March 31, 2010
Ever seen a grasshopper jump into a pool? Probably not. The reason is normal, healthy individuals would never take a dive to almost certain death. Spindochordodes tellinii on the other hand, has different intentions. This parasitic nematomorph hairworm is able to override the grasshopper’s instinct to stay out of water. Spindochordodes tellinii larvae are consumed by grasshoppers or crickets and develop inside their hosts. The hairworm can grow to enormous lengths yet allow the grasshopper or cricket to stay alive. The exact process S. tellinii uses to manipulate its host is still largely unknown. We do know that the parasite produces proteins that affect the central nervous system and that infected grasshoppers/crickets also produce different proteins in their brains which healthy individuals do not. Mature adult S. tellinii use their abilities to force their host to jump into some body of water allowing the parasite to escape to find a mate. Understanding how parasites can manipulate behaviors of other organisms may help us to further understand human behavior-system links.
See: Bhattacharya, S. 2005. Parasites brainwash grasshoppers into death dive.
Contributed by Zander Crawford, Bucknell University.
March 30, 2010
Loa loa, also known as the “eye worm,” gets its name from an affinity for subcutaneous tissue like the tissue found in human eyes. This nematode parasite finds its way into humans through the deer fly, in which the Loa loa worm larvae develop. Once in its third stage, a larva can enter a human when a deer fly bites. When larvae mature within subcutaneous tissue, they produce microfilariae – an uninfective stage of the Loa loa, which are then picked up by other deer flies. These parasites can be removed surgically, but drugs are required to kill microfilaria within the bloodstream. Adults can survive in subcutaneous tissue for up to 17 years, and take one year to fully mature. The first recorded case of Loa loa dates back to the year 1770 when a surgeon failed to remove a worm in a woman’s eye in the Caribbean. Loa loa was again found in slave ships coming to America. Loa loa has not been diagnosed in the United States in almost a century, but the parasite is still endemic to western and central Africa. While not fatal, Loa loa can be a complication for patients with other diseases. These microscopic worms are hard to see, unless they’re in your eye.
1. Loa loa: A cutaneous filarial parasite of humans. Filarial Biology.
2. Muller, R. Worms and Human Disease. New York: CABI, 2002.
Contributed by Prath Devre, Bucknell University.
March 29, 2010
Naegleria fowleri is a protist that seems to be straight out of science fiction. Ranking at number five on the Science Channel’s "Top Ten Infectious Diseases", N. fowleri is a free-living amoeba capable of devouring your brain! This insidious creature makes its home as a flagellated amoeboid in characteristically warm freshwater sites such as lakes, rivers, geothermal hot springs, warm water discharge from industrial plants, poorly maintained and minimally-chlorinated or unchlorinated swimming pools and Jacuzzis. However, it has also been documented that it can be contracted by the inhalation of dust containing its cyst form, and has been isolated in places such as soil or air conditioning units. Although it prefers warm conditions that can reach up to 46°C, N. fowleri can endure winters by becoming cysts that settle into bottom-lying sediment. Capable of parasitizing a variety of mammals, including humans, the amoeba causes primary amebic meningoencephalitis (PAM), a fatal disease that has been recorded as the cause of death in over 150 worldwide cases reported. In all of these cases, the victim of this lethal microbe died within two to three days of infection. Infection occurs almost exclusively through the olfactory tract whereupon it migrates to the brain or spine of its host by traversing the olfactory nerve. It then feeds upon brain tissue and blood cells as an amoeboid trophozoite via phagocytosis and pinocytosis. Thankfully, it isn’t contagious between hosts.
Contributed by Jameson Clarke, Bucknell University.
March 28, 2010
Wuchereria bancrofti is a nematode parasite found in Africa, South America, and tropical and sub- tropical countries in other locations. This worm uses two hosts: mosquitoes and humans. The microfilarias inhabit a mosquito until they grow into their motile larvae stage. They then move on to a human host; being transmitted during the blood meal of the mosquito. While in the human host they move to the lymph nodes over the course of a year where they then develop into the adult worm stage. Adult worms live 4-6 years in their host and produce millions of microfilaria which make their way into the circulatory system from the lymph nodes. This parasite can cause permanent damage to both the kidneys and the lymphatic system. Damage to the lymphatic system can cause a disease known as lymphatic filariasis in which the lymphatic system stops working properly and the lymph nodes become enlarged. It is estimated that 120 million people in 80 countries have suffered from filariasis. Untreated, this could lead to elephantiasis, a thickening of the skin and tissues which produces large growths on the body. Some drugs have been found that kill these parasites but only in their developmental stage. No current treatments have been found to eliminate adult parasites.
Contributed by Laura Rycek, Bucknell University.
March 27, 2010
Haemobaphes diceraus is a parasitic pennellid copepod that is found on a variety of fish species. This is an interesting species because it is a type of crustacean and many people would never think of a crustacean as a parasite. It is also an interesting parasite because it looks nothing like a crustacean in its adult form. This parasitic copepod extends from the gills and into the bulbous ateriosus of the heart where the parasite is anchored. The distinguishing feature of this parasite is the large, spirally coiled egg sacks. These egg sacks project from the gill arch of the host fish. The egg sacks are attached to a trunk which extends into the heart. While some copepods are able to move about freely, this copepod has reduced segmentation and appendages in its adult form (Goater 1996). When the eggs hatch they are released into the water where they undergo a series of molts until they are developed enough to find a host. Pennellids such as the Haemobahes diceraus are unique in that they require an intermediate host. After fertilization of the egg the newly hatched parasite has a free swimming phase. It then locates a fish, attaches itself and grows to adulthood. (Goater and Jepps 2002).
Goater, Tim. 1996. “Parasitic Copepoda.”
Goater, T. and Jepps, S. 2002. Prevalence and Intensity of Haemobaphes diceraus (Copepoda: Pennellidae) from Shiner Perch, Cymatogaster aggregata (Embiotocidae). Journal of Parasitology 88: 194-197.
Contributed by Taylor Phillips, Bucknell University.
Image from this site.
March 26, 2010
Trichuris trichiura is a parasite found in human intestines. Also known as the human whipworm, this parasite’s adult and larval forms can live in the large intestine for up to 5 years, feeding on intestinal tissue secretions. These roundworms are pinkish-white in color and resemble a whip in shape and movement. Females lay 2,000-10,000 larvae per day, which are shed in human feces. With the right amount of moisture and warmth, in 2-3 weeks these eggs become infectious. Humans may become infected by accidental ingestion of eggs from fecal contaminated soil. Infectious eggs are sometimes found in water or in dry foods such as rice, grains, vegetables, and beans. Once ingested, the eggs hatch and burrow into the wall of the small intestine where they grow. About 300-500 million people are infected worldwide, mostly located in tropical places. Diagnosis occurs when eggs are observed in patients’ feces. Although rare in the U.S., people who do not dispose of human waste properly, have poor hygiene, and children playing in dirt contaminated with animal feces are especially prone to the disease. Recent studies have also shown that people with trait characteristics in chromosomes 9 and 18 may also be susceptible. Humans with over 100 parasites may have symptoms associated with intestinal disease. Very serious cases may cause diarrhea, vomiting, loss of appetite, constipation, blood loss, anemia, rectal prolapse, inflammatory and toxic damage to intestines. Medication as well as anti-parasitics are effective to promote healing.
Contributed by Allison Gittings, Bucknell University.
Image from the CDC Public Health Image Library.
March 25, 2010
In the aftermath of the earthquake, aid workers report that scabies has been running rampant in tent cities in Haiti. Scabies is a contagious disease caused by Sarcoptes scabiei, parasitic mites that are hosted on humans, dogs, cats, and other wild animals such as koalas, gorillas, and wild boar. Sarcoptes scabiei are Acariformes, members of the subclass Arachnida (spiders, scorpions, mites and ticks), subphylum Cheliceriformes, phylum Arthropoda. Up to 104 species are known to have been infected with Sarcoptes scabiei, producing a condition called sarcoptic mange. All four stages of the parasite’s life, egg, larva, nymph and adult, take place on the host’s epidermis. The adult female burrows under the skin and lays 2 or 3 of her eggs each day. To enter the skin, the mites use cutting mouth parts and cutting hooks on the legs. As the life cycle progresses, the mites come to the surface of the skin, then burrow into molting patches to complete the stages. Burrowing mites feed on living cells and tissue fluid. The first hosts of S. scabiei are thought to have been humans. The mites then infected domestic animals that later transferred the parasite to wild animals. The movement of the mites into and on the skin produces an allergic reaction and is extremely itchy. On humans, scabies is most common in areas of the body that come in contact with the skin of other humans, such as the hands and arms. Scabies can be treated with prescribed medical cream.
Contributed by Sara Baughn, Bucknell University.
March 24, 2010
Dracunculus medinensis is a creature in the phylum Nematoda that is behind the dreaded Guinea Worm Disease. The disease is actually caused by the significantly bigger female nematode. Their life starts off with the larvae living inside of small crustaceans (copepods). When a human drinks unfiltered water, they are incidentally ingesting these small crustaceans and this is the beginning of Guinea Worm Disease. Shortly after being ingested, the small crustaceans die and release the nematode larva, which then penetrates the host stomach, intestinal wall, and enters the abdominal cavity. After reaching maturity, which takes about a year, the males die and the females survive and start to migrate through the subcutaneous tissue layer towards the surface of the skin. At this point, the female can emerge from any part of the body including the head, torso, upper body, buttocks, and genitalia, although the bottom of the foot is where they emerge from most of the time. On the bottom of the foot, the female causes painful blisters which cause the host to look for a form of relief by placing their foot into water. When the female parasite comes into contact with water, she will release her larvae which are then injested by small crustaceans and after two weeks the larvae become infectious and the cycle is ready to begin again. As a side note, the only way to remove the parasite is to pull it out through the hole it has made in the surface of the skin. OUCH!!!
Contributed by Tracey Brooks, Bucknell University.
March 23, 2010
Argulus foliaceus, also known as the common fish louse or the carp louse, is actually not a louse or even an insect at all, but a crustacean. Within the class Maxillopoda, the subclass Branchiura consists of about 150 species of freshwater and marine fish ectoparasites. The genus Argulus is found throughout the world. Argulus foliaceus is native to Europe, but is also common on aquarium and pond fish worldwide. Although the louse shows some host preference, especially for carp, it is usually considered a generalist and is found on a variety of fish species. The oval-shaped, flat adults attach to fish hosts using hooked suckers. They inject digestive enzymes into the host and feed on blood and tissue fluids. Symptoms of lice infestation include abnormal swimming, rubbing, and deteriorating physical condition. Because of tissue damage caused by the parasite, secondary bacterial and fungal infections frequently occur. Adult females leave their hosts and lay eggs on vegetation or other submerged objects. Adults can live free of hosts for two to three weeks, but newly hatched larvae only survive a couple of days if they do not find a host. Treating an infested aquarium may require several approaches, so prevention is best. Always visually inspect and quarantine new fish. Lice may be removed from fish manually with forceps. Fish should be transferred to an alternate aquarium while chemical treatments are used to kill remaining adults, larvae, and eggs.
Contributed by Elizabeth McCarthy, Bucknell University.
Photo from this site.
March 22, 2010
Few species exhibit behavior as gruesome and horrifying as the parasitic wasp, Cotesia congregata. As the great naturalist Charles Darwin once wrote, “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae [one group of parasitic wasps] with the express intention of their feeding within the living bodies of Caterpillars.” Cotesia congregata belongs to this superfamily of Hymenoptera and their sinister life cycle begins when the adult female oviposits up to eighty eggs, as well as a host of symbiotic viruses, into the body of a young tobacco hornworm While the viruses suppress the caterpillar’s immune responses, the wasp larvae will hatch and undergo a series of molts within the caterpillar. Feeding on the host’s bodily fluids, but carefully avoiding any damage to the vital organs, the mature larva will eventually eat through the caterpillar’s skin and find a nearby branch on which to build a cocoon. At this point the hornworm, remarkably still alive, will arch over the cocoons and vigilantly stand guard over the brood. The host will remain in this position without moving or eating until the wasps have all emerged from their cocoons. The caterpillar will sometimes go so far as to spin a protective layer of silk over the pupae as they grow and voraciously defend the cocoons from predation. The mechanism by which the Cotesia wasps control the host’s strange behavior is not fully understood. However, because a few larval Cotesia remain behind (staying within the host) during pupation, popular theory has implicated them as the primary forces dictating the host’s behavior.
See more in: Zimmer, Carl. Parasite Rex. New York: Simon & Schuster, 2001.
Contributed by Phillip Zook, Bucknell University.
Thanks to Alex Wild for the photo.
March 21, 2010
Often times endoparasites will alter the behavior of a host to complete their lifecycles. The acanthocephalan, Plagiorhynchus cylindraceus, is a common parasite of songbirds in North America, typically robins (Turdus migratorius) or Europeans starlings (Sturnus vulgaris). While inside the bird, the worm produces eggs that pass out in the bird’s feces and are consumed by pillbugs (Armadillidium vulgare, shown in photo), the main intermediate host. This worm is capable of activating a suicidal behavior in the pillbugs to propogate its own lifecycle. Once infected with the acanthocephalan, the pillbugs become more active and frequent uncovered, light-colored areas on the forest floor while avoiding hiding underneath objects, such as leaves. By exposing themselves, the pillbugs are more likely to be eaten by a predator, such as robins or starlings. Once consumed by the bird the worm is free to reproduce, thus completing its lifecycle. Pillbugs are not the only animals to become infected with this worm. Some North American shrews (Soricidae) have been found with these worms encapsulated in their intestinal mesenteries, although this becomes a dead-end for the parasite because it cannot be passed on to a songbird from the shrew’s intestines. The proboscis of this parasite has many hooks that it imbeds in the host’s intestinal walls and prevent it from passing through with a host’s meal. Nutrients from such a meal are absorbed through the body surfaces of the parasite; the only way the worm receives nutrition since it lacks a gut tract.
Contributed by Anna Phillips.
March 20, 2010
The next time you emerge from a lake and soon find yourself covered in itchy, red papules, you probably have a schistosome like Trichobilharzia ocellata to blame. Cercarial dermatitis, or Swimmers’ Itch, is a skin rash caused by the larval stage of a schistosome flatworm like T. ocellata mistaking a human for their primary host and burrowing into their skin. In humans, small blisters form around the larvae, which soon die because they cannot continue developing. The infected person’s immune response leads to tingling, burning, and itching of the skin.
Here’s what the T. ocellata was supposed to do: The adult schistosomes live in the blood of infected waterfowl, such as ducks and geese. Eggs produced by the adults are passed through the host’s feces and, if the eggs land in water, they hatch and release small, free-swimming larvae called miracidia. These larvae then find, and infect their intermediate hosts, freshwater snails. Once inside a snail the larvae multiply and continue to develop, eventually become cercariae. Cercariae are released through the snail’s feces, and this larval stage is the one that will infect the parasite’s primary host and become an adult. If the cercariae infect you instead, they won’t become adults but you will have an itchy few days.
Contributed by Kate Bowell.
March 19, 2010
This is is an undescribed species of Trichodina sp. from the gills of Mugil cephalus in brackish waters around Brisbane, Australia. There are over 150 species in the genus Trichodina sp., making it one of the most species-rich parasite genera. They occur in fresh, brackish and salt water and are most prevalent when organic loads in the water are high. Al Dove did a good chunk of his doctoral thesis on trichodinids and he says, “Lets face it, they’re the prettiest parasites ever. I like this picture because it’s NOT the usual pretty silver nitrate denticle photo, and it shows off their “scrubbing bubbles” body shape, which gets lost when you dry them onto a slide. I also like that you can see bacterial rods adhering to the cell surface just near the cytostome, which faces away from the host, consistent with their commensal habits.”
Contributed by Al Dove.
March 18, 2010
Caullerya mesnili is a unicellular parasite that infects the gut of several species of waterfleas (Daphnia spp.), a type of abundant zooplankton, commonly found in many freshwater lakes. This parasite is very virulent (harmful) to its host. Once the infection becomes established, the host is castrated and eventually dies less than 3 weeks later. During this entire period, the infected individual will be releasing spores that then infect other waterfleas in the environment.
There is evidence that the genotype of the waterflea affects the infection success of C. mesnili, with the most common genotype in a given population being more frequently infected by this deadly parasite. Thus both the waterflea and parasite are engaged in a coevolutionary relationship which maintains genetic diversity in both populations, operating in a manner predicted by the "Red Queen" hypothesis.
You can read lots more about this parasite in this paper and/or this one.
Contributed by Tommy Leung and Justyna Wolinska.
Photo by Justyna Wolinska.
March 13, 2010
Today, millions of people are celebrating St. Patrick’s Day, whether Irish or not. One of the legends surrounding St. Patrick is that he supposedly purged Ireland of snakes, so today I thought I’d feature a parasite that might have done the trick for ol’ Paddy, Cryptosporidium serpentis. Like its cousin, Cryptosporidium parvum, whom you’ve met before, C. serpentis is an apicomplexan parasite that produces very resistant oocysts that are passed out in the feces and can remain in the environment for long periods of time. These parasites have been very deadly in zoo snakes and also potentially among some pet snakes if they are housed in ways that they might be exposed to the infective oocysts.
Image comes from this paper.
Huh? A flightless fly? These highly specialized bat flies (Diptera: Hippoboscoidea) feed exclusively on the blood of bats and live their lives clinging mightily to the fur of their volant hosts. Although considered true flies, these derived creatures have lost their wings entirely and evolved specialized structures for ‘swimming’ through or ‘running’ across the fur of their hosts. They have a bizarre life-history, bat flies do not lay eggs, but rather eggs develop internally within the females nourished by uterine “milk” and a single prepupa (3rd instar larva) is deposited on the roost substrate. When young flies emerge, they crawl on to the nearest bat and live out the rest of their life on their host. Interestingly, bat flies are generally quite host-specific but Cyclopodia horsfieldi is known to occur on three species of “flying fox”, or Old-World fruit bats (Pteropus), found in Southeast Asia. If bats aren’t your cup of tea, then an experience with the World’s largest bats teaming with a bunch of wingless blood-sucking flies is sure to induce nightmares!
Contributed by Kevin Olival.
One of these eggs is not like the other…one of these eggs just doesn’t belong. We can see this very obviously, but for some songbirds, not noticing this different egg can have very negative consequences. The different egg is that of a Brown-headed Cowbird, Molothrus ater, a brood parasite. These birds range widely across North America and as adults, they feed primarily on insects, often following grazing animals to eat the insects that they stir up and attract. These brood parasites have been documented using over 200 different species of birds as hosts. Though they’re lazy parents, they are very demanding parasites and check back on their eggs' progress. And, these birds can also demonstrate a very nasty retaliatory behavior. If the host bird recognizes the Cowbird egg and kicks it out, the Cowbird will often trash the host nest, punishing the discriminating host. You can read more about this here.
See photos of the adult birds here.
In the days and weeks after September 11, 2001, panic and suspicion seemed to be everywhere. After the terrorist attacks with airplanes, new threats in the form of letters sent to such famous people as newscaster Tom Brokaw and Senators Patrick Leahy and Tom Daschle were found to contain purified spores of Bacillus anthracis. B. anthracis is a Gram-positive bacterium that is usually found in the soil. When the spores of the bacteria are inhaled or ingested, they reproduce in the animal or human’s body, and can cause the disease anthrax, characterized by a multitude of health problems ranging from skin lesions (cutaneous anthrax) to gastrointestinal and pulmonary problems. B. anthracis is also notable as a parasite because it was the organism that the German microbiologist, Robert Koch used to formulate Koch’s postulates, the set of criteria that are necessary to define that an organism is the causative agent of a disease.
Image is from the CDC Public Health Image Library.
Ixodes scapularis, the blacklegged or deer tick, is a hard-bodied (ixodid) tick that is common across the eastern and Midwestern U.S. These ticks have become recognized as important vectors of several emerging diseases, most notably Lyme Disease, but also Babesia and Anaplasma. Like many other ticks (see Dermacentor variabilis, for example), the life cycle of I. scapularis involves three stages: a larva, a nymph, and an adult. Larval and nymphal I. scapularis often take their blood meals from deermice, but the adults favor larger mammals, particularly white-tailed deer. Humans (and domestic animals) can become infected when they are accidental hosts to nymphal or adult ticks that became infected when they acquired the bacterial or protozoan parasites from their first or second hosts.
March 12, 2010
Here’s Lepidapedon, a lepocreadiid digenean. Lepocreadiids are very common in marine fishes and are almost a prototypical digenean; they have oral and ventral suckers, two testes (the big medial blue blobs), one ovary (darker blue blob in front), a lot of cortical vitelline follicles for making egg shells (the brown blobs all round the outside) and a lightly spiny tegument, which probably aids them in holding onto the intestinal mucosa of their teleost fish hosts. Like all digeneans, they have complex life cycles involving a mollusk first intermediate host, but in most cases, including this one, that host is not known. After the mollusk comes a crustacean of some sort, again unknown in this case, which is actively penetrated by the cercarial stage that emerges from the mollusk. The definitive fish host becomes infected by eating the crustacean. This Lepidapedon is from the intestine of the butterfish, Peprilus triacanthus, a common midwater schooling fish on the Atlantic coast.
Contributed by Al Dove.
March 11, 2010
As noted by the Jonathan Swift quote at the top of this blog, many parasite themselves are infected with parasites. These obligate parasites of other parasites are called "hyperparasites". Parasitoid wasps that infect and enslave caterpillars can themselves be impregnated by hyperparasitoid wasps, parasitic crustaceans like Sacculina are parasitized by bizarre hyperparasitic isopods, some parasitic flukes are infected by protozoan and bacterial parasites. Viruses cannot replicate on their own and must inject their genetic material into the cell of their host, hijacking its cellular machinery for its own replication, thus making them obligate intracellular parasites. In 2008, it was found that some viruses themselves can become infected by other viruses. In this case, the host is the virus you met yesterday, a strain of mimivirus, and the parasite belongs to a previously unknown group of virus that have been termed "virophages". Bernard La Scola and colleagues discovered that these hyperparasitic viruses, which they named "Sputnik". Each of these Sputnik measuring 50 nm in size, and just as more traditional virus hijack the machinery of their host cells for replication, the Sputnik commandeers the "viral factories" of the mimivirus to churn out more virophages at the host's expense. In a case of "you are what you eat" (in this case "you are what you infect"), the virophage's own genome is littered with genes from its own host, some of which are genes that the mimivirus itself had also acquired from the cells it infects, making the virophage a strange genetic chimaera.
Contributed by Tommy Leung.
Image from this source.
March 10, 2010
Mimivirus is part of the Mimiviridae, a group of "giant viruses", which compared with viruses most people are for familiar, with such as influenza virus, HIV, or Ebola virus, are unusual in many ways. In fact, mimiviruses are so different that they challenge the traditional concept of a virus and even the definition of life itself. Measuring 400 - 800 nm in diameter, mimiviruses are the giants of the virus world. Their viral particles themselves are unusually large and complex and this complexity is also reflected in their genome which is huge for a virus. Their genomes contain 1.18 million basepairs, which is more than 600 times larger than the genomes of any of the viruses named above, but also even larger than many bacteria (e.g. Treponema and Chlamydia). And unlike "normal" viruses, which only have a few genes (e.g. 9 genes in influenza), mimivirus has more than 900 genes and many are genes that otherwise have only been seen in cellular organisms. The strain of mimivirus in this context infects Acanthamoeba spp, which are free-living, bacteria-eating amoeba, commonly found in soil and freshwater habitats.
Contributed by Tommy Leung.
Image from this site.
March 9, 2010
Moniliformis moniliformis is an acanthocephalan, or thorny-headed worm. Like others in this group. M. moniliformis alternates between two hosts. The first is usually an insect such as a cockroach or a beetle, and then the definitive host is often a rodent such as a mouse or rat. Janice Moore and colleagues have used M. moniliformis to conduct a variety of studies on the manipulation of host behavior and have found that some cockroaches that are infected with M. moniliformis move more slowly, though other cockroach species do not have detectable changes in behavior. Humans can become infected if they ingest the intermediate hosts accidentally (but so far there is no evidence that they turn into couch potatoes who like dark rooms.)
March 8, 2010
Many people, myself included, enjoy the beautiful flowers of orchids. And right now, at least three U.S. botanical gardens (MOBOT ,NYBG, and the Cleveland Botanical Garden) are featuring their yearly orchid shows. The ones that are out for display and that are kept as houseplants typically feature long, delicate flower stalks that are peppered with multiple, brightly colored flowers. Rhizanthella gardneri is an orchid as well, albeit not one that most people would use to decorate their home or office. It’s a parasitic orchid native to Australia, that spends its entire life completely underground, feeding off another species of plant, the broom honey myrtle plant, Melaleuca uncinata, using a fungal partner called Thanetophorus gardneri. Surprisingly, R. gardneri can reproduce sexually, and it’s thought that it attracts pollinators via its strong-smelling flowers that animals dig up. Some have speculated that it is dispersed via fruit-eating marsupials, but very little is known about these plants.
Image from this site.
March 7, 2010
Yesterday, you met the cat flea. Believe it or not, these tiny blood-feeding insects are the intermediate hosts to a tapeworm that as adults can grow up to 18 inches (or 40-50 cm) long once they are ensconced in the intestine of their mammalian host! The eggs of the tapeworm are expelled in the host’s feces and are ingested by fleas. Inside the flea, the eggs hatch and the larval tapeworms travel into the body cavity and wait there for a mammal to eat the flea – usually when they are grooming an itchy spot. Children can become infected with D. caninum if they accidentally (or purposefully?) ingest infected fleas.
March 6, 2010
The cat flea, Ctenocephalides felis, is by no means restricted to just cats. In fact, it is quite happy taking blood meals from just about any warm-blooded mammal, though it is in fact, most commonly found on cats and dogs. Adult fleas take blood meals from their mammalian hosts and then lay their eggs on the host’s fur. The eggs don’t usually stick there, though and will fall out with the fur into the bedding or other environment. Larvae hatch out of the eggs and then will begin to eat just about anything organic lying around – commonly their parents’ feces, which are of course made of dried blood (shown in photo). The larvae will eventually spin a cocoon and pupate and then the adult pops out and looks for a mammal so it can start feeding. Generally, C. felis does not cause many problems, other than the annoyance of feeling them jump around and bite and the allergic reactions that occur in some animals and people. They do transmit a worm, however. We will meet that parasite tomorrow.
March 5, 2010
“I’ll have the pork chops, please.”
“Excellent choice, sir. How would you like those cooked?”
You’ll never hear that dialog in a restaurant (I hope!) and Trichinella spiralis is one of the main reasons. The adults of these nematode worms live in the intestines of their host, and like many nematodes we’ve seen, the females lay larvae, derived from eggs that have already hatched inside her. But unlike so many other worms, the larvae don’t exit the host. Instead, they burrow through the host’s intestine and travel, via the blood system, to striated muscles. Inside the muscle, they encyst, transforming the host cell into a nurse cell (as seen in the photo). When the muscle is ingested by another animal, the larvae emerge, mature and take up residence in the intestine. T. spiralis can cycle repeatedly in pigs, that is if carnivory or scavenging occurs in them. It can also sometimes involve rodent hosts, such as the rats on a farm that cohabitate with pigs. And there are less-studied sylvatic cycles that can involve multiple carnivores and scavengers. Humans become infected when they eat undercooked pork and while the disease has become quite rare – at least in the U.S. – the symptoms are quite severe and the infection can result in death.
March 4, 2010
In the late 1980's and 1990's, a disease killing hard clams along the eastern seaboard popped up - particularly those in aquaculture environments. At first, it was unknown what it was and so was referred to simply as Quahog Parasite Unknown, or QPX. Eventually it was identified as a member of the phylum Labyrinthulomycota, a group of unicellular eukaryotes commonly known as "slime nets." Members of this group are common in the water column and in sediments, but it is not known if the disease is a novel one of shellfish or not. Scientists are studying more about the pathology of the parasite - but in most cases, the only sign of it is a large number of dead clams. It is not dangerous to humans, but it has caused severe economic impacts. An outbreak near New York in 2002 destroyed an estimated $4 million worth of clams.
Photo from Bassem Allam.
March 3, 2010
Here’s Neobenedenia melleni, a pesky monogenean parasite on the skin and gills of tropical and subtropical fishes. It probably hails from the Caribbean, but will infect pretty much any warmwater marine fish with scales (for some reason it can’t or doesn’t infect eels and other scale-free fishes). N. melleni is a capsalid, a group that includes several species that are problematic in aquaculture. They can be damaging because they have a direct life cycle (no intermediate host) so in dense host populations like aquariums and aquaculture pens, they multiply rapidly. They mostly eat skin and mucus, which is a pretty renewable food source until it is removed faster than it can be replaced. At that point the fish suffers from salt and water imbalances and can die quickly or succumb to secondary infections. This photo shows a juvenile, with the head and “Mickey Mouse” anterior attachment pads at the top, the four pigmented eyes, the two excretory vessels and gut in the middle, and the large and complex posterior attachment organ or haptor, which features tiny marginal hooks, two pairs of major hooks in the middle, and a valve or seal flap around the edge. These guys invest a lot in staying attached, but when you are trying to hold onto wet fish skin in a viscous medium like water, you need to!
Contributed by Al Dove.
March 2, 2010
Echinostoma trivolvis, as well as other species of echinostome trematodes, are best known from their ubiquitous distributions and high abundance. The basic life cycle of E. trivolvis involves ramshorn snails (Planorbidae) as first intermediate hosts, a variety of snails, amphibians, fish, and even reptiles as second intermediate hosts, and aquatic birds and mammals as definitive hosts. Recently, E. trivolvis has gained attention due to the pathology it induces in larval amphibian hosts. Within the amphibian, E. trivolvis encysts within the kidney system, sometimes reaching extreme abundances (~1,000 cysts per frog). Large numbers of cysts, coupled with young, early developmental tadpoles can cause delayed growth and edema or swelling, and even mortality. Concerns over the impact of E. trivolvis on amphibian populations has led to studies on its influence on tadpole survival and physiology, competitive ability, and interactions with other environmental stressors including eutrophication and agricultural pollution. In general, species of Echinostoma are also useful subjects for laboratory and field research of host-parasite interactions in ecology, physiology, and immunology.
Contributed by Sarah Orlofske
March 1, 2010
Philornis downsi (Diptera: Muscidae) is a parasitic fly, originally found in Trinidad and Tobago and recently introduced to the Galapagos Islands. Adult flies, which are non-parasitic, feed on decaying, organic matter, while larval instars are hematophagous parasites that feed on the blood and tissues of nestling and adult birds, including Darwin’s finches. The adult flies lay their eggs in the nares of nestlings and in the bottom of nests. Even if the nestlings survive, their nares (on their bills) can be permanently deformed. The picture seen here is of 3rd instar larvae. The maggots develop through 3 pupae stages before emerging as adults. They are implicated in the reduced reproductive success of Darwin’s finches, which are a conservation concern.
Contributed by Sarah Knutie.