March 10 – Mimivirus

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 - Moniliformis moniliformis

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 - Rhizanthella gardneri

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- Dipylidium caninum

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 - Ctenocephalides felis

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 - Trichinella spiralis

“I’ll have the pork chops, please.”
“Excellent choice, sir. How would you like those cooked?”
“Medium rare.”

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 - Quahog Parasite Unknown (QPX)

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 - Neobenedenia melleni

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 - Echinostoma trivolvis

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 - Philornis downsi

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.