May 10 - Hemileia vastatrix

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 - Thelazia callipaeda

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 - Dientamoeba fragilis

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 - Gyrocotyle urna

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 - Armillifer agkistrodontis

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 - Acarapis woodi

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 - Anelasma squalicola

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 - Capillaria hepatica

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 - Trypanosoma evansi

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 - Ambylomma variegatum

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.