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.

November 20 - Pedicularis groenlandica

Pedicularis groenlandica, or as it is commonly known as because of the shape of its flowers (see insert), Elephant's Head or Elephanthead Lousewort (a big handle for a little flower!) is a parasitic plant in the broomrape family (see also Boschniakia hookeri and Orobranche californica). These plants can be found in - you guessed it - Greenland, but also across Canada and into western North America. P. groenlandica uses haustoria to penetrate the roots of other plants and then suck their water and nutrients out.

November 19 - Asymphylodora tincae

Today's parasite is commonly found in freshwater fishes of the Palaearctic region. This particular worm has evolved to skip a few steps to the usual three-host life-cycle of most digeneans. Asymphylodora tincae uses a snails as a first intermediate host, where larval stages known as cercariae are produced through asexual multiplication - so far so usual for digeneans. However, instead of leaving the snail like most digeneans, the tailless cercariae stay inside the snail. Additionally, instead of then developing into the cyst-like metacercariae stage as a prelude to infecting the definitive host, this species has done away with that altogether. The cercariae of A. tincae can directly infect the fish definitive host, which occurs when the fish consumes an parasitised snail.

Reference and photo source:
Našincová, V. and Scholz, T. (1994) The life cycle of Asymphylodora tincae (Modeer 1790) (Trematoda: Monorchiidae): a unique development in monorchiid trematodes. Parasitology Research 80:192-197.

Contributed by Tommy Leung.

November 18 - Clinostomum sp.

This is a metacercarium of a Clinostomum species that was found encysted in the fin of Perca flavescens, the yellow perch. The definitive hosts of these trematodes are fish-eating birds and reptiles, and adult clinostomes are commonly found in the mouth and esophagus. Eggs of Clinostomum are shed in the feces, hopefully in the water. Miricidia then infect planorbid snails. Cercariae released from the snails penetrate the skin fish and amphibians (the second intermediate hosts), encysting as metacercariae throughout the body. Definitive hosts become infected when feeding on infected fish. Clinstomum metacercaria are often large and yellow in appearance, thus their presence is often called “yellow grub disease”.

Contributed by Jessica Light.

November 17 - Tetrabothrius sp.

The parasite for today is a tapeworm recovered from the intestine of an Andrews' Beak Whale (Mesoplodon bowdoini). This worm belongs to the genus Tetrabothrius, and while this particular species infects beaked whales (obviously), other species of Tetrabothrius have been found in a range of dissimilar marine hosts ranging from baleen whales to fish-eating birds such as albatross and penguins. Tapeworms like Tetrabothrius often have species-specific morphology of their scolex (which is the organ they use to attach themselves to the intestinal wall), and such features can be used to distinguish different species. Larval stages of tapeworm often lack such distinguishing characteristics, making their identification practically impossible. However, the advent of molecular biology technique has enable scientists to use DNA sequences from the larval stages and match them up to those taken from adult worms, allowing their full life-cycle to be mapped out.

Contributed by Tommy Leung.

November 16 - Opisthorchis viverrini

Stay out of the sun to avoid skin cancer. Don't smoke to avoid lung cancer. Don't eat raw fish to avoid liver cancer? It sounds a little strange, but in fact, the liver flukes Clonorchis sinensis and Opisthorchis viverrini have been found to be carcinogenic, inducing a cancer of the bile ducts that is very often fatal. The life cycle of O. viverrini is very similar to C. sinensis - they first pass through snails, then fish, and then finally the adults inhabit mammals that like to eat fish, including cats, dogs, and humans. The region of Khon Kaen, in northeast Thailand, has the highest incidence of these bile-duct cancers in the world - and 70% of the people in this region are infected with O. viverrini. A recent study produced large libraries of sequences of the transcriptomes - the genes that are transcribed at various stages - of these two important parasites, thus it is hopeful that new drug targets can be identified.

You can read more about the fluke/cancer link here.

November 15 - Pharyngodon australis

I was on my way home from grocery shopping when I spotted something in the middle of the road near where I live. As I got closer I saw that it was a dead lizard. So like any good parasitologist, I quickly got home, parked my car, grabbed some plastic bags and dashed across the road, scooping up the lizard in the process. It must have only just been recently killed because rigor mortis hasn't even set in. So I thought I'd make something worthwhile out of an otherwise senseless death, drove to work and started dissecting the dead lizard, and sure enough, found this parasite! Pharyngodon australis is a species of nematode found in the large intestine of Eastern blue-tongue lizard (Tiliqua scincoides), a large ominvorous skink from Australia. Thousands of nematodes live in the gastrointestinal tract of skinks and other lizards. Stable isotope studies have indicate that some of these nematodes might be consuming microbes living in the host's gut, while other experiments showed that they might even contribute to gut fermentation. So this might be a case of what would normally be assumed to be a parasitic organism actually being a welcome guest!

Contributed by Tommy Leung.

November 14 - Pseudolynchia canariensis

Pseudolynchia canariensis is a hippoboscid or louse fly that feeds on pigeons and doves and can transmit the blood parasite Haemoproteus columbae. This species is primarily found in Africa and Asia. If you click on this photo of a P. canariensis fly and look at it carefully, you can see tiny little pink dots near the back of its abdomen. These even smaller things are mites, though in this case they are not really parasitic, but rather phoretic, a phenomenon whereby one kind of organism uses another as a means of transportation. All aboard! This fly is now departing...

November 13 - Brugia malayi

Like Wuchereria bancrofti, Brugia malayi is another type of filarial nematode that is responsible for the disease known as lymphatic filariasis or, as it is better known, elephantiasis. The name comes from the fact that the adults inhabit the lymphatic system and their presence induces intense swelling, such that the skin resembles that of a saggy elephants. This species is found in Southeast Asia, including Vietnam, China, India, and other neighboring countries. It's estimated to infect over 13 million people in this part of the world. Prevention and treatment strategies include vector control and drugs, some of which are being newly developed thanks to the availability of a complete genome sequence.

November 12 - Amphibiocystidium ranae

Today we are featuring a fungal parasite of frogs. This parasite is former known as Dermocystidium ranae and was classified within a genus which also included a number of fungal parasites of fishes. However, further research on D. ranae found that it has a number of life-cycle and morphological features which separate this parasite from others within the Dermocystidium genus. Because of those distinguishing characteristics, it has now been reclassified and placed in a genus of its own - Amphibiocystidium - to reflect its unique status. While the parasite in the fish-infecting sister genus, Dermocystidium, has recieved much scientific interest over the last 50 or so years, far less research has been conducted on Amphibiocystidium ranae and it is not clear if it cause any actual harm to its amphibian host or if it is more of a benign parasite.

Reference:
Pascolini, R., Daszak, P., Cunningham, A.A., Tei, S., Vagnetti, D., Bucci, S., Fagotti, A. and Di Rosa, I. (2003) Parasitism by Dermocystidium ranae in a population of Rana esculenta complex in Central Italy and descriptiion of Amphibiocystidium n. gen. Diseases of Aquatic Organisms 56: 65-74

Contributed by Tommy Leung.

November 11 - Sanguilevator yearsleyi

This parasite was almost one that was featured for Halloween - you'll see why soon - before worms in the eyes of giant birds and blood-lapping/swapping bats took over. But, this tapeworm is really fascinating, so I wanted to feature it now. Sanguilevator yearsleyi was recently discovered in the spiral intestine of a broadfin shark (Lamiopsis temmincki), in Sarawak, Borneo. Histological examination of the tapeworms' scoleces (plural of scolex) revealed spherical and transverse channels that were then found to contain white and red blood cells, respectively, suggesting that the tapeworm sorts and stores these host cells. Why it does this, though, is a bit of a mystery, as tapeworms lack a digestive system per se, and typically just absorb simple nutrients from their hosts.

Nominated by Joanna Cielocha and image comes from the paper describing the species.

November 10 - Holobomolochus confusus

Here’s another ectoparasite of the European flounder, Platichthys flesus (Linnaeus, 1758) (Teleostei: Pleuronectidae). This time, it is Holobomolochus confusus (Stock, 1959) (Copepoda: Bomolochidae). The photo shows an adult female with 2 egg sacs. This specimen was isolated from the fish’s nasal cavity, which is the typical infection site. In comparison with other ectoparasitic copepods of the European flounder, i.e., Acanthochondria cornuta and Lepeophtheirus pectoralis, it is remarkably smaller, occurring less frequently and in lower numbers. This parasite is commonly found infecting the cod, Gadus morhua (Linnaeus, 1758) (Teleostei: Gadidae), and has also been reported from other species of fish.

For details, see the papers below:
1. Cavaleiro, F. I. & Santos, M. J. (2007) Survey of the metazoan ectoparasites of the European flounder Platichthys flesus (Linnaeus, 1758) along the north-central Portuguese coast. Journal of Parasitology 93, 1218-1222.
2. Cavaleiro, F. I. & Santos, M. J. (2009) Seasonality of metazoan ectoparasites in marine European flounder Platichthys flesus (Teleostei: Pleuronectidae). Parasitology 136, 855-865.

Contributed by Francisca I. Cavaleiro & Maria J. Santos, Universidade do Porto, Faculdade de Ciências, Departamento de Biologia, Rua do Campo Alegre, s/n, FC4, 4169-007 Porto, Portugal.

November 9 - Meloe franciscanus

Today's parasite is the larval stage of the blister beetle Meloe franciscanus. The beetle larvae are brood parasites that feed on eggs and the young of the solitary bee Habropoda pallida. The problem is, how do they get into the nest of a female bee on the first place? Well they do it by imitating the real thing. They gather into a swarm and climb to the tip of a grass stem. Once there, they clump together to form a small brown blob. While it might not look like much to you, but beetles give off a smell and produce vibrations that fool a male bee into thinking that the blob is one fine hottie. For the beetle larvae, it's a collective effort - the more of them there are in the blob, the more attractive they appear to a male bee. As soon as the bee comes into range expecting to get lucky, all the beetle larvae jump onboard. The experience leaves the bee slightly shaken, but unstirred, and he continue on his quest to find a female bee. However, once he does find a real female, he also ends up passing on his sticky hitch-hikers as a sexually transmitted infection. Once the beetles are all onboard the poor female, they cling on for dear life, eventually disembarking at her nest where they will be surrounded by all the food they'll ever need to grow up.

Photo credit: SFSU

Contributed by Tommy Leung.

November 8 - Baylisascaris procyonis

Baylisascaris procyonis is a nematode parasite, related to Toxocara canis. The adults live in the intestine of their hosts and lay eggs that pass out with the feces. If an animal swallows these eggs, the larvae hatch out in the intestine of this host and then one of two things can happen. If they find themselves in their final, i.e. definitive, host, then they will basically stay put - maturing into adults and beginning the cycle all over again. But, if the animal that swallowed them is not the definitive host, then well, things get a little messy. In these cases, the larvae leave the intestine and travel through the bloodstream, invading other tissues and usually making temporary homes in the central nervous system. If that host is a mouse, they can kill it or at the least cause it to act strangely, which can increase the chances of it being consumed by the definitive host. B. procyonis is a parasite of raccoons, and is very common in them (prevalence >70%). Recently, with raccoon populations expanding and coming into closer and closer contact with humans, people, especially children, are increasingly becoming accidentally infected with this parasite. Since we're not the definitive hosts, the larvae undergo visceral migrans and can cause very serious disease and even kill the human. There have been at least four reported deaths due to this parasite in the U.S. since 1980 and there is not currently an effective treatment.

You can read more about the human cases of B. procyonis here.

November 7 - Syngamus trachea

Syngamus trachea is a nematode known as the gapeworm, which infects birds such as chickens and turkeys. The name comes from the fact that they live in the birds' trachea and, when there are enough of them, they can cut off the airways, causing the bird to gape open their mouths. Females live in permanent conjoinment with males. When they lay eggs, the bird will cough them up and swallow them, and then they will pass out with its feces. Another bird may come along and ingest them or a snail or a worm may serve as an intermediate host.

November 6 - Otodectes cynotis

Many people who have had a dog or a cat as a pet are probably familiar with ear mites - infections that can cause your pet to have brown, cruddy material in their ears, shake their heads, and even itch frantically at their ears. Here's a close-up look at the culprits - Otodectes cynotis. These tiny arachnids are spread from animal to animal via direct contact and then take up residence in the ear canal. The adults lay eggs in the ears and then the mites hatch out and go through a larval stage and two nymphal stage before becoming mature. If left untreated, the mites can induce secondary bacterial or yeast infections, and, in rare severe cases, even deafness in the ear as well.

November 5 - Armillaria ostoyae

Yesterday, you met the smallest wasp known. Today meet one of the largest fungi known. Armillaria ostoyae is a species of parasitic fungus that is commonly known by the pleasant name of "Honey mushroom", but which causes the disease of both hardwood and coniferous trees called "Shoestring Rot." That latter name come from the appearance of rhizomorphs that the fungus can use to move between trees and infect them. Although relatives are edible and this fungus may be fine for most people to eat, others have experienced poisoning-type symptoms, thus you should probably avoid this one unless you really know what it is and that you are tolerant of it. This particular species is found in the Pacific Northwest and a few years ago, a colony of A. ostoyae in the Strawberry Mountains of Oregon was measured to be 2200 acres (8.9 square kilometers!) in size and was estimated to be over 2000 years old. That's one humongous fungus!
Photo from biopix.dk

November 4 - Camptopteroides verrucosa

Camptopteroides verrucosa is a species of fairyfly (family Mymaridae) - which is to say that it's not a fly at all, but rather a tiny little wasp. The very largest of these wasps only has a wingspan of 3 millimeters, so we are definitely talking tiny! Although not much is known about them, it has been observed that they can move and even mate underwater. The females inject their eggs into those of other insects and use an enormous variety of different hosts. These little parasitoids have recently been used in biocontrol efforts.

November 3 - Telogaster opisthorchis

Previously, we met Ribeiroia ondatrae, the trematode parasite which causes limb malformation in frogs. Now meet Telogaster opisthorchis, a trematode that causes malformation in fishes, specifically the larvae of Galaxias anomalus, a freshwater fish native to New Zealand which is only found in two catchment in the Otago region. If the metacercariae of T. opisthorchis happens to lodge themselves in the right spot, they can induce spinal deformities, resulting in "kinky" fish (see photo - the top fish is normal for comparison) that, like malformed frogs, are more susceptible to predation. As you can easily imagine, even without predation pressure, the survival of such malformed fish would be heavily compromised.

Interestingly, it has been found that the parasite combined with herbicide run-off has a synergistic effect on the fish larvae. While the trematode infection alone can induce the spinal deformities, exposure to the herbicide increases the severity of malformation. In addition, snail hosts that produce the cercariae - the infective stage of T. opisthorchis which infects the fish - also release more cercariae after exposure to moderate level of herbicide. Such an example illustrates how human activities can severely alter the dynamics of pre-existing ecological processes in the environment, such as those relating to the transmission of infectious diseases.

Reference:
Kelly, D.W., R. Poulin, D.M. Tompkins, and C.R. Townsend. 2010. Synergistic effects of glyphosate formulation and parasite infection on fish malformations and survival. Journal of Applied Ecology 47: 498-504.

Contributed by Tommy Leung.

November 2 - Heduris spinigera

Heduris spinigera is a species of parasitic nematode found in the stomach of a number of New Zealand's brackish water fishes. While this parasite was initially described decades ago, its lifecycle was only recently determined using a combination of both morphological and genetic identification techniques. This parasite uses a small crustacean as its intermediate host - the benthic amphipod Paracorophium excavatum. While this amphipod is consumed by many different species of fish, it seems that not all fish are equally suitable as hosts for H. spinigera. While their diets potentially expose them to H. spinigera, the nematode fails to become establish in these potential hosts, possibly due to factors such as host anatomy or physiology.

Like most parasites, H. spinigera is restricted to infecting a limited range of host species. Most parasites display some degrees of host specificity, and there are only very few parasites which can truly infect a wide range of different hosts. We now know that many species of parasites, which were previously believed to be host generalists, are actually cryptic species complexes, composed of morphologically similar but genetically distinct species, each infecting a different species of host.

Reference:
Luque, J.L., F.M. Vieira, K. Herrmann, T.M. King, R. Poulin, and C. Lagrue. 2010. New evidence on a cold case: trophic transmission, distribution and host specificity in Hedruris spinigera (Nematoda: Hedruridae). Folia Parasitologica 57: 223-231.

Contributed by Tommy Leung.

Link to paper here.

November 1 - Onchocerca volvulus

Onchocerca volvulus is a filarial nematode parasite of humans that causes the disease river blindness or onchocerciasis, primarily in Africa. These nematodes are transmitted by black flies, which release the larval nematodes with their saliva when they take a blood meal. The larvae mature in the human's subcutaneous tissue and mature in nodule structures. Females will produce over a thousand microfilarial larvae per day - these tiny larvae circulate in the blood, waiting to be picked up by another black fly. Although the mature worms can live in the host for over a decade, it is the larvae that truly produce the disease symptoms - and more specifically, it is their endosymbiotic Wolbachia bacteria that cause the distress. When microfilariae die and begin to degrade, the surface proteins that these bacteria produce cause the human immune system to react quite violently - and this can cause both severe skin issues as well as cause the cornea to become opaque, thus producing the characteristic blindness. Ivermectin, an antihelminthic drug is very effective against this disease.

Image is from this website.