May 31, 2010
On Memorial Day, we honor the many soldiers who fought for our country. While bullets and other forms of arms are certainly the primary concern for soldiers at war, diseases that are spread under the conditions of warfare have taken their share of casualties as well. One of the most important ones, from the times of the Peloponnesian Wars in ancient Greece up through World War II, was epidemic typhus, caused by the bacterium, Rickettsia prowazekii. The bacteria are transmitted from person to person by the human body louse (Pediculus humanus humanus) and causes high fevers, rashes, headaches. muscle pains and delirium. Typhus has played a major role in history: the disease killed more of Napoleon's soldiers than the Russians did and then in World War I, over 3 million Russians died from typhus. The disease was rampant in Nazi concentration camps - both Anne Frank and her sister died of it.
The photo, from Wikipedia, shows two soldiers demonstrating a DDT gun, which was used to kill lice.
May 30, 2010
Although most commonly found infecting pigs, Ascaris suum, a large roundworm nematode, can also infect humans. This species has the same lifecycle as Ascaris lumbricoides, and also like its cousin, has eggs that are extremely durable in the environment. Although they were long popular in biology classes as a large, easy-to-dissect representative of Nematoda, because the eggs are so resistant and easily spread, the represent a health risk and their use has largely been discontinued. You can virtually dissect one here.
May 29, 2010
While it is far from a universal rule that the largest worms are found in the largest hosts, it is true that the longest tapeworm known is from a whale. And this may be the candidate for the smallest tapeworm- Protogynella sp. from a shrew, Sorex vagrans. It is only 250 microns (a quarter of a millimeter) long. Shrews are among the smallest mammals (some weigh less than 5 grams) and most of their parasites (trematodes, cestodes, nematodes) are correspondingly tiny. The darker staining structures are the eggs, which probably infect an arthropod intermediate host since shrews are primarily insectivorous.
Contributed by Mike Kinsella.
Contributed by Mike Kinsella.
May 28, 2010
If you’ve ever had chiggers, you know they’re really, really irritating. These are the parasitic larval stages of free-living mites, and Eutrombicula (Trombicula) alfreddugesi is the most familiar in North America. Chiggers perch on foliage, climb aboard passing pedestrians, and find their way to the new host’s skin. Once there, the tiny mite positions itself atop a hair follicle or pore, and secretes highly digestive saliva that liquefies the host’s skin cells. The surrounding cells harden in defense, forming a stylostome. But it’s a poor defense – the stylostome helps the parasite by functioning as a straw for the chigger to slurp his slurry of dead cells. Moreover, the stylostome contributes to that really, really irritating inflammatory (i.e., itchy) response in the host’s skin. Thankfully, E. alfreddugesi is not a vector for disease, and the discomfort subsides after a few days.
Eutrombicula alfreddugesi isn’t picky, and infects numerable hosts besides humans. It’s a parasite of many vertebrates, including birds, mammals, and reptiles (the photo shows several chiggers on the dewlap, or throat fan, of an anole lizard). In fact, host habitat is probably more important that host taxonomy for this species. Chigger infestations usually occur in warm, shady, and moist environments, as this is best for the soil-dwelling and detritus-eating adult stages (meaning that this is where most eggs are laid). Similarly, these chiggers prefer certain areas on the host, from the undergarment areas of humans, to the “mite pockets” of some lizards. Mite pockets are small, but relatively deep, cavitations that are typically located just behind the lizard’s forelimbs. When these lizards have mites, most are in the pockets, leading some scientists to speculate (and others to dispute) that a pocketful of mites is advantageous for the lizard. The chiggers are bright red, and on a drab lizard, they present a flashy spot of color that can be turned on and off as the lizard moves its legs.
Contributed by Bryan Falk.
May 27, 2010
Some crabs, like hermit crabs, live in the discarded shells of mollusks, but some, like the pea crab Pinnotheres pisum, just can't wait for the resident to move out first and move in as a roommate -- but the kind of bad roommate that steals your food and damages your house. P. pisum, which is at most about half and inch wide, lives in the mantle cavities of bivalves such as mussels and clams where it picks the food off their gills and can severely damage them in the process (kind of like you might imagine if something with 10 legs lived in your fridge full-time.) I chose this photo from wikipedia (click on it for a blown-up view), which shows a pea crab that has fallen out of the clam that an otter is eating. Better go find another landlord, little crab!
May 26, 2010
It is thought that Balantidium coli is the only ciliate (think Paramecium) that is parasitic in people (causing the disease Balantidiasis), however in humans, these protozoans are zoonotic, with pigs as the primary reservoirs. To our porcine friends, the ciliates appear to not cause symptoms, but humans can suffer severe GI distress if they become infected by ingesting contaminated water or food. This parasite has been found worldwide, but is not a common pathogen of humans, except in the Philippines. Recent work identified the same ciliate in several other kinds of mammals including other primates and rodents, so a better epidemiological understanding is clearly in order.
May 25, 2010
This photo may exceed the “yuck factor” for some. Taenia taniaeformis is the common tapeworm of house cats and is also found in other species of felids. The eggs pass out in the feces and are ingested by various species of rodents, where they develop into cysts, usually in the liver. Pictured is a cotton rat, a very common rodent in the southeastern United States. The dissected liver has some large white cysts. If a cyst is opened, it contains what looks like an adult tapeworm with a fluid-filled bladder at the end. This stage is called a strobilocercus. When the rodent is ingested by a cat, only the head of the tapeworm survives, which then develops into an adult. Because of this type of life cycle, a house cat with tapeworms poses little danger to its owners. Thanks to Dr. Christine Miller of the Miami Metrozoo for providing this (yucky) photo.
Contributed by Mike Kinsella.
May 24, 2010
If you suddenly experience a sharp abdominal pain and have recently eaten sushi, ceviche, or pickled herring, there's a chance you might have just become infected with Anisakis simplex. This species is a nematode that primarily uses marine mammals as its hosts. Eggs are excreted in feces, where they will then infect small crustaceans. There they mature into what are called L3 stage larvae. When the crustacean is eaten by a squid or a small fish, they will migrate to the muscle tissue and wait there for a mammal to eat that fish. If another fish eats it, they just repeat the process, and wait in the muscles of the second fish. When a whale, seal or dolphin eats the fish, the larvae mature into adults, mate, and lay eggs to begin the cycle all over again. Because a human body is - at least to these nematodes - about the same as a seal's, the worms can infect a person who eats an infected fish or squid. The result is pain, nausea, and/or vomiting, but as we humans are dead-end hosts, the treatment is usually just to relieve those symptoms and wait for the adult worms to die and pass. However, if individuals are sensitive to Immunoglobin E, however, ingestion of Anisakis can cause anaphylactic shock. Luckily these worms are fairly rare in the U.S., but cases do occur more frequently in Scandanavia, Japan, and western South America.
The photo is of L3 larvae in a herring.
May 23, 2010
Proteocephalus pinguis parasitizes pike (how about them P's??). These are tapeworms (cestodes) that alternate between their fish hosts and copepod intermediate hosts. They have extremely simple scoleces and are small even as adults. The genus contains many other species that have similar life cycles, alternating between vertebrates and copepods. If the first vertebrate host gets gobbled up by a bigger one, then the tapeworms simply infect this host instead.
The photo is from this website.
May 22, 2010
Today's parasite, the leech Placobdella parasitica is an excellent parent. Not only can it perform both motherly and fatherly duties simultaneously (it's a hermaphrodite), it also takes good care of its young. These leeches spend most of their lives on turtles, particularly snapping turtles, where they will feed on the blood primarily around the leg pits and tail (where the turtle's formidable jaws can't reach them.) They brood their young on their ventral surface protecting them there until they are big enough to feed on their own, which sometimes means transporting them to their first meal. Despite the caring nature of the leeches post reproduction, the conception of those young is actually quite violent. Leeches will stab small spermatophores into each other in a process known as traumatic insemination. Yipes.
Photo by Mark Siddall.
May 21, 2010
Yesterday was an instance of an animal parasite that was recently discovered in a human. Today's parasite, Paragonimus westermanni, is another fluke that can infect both humans and animals. Commonly known as the oriental lung fluke, humans become infected when they eat undercooked crab or crayfish, which are serving as intermediate hosts. Before the crustacean, the parasite was in a snail (oh how trematodes love their snails!) and how did they get there, you ask. The eggs of the flukes are coughed up by humans -- or by cats, it turns out. The parasites are very prevalent in many parts of Asia and as many as 80% of crabs can be infected. Common preparation methods such as pickling or salting will not kill the metacercariae and thus are easy routes to vertebrate hosts. Another popular Chinese dish - "drunken crab" - made by dousing crabs in wine is another means of infection. The species name is an honorific of a zookeeper who also observed the flukes in Bengal tigers.
May 20, 2010
I didn't intend to do this, but the parasites so far this week have all started with "P" - so let's keep that up! This is Plagiorchis vespertilionis, a trematode fluke. These parasites have complex life cycles which go from snails to insects such as caddisflies or dragonflies and then eventually make their way to insectivorous bats when they gobble these bugs up. A recent paper reported a case of this parasite in a Korean man, but how this individual became infected is not clear. The man did not admit to eating dragonflies, nor being an Ozzy Osborne impersonator, but he had recently eaten raw freshwater fish (this is never a good idea, by the way...). Thus, either there is convergence between a species that looks a lot like P. vespertilionis and one that is found in fish, or the host use patterns of this parasite are much more general than originally thought.
The image is from this paper, which named a subspecies of the parasite in American bats.
May 19, 2010
Oh man - this is a nasty one. I had a really hard time finding a photo that wasn't completely disgusting and opted for just a nice image of the simple fungi themselves. The parasite is Pythium insidiosum, a fungal parasite that causes a disease known as pythiosis in dogs and horses. It's a common parasite in warmer parts of the world including the American South, eastern Australia, and south America and primarily exists in swampy, standing water. Dogs can become infected in their GI tract from drinking tainted water and it can cause thickening of the tissues or granulated lumps. Horses more often have subcutaneous lesions of these fungi, which they get from standing in the swampy water. The damage to their legs, bellies, and chests can be quite gruesome and often the lesions will have bits of dead tissue in them with the somewhat amusing name of "klunkers."
The disease is apparently on the rise in the U.S. and is troublesome because many vets are not familiar with it. I found this website with some rather sad tales of beloved pets who have been lost to the disease.
The image is from this site.
May 18, 2010
Today’s parasite is the pinworm Parapharyngodon cubensis. Species in this genus are parasites of reptiles and amphibians, with over 40 taxa known worldwide. These are characterized by a direct life cycle and fecal-oral transmission. Except for this brief transmission period, the parasite spends its entire life within and dependent on the host (usually its large intestine). P. cubensis is broadly distributed in the Caribbean and the only known non-Caribbean population is found on Bermuda in introduced populations of Caribbean anole lizards.
Like other pinworms, P. cubensis is haplodiploid. In low densities, the worms reproduce asexually, and have just one set of chromosomes (i.e., they’re haploid). Once the populations get bigger, and the parasites begin encountering one another, they have sex. Their offspring have two sets of chromosomes – one from each parent (i.e., they’re diploid, like us). This is a pretty good reproductive strategy for an otherwise lonely animal that may not encounter another of it’s kind in its lifetime.
Contributed by Bryan Falk.
May 17, 2010
Dinoflagellates are single-celled organisms that are related to ciliates (like Paramecium) and apicomplexans (like Plasmodium and Toxoplasma). Many are mutualists of other organisms - Symbiodinium in corals is a good example. Some, however, are parasites. Piscinoodinium limneticum is one such parasitic dinoflagellate. These protists infect fish and cause a disease known as piscinoodiniosis - or, if your tongue gets too wrapped up on that term - velvet disease. P. limneticum can infect a wide variety of both aquarium and food fishes. The parasites attach to the skin and cause it to weaken and some observations indicate that the parasites may cause physical damage from increasing drag - essentially the force from the water "catching" on the parasites as the fish swims does more damage. And it also appears that damage attracts more parasites to glom on, producing a clustered pattern of parasites on a fish's epidermis (see photos). Young fish may actually die from an infection of these nasty little dinoflagellates.
The image comes from this paper and shows both clusters of the parasites and a close-up of one.
May 16, 2010
Of all of the nasty parasites out there, this one just might be my personal least favorite - only because it attacks so many of my very favorite plants - coffee, tea, avocado, mango, vanilla, and cacao. Cephaleuros virescens is a parasitic green algae (sometimes known as "red rust" because of the characteristic spots that it makes) that is common in sub-tropical and tropical parts of the world. Although it is generally fairly harmless to plants, it can cause economic woe when it infects crop plants such as the ones I just mentioned, via lowered rates of photosynthesis or causing the fruits to look damaged and spotty. The life history of these algae is such that they alternate between sexual and asexual reproduction. When spores are blown or splashed onto a plant, the parasite grows into the epidermis of the leaf or fruit, where they form disc-like, filamentous thalli. This parasite has become a particular problem in Hawai'i where it seems to have a special penchant for guava.
May 15, 2010
The weekend is here - and perhaps that means a nice cold beer or two. One of the main ingredients in beer, of course, is hops, which give brews their characteristic bitter flavor. Hops are dried flowers of the Humulus lupulus plant. Pseudoperonospora humuli is a parasite that could get in the way of your thirst-quenching IPA or ESB, however. This fungus, known as downy mildew infects hop plants and destroys their leaves and those wonderful flowers. A recent molecular phylogenetic study has suggested that P. humuli is not actually genetically distinct from Pseudoperonospora cubensis, another mildew fungus that was described from cucurbits (cucumbers, melons, etc.) So, if you're not a beer-drinker, but do like to enjoy a nice gherkin or melon ball as part your Saturday evening activities, well then, you can be annoyed at the very same parasite.
Image come from this site.
May 14, 2010
Ahhh...it's Friday. And you might be thinking about enjoying a nice glass of wine after work today. If so, then you probably won't be a fan of today's parasite, Desmia funeralis, or the grape leaffolder. These moth larvae not only gobble up the leaves, they also do a little construction to convert their food sources to houses as well, and that's what gives them their common name. Using silk threads, the caterpillars pull the leaves together, either making rolls or folds, depending on the size and thickness of the leaf that they're on. When they're ready to pupate, they make three cuts in the leaf and fold it so as to create an envelope (who knew that insects practiced origami?). They like both wild and cultivated grapes, but will also parasitize redbud trees.
Image come from this site and you can read more about the worms and see the damage here.
May 13, 2010
Too bad it isn't Halloween yet - today's parasite is Crinipellis perniciosa, a fungus that causes a disease known as "Witches' Broom Disease" in cacao, the plant that we get chocolate from. The basidiospores of this fungus are spread by wind and if they invade younger, developing seed pods, can cause the plant to never produce any cocoa beans. The fungus can invade many other portions of the cacao plant as well, and if they get into the meristem, they will produce vegetative "brooms" that inspired their name. Its invasion into the Bahia region of Brazil caused the production of cocoa to plummet by more than half. Researchers are now searching for plants in other regions that might harbor genes that confer resistance genes, so that they can breed them to the Brazilian plants.
Image is from Invasive.org.
May 12, 2010
If you're having bananas on your cereal this morning, while sipping a little coffee, and dabbing your chin with a cotton napkin, feel lucky that all of those original plants survived Meloidogyne incognita, the root-knot nematode. These common pests invade the roots of over 1700 different species of plants. Infective larval worms enter into the growing parts of roots and induce a cell to undergo nuclear division without the cells dividing (cytokinesis), which results in giant "nurse" cells for the worms and produces the characteristic knots. When the worms gobble up the plant's nutrients, severe damage and death can ensue. Because of its tremendous economic importance (estimated at something like $5 billion U.S), the complete genome of this nematode was recently sequenced. What was an especially surprising was that there were 61 proteins that were involved in plant cell wall degradation - higher than ever found in another organism - and that many of them appear to have had a bacterial origin. Thus, these nematodes apparently have acquired genes that enhance their parasitism via horizontal gene transfer from bacteria.
May 11, 2010
The citrus leafminer, Phyllocnistis citrella, is native to Asia, but has sadly recently invaded many important citrus-growing regions in the New World, including Florida, the Caribbean, and now southern California. These insects are moths and the female lays her eggs on the new leaves of citrus trees. The larvae bury into the leaves and create trails of damage behind them, causing the leaves to uncurl poorly. On top of that, the damage caused by the hungry little caterpillars can leave the trees vulnerable to secondary infections, including citrus canker bacteria, Xanthomonas axonopodis. What's the hope for controlling these persistent pests? Luckily, Nature has answered the call in the form of parasitoids and at least nine species of parasitoid wasps have been documents using the invasive leafminer larvae as hosts, including one that was specifically introduced from Vietnam to control P. citrella after the Florida outbreak called Ageniaspis citricola.
May 10, 2010
Monday mornings would be impossible without coffee, so I have a real issue with this parasite, known as Hemileia vastatrix, or coffee rust. This species of fungus attacks the leaves of the coffee plant (Coffea arabica), but not the fruit or other parts. It was first discovered in East Africa, but since then has spread to most of the other major coffee-growing regions of the world, such as Java, and Brazil. This parasite, in fact, might get some credit for the fact that Brits now drink so much tea. In the 1870's and 1880's, an epidemic of coffee rust essentially destroyed coffee production in many parts of Africa and Asia, including many countries that were British colonies. Some places, such as Sri Lanka (then known as Ceylong) upped their tea production instead.
May 9, 2010
Oriental eyeworm, Thelazia callipaeda, is kind of a gruesome parasite. These nematodes are transmitted by flies - but not biting flies - just those that come to lap up tears from the eyes of vertebrate animals. The larvae are swallowed by these flies where they will go through a couple of developmental stages and then move to the mouthparts of the fly, where they can be released the next time the insect feeds from the tears or secretions. This species has an almost world-wide distribution and can infect many canids, cats and rabbits - and, in some cases, humans. On top of the gross factor (sorry about the photo), they can cause health issues such as conjunctivitis, visual impairment and corneal scarring.
May 8, 2010
Although Dientamoeba fragilis is an extremely common parasite, many details about its biology remain to be answered. Originally taxonomically grouped with amoebas, later ultrastructural studies followed by molecular work has instead showed that it is more closely related to Trichomonas than Entamoeba. The single-celled organisms are primarily found in the large intestines of people and other animals and can produce classic symptoms of traveler's diarrhea. The name of this species comes from the fact that it typically exists in a binucleated state (as in the photo - I think it looks like a Pacman ghost). The exact mechanism of transmission of D. fragilis is still not known. Cysts have never been observed - at least in humans, though a fecal-oral route is presumed. Some theorize that pinworms (Enterobius) or other helminths act as mechanical vectors for the D. fragilis, but this has not borne out in all cases.
May 7, 2010
This bizarre parasite is a non-segmented flatworm that lives in the spiral intestine of deepsea chondrichthyen fish such as ratfish and chimaeras. Distantly related to tapeworms, these parasites don't have mouths or intestines - instead they attach via a unique "ruffle" structure known as the rosette, and then absorb nutrients from their host via microvilli. This whole arrangement baffled parasitologists for quite a while, exasperating them to the point of not even knowing which end of the worm was the anterior and which was the posterior! The complete life cycle of these parasites has yet to be worked out, though it's known that they produce small larvae covered in cilia.
Photo by Willi Xylander and comes from this website.
May 6, 2010
Cultural practices sometimes cause harm, such as when they threaten rare species - or, in this case, exposing a person to a dangerous parasite - like this one. Armillifer agkistrodontis is a pentastomid "worm" (we'll come back to that) that naturally cycles between snake and rodent hosts. The serpent host, Agkistrodon acutus (or the "hundred-pace snake" due to its highly venomous nature) will house adult pentastomids in its respiratory tract. The parasites lay eggs, which get into the environment and are subsequently consumed by rodent hosts. The eggs hatch in the rodent's small intestine and then become larvae, which migrate to the liver or spleen. Snakes become infected when they eat a parasitized rodent. Chinese cultural practices and medicine, however, sometimes involve either the consumption of the pitvipers or their gallbladders or the drinking of their blood. And that can open the door to a pentastomid infection in humans. These occurrences are very rare, luckily.
Above, I put "worm" in quotes. That's because even though pentastomids have very worm-like bodies, their phylogenetic affiliations are not with any real worm groups. Although in the past they've been placed in Nematoda, Annelida, Platyhelminthes (your classic worm clades), modern phylogenetic analyses have instead supported their relationship within Arthropoda.
The photo comes from this paper.
May 5, 2010
Earlier, you saw the mite Varroa destructor, that hitches rides on honeybees. Now meet Acarapis woodi, another teeny tiny little mite that also infects honeybees. But, unlike Varroa, this species gets inside the trachea (the tubes that it uses to exchange gases) of the bees. The mites pierce the trachea and suck up the hemoplymph to get their nutrients. Bees can be infected with huge numbers of these things, and even though they're tiny, it's got to be hard to fly when you've got 100 little passengers!
May 4, 2010
While many barnacles can be found using large marine vertebrates such as whales and turtles as substrate for attachment, surprisingly few are actually true parasites of marine vertebrates. However, there's always a species to buck the trend. Anelasma squalicola is a rather strange parasite. This barnacle is a parasite of deepwater squaliforme (dogfish-type) sharks such as the velvet belly lantern shark, Etmopterus spinax. It seems to be rather specific about where it embeds itself in the host, and most Anelasma are found attached near the front or alongside the shark's first dorsal fin, in numbers ranging from one all the way up to four in a cluster.
Unlike the heavily derived order of parasitic barnacles, the rhizocephalan (such as the Sacculina carcini), Anelasma looks superficially like most barnacle, especially the part that protrude from the body of the host, with the exception of the soft body and the lack of calcerous plates. However, the similarity to the usual barnacle ends there. Anelasma has no feeding limbs and the rest of this peculiar barnacle is an onion-shaped bulb inserted into the host tissue. This bulbous structure is equipped with numerous root-like tendrils that infiltrate the host tissue enabling the parasite to absorb nutrienst from its host.
Anelasma severely imparis the development of the shark's reproductive organs. While many parasites are known to castrate their host, and indeed all trematodes castrate their first intermediate host during the asexual stage of their life cycle (see Maritrema novaezealandensis for example and details), this is one of the few known parasitic castrators of a vertebrate host.
For more details see:
Yano, K. and Musick, J.A. 2000. The effect of the mesoparasitic barnacle Anelasma on the development of reproductive organs of deep-sea squaloid sharks, Centroscyllium and Etmopterus. Environmental Biology of Fishes, 59:329-339.
Contributed by Tommy Leung.
May 3, 2010
Capillaria hepatica is a parasitic nematode that has an utter death wish for its host - it's the only way that it can be transmitted. Larvae are ingested by a host - normally a rodent, but occasionally man, and they make their way from the intestine to the liver. There they mature and begin to lay eggs, but unlike many parasites, these eggs don't go anywhere just yet. They just wait, paused in their development until they get a little fresh air. The adults eventually die and all of these eggs and dead worms cause some nasty damage to the liver, which can kill the host - or make it easy prey to another animal. If the animal dies and rots, the eggs will eventually be released and become infective L1 larvae. Or, if the original host is eaten or scavenged, the eggs pass through that host, out into its feces, and then become ready to infect their new hosts. In some parts of the world, such as southeast Asia, this parasite is extremely common in rodents, but luckily it's very rare in people and fewer than 40 cases have ever been reported.
May 2, 2010
Trypanosoma evansi was the first pathogenic trypanosome that was discovered and infects a very wide range of other mammals, including horses, camels, sheep, goats, buffalo, deer, dogs, and cats. It causes a disease known as "surra", named from an Indian word for "heavy breathing" because infected animals are often weak and lethargic. The taxonomy of this species is in a bit of flux. A sexually transmitted parasite of horses, Trypanosoma equiperdum, was synonymized with T. evansi, but T. evansi, may actually be part of Trypanosoma brucei. This is undoubtedly yet another example of parasite species originally being given distinct names depending on what kind of host animal they were found in and where they were found, but later, via molecular data, being found to have different relationships and thus names.
May 1, 2010
Yesterday you saw the bacteria that are responsible for Q fever – Coxiella burnetii and learned that they can be transmitted by ticks. This tick, Ambylomma variegatum, is one of those ticks – and what a handsome tick that it is (well, at least the males)! These ticks are present in sub-Saharan Africa, but they have been introduced to several islands in the Caribbean as well. They have a wide range of hosts that they take bloodmeals from – as larvae and nymphs they feed on birds, reptiles, sheep or goats and as adults they like cattle, horses, camels, and some antelope as well. These ticks vector not only Q fever but also heartwater and African tick-bite fever (we’ll meet these later), and on top of that, they also have a really nasty bite due to their very long mouthparts. These bites can be painful and sometimes are also sources for secondary infections of both bacteria and screwworms. So, they might be good-looking, but they’re pretty nasty little arachnids.
Photo of male (left) and female (right) A. variegatum ticks, from this recent paper on Q fever in Senegal.