anti-parasite drugs that rid them of their worms, they were able to stop the TB bacteria dead in their tracks. Who would have thought treating buffaloes for their worm infections would also rid them of TB? Ezenwa's study shows the importance of considering the entire parasite community of a host animal and taking an ecological approach to considering host-parasite interactions.

On the subject of ecology, Haylee Weaver presented a talk based on a project that we have been collaborating on regarding parasites that infects animals with semelparous life-cycle - like the Sockeye Salmon, or the Antechinus - better known as the the little Australian marsupial that "has so much sex it disintegrates" followed by a talk I gave on a comparative analysis study I conducted on with Janet Koprivnikar which compared the nematodes fauna of migratory and non-migratory birds.
Photo of sea lion family by DaveDiver from Wikipedia

Jan Šlapeta presented research into a species of hookworm in Australian Sea Lions (Neophoca cinerea). This parasite - Uncinaria sanguinis - exploits the dependency between mother and offspring. The hookworm lives in female sea lions but unlike other hookworms, it does not lay eggs which are passed out in the host's fece, instead it is transferred to the pup via the mother's milk - only then does the worm mature into an egg-laying adult stage like other hookworms. Because of this transmammary transmission, male sea lions are considered to be a dead-end host for U. sangunis.

Because female sea lions do not tend to dispersed, it would be expected that the population of the parasite would be highly structured, but Šlapeta and colleagues found that was not the case, and that the population genetics of U. sanguinis is not as well segregated as expected. This raise many questions about the ecology of this parasites, such as whether other species of sea lions and seals serve as alternative hosts? Or perhaps the males are not dead-end hosts after all? Or can crustaceans like shrimps act as paratenic (transport) hosts for the parasite?

Elsewhere at the conference, there were many posters and talks on Cryptosporidium which seems to be a popular topic of research among Australian parasitologists. There are many different species of Cryptosporidium and not all of them infect humans - though some have potential to jump from their usual hosts into humans. For example, Australian marsupials and multitude of other wildlife are host to various species of Cryptosporidium and Michelle Powers presented a talk on the current state of knowledge about this genus of parasite and concluded there are still many different host species that can be harbouring undescribed species of Cryptosporidium.

Mammal ectoparasites were also also featured at the conference, with a poster presentation by Clare Anstead on the specificity of ticks that infects small mammals as well as their bacterial communities - just as there are generalists ticks that feed from a variety of host species and more picky specialists that stick to just one or two, it seems that the same goes for their bacterial occupants in regards to the species of ticks they inhabit. Speaking of ticks, Stephen Barker announced the launch of a 140 page monograph he and Alan Walker wrote on the ticks of Australia which are found on domesticated animals and humans. And it is available for free for all to download here, which I am sure will tickle the fancies of all tick fans.
Photo of crocodile farm by Cecil Lee
Moving on from parasites of furry hosts to more scaly ones, Simon Reid presented an unusual case of parasitism on a crocodile farm. We have featured various crocodilian parasites on this blog before, in this case these crocodiles on the farm end up being infected with a muscle-burrowing worm due to human action.

The practice of raising crocodilians in a farm setting has come about due to the demand for crocodilian skin product, but another product of such farms is crocodile meat. Since the meat is meant for human consumption, this has led to them being tested for parasites and pathogens, which in turn led to the discovery of an unexpected species parasitic worm in the muscles - Trichinella papuae. Trichinella is also known as "the worm that would be a virus" and normally, crocodiles are known to be infected by their own species of Trichinella - Trichinella zimbawensis. But T. papuae is normally a pig parasites - so how did they end up in a crocodile? Well the obvious answer is that those crocodiles were being fed with pigs - but it also provides an interesting insight into the biology of the parasite itself because their presence in crocodile muscles means that even though  T. papuae normally dwell in an mammal, it is also adaptable enough that it can also survive in a host with a rather different physiology to its usual host.

Speaking of scaly hosts, fish are the most diverse vertebrate animal on the planet and talks about their parasites had a considerable presence at this conference. In Part Two of my special report on ASP 2014, I will be covering fish parasites - including how to make invisible parasites visible, what is the relationship between tongue-biters and face-huggers, and what parasite you might find in the fins of an epaulette shark. All that and more will be revealed in my next post on ASP 2014.