November 30 - Pneunonema tiliquae

Our parasite for today is a nematode called Pneunonema tiliquae and it is the only species within its genus. It is found in the lungs of the Eastern blue-tongue lizard (Tiliqua scincoides), a cute-looking skink from Australia which can grow to 30 cm (about a foot) long or more. Nothing is known about this parasite's life-cycle or how it enters the host. Based on what is known about other species of lung-dwelling nematodes in reptiles, it is likely that the blue-tongue lizard becomes infected through the oral route, when infective larvae in the environment are accidentally ingested by the lizard alongside its food.

A second parasite found by Tommy Leung in a roadkill skink he found. Click here to see the first.

November 29 - Equinurbia blakei

The scanning electron microscope has allowed us to see the awesome symmetry of some nematodes up close and personal. Equinurbia blakei is an intestinal parasite of African elephants and one of a group called “large strongyles.” This group is characterized by complicated mouthparts called the corona radiata (radial crown) seen here. The four structures outside the crown are called amphids and are sensory organs. Large strongyles are characteristic of ruminants and some hosts, such as zebras, can harbor up to 20 species and over a million total worms per animal.

Contributed by Mike Kinsella.

November 28 - Halipegus eccentricus

Halipegus eccentricus is a trematode parasite of North American frogs such as the bullfrog, Rana catesbeiana. Like many of the other trematodes we have met, H. eccentricus has a complex life cycle involving many different hosts. The first intermediate host is a snail of the genera Physa or Planorbella. The cercariae are then ingested by the second intermediate host, a small crustacean, such as a copepod or an ostracod. The metacercariae were then thought to be ingested by tadpoles where they waited for the amphibian to develop into a mature frog, at which point, the parasite would migrate to the frog's eustachian tubes (yes, these worms live in frog ears.) A recent study, however, showed that odonate insects (damselflies, dragonflies) serve as paratenic hosts for the trematodes and that only adult frogs are becoming infected. We are always learning more about parasites!

The image comes from the paper above and shows a redia of H. eccentricus, with the minute cercaria developing inside.

November 27 - Fregata minor

Imagine someone waiting until just after you've swallowed your last bite of Aunt Tillie's famous pumpkin pie this Thanksgiving, and then forcing you to run a marathon until the inevitable gastric upheaval. Then, without as much as a "thank you", they catch the product of your upheaval, eat it, and run away. Shamelessly disgusting! This is how the Great Frigatebird (Fregata minor) makes a portion of its living, as an "on-the-wing" kleptoparasite. This Blog has featured "kleptos" before, but none as disgustingly brash and acrobatic as the Frigatebird. This enormous (2 meter wingspan) iridescent black seabird literally harasses (often at breakneck speeds) other self-respecting piscivorous birds until they "toss their fish-sticks". It doesn't stop here; because this bird cannot take off without a freefall (an evolutionary compromise of having the highest wing-size to body-size ratio of any bird) it cannot land on the water to eat its meal. Instead it has to perform amazing acrobatics to "catch the retch" before splashdown. When not "downing up-chuck" it feeds on flying fish caught "on-the-wing". Frigatebirds are also interesting in many less vile ways, not the least of which is the fact that they look a little like pterodactyls!

Post and photo by Matt Leslie.

November 26 - Genarchella astyanactis

Today's parasite - Genarchella astyanactis - belongs to family of digenean trematodes called the Derogenidae, which have evolved a unique way of infecting their second intermediate hosts. They use copepods and other small crustaceans as second intermediate hosts, and their strangely-shaped cercariae are propelled from the snail first intermediate host by a forked appendage. The cercariae are also armed with a coiled structure call a "delivery tube" (shown extended in the drawing) that they use to gain access to the copepod host. For some reason, copepods identify the strange cercaria as a food item and avidly seize any that they encounter. However, as the crustacean manipulates the parasite with its mouth parts, the delivery tube of the cercaria rapidly extends and penetrates the copepod's gut wall. At the same time the cercaria body is propelled through the delivery tube into the body cavity. Imagine eating a muffin which stabs the back of your throat the moment that you bite it, and then injects a squirming parasite into your body!

Reference:
Ditrich, O., Scholz, T., Aguirre-Macedo, L. and Vargas-Vázquez, J. 1997. Larval stages of trematodes from freshwater mollusc of the Yucatan Peninsula, Mexico. Folia Parasitologica 44:109-127.

Contributed by Tommy Leung.

November 25 - Chelopistes meleagridis

Happy Thanksgiving to all the U.S. readers out there! Seemed appropriate to feature another turkey parasite today (we've had two others recently, i.e. Syngamus trachaea and Trichomonas gallinae ), but this one is something that anyone whose exposure to turkeys is limited to defrosting a Butterball will have no opportunity to come into contact with: the Large Turkey Louse, Chelopistes meleagridis. These lice are very common, especially on wild turkeys and have been introduced to many places via transport of their avian hosts.

November 24 - Lemurpediculus verruculosus

Lemurpediculus verruculosus is a species of louse that infects Microcebus rufus, commonly known as the Eastern Rufous Lemur or the Brown Mouse Lemur. L. verruculosus has a penchant for areas of its host where the skin is thin, the peripheral blood supply is good and where the animal cannot easily groom - thus the ears and, if it is on a male, the testes. This species was originally discovered back in 1951 as part of a collecting expedition by the famous medical entomologist Harry Hoogstraal, but the species description was based only on a single female that had been collected. Recent work on mouse lemurs yielded many more specimens of these lice, allowing the description to be expanded to include males and instar stages as well.

Photo contributed by Lance Durden, one of the authors of the new paper.

November 23 - Transvena annulospinosa

Today's parasite is an acanthocephalan (thorny-headed worm) which lives in the Blackback Wrasse (Anampses neoguinaicus), a species of fish found on the Great Barrier Reef of Australia. The picture shows the anterior hook-lined proboscis that the worm uses to anchor itself firmly in the intestinal wall of the host. The photo is actually that of a male worm, and interestingly the males of this species have a pair of paddle-like protrusions at the posterior end of the body. The function of the protrusions are completely unknown. Because it is a purely male characteristic, it is possible that they play a role in sexual competition, though that is purely speculative. However, it has been well established that sexual competition is particularly fierce among the thorny-head worms - male acanthocephalans (including the species in today's post) are armed with a "cement gland" that secretes a substance that they use to block up the female's reproductive tract post-mating. This ensures that she cannot receive future sperm from rival males.

Reference:
Pichelin, S. and Cribb, T.H. (2001) The status of the Diplosentidae (Acanthocephala: Palaeacanthocephala) and a new family of acanthocephalan from Australian wrasses (Pisces: Labridae). Folia Parasitologica 48: 289-303.

Contributed by Tommy Leung.

November 22 - Trichomonas gallinae

There's certainly no doubt that dinosaurs had parasites. The problem is, soft-bodied things like tapeworms and nematodes, let alone smaller things like trypanosomes or malaria parasites just don't fossilize well, so actually being able to say which species of parasites the "terrible lizards" might have been infected with is close to impossible. Recently, though, jaw bones from Tyrannosaurus rex specimens were re-examined and lesions in them were attributed to a parasite that continues to plague modern-day birds, Trichomonas gallinae. These single-celled parasites, closely related to the human STD, Trichomonas vaginalis, produce "cheesy" lesions in the mouth, pharynx and crop of birds such as pigeons, chickens, and your soon-to-be Thanksgiving turkey, causing a disease that is sometimes called "canker". These birds acquire the infection through consumption of contaminated water, but avian predators, such as falcons, can also be infected from eating parasitized prey. The authors of the paper that makes this link between lesions and T. gallinae hypothesize that even the Field Museum's famous "Sue" may have died of starvation as a result of this parasite damaging its mouth so badly. The image is an artist's vision of what the parasitized dino may have looked like. (Click on the thumbnail to get a better look and see the "cheesy" lesions in its mouth and check out this site for pictures of the parasite in pigeons.)

November 21 - Tetracladium sternae

Although most digenetic trematodes (except for schistosomes) are hermaphroditic and thus, by definition, capable of self-fertilization, there is some evidence that cross-fertilization may be quite common and maybe even the norm. But it is unusual to catch trematodes in the act of fertilization. There is one exception - Tetracladium sternae is a trematode found in shorebirds such as terns and shearwaters and it is often found in copulating pairs.

Post and image by Mike Kinsella.