April 10 - Cuscuta europaea

Cuscuta europaea, is a parasitic plant commonly known as European dodder. These insidious plants twirl around the stems of their hosts and probe into their vascular systems, stealing their water and nutrients. The leaves of dodder are virtually non-existent, reduced to just tiny scales, and many species, including this one, do not engage in photosynthesis any longer and once they are wrapped around their host and soaking up its nutrients, dodder even loses its roots. Dodder may be the most reviled plant parasite as it can infest a huge variety of hosts including both agricultural plants and horticulture species. These plants were originally in their own family, the Cuscutaceae , but new phylogenetic work has placed them in Convolvulaceae, the same family as morning glories. What might be the coolest thing about the dodder? It finds its host plant by "smell"! See this site for more info.

April 9 - Pneumocystis jirovecii

Pneumocystis jirovecii is a fungus that can be an opportunistic pathogen and produce pneumonia in humans. This species was previously known as Pneumocystis carinii, thus these pneumonias are still usually called "PCP." These infections principally infect immunocompromised people and have become associated with AIDS. These fungi are geographically widespread and most people are exposed to them by a young age. In addition to the change in the species name, these pathogens were also previously classified as protozoa since they are single-celled, however genetic and biochemical evidence all places them in with fungi.

April 8 - Maritrema novaezealandensis

The parasite Maritrema novaezealandensis is commonly found on the coast of South Island, New Zealand. It is a trematode with a typical three host life-cycle, using a snail as a first host intermediate host where clonal multiplication occurs, a crustacean as a second intermediate host where it form a cyst-like waiting stage, and gulls as the definitive host where it matures into a hermaphroditic adults and sexually reproduces.

This trematode parasite uses the New Zealand mudsnail (Zeacumantus subcarinatus) to asexually multiply, and in certain areas, more than 60% of the snails found are infected with this parasite. The parasite takes over the most of the innard of the snail, filling it up with clones of itself and diverting resources from its reproductive organs, thus castrating it. The snail is essentially a zombie under the control of the parasite. Maritrema then use the snail as a kind of "parasite factory" producing free-living swimming larval stages (also clones) call cercariae (pictured) which are released into the environment to infect the next host in the cycle which are crustaceans such small crabs and amphipods (tiny beachhopper-type animals). The cercariae penerate weak spots in the cuticle using a specialised structure known as a stylet which functions rather like a cross between a scalpel and a saw. The little cercariae (which are less than 0.15 mm long) use the stylet to cut their way into the crustacean. Once inside, they grow over the course of a few weeks and develop into a cyst. There, they wait to be eaten by a sea gull to complete their life-cycle.

The cue for the infected snails to release the free-swimming cercariae stage is an increase in temperature, and when that happens, hundreds of cercariae swarm out of an infected snail. The hotter it gets, the more parasites are released. In the summer during low tide, pools or puddles gathered on the mudflat can get quite warm in the glare of the afternoon sun. Trapped within those tide pools are various crustaceans and many, many infected snails. Triggered by the heat, each infected snail releases hundreds of cercariae into the water, turning the water into a swarming "cercariae soup" and rendering any crustaceans in the area into hapless parasite pin-cushions. For tiny crustaceans like amphipods, the experience of being penetrated simultaneously by multiple cercariae can be quite traumatic (imagine being stabbed multiple times by scalpels) and the experience can often be lethal. While killing the intermediate host before it can be passed on to the next host is not good for the parasite either, it demonstrates one of the ways that parasites can regulate the population of its host.


Some relevant papers on this parasite are:

Fredensborg, B.L., K.N. Mouritsen, and R. Poulin. 2004. Intensity-dependent mortality of Paracalliope novizealandiae (Amphipoda: Crustacea) infected by a trematode: experimental infections and field observations. Journal of Experimental Marine Biology and Ecology 311: 253-265.

Fredensborg, B.L., K.N. Mouritsen, and R. Poulin. 2005. Impact of trematodes on host survival and population density in the intertidal gastropod Zeacumantus subcarinatus. Marine Ecology Progress Series 290: 109-117.

Keeney, D.B., J.M. Waters, and R. Poulin. 2007. Clonal diversity of the marine trematode Maritrema novaezealandensis within intermediate hosts: the molecular ecology of parasite life cycles. Molecular Ecology 16: 431-439.

Martorelli, S.R., B.L. Fredensborg, K.N. Mouritsen, and R. Poulin. 2004. Description and proposed life cycle of Maritrema novaezealandensis n.sp. (Microphallidae) parasitic in red-billed gulls Larus novaehollandiae scopulinus from Otago Harbor, South Island, New Zealand. Journal of Parasitology 90: 272-277.

Contributed by Tommy Leung.

April 7 - Brucella abortus

Brucella abortus is a gram-negative bacterium that uses cattle and other ruminants as its primary host. It can however, also be transmitted to humans and will produce a disease known as "Malta fever" or "undulant fever", characterized by sweating and joint pain and the latter name specifically referring to the waves of fever that a patient can show. Brucellosis is a major health threat to cattle because it causes a high degree of spontaneous abortions, thus all cattle in the U.S. (and many other countries, for that matter) must be vaccinated against this pathogen. Recently farmers in the U.S. West have become worried that wild ungulates such as elk and bison might transfer the bacteria to their herds. Humans can acquire the bacteria either from coming into physical contact with infected cattle or even by drinking milk or eating meat from infected animals. The genomes of two strains of B. abortus have been completely sequenced and these bacteria are somewhat unusual in having two separate chromosomes.

Image from this page.

April 6 - Plasmodium ovale

Plasmodium ovale is one of the two rare species of human malaria parasites, usually present in fewer than 5% of people in any region where it is present. Although probably native to West Africa, P. ovale has now spread into several parts of Southeastern Asia and Papua New Guinea. P. ovale is commonly called tertian malaria because it produces fever cycles every two days (note that the Romans had no zero, thus the term) and very often is difficult to diagnose in a bloodsmear from Plasmodium vivax. P. ovale can relapse for several years as well, via dormant stages in the liver known as hypnozoites. Like the other mammalian Plasmodium species, P. ovale is vectored by Anopheles mosquitoes. The taxonomy of P. ovale has been somewhat troublesome as this parasite seems to be genetically quite different from other species. Some studies have placed it as closely related to Hepatocystis parasites in bats and baboons, but a recent paper reported parasites in wild chimpanzees that were closely related to P. ovale.

April 5 - Cimex lectularius

Ask any New Yorker what their greatest fear is and what do you think it will be? Runaway subway? Nah. Shoddy cranes? Well, maybe. But, my guess is that most will say bed bugs. These insects hatch from eggs into nymphs which are quite small and hard to see, but go through repeated moltings until they are about 5 mm in length and darker brown. They live in mattresses, bedding, and furniture and emerge at night to take a blood meal from a sleeping human, which they are attracted to because of the body heat and carbon dioxide. To get the blood, they insert their proboscis, and pump saliva and anticoagulants into the wound (shown in purple in the colorized micrograph). With the other part of their mouthparts (in red), they suck blood up. In recent times, bedbugs have become something of an epidemic, both in New York and globally as well. This is likely due to a decrease use in pesticides (for fighting cockroaches) and the fact the travelers spread them so easily in bedding (do *not* bring your favorite pillow to hotels!), luggage, or sometimes clothing or pets. They are extremely hard to get rid of because they are so good at hiding in very small, tight spots. Recently, dogs have been trained to sniff them out in apartments and hotels, which is helping with their extermination.

There is lots more info on bedbugs, including their historical association with humans and the best methods for detecting them and getting rid of them on their Wikipedia page.

Ok, I'm itchy now.

Image is from the CDC Public Health Image Library.

April 4 - Synodontis multipunctatus

Well, we've had cuckoo birds on this blog before, which most people would at least have heard of, but what about the cuckoo catfish? The cuckoo catfish, Synodontis multipunctatus, a popular ornamental fish that is somewhat well-known amongst aquarium enthusiasts. It is originally from Lake Tanganyika in Africa which is hotspot of cichlid fish biodiversity. The cuckoo catfish has a rather unusual breeding habit, it is a brood parasite of mouthbrooding cichlids found in Lake Tanganyika. Just like their bird namesake, the cuckoo catfish displaces the legitimate offspring of its host, forcing the cichlid to rear its young, and they have a rather clever way of accomplishing this. The catfish is attracted by the scent of the brooding cichlids, and as soon as they detect any such brooding cichlid in the vicinity, they race to the scene of the coupling. The catfish mob the pair of spawning cichlids and as soon as their eggs are fertilised, a mating pair of cuckoo catfish dash in, the female laying her own eggs amidst the brood, with the male following closely behind to fertilise them. When the brooding cichlid scoop up the clutch of eggs to brood them in its mouth, it's a mixed-bag of cichlid and catfish eggs. The catfish fry hatch a few days earlier than the cichlid fry and proceed to feed on the host's eggs with which they are sharing the brood chamber. So the cichlid is unknowingly and unwittingly carry a brood composed of juvenile catfish - imagine seeing a mouthbrooding cichlid open its mouth and out swim a swarm of splotchy little catfish!


The paper that originally described this fishy brood parasite is:
Sato, T. 1986. A brood parasitic catfish of mouthbrooding cichlid fishes in Lake Tanganyika. Nature 323:58-59

Contributed by Tommy Leung.

April 3 - Santalum spp.

Parasites often exact a heavy toll on their hosts in ways that we are all familiar with. For example, in a recent video, New York Times columnist Nicholas Kristof marveled at the crushing physical labor performed by Congolese women with heavy parasite loads. Malaria is among the deadliest diseases, infecting up to 500 million people each year, causing untold suffering and millions of deaths.

In a twist on this theme, a much-beloved parasitic plant, sandalwood, has played an important and unexpected role in human suffering. I know a native Hawaiian woman whose grandmother ripped young shoots of native sandalwood out of the ground whenever she encountered them. That plant had caused her own grandparents so much pain that she never wanted her people to experience it again.

The name sandalwood refers to any of the 15 extant described members of the genus Santalum L. of the Santalaceae, a large family of parasitic plants that includes mistletoe. Santalum has a distribution ranging from India through Southeast Asia, Australia, and across the islands of the Pacific. It is a culturally and economically important group, and its members are hemiparasitic root parasites. This means that they use a modified root called a haustorium to physically penetrate the roots of neighboring plants, thus diverting water, inorganic, and organic nutrients to themselves. Hemiparasitic means that these plants are also capable of photosynthesis themselves, unlike holoparasitic plants that mostly lack chlorophyll.

The natural oils of sandalwood bear odors that are among the most sought-after in human history. The scent is distinctive and soothing, and items carved from sandalwood can perfume a room for decades. Many ancient texts mention sandalwood, and it has been an important trade item for millennia.

Hawaii has four endemic species of sandalwood that have important traditional uses in native culture. When Europeans recognized the value of these trees (called `iliahi in the native Hawaiian language) in the late 18th century, a massive deforestation program began, fueled in large part by labor forced on native Hawaiians by their chiefs and king, who enriched themselves in the process. The ecological effects linger: sandalwood is rare in Hawaii. The social effects are made clear in this passage:

Within a few years the supply of ‘iliahi began to dwindle. This contributed to the decline of the Hawaiian population. The work in the damp uplands combined with near starvation conditions and the scourge of the white man's diseases wiped out large numbers of the native Hawaiians.

In 1827 the first written tax law in Hawaii imposed a sandalwood levy.

Every man is required to deliver a half picul of good sandalwood [a picul being 133 lbs.] to the governor of the district to which he belongs, … No person, except those who are infirm, or too advanced an age to go to the mountains, will be exempted from this law.

And so it is easier to understand the visceral reaction of my friend’s grandmother, trying to eradicate this hated plant that she thought had harmed her ancestors. The Hawaiian sandalwoods have never regained their former abundance, with one variety federally listed as endangered and two as threatened. Recent molecular work has shown that these four species are likely the result of two separate colonization events of Hawaii 1 to 1.5 million years ago from the original Santalum homeland in Australia.

If you are a fan of essential oils, remember that the soothing scent of sandalwood has a fascinating natural and cultural history, and is a lovely product of parasitism.

April 2 - Dolops sp.

Dolops lacks the stalked suckers that Argulus uses for running around on the surfaces of fish. Instead it has pretty hefty hooks that it can use to dig into the skin of the fish to hang on. Just like Argulus, though, Dolops is a really fast swimmer, and if disturbed it can actively swim away with alarming speed. It will survive in the water column without a host just fine, for a while at least. That active swimming also enhances transmission, especially in schooling fish like Piranha, where the next host is just a hop, skip and swim away.

Contributed by Al Dove.

April 1 – Polypodium hydriforme

Now here's a parasite with an expensive taste - Polypodium hydriforme. The exact taxonomic affinity of this parasite is presently unclear, though it appears to be related to jellyfish. Part of the life-cycle of P. hydriforme involves the parasitic larval stage developing in sturgeon eggs - yes, the sturgeon eggs that most people are familiar with in the form of black caviar. As the parasite grows, it consumes the content of the sturgeon egg and develops into a "stolon" which is made of a chain of multiple individuals or "bud" - each bud will grow into an individual P. hydriforme. There can be as many 30-40 buds contained within each egg, with larger eggs containing up to 100 buds.

Just prior to the sturgeon spawning, the parasite prepares itself for the transition from its parasitic to its free-living stage. It accumulates all the remaining yolk within the egg into its gastric cavity, which will act as its energy reserve for the first 6-8 days of its non-parasitic life. After this reserve is depleted, P. hydriforme develops a mouth and begins feeding on various tiny benthic organisms such as Tubifex worms (what you might feed your aquarium fish), free-living turbellarian flatworms, and rotifers. Once it reaches sexual maturity, it mates to produce the next generation of larvae which will then infect the eggs of another sturgeon - however, just exactly how the larvae manage to accomplish that is still presently unclear.

The peculiar life-cycle of P. hydriforme not only makes it one of the few (if not the only) known species of parasitic cnidarian, but also one of the few multicellular organism that has evolved to be an intracellular parasite (another notable example being the nematode Trichinella spiralis which enters muscle cells and converting it into a "nurse cell").

Contributed by Tommy Leung.