"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
February 28, 2010
February 28 - Edwardsiella lineata
It seems that just about every group of organisms has evolved parasitism, but we haven't seen one of these yet - a parasitic sea anemone. And what do parasitic sea anemones feast on? (Don't be afraid...) Ctenophores - or comb jellies - are the hosts to these parasites. It's just the larvae of Edwardsiella lineata that are parasitic and the evidence is such that it's thought that this is a very recent strategy as all other members of the family have free-living larvae. Larval E. lineata embed themselves in their ctenophore hosts (they can do this from either direction - they can burrow in from the outside, or they can go through the gut if the ctenophore eats them first!). Once in position, they extend their mouths right into the ctenophore's gut, and ingest anything that the comb jelly has worked hard to eat. When it's had its fill, it simply removes itself and transforms into a regular looking sea anemone larva. Is it content to stop there? No, not always, as it turns out. Sometimes it is – and develops into a polyp (the anemone-looking thing). But sometimes it actually invades a second ctenophore and reverts back to the parasitic body form while it sucks away at more of the new host’s food. Greedy little buggers, aren't they?
Image and more info from this paper.
Click on the image to enlarge.
February 27, 2010
February 27 - Myrmeconema neotropicum
Yesterday, the parasite was saving coffee berries, today the parasite is making ants look like berries. Myrmeconema neotropicum is another nematode parasite that infects the ant, Cephalotes atratus in South America. The life cycle is somewhat similar to that of yesterday's parasite. Foraging ants pick up the nematode's eggs which have been shed in bird feces and feed them to their larvae. Inside the ant pupa, the worms hatch, mature and mate. As the embryos inside the female nematode mature, the gaster, or abdomen of the ant, swells and goes from being black, to translucent, to bright red. Adult ants then walk around with bright red abdomens held up into the air and are also slower and "clumsier" - perfect targets for frugivorous birds. The species, described in 2008, also changed the taxonomy of the ant hosts. Over a century before, a variety of tropical ants had been described based on their unusual red abdomens. We now know that they were just parasitized individuals. Makes me wonder how many other "species" have been erected based on parasite-induced morphological changes...
Image from figure of the paper.
You can read the original paper here.
You can read the original paper here.
February 26, 2010
February 26 - Metaparasitylenchus hypothenemi
It’s been a long week for me here at the AMNH. We’ve just finished up the interviews for prospective students for our Richard Gilder Graduate School and I am definitely in need of an extra cup of coffee this morning. So, perhaps it’s fitting to finish up this week of newly described Mexican parasites with Metaparasitylenchus hypothenemi (you’ll need a cup of coffee - or eight cups -to wrap your tongue around that moniker!). These are nematode parasites that infect coffee berry borers, beetles that are one of the most important coffee pests. The free-living adult worms are thought to mate in the coffee berries themselves and then the female nematodes penetrate into the larval beetles’ cuticles. There they wait, as the beetles proceed through their own developmental process, though pupal stage into the adult form. Like many nematodes, the eggs hatch within their mother (the photo shows a female filled with eggs and first-stage larvae) and even go through their first molt within the egg or soon after. Third-stage larvae leave the beetle hosts via the typical exit routes – the gastrointestinal and/or genital openings.
These nematodes pose an interesting biogeographic question as well. The coffee borer itself is native to Africa, so it is possible that the beetles brought this parasite to the New World with them, but it is also possible that the nematodes were native to the New World and hopped into these hosts when they encountered them. It is currently being studied as a possible biocontrol agent for these coffee pests. Go parasites! I need my coffee!
February 25, 2010
February 25 - Rallicola deckeri
Rallicola deckeri is a new species of chewing louse that was recently discovered on a Ruddy Woodcreeper in Campeche, Mexico. The other lice that have graced this site, Pediculus humanus humanus and Pediculus humanus capitis were both sucking lice. Chewing lice (Mallophaga) typically feed on skin or feathers and most commonly parasitize birds. They often have elongated bodies, but wide, flat heads.
February 24, 2010
February 24 - Gnathostoma lamothei
This nematode, with spines and hooks covering its body lives attached inside the stomach of racoons in Southern Mexico. These worms lay their eggs in the host’s stomach and the eggs find their way to outside when the vertabrates poop. If this happens close to freshwater and the parasite is lucky enough, a free-living larva is liberated from each egg. These larvae can live for a few days in the water until it dies or… is swallow by a copepod. The nematode then penetrates the digestive system of the copepod and lives there until the copepod is ingested by a fish. Once in the fish, the nematode again penetrate the intestine and finds its way into the muscles where it encysts. The life cycle of Gnathostoma lamothei comes full circle when a racoon eats fish flesh with the parasite encysted in the muscles. Inside the raccoon, the parasite penetrates the intestine, spends some time there, and then finally enters the stomach to start the cycle again.
The life cycle of G. lamothei is fascinating but in reality is much more complicated. Larvae allocated in the muscle of fish can infect an extraordinary number of animals other that dogs and cats. For example, if a frog or snake eats the infected fish, the nematode penetrates the intestine again to encyst in the muscles. The nematode larvae can move from animal to animal until it reaches a racoon.
Humans can be infected by this parasite or by closely related species while eating raw freshwater fish. Human gnathostomiosis is a common food-borne parasitic disease in several countries of Asia and now is becoming a serious health problem in some areas of Latin America. In most of the cases the larvae of Gnathostoma don’t encyst in humans. On the contrary, the larva migrates erratically throughout the body, most of the cases close to the skin. Remember, the next time you eat sushi, sashimi, ceviche or any kind of raw fish, be sure that is not fresh-water fish!!
You can read more about it here.
Contributed by Alejandro Oceguera-Figueroa.
February 23, 2010
February 23 - Sciruodendrium bravohollisae
This new species of nematode was discovered infecting red-bellied squirrels (Sciurus aureogaster) as part of a survey in Morelos, Mexico in 2003. Both squirrels that were examined had these parasites in quite high numbers. These parasites are part of the suborder Strongylida, which are typically gastro-intestinal parasites of mammals.
February 22, 2010
February 22 - Thaumasioscolex didelphidis
Up until the point at which this parasite was found, tapeworms in the group Proteocephalidea were thought to only infect fishes, amphibians and reptiles. But, in the late 1990’s, these cestodes were found in black-eared opossums in Veracruz, Mexico. The authors erected a new genus for these tapeworms, calling it Thaumasioscolex, from the Greek “thaumasio” which means “to surprise” because of its presence in a mammal and then described this single species in that genus, Thaumasioscolex didelphidis. Molecular data were consistent with the parasite’s relatedness to members of the Proteocephalidea that infect fishes. The life cycle is not yet known, though aquatic intermediate hosts including crustaceans and frogs are suspected.
February 21, 2010
February 21 - Tricophyton rubrum
Tricophyton rubrum is a dermatophyte - a fungus that is an obligate parasite of the skin or other keratinized tissues like nails. This species is the most frequent culprit behind the most common fungal infections of humans - ringworm, athlete's foot and jock itch. The fungi typically only colonize the outermost layers of skin and do not invade the true living tissues beneath. They make us itch when our immune systems respond to the metabolic waste they exude out. Although ringworm isn't usually a severe health threat to an infected person, and can be treated with aggressive topical medications, it's often horrifically hard it can be to get rid of in one's house. The fungi can remain in clothes, on sheets, even on furniture and other parts of the environment for over a year and transmission can occur between humans and pets. It's very common in showers and locker rooms so wearing flip-flops is always a good idea in these public places. The name "ringworm" comes from the tendency of the fungus to form a ring in the skin, though they do not always do this.
February 20, 2010
February 20 - Zeylanicobdella arugamensis
The piscicolid leeches inhabit marine environments and take their blood meals from fish hosts. Recently, these leeches were found on mudskippers – unusual fish in the goby family that are amphibious, spending part of their time out of the water. Zeylanicobdella arugamensis was discovered feeding from the mudskipper Scartelaos tenuis, which lives in the Persian Gulf and leeches also readily attached to a second species, Periophthalmus waltoni, in aquaria (shown in photo). Although this second fish species is sympatric with S. tenuis, the authors of the paper did not find any leeches on them in the wild. They proposed that perhaps in nature, P. waltoni spends too much time out of the water and thus the leeches prefer the more aquatic S. tenuis. Z. arugamensis has a wide distribution in the Indian Ocean and infects numerous species of fish, but this was the first time one had ever been found on mudskippers.
Photo kindly provided by Gianluca Polgar.
February 19, 2010
February 19 - Pterygodermatites peromysci
Pterygodermatites peromysci is a common intestinal nematode of Peromyscus leucopus, the white-footed mouse and Peromyscus maniculatus, the deer mouse. P. peromysci inhabits the small intestines of these two rodents where it lives out its days feeding on the nutrients taken in by the mouse. The life cycle of this parasite is complex and requires passage through an intermediate host Ceuthophilus pallidipes, the camel cricket. Eggs are shed in the mouse faeces and ingested by the cricket. The nematode develops inside of the crickets hemocoel, or body cavity where it floats around encysted inside gut epithelium until a hungry mouse gobbles up the tasty cricket treat, continuing the parasites life cycle. The parasite in the photo was isolated from Peromyscus maniculatus captured in the Great Basin desert in Utah.
Contributed by Craig Gritzen.
February 18, 2010
February 18 - Gigantolina elongata
Gigantolina elongata belongs to a small group (as in only 8 species are known!) of parasitic worms known as amphilinids. Although some of these parasites infect fish, this species is found in freshwater turtles of Australia. The parasites are bright yellow in color and as many as 30 of the large (150+ mm) worms can be found in a single host. It is unclear exactly how the eggs of the worm are released in the water, but once they do, larvae hatch out and find a young crayfish where they penetrate the cuticle of their host by a complex process that involves both chemical digestion of the cuticle and sawing it open with tiny hooks. When turtles eat the crayfish, the young worms pentrate the turtle’s esophagus and make their way to the body cavity where they will grow and mature into adults.
Nominated by Klaus Rhode
February 17, 2010
February 17 - Cordylobia anthropophaga
Last year, I was doing some field work in Tanzania and we were staying up at a small station in the highlands. The station staff agreed to do our laundry for us – a welcome thing after several days of muddy work. Our clothes were washed by hand and then put on racks to dry. Soon, one of the women took our clothes – even our underwear – and ironed everything. Are Tanzanians incredibly finicky about pressed clothes? No, she was trying to protect us from tunga flies, Cordylobia anthropophaga. These flies usually lay their eggs in the feces of animals. The larvae hatch out and wiggle around, looking for the warm body of a mammal to latch onto. They proceed to bury themselves beneath the skin where they grow (much like a botfly does) for about a week and a half until they are ready to pupate, when they crawl back out of the skin, drop to the ground, and pupate. Tunga flies also have a predilection for laying their eggs on damp clothes, however – and so when you put these clothes on,the larvae will crawl into your skin. The result is a nasty condition known as myiasis – painful boil-like lesions. Ironing the clothing will kill the eggs - thankfully.
Image from the CDC Public Health Image Library.
February 16, 2010
February 16 - Holospora undulata
So, according to the news, one of the big trends in fashion this year is that prints are back – especially paisley. And one cannot think of paisley (if one is a biologist, anyway), without picturing Paramecium. But, of course, paramecium is not a parasite – they are free-living unicellular organisms that zip around with their cilia and gobble up bacteria. But they have parasites, including the alphaproteobacterium, Holospora undulata. Paramecium have two kinds of nuclei – there is one macronucleus, which contains the genes for all the proteins involved in being a Paramecium on a day-to-day basis, and one or more micronuclei, which contain the genes involved in reproduction and essentially represent its “germ line.” Holospora undulata bacteria live in the micronuclei of their hosts. (A different species, Holospora obtusa, lives in the macronucleus.) These bacteria exist in two different forms – short rods, which are the reproductive forms, busily dividing in the nucleus, and a longer infectious form, which leave the host cell and enter the environment. Paramecia become infected when they ingest H. undulata along with the other bacteria that they’re munching up. The Holospora escape from the phagosome and move to the nuclear membrane where they bind to receptors and then enter inside. Because these bacteria infect one of biology’s favorite lab organisms, not surprisingly some very nice research on infectious disease and the ecology of hosts and parasites have been done using this system as a model.
Photo from the Encyclopedia of Life.
February 15, 2010
February 15 - Dactylopius coccus
Fashion week + President’s Day = cochineal!
Dactylopius coccus, commonly known as cochineal, is a scale insect (a sternorrhynchan, like the aphids), which is widely used in the fashion industry. These insects produce carminic acid, which, when combined with aluminum or calcium salts, is used to make carmine dye. D. coccus is native to Mexico and South America, where the females are parasites on cactus plants in the genus Opuntia. Only the male D. coccus insects have wings. The juvenile stages of D. coccus, the nymphs, disperse using long wax filaments that allow them to parachute in the wind (much like many spiders do with silk). Ever since the time of the Aztecs and Mayans, people have been harvesting these insects for their red pigment. The scale insects are collected from the cacti, boiled in water and allowed to dry thoroughly. For pure carmine, a more involved chemical process is used, whereby the pulverized insects are boiled in ammonia and then the red salts are precipitated with alum. In colonial times, Europeans began to use carmine dye as well, particularly to make fabrics, including those of the British “Redcoats”. Although synthetic red dyes were used for a time being, their link to cancer and expense to make has led to a resurgence in “natural red coloring” – in other words, for carmine dyes derived from D. coccus. It is widely used in the U.S. as a food coloring, but is also used as a fabric dye and as a pigment to make cosmetics such as lipsticks and blushes. Check the ingredients label the next time you eat something red or use make-up – chances are, you’re enjoying a dye derived from a parasitic insect.
February 14, 2010
February 14 - Giardia lamblia
Giardia is a very common parasite found all over the world and one that is capable of infecting humans as well as other animals. It is frequently found in water sources particularly those where human and animal contamination is likely. It's frequency of infecting hikers and campers who drink untreated water has led to its common name, "Beaver Fever." Humans or animals become infected when they ingest cysts. Trophozoites, the feeding stages emerge from these cysts in the digestive tract. These stages can asexually divide (as shown in the photo). The symptoms of a Giardia infection are a suite of gastrointestinal unpleasantries, some of which have been described as "explosive" and "violent." Giardia can be difficult to confirm medically but the good news is that it usually resolves itself in healthy people. This organism was discovered by Anton von Leeuwenhoek, who developed one of the very first microscopes, when he opted to examine his own feces using his new invention.
Giardia is a unicellular eukaryotic organism that possesses flagella. The placement of Giardia in the "tree of life" has been rather controversial. Initially, it was contended that these organisms represented the deepest branch of all eukaryotes, because they lacked mitochondria (like Trichomonas and Entoamoeba, two parasites we will see here in the near future). The belief was that these organisms, collectively termed the "Archezoa" diverged from other eukaryotes before the acquisition of mitochondria. However, it was later discovered that not only did Giardia have genes much like those of the alpha-proteobacterial ancestor of mitochondria within its nuclear genome, but that it also had structures, termed "mitosomes", that were thought to be remnants of previous true mitochondria in these cells. This is still something of an open question, partly because Giardia and some of these other amitochondriate organisms do not have many close relatives and so are subject to phylogenetic vagaries in the construction of the tree. Hopefully more genome sequences of protozoa and better methods to understand horizontal gene transfer processes can help to solve this riddle. In the meantime, filter your water when you're camping - and happy Valentine's Day.
February 13, 2010
February 13 - Afenestrata koreana
Eco-friendly fashionistas are frequently turning to bamboo as an alternative to cotton. It doesn't need irrigation, it grows faster, and does not need fertilizers - and it's incredibly soft and durable. But, of course, it has parasites. One of them is a tiny little nematode (roundworm) that makes cysts in its roots. Juveniles invade the roots and feed from the plant. Females swell up and fill with eggs (see photo). Plant nematodes are very important agricultural pests and are very diverse, but this species, the bamboo cyst nematode, Afenestrata koreana, was only just described in 1992.
Photo from the original description by Vovlas et al.
February 12, 2010
February 12 - Nosema bombycis
Busy little Bombyx mori caterpillers happily crunch up mulberry leaves and spin cocoons where they will pupate and transform into moths. These cocoons are made of silk fibers that are harvested and processed to produce silk - in fact, 70 million pounds of silk, every year. But, of course, like virtually all creatures on the planet, silkworms suffer from parasites, too. One of the best known is Nosema bombycis, a microsproridian parasite, that causes a disease known as pébrine - so called because it produces pepper-like spots on the caterpillars. The disease is highly infectious and can pass from mother moth to her eggs, so it has long been a major concern for silkworm breeders. Louis Pasteur, the famous French microbiologist discovered that infectious agents were causing the disease in silkworms and is credited for saving the industry at the time. Microsproridia are a very diverse group of spore-forming unicellular parasites, many of which infect insects. They were once thought to be primitive eukaryotes, but they are now thought to be more closely related to fungi.
Image from this website.
February 11, 2010
February 11 - Pediculus humanus humanus
In honor of "Fashion Week" in New York this week, six of the posts this coming week will involve parasites that relate to fashion in some way.
Today's: Body lice - I thought it would be fitting to start with these little creatures, which are a little "bonus" that we acquired when humans began to wear clothes.
Body lice, Pediculus humanus humanus (also called clothing lice) are believed to have evolved from head lice, likely invading the body region only recently with the advent of clothing use in modern humans. These wingless insects are found on the body and in clothing and prefer to attach their eggs to clothing rather than body hair. Compared to head lice, body lice are less prevalent parasites, associated mainly with those living in poor conditions in colder climates. Body lice are, however, potentially more harmful because they are known vectors of at least three bacterial pathogens in humans: Rickettsia prowazekii (epidemic or louse-borne typhus), Borrelia recurrentis (louse-borne relapsing fever) and Bartonella quintana (trench fever). Body lice, and the diseases they carry, can be transmitted fairly easily and quickly, especially in crowded situations such as war. In fact, body lice are known to have been prevalent amongst soldiers in Napoleon’s Grand Army and it’s possible that the diseases they carried may have played a role in the French retreat from Russia.
Contributed by Jessica Light.
Image from the CDC Public Health Image Library.
February 10, 2010
February 10 - Ascaris lumbricoides
Adult Ascaris lumbricoides, the most common nematode parasite of humans, live in the small intestines. Their eggs are passed in feces, with those finding their way into contaminated food capable of infecting new unwary diners. Once eggs are swallowed, stomach acid and bile release the larval worms in the small intestine. You might think that they’d be sensible and just grow up there, completing the infection cycle. Nope! The larval worms leave the intestine, burrowing through the mucosa and get picked up by circulating blood. Those that don’t get lost in random tissues are carried to the lungs where they break out into the alveolar spaces, migrate up the trachea, or are coughed up, whereupon they are swallowed and arrive right back where they started, growing up to become reproductive adults in the small intestine - not unlike going from the White House to the Capitol Building via a side trip to Philadelphia!
As bizarre as their migration might seem, there also are bizarre human stories surrounding these amazing worms. In 1922, Shimesu Koino ate 2000 eggs of Ascaris lumbricoides, and fed 500 Acaris suum eggs from pigs to his younger brother! Koino didn’t fare so well, but he did demonstrate the pulmonary syndrome associated with early Ascaris infections. He also inferred the route of migration by finding larvae in his sputum. In 1970, annoyed that his roommates were bugging him to pay his rent on time, a postdoc at McGill University in Montreal, Eric Kranz, laced their food with hundreds of thousands of Ascaris lumbricoides eggs that he had taken from the parasitology lab at Macdonald College. Richard Davis, William Butler, David Fisk, and Keith Fern were each hospitalized and Kranz was charged with attempted murder. Ascaris eggs are extremely resistant to destruction; they remain viable for months to years. In 1920, Yoshido even demonstrated their ability to remain viable in the face of hydrochloric, acetic, and nitric acids or even after they’ve been immersed in formalin – a real danger for biology classes that incorporate dissection of Ascaris in their studies.
Adult female Ascaris lumbricoides have a strong tropism for tight curved spaces that mimic the curved tail of males they must seek out in order to be fertilized by unusual, crawling amoeboid sperm. Alas, this predeliction has more than once revealed an otherwise asymptomatic infection when a female alarmingly crawls her way out through a victim's nostril!
Contributed by Mark Siddall.
February 9, 2010
February 9 - Monotropa uniflora
Monotropa uniflora, also known as the Indian Pipe plant or the Ghost Plant, is a kind of parasitic plant known as a myco-heterotroph. These plants use the symbiotic fungi that associate with other plants, in this case trees, to get their nutrients. Because they do not need to photosynthesize themselves, they can grow in very dark conditions. At present, there is just a single species described, which has a wide, but highly discontinuous distribution in North America, Central America, and eastern Asia, but a recent paper based on DNA sequences from the plants has suggested that these are distinct evolutionary lineages.
Photo from here.
February 8, 2010
February 8 - Coelioxys coturnix
A female Coelioxys (Allocoelioxys) coturnix Pérez bee dashes into the nest of another bee species, Megachile minutissima Radoszkowski, and lays an egg on top of her host’s. She has waited—loitering outside the nest while assessing the whereabouts of the other female —for the other’s moment of weakness: leaving the nest to collect the last bit of material to close the brood chamber containing her egg and the pollen and nectar provisions for the larva that will emerge from the egg. Coelioxys coturnix is a cleptoparasitic (sometimes spelled “kleptoparasitic”) bee, an entomological version of the cuckoo bird, that does not collect food or nesting material for her offspring but uses the nests and, in bees, larval provisions of other species. Depending on the species of parasitic bee, its newly hatched larva might have disproportionately large, fang-like jaws to kill the host’s brood, might feed on the host’s egg, or might (in one very unusual species from Florida currently being described) wait until it is almost too late, during its last larval stage, to do away with the competition. Cleptoparasitism has evolved many times among bees using different pathways, according to Jerry Rozen, a Curator at the American Museum of Natural History for nearly 50 years, who has studied these bee species for much of his career.
Contributed by Kristin Phillips.
Photography by Rollin Coville.
February 7, 2010
February 7 - Legionella pneumophila
In 1976, the nation celebrated the American bicentennial. One event, a convention of members of the American Legion in Philadelphia, had tragic results that led to the discovery of a new pathogenic bacterium. In the weeks following the convention, over 200 people became ill and 34 of them died, triggering public health officials to track down the unknown culprit. The guilty party was Legionella pneumophila, a Gram-negative, rod-shaped bacterium that is both an intracellular parasite of protists (like the ciliate shown here - the long red bits that look like yarn are chains of bacteria inside these cells), and also free-living in the environment, particularly warm, wet places like air-conditioners at convention centers and saunas. People acquire the bacteria when they breathe in vapor containing them, but the disease cannot be spread from person to person. For some, particularly elderly people, people with weak immune systems, and smokers, the bacteria can present a very serious health problem in the form of pneumonia. For others, a milder infection produces what has come to be called "Pontiac fever", named for a similar outbreak that occurred (in all places, amongst county public health department employees) in Pontiac, Michigan eight years before the Legionnaire's convention of 1976. At that point, they could not find the pathogen, but were later able to tie those cases to Legionella pneumophila.
Image from the CDC Public Health Image Library.
February 6, 2010
February 6 - Triloculatum geeceearelensis
My colleagues Janine Caira and Kirsten Jensen travel around the world collecting tapeworms that live in sharks and skates - their specialty. The diversity of cestodes in these marine creatures is enormous and these two scientists have discovered and described dozens. In a recent paper, they presented a whole new genus of tapeworms from whaler sharks and described five new species. One of my favorites of the pack is Triloculatum geeceearelensis, a species that they found in the finetooth shark, Carcharhinus isodon in the Gulf of Mexico. They named this species after the Gulf Coast Research Laboratory, or "GCRL" to thank the facility for hosting them while they did their work. Sound out the species name and this will make sense! The image is a scanning electron micrograph of the scolex of the tapeworm - the "head" bit that it uses to attach to its host's intestine.
February 5, 2010
February 5 - Lampsilis fasciola
Mussels may seem like unassuming creatures, hanging out on the riverbed until they’re caught and served with a delicious garlic butter sauce, but many species have parasitic larvae that are crafty and downright aggressive when it comes to attracting their hosts. The larvae, known as glochida, usually can’t move around to seek out their hosts, so they employ a wide variety of lures to bring those hosts to them. Meet Lampsilis fasciola, commonly known as a "pocketbook mussel". The glochidia of this species develop inside their mother for approximately one year, and then the mother mussel moves them to the outside of her shell into a pouch on her mantle. Here’s where it gets interesting. The mantle looks remarkably like a small fish, complete with eyespots, and the movement of the mantle looks like a small fish swimming – just the right meal for a larger fish passing by. When a hungry fish bites the mantle, the glochidia-filled pouch ruptures and the larvae emerge, latching onto the inside of the fish’s gills with adhesive threads and teeth on their shells’ valves. Once in their host, the glochidia encyst and develop into juvenile mussels and then drop down to the riverbed to mature, mate, and get ready to lure the next generation of host fish.
Contributed by Kate Bowell.
February 4, 2010
February 4 - Fasciolopsis buski
Trematodes, or flukes, usually have complex life cycles involving multiple hosts, one of which is a snail. The giant liver fluke, Fasciolopsis buski, is a common parasite in southeastern Asia, including India and China. Eggs are released in feces where they excyst as miracidia, which infect snails. Further development occurs in the snails, until cercariae leave the snail, transform into metacercariae and attach themselves to water plants such as water chestnuts. Humans (and pigs) become infected if they eat unwashed/uncooked plants. Despite the fact that they are called “giant liver flukes”, they are only about 3 inches long. But, that’s long enough if you’ve got one (or more!) attached to your small intestine.
February 3, 2010
February 3 - Dermatobia hominis
The tórsalo or human bot fly, Dermatobia hominis, undergoes larval development in the skin of a vertebrate host. They frequently infest cattle, but can use primates, sheep, and other domestic and wild animals. The method by which larvae reach a host is unique among the family Oestridae. Adult female botflies catch a porter, which is commonly a mosquito, and lays eggs on it. This porter then transports the eggs to a vertebrate host during the course of its natural behavior (e.g., blood-feeding). The eggs hatch while the porter is on the vertebrate host, in response to body heat. First stage larvae gain entry to the host through the arthropod bite or hair follicles. In the host, larvae develop through three instars over 1.5 – 2.5 months. The boil-like lesion caused by the developing larvae stays clean through bacteriostatic action in the larval gut. After development, the maggot exits its host, drops to the ground and pupates in soil, emerging 1 – 3 months later as an adult fly.
In the tropics, where botflies are common, people specialize in popping bots (like American teenagers pop a zit). Massaging the site and knowing just when to press is a skill. Some people prepare the area first by applying an oily paste (e.g., petroleum jelly) to the site for several hours; this causes the bot to retract the cuticular spines it uses to hold itself in place and move closer to the surface as they breathe through a respiratory siphon that exits at the skin surface. Although some think that putting a steak on the furuncle caused by the bot will cause the maggot migrate to the other, more attractive, meat source;, the bot only emerges because it's suffocating. So, use petroleum jelly -- it's cheaper than steak! Prior to the extraction in the video, the site was kept under Vaseline and bandages for over a day, which is probably why it came out so easily. Please do not attempt extracting a bot by yourself – see a doctor. You could rip off the respiratory siphon of the larva causing it to die inside of you, where it might become infected - and then you'll have more serious problems than a baby fly temporarily using you as its home.
Contributed by Holly Tuten.
Video by Brandon Mellin, Clemson University.
February 2, 2010
February 2 - Eimeria monacis
Because today is Groundhog Day, it seemed only fitting to highlight a parasite of Marmota monax, the groundhog or woodchuck. Eimeria monacis is a coccidial parasite – a group of parasites that are thought to be very host specific. Eimeria is an apicomplexan, like Toxoplasma, Plasmodium, and Cryptosproridium. Their life cycle contains many of the same stages and processes, but unlike vector-borne apicomplexans like malaria, Eimeria and other coccidians only use one host and are transmitted from host to host via oral-fecal pathways. (You can see a nice animation of the life cycle here, albeit in a goat, not a groundhog.) The picture is from Frederick Fish's original 1930 description of E. monacis. Fish was a parastiologist from Johns Hopkins University, who caught the type host outside of Washington D.C.
February 1, 2010
February 1 - Echinococcus granulosis
When people think of tapeworms, they often think of very long ones, like Taenia saginata. Echinococcus granulosis is a tiny tapeworm – tiny, but nasty. The main vertebrate hosts of E. granulosis are canids, where the 5 millimeter-long adult tapeworms live in the small intestine. Eggs are expelled in the dog’s feces, where they are eaten by herbivores such as sheep or deer or rodents. Inside the herbivore, the larvae travel through the intermediate host’s blood and take residence in various organs where they form hydatid cysts, which can grow very large in some cases – as big as a grapefruit or even larger. It is thought that these cysts make the herbivore more vulnerable to predation by – canids, of course. Humans can serve as intermediate hosts if they are exposed to contaminated dog (or coyote or wolf or other canid) feces and will suffer from hydatid disease when the larval tapeforms form cysts in our organs. This can be a serious condition, not only because the large cysts can put pressure on organs, but also because should the cysts rupture within the body, a person can suffer from severe shock. The disease can be common in areas with many sheep.
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