Sarcocystis spp.

Student guest post time! One of the assessments that I set for students in my ZOOL329 Evolutionary Parasitology class is for them to write about a paper that they have read, in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) on here. So from the class of 2025, here is a guest post by Hayley Doggen titled "Sarcocystis: You can’t see me" about a hidden danger in wild deer.

Wild deer and feral pigs are found pretty much everywhere in Australia, which is what makes them such great game animals for hunters. It also makes them really good at spreading parasites to livestock, other wild animals or even to humans. But how much do we really know about the parasites carried by deer and pigs in Australia? Well, compared to other places like the UK, we know very little. In fact, in 2020, when hunters found white cysts in the rump of a wild deer shot in Taree, New South Wales, this was the very first report of a Sarcocystis-like infection in Australian wild deer, even though we already knew that Sarcocystis parasites can live in Australian livestock (including sheep) and wild deer found in other countries.

A) Image of cysts in a deer caught in Taree which prompted the study; (B) to (D) microscopy images of Sarcocystis in animals caught in the study. All from Figure 3 of the paper.

Sarcocystis is part of a group of parasites known as Apicomplexa. When these guys are eaten up by their intermediate hosts - usually herbivores (e.g. deer) or omnivores (e.g. pigs) - they pierce the animal’s intestinal wall and, using blood vessels like highways, are able to crawl into the animal’s muscles. Inside the muscles, the Sarcocystis can form special cysts, known as sarcocysts. The sarcocysts begin as a single parasite which then multiplies, expanding the sarcocyst. Inside the cyst, the parasites mature and become infective, ready for when a carnivore eats the parasite’s current host. Often, the cysts are big enough to see with the naked eye, which is why visual inspection of meat is an important part of Australia’s food safety policies. Alas, not all the 200+ species of Sarcocystis form cysts big enough to see. As the researchers in this study found out, some species have cysts which are microscopic.

This post focuses on a study conducted in southeastern Australia, where researchers examined muscle tissues of wild deer and feral pigs for Sarcocystis parasites. Previously, two other studies examining the carcasses of deer in Australia found no signs of infection from Sarcocystis, but after the unique discovery in Taree, these researchers thought the lack of results might be due to the way the meat were examined for parasites. The researchers of this study decided to use different techniques which included mashing the muscle tissue and straining it to find parasites, which were then looked at under a microscope, while their DNA was examined to confirm if the parasite was a species of Sarcocystis.

The researchers confirmed that seven of the animals that they examined had been infected by three different species of Sarcocystis, one of which hasn’t been described before. Five of the animals didn’t have any sarcocysts that were visible to the naked eye, instead they had microscopic cysts. Of the microscopic species found in the feral pigs in this study, they have also been reported in domestic pigs in other countries.

Since this parasite is comfortable in both types of pig, there is the possibility that feral pigs will (or have already) spread the parasite to domestic pigs, especially in the increasingly common free-range farms. This is particularly concerning since the only protection we have in place in Australia against Sarcocystis is visual inspection of meat. So, it is likely that infected meat may make its way into unsuspecting homes.

On top of this, we already know of three species of Sarcocystis that attack humans, causing vomiting and diarrhea among other symptoms. Because of this, it is reasonable to consider the possibility that other species of Sarcocystis, including the one discovered in this study, could leave anyone unfortunate enough to eat infected meat with a really bad day ahead of them.

Reference:

Shamsi, S, Brown, K, Francis, N, Barton, D. P., Jenkins, D. J. (2024) First findings of Sarcocystis species in game deer and feral pigs in Australia. International Journal of Food Microbiology 421: 110780.

Selenidium elongatum

A passing glance at the parasite in today's post might lead you to think that it is a worm, perhaps a nematode. But a closer look would reveal that not only is it much, much smaller than most nematodes, it also has a visible nucleus - like what you'd find with say, a cell. Despite how it looks, this parasite is not a worm, but a gregarine - which is a group of single-celled parasites that infect all kinds of invertebrates, including insects, crustaceans, sea cucumbers, and even sea squirts.

Left: Selenidium elongatum from Myxicola sp. Quadra. Right: Selenidium elongatum from M. aesthetica
scale bar = 20 μm. m = mucron; n = nucleus. Photomicrographs from Figure 1 of the paper 

Gregarine belongs to the phylum Apicomplexa - which includes Toxoplasma gondii, Plasmodium (the malaria parasite), and Cryptosporidium among its ranks. But the cells of gregarines grow much larger than those human parasites, with some species reaching half a millimetre in length (and one species, Porospora gigantea, exceeding 10 mm in length). They also come in all kinds of different shapes, including one species which is shaped like a microscopic rubber chicken, and they cling to the host's tissue using their mucron, an organelle which functions like the suckers of a fluke or a tapeworm.

The study featured in this post looked at gregarines and other symbionts living in two species of feather duster worms from Harriot Bay in British Columbia. As their names indicate, those worms are shaped like feather dusters, they live in tubes and use their long feathery appendages to filter food particles and plankton from the surrounding waters. The two species that the researchers examined were Myxicola sp. Quadra, which lives in tubes on muddy seafloors, and Myxicola aesthetica, a shallower water dweller that attaches to firmer substrates like rocks or shells.

The researchers examined about 50 of those worms and found that nearly all of them were infected with gregarine parasites, consisting of two species in the Selenidium genus - S. mesnili and S. elongatum. Those gregarines lived in the gut of the marine worms in a comparable way to how parasitic worms inhabit the gut of vertebrate animals. Though they belong to the same genus, the two Selenidium species are different to each other in many ways. The cells of S. mesnili are shaped kind of like skinny lemons, while S. elongatum, as its name indicates, has a long cell that makes it look like a single-celled version of a roundworm.

Aside from their size and shape, they also differ in other ways. Selenidium elongatum lives in the intestine of its worm host, and is found in both species of feather duster worms that the researchers sampled. Meanwhile, S. mesnili was only found in Myxicola sp. Quadra, and it lives exclusively in the host's pharynx and oesophagus. These differences might have arisen from the way these gregarines obtain nutrients from the host's digestive tract, or it might have something to do with the life cycles and transmission routes of these parasites. But Selenidium were not alone in the guts of those feather duster worms, living inside the gut of Myxicola aesthetica next to S. elongatum was a species of ciliate called Pennarella elegantia that swam freely in the worm's gut content.

Gregarines are poorly known but they seem ubiquitous in invertebrates, and their relationship with the host isn't always parasitic - there are evidence to indicate they can sometimes be beneficial to their host. And there are many more of them out there which are waiting to be discovered. What these gregarines show is that if you know where to look and what to look for, you will find a rich vibrant world even within the guts of a mud-dwelling worm.

Reference:

Park, E., & Leander, B. (2024). Coinfection of slime feather duster worms (Annelida, Myxicola) by different gregarine apicomplexans (Selenidium) and astome ciliates reflects spatial niche partitioning and host specificity. Parasitology, 151: 400-411.

Aggregata sinensis

Apicomplexa is a diverse phylum of single-celled parasites. They are found in a wide range of different animals, and includes some well-known species which can infect humans such as the malaria-causing Plasmodium, the infamous and widespread Toxoplasma gondii, and the gut-busting Cryptosporidium. But it is not as if this group has any particular affinity for humanity - humans are just one species among many across the animal kingdom that are hosts for apicomplexan parasites. Most of the more well-studied apicomplexans are those that infect terrestrial animals, especially domesticated species, but far less is known about apicomplexan parasites that are found in the marine realm.

Top left: Aggregata sinensis oocysts in the membrane between the arms of an octopus. Top right: Oocysts in the branchial heart.
Bottom left: Sporocysts found within an oocyst. Bottom right: Sporozoite released from a sporocyst.
Photos from Fig. 1 and Fig. 2 of the paper. 

Aggregata is a genus of apicomplexan which specifically targets cephalopods - mainly octopuses. Octopus can become infected from eating crustaceans such as shrimps which harbours the asexual stage of the parasite. Once they get into the octopus gut, the parasite takes over the digestive tract, and undergo sexual reproduction in the cells of the gut lining. There are twenty different known species of Aggregata, and it seems that for octopuses, there is no escape from this genus of parasite - even deep sea species living around hydrothermal vents are targeted by their own specialised species of Aggregata parasite.

So there are no doubt many other species of Aggregata out there which are still undiscovered. The paper featured in this blog post describes a species of Aggregata called Aggregata sinensis which has been found in octopus from the eastern-central coastal waters of China and the northern tip of Taiwan. The parasite was found infecting two species of octopus - the webfoot octopus and the long arm octopus - both of which are commercially important species that are caught by the local fishermen. 

The parasite was rather common, and depending on the location, between 20-100% of the octopuses that the researchers examined were afflicted with A. sinensis. Because the way an octopus becomes infected is from eating parasitised prey, Aggregata infection initially starts in the digestive tract, but it doesn't stay there for long. In heavy infections, the parasite spills over into other parts of the body in a very visible way. As Aggregata proliferates in the octopus, it leaves tell-tale signs of their presence in the form of white cysts that speckle the octopus' body. Those white cysts are called oocysts, which are the results of the parasite's sexual reproduction. Aggregata can wreak a destructive toll on the octopus's health. As the parasite proliferates, they smother the gut lining and destroy the submucosa cells, which compromise the octopus' ability to absorb nutrients. 

As if that's not enough, those white oocysts are filled with microscopic spheres called sporocysts which need to depart from the octopus' body to continue the life cycle, and they do so in a destructive manner. The release of those Aggregata oocysts necessitates the rupture and shedding of the surrounding hosts cells, resulting in ulcers and atrophy of the gut lining and connective tissues. Once free in the surrounding waters, should the sporocysts find themselves in an unlucky crustacean, they unravel to reveal their payload of worms-shaped sporozoites. These squirm out and settle in the crustacean's gut where they undergo asexual reproduction, and start the life cycle anew.

A recent study on the phylogeny of Apicomplexa suggests that Aggregata belongs to a group called the Marosporida - which occupies a key evolutionary position within Apicomplexa, separate from the rest of the phylum. Which means that understanding parasites like Aggregata may also help us understand the evolution of the Apicomplexa phylum as a whole, and how they became one of the most successful and ubiquitous group of parasites on the planet.

Reference:

Ren, J., & Zheng, X. (2022). Aggregata sinensis n. sp.(Apicomplexa: Aggregatidae), a new coccidian parasite from Amphioctopus fangsiao and Octopus minor (Mollusca: Octopodidae) in the Western Pacific Ocean. Parasitology Research 121: 373-381.

Goussia ameliae

The fate of parasites are often inextricably linked to that of their hosts, and when there are changes in the host population, the effects cascade onto their parasites. The study featured today is focused on Goussia amelia - it is a newly described single-cell protozoan parasite which infects alewives and is known to cause erosion in the intestinal wall of their fish host.

Image modified from Figure 2 and 3 of the paper

Alewife is a species of herring native to the east coast of North America. They are anadromous fish that live in the coastal marine environments as adults, but enter freshwater streams to breed, much like salmon. Sometimes populations of alewives become trapped in lakes for one reason or the other during their migratory journey. These isolated fish eventually become adapted to the freshwater environment and evolved on divergent paths to their anadromous relatives. This is a relatively common occurrence which has happened multiple time in the last few thousand years, and it is also the origin for the population of alewives found in Lake Hopatcong. This lake was originally connected via a canal to the Delaware River and alewives from the coast of New Jersey used to migrate to Lake Hopatcong to spawn. But during the start of the 1900s the canal was blocked off, and the alewives that were in the lake at the time became isolated from their relatives on the New Jersey coast.

So how did this affect parasites like G. ameliae? A pair of scientists compared G. ameliae found in alewives from Lake Hopatcong to those found in the anadromous alewives from Maurice River and noted some key differences in the two forms. For example, G. ameliae from anadromous alewives have oocysts (the infective stage of the parasite) which are comparatively shorter and wider than those from landlocked hosts.

They also have different trends in their prevalence and distribution; adult anadromous alewives are more commonly and heavily infected with G. ameliae than young fish, possibly because adult fish become stressed while migrating upstream and dealing with changing salinity levels as they move from the marine environment to a freshwater one, making them more susceptible to parasitic infections. In contrast, G. amelia was very common in younger landlocked alewives, infecting over ninety percent of young fish, but it was only found in about a third of the adult fish, which may indicate that the landlocked alewives can acquire resistance to the parasite as they mature.

Given those differences, are the anadromous and landlocked G. amelia actually different species? The scientists compared the DNA of G. ameliae from the anadromous and landlocked hosts, focusing on the 18S RNA gene which can function like a barcode for distinguish different species of parasites. They found that despite the two form having slightly different morphology and ecology, it was not enough to make them separate species - their 18S RNA gene sequences were identical. But given their differences, much like their hosts, those separate populations might be in the process of diverging into two different species - it is just a matter of time.

Reference:
Lovy, J., & Friend, S. E. (2015). Intestinal coccidiosis of anadromous and landlocked alewives, Alosa pseudoharengus, caused by Goussia ameliae n. sp. and G. alosii n. sp.(Apicomplexa: Eimeriidae). International Journal for Parasitology: Parasites and Wildlife, 4: 159-170.

Plasmodium falciparum (revisited)

This is the seventh and final post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Brianna Barwise about how Plasmodium falciparum - the most deadly strain of malaria - give their mosquito host a sugar craving (you can read the previous post about how the Emerald Cockroach Wasp acquires its skills for wrestling a cockroach into a submissive zombie here).

Photo by AFPMB

Ever felt like you had no control over your sugar cravings? Well, for mosquitoes infected with the apicomplexan parasite Plasmodium falciparum, that can certainly be the case. A recent study conducted by Vincent Nyasembe and colleagues have found that parasitized Anopheles gambiae mosquitoes have a significantly increased sugar uptake and attraction to nectar sources. Mosquitoes infected with the oocyst and sporozoite stages of P. falciparum showed a respective 30% and 24% increase in attraction to plant odours than those that were uninfected, with a respective 70% and 80% increase in probing activity. The study also revealed an increase in sugar uptake of those mosquitos infected with the oocyst stage of the parasite.

The relationship between these microscopic parasites and their pesky insect hosts is actually one of upmost importance to people. Plasmodium falciparum causes malaria in humans, and is transmitted by female mosquitos of the Anopheles genus. Anopheles gambiae is one of the most efficient malaria vectors and with the majority of malarial death being caused by P. falciparum, developing our understanding of this host/parasite relationship is crucial.

Behavioural manipulation of hosts by parasites to enhance their own survival and transmission rates has been well documented - from viruses that alter the egg-laying behaviour of wasps to hairworms that cause their landlubber cricket hosts to plunge themselves into water. Previous studies of Plasmodium parasites have shown they manipulate vector behaviour, with infected vectors having an increased attraction to their vertebrate hosts for a blood meal. However, this is the first study to demonstrate changed behaviour in mosquito vectors towards nectar sources.

Feeding on nectar is critical for the survival of malaria vectors. Increased attraction to nectar sources and sugar uptake could be explained by parasite manipulation to increase available energy for its own metabolism and improve survival of its vector (and thus likelihood the parasite will be transmitted). Further, an increased attraction to vertebrate hosts during non-transmissible stages of the parasite's development would be disadvantageous as it increases the risk of vector mortality. Thus, selective pressure would favour the parasite to drive a preference for nectar feeding during this time.

Alternatively, the change in behaviour could be attributed to a compensation made by the mosquito itself for the energy deficit created by the parasite. Generally speaking, parasitic infection inflicts energetic costs in the host vector, which leads to a decrease in reproductive potential and reduction in lifespan. Nyasembe suggests that it is possible the increased probing is to satisfy its own metabolic demands along with that of the parasite growing inside it.

Therefore, further study is required to establish whether the increased attraction to nectar sources and sugar uptake is a physiological adjustment by An. Gambiae in response to infection or if it is direct behavioural manipulation by the parasite. Either way, unlike much of humanity, at least they have some excuse for consuming an excess of sugar.

Reference:
Nyasembe, V., Teal, P., Sawa, P., Tumlinson, J., Borgemeister, C. & Torto, B. 2014. Plasmodium falciparum Infection Increases Anopheles gambiae Attraction to Nectar Sources and Sugar Uptake. Current Biology 24: 217-221.

This post was written by Brianna Barwise

Sarcocystis cernae

This is the fifth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Reece Dalais that he had titled "A fuzzy shuttle bus to a feathery airport" about what the parasite Sarcocystis does to its vole host (you can read the previous post about a midge that sucks blood from the belly of mosquitoes here).

Photo from here

Many protozoan parasites make use of one or more hosts before finally infecting the host species with suitable real estate for sexual reproduction (e.g. Sarcocystis dispersa and S. putorii). These ‘intermediate’ hosts act as temporary living quarters, in which the parasite accumulates resources, multiplies and then prepares for the trip to the next neighbourhood. In the Netherlands, the protozoan parasite Sarcocystis cernae, uses its intermediate host, the common vole (Microtus arvalis), to multiply itself and then as a vehicle to its honeymoon suite – the small intestine of the common kestrel (Falco tinnunculus). In the lining of the kestrel’s intestine, S. cernae lays its sporocysts, (which are equivalent to eggs) which leave the intestine with the stool of the bird.

Voles forage daily at regular intervals before scurrying back underground. During this time, they can accidentally consume kestrel faeces as they eat vegetation. Once inside the common vole, S. cernae develop in the rodent’s liver before entering its bloodstream and then declaring war on its muscles. In the vole’s musculature the parasite sits tight, and multiplies (asexually) to form large cysts – known as statocysts – which contain numerous bodies capable of sexual reproduction – or cystozoites. These cystozoites break free to reproduce (sexually) once the vole is torn apart and ingested by an adult kestrel or its young – which become the future protozoan distributors. In the mid to late 1980s, it was been discovered by a pair of scientists (Hoogenboom and Dijkstra) that infection with S. cernae makes the vole twice as likely to be taken in aerial attacks. The reason for this is still under question, and has oddly been ignored by researchers since 1987. Could it be due to some form of host manipulation whereby S. cernae forces a change in the behaviour in the vole? Or is it merely a helpful side effect caused by the protozoan running amuck inside the vole’s muscles?

Photo by Małgorzata Miłaszewska

The researchers collected vole samples by snap trapping and from nest boxes during the breeding season. Voles brought to the kestrel nestboxes for their young were taken and replaced them with lab mice of a similar weight – so feeding could continue as usual. Once these voles were dissected, the results revealed that 92% of infected voles had cysts present in the locomotory muscles (the biceps, triceps and quadriceps) – the muscles responsible for movement. Hence it is likely that infected voles were slower to escape the kestrels than their Sarcocystis-free pals. However, it was also proposed that once a vole becomes infected with S. cernae they may be forced to find food at dangerous times. Without infection, voles forage at the same time as other voles and, as a group, are more aware of predators. So if these inbuilt rhythms were to be interrupted by a parasite, the vole would become an easier target. This would be an example of host manipulation, as S. cernae, would be forcing the vole to change its foraging behaviour.

Although the effect of S. cernae on the common vole is not completely understood, it is without doubt that the cunning protozoan helps to drive its furry rodent host towards a feathery final destination.

Reference:
Hoogenboom, I., Dijkstra, C. (1987) Sarcocystis cernae: A parasite increasing the risk of predation of its intermediate host, Microtis arvalis. Oecologia 74: 86-92

This post was written by Reece Dalais

Eimeria echidnae

We have previously featured a number of coccidian parasites on this blog from birds (here and here), alligators, and groundhogs. Today's coccidian parasite lives in a strange ant-eating, egg-laying mammal from Australia - the short-beaked echidna Tachyglossus aculeatus.

photo from Figure 1 of the paper

The parasite we are featuring today is found in the gut of the echidna where it resides alongside another species of Eimeria - E. tachyglossi. Both these coccidians are found exclusively in echidna guts (generally coccidians are highly host-specific), and both are known to cause mild to severe inflammation of the small intestine, and in some cases, associated with fatality in systemic infections where the parasites have spread to the echidna's other organs. However, the exact role they might play in disease is still unclear. The study we are featuring today was conducted to establish the baseline, background level of Eimeria infection found in healthy echidnas.

The researchers of this study collected fecal sample from echidnas from various zoos and wildlife parks, and examined them for oocysts (see accompanying photo) - the infective stage of coccidia that are shed by infected animals. They found that most echidna shed between a few thousand to tens of thousands of oocysts in each gram of feces. While that may sound a like lot, all the echidnas involved in the study were clinically healthy, and the oocyst numbers were comparable to those from wild marsupials. Furthermore, infection intensity did not change over the different seasons, though oocysts (the parasite's infective stage) were more commonly shed by animals that were housed in outdoor enclosures

Additionally, they also found that while wild and short-term captive echidna shed oocyst of both E. echidnae and E. tachyglossi, echidna that have been held in captivity for an extended period of time only shed E. echidnae, indicating that captive conditions are unfavourable for E. tachyglossi transmission . Because coccidian oocysts are commonly found in the soil, presumably the echidnas become infected while feeding on ants; as they poke their snout in the dirt and use their long sticky tongue to lick up ants, they also end up ingesting a lot of soil (see this video of a hungry echidna on the prowl)

Most newborn mammals become infected with coccidia within their first week or month of life. In contrast, juvenile echidnas that have not been weaned were found to be free of coccidia. Given that echidnas become infected with E. echidnae through exposure to oocysts while feeding on ants, and young echidnas do not start feeding on ants until they are weaned at 6 months old, this age-dependent diet shift most likely explains the absence of E. echidnae infection in juvenile echidnas.

Reference:
Debenham JJ, Johnson R, Vogelnest L, Phalen DN, Whittington R, Slapeta J. (2012) Year-long presence of Eimeria echidnae and absence of Eimeria tachyglossi in captive short-beaked echidnas (Tachyglossus aculeatus). Journal of Parasitology 98:543-549

Isospora plectrophenaxia

Today's parasite is Isospora plectrophenaxia. A few weeks ago, you met a related species - Isospora lesouefi - the coccidian parasite found in the Regent Honeyeater which keeps a daily timetable, shedding most of its oocysts (the parasite's infective stage) in the afternoon. This is a well-described phenomenon among different species of Isospora - the parasite's shedding schedule appears to be calibrated by the light-dark cycle experienced by the bird host throughout the day. Indeed, experiments conducted on Isospora in house sparrow shows that if you disrupt the circadian rhythm of the host, you also mess up the parasite's shedding schedule.

Under natural condition, the usual light-dark cycle works just fine for most species of Isospora. But I. plectrophenaxia is found in the Snow Bunting (Plectrophenax nivalis) - a bird living in the High Arctic where there is perpetual sunlight during summer. So you'd think the shedding schedule of I. plectrophenaxia would be all messed up, right? Not so, researchers found that the parasite continues to stick to its regular regime of late afternoon shedding, just like all the other Isospora. At the moment researchers are unsure how I. plectrophenaxia is able to perform this feat. Perhaps this species is more sensitive to very low concentration of melatonin - the chemical secreted by the pineal organ which coordinates the bird's circadian rhythm, or perhaps it sets its timetable on different level of UV (ultraviolet) radiation exposure, which still varies throughout the Arctic summer day. Hopefully, ongoing research on this host-parasite system will shed further light on this little mystery, so watch this space!

Reference:
Dolnik O.V., Metzger B.J., Loonen M.J. (2011) Keeping the clock set under the midnight sun: diurnal periodicity and synchrony of avian Isospora parasites cycle in the High Arctic. Parasitology 138:1077-1081.

Isospora lesouefi

Isospora lesouefi is a coccidian parasite which infects the Regent Honeyeater (Xanthomyza phrygia), an endangered species of bird found in Australia. This parasite was found and described during a parasitological survey conducted on a group of honeyeaters at Taronga Zoo as a part of their captive breeding programme.

Before the birds can be released into the wild, their health needs to be assessed and a part of that procedure involves determining their parasite load. For animals that you want to keep alive, this usually involves counting the number of parasite eggs or spores found in their faeces. But here's the tricky bit - it turns out that I. lesouefi keeps to a daily timetable. The researchers in this study found that bird faeces collected in the afternoon contained about 200 times more oocysts (the parasite's infective stage) than those collected in the morning. Other species of Isospora also keep similar shedding schedules, and it is likely to be an adaptive trait which minimise the oocysts' exposure to desiccation and ultraviolet radiation.

This study illustrates the importance of taking multiple samples, as well as understanding the life history of the parasites when you want to obtain an accurate picture of parasite burden, and its actual impact on the health of an animal.

Reference:
Morin-Adeline, V., Vogelnest, L. Dhand, N.K., Shiels, M., Angus, W. and Šlapeta, J. (2011) Afternoon shedding of a new species of Isospora (Apicomplexa) in the endangered Regent Honeyeater (Xanthomyza phrygia). Parasitology 138: 713-724

December 26 - Plasmodium vivax

In Christian lore, three wise men, the magi, traveled from the East bearing gifts for the baby Jesus. These gifts were gold, myrrh and frankincense, a resin made from trees in the genus Boswellia. The reason for the gold seems obvious, myrrh was used as an incense, which had to have made the stable smell better, and frankincense was used for many things, several related to improving ones health, including ingesting the resin to combat arthritis and other ailments. Frankincense was also burned to ward off mosquitoes and thus the diseases that they carry. One of the most important mosquito-borne diseases at that point in time in that region was malaria, in this case caused by the parasite, Plasmodium vivax. Unlike it's cousin, Plasmodium falciparum, which kills many of the people it infects, P. vivax produces a milder form of the disease, though still with the classic symptoms of profound fever and chills. P. vivax has cycles every 48 hours and is sometimes thus known as "tertian malaria." (See the entry for Plasmodium malariae if that's confusing to you.) This species has a very widespread distribution and, in fact, used to cause early Americans as far north as Philadelphia and New York City to get sick every summer. Though it may kill fewer people, this parasite maintains stages in the liver of its host and can cause relapses of the disease for decades after the initial infection.

October 8 - Plasmodium relictum

The beautiful birds of Hawai'i have been battling with an invasive malaria parasite known as Plasmodium relictum, and several - perhaps 10 or more - species have been lost to extinction, due, in part to this novel pathogen. In the early 1800's, the mosquito, Culex quinquefasciatus was brought to Hawai'i, and this vector allowed the parasite to take hold on the islands as well. Because the mosquito does not go much above 4000 meters in elevation, many native lowland species have pushed their ranges up in altitude, but since most of the islands are lower than 5,000 meters, there's just not very far to go. P. relictum has an incredibly wide geographic range and infects a large number of bird species, making it an unusual generalist amongst its kin.

The image is from the USGS Microbiology Image Gallery and was taken by Carter Atkinson.

September 30 - Aggregata octopiana

This year, a particular octopus named Paul achieved fame and stardom due to some of his famous shenanigans relating to the World Cup. However, even an invertebrate celebrity such as Paul is not without a parasitic nemesis. Aggregata octopiana is a species of single-celled parasite that infects the common octopus, forming cysts in various parts of the body including the gills, digestive tract, and epidermis. The details of the parasite's life-cycle are currently not clear, though it is known to be a two-host life-cycle involving alternating phases of sexual and asexual reproduction. The sexual phase of this parasite occurs within the octopus where it undergoes a series of differentiation and cell divisions to produce produce infective stages that are shed into the environment. The parasite then infects prawns or other crustaceans that act as the intermediate hosts where asexual phase occurs. The life-cycle starts anew when the infected crustacean is eaten by an octopus.

Contributed by Tommy Leung.

September 25 - Isospora felis

Isospora felis is a coccidian parasite of cats that typically has a direct life cycle, but may also pass through small rodents , which can act as vectors for these parasites. They infect the cells of the small intestine and can produce GI distress in their feline hosts. This genus is quite large, but not much work, particularly molecular work has been done on the group, to tease apart which hosts might be paratenic and which species might be cryptic.

Image by Steve Upton.

September 20 - Neospora caninum

Originally confused with Toxoplasma gondii, Neospora caninum is a coccidian parasite that alternates between cattle hosts where it forms cysts in their tissues and canines such as dogs and coyotes, though transplacental transmission has been demonstrated in both intermediate and determinant hosts. Although this parasite does not seem to infect humans, it is of interest because it can cause spontaneous abortions in livestock if they are infected (resulting in economic losses perhaps as much as $24 million in Texas alone) and has also been linked to neurological disorders in dogs. The parasite is found virtually everywhere in the world where there are canines and cattle.

Photo of N. caninum in calf brain by Steve Upton.

September 8 - Eimeria alligator

Eimeria is a genus of apicomplexan parasites, but are coccidia, so unlike their cousins such as Plasmodium and Babesia, which alternate between an insect vector and a vertebrate, these parasites are transmitted via the oral-fecal route. Eimeria alligator was described from American Alligators (Alligator mississippiensis) in 1990, after sampling gators that had been shot in Texas during the alligator hunting season. Seven other species of Eimeria have been reported from crocodilian hosts in both the New and Old Worlds, as have two species of Isospora, another genus of coccidia.

August 26 - Plasmodium malariae

Plasmodium malariae is another of the five species of Plasmodium that cause the disease malaria in humans, but this is the one you need to worry about least. It's not because it's only found in a tiny area - to the contrary, it has an almost worldwide distribution. But, the symptoms that it produces are fairly mild and it's rarely fatal. The fevers induced from infection with P. malariae occur every three days, thus it was known as "quarten" malaria in the ancient world (the Romans did not use zero). A species originally isolated from New World monkeys known as Plasmodium brasilianum was recently found to be genetically indistinguishable from P. malariae and probably represents a shared parasite, though the order of the move is still somewhat uncertain, i.e. whether human infections in the New World have recently spilled over into monkeys or whether this is a recent zoonosis acquired by humans.

July 10 -New gregarine sp.

Dragonflies and damselfies are attractive creatures, yet they too have parasites! These include gregarines, which live in the intestine. Gregarines are single celled parasites known as apicomplexans, a group that also includes Plasmodium species, which cause malaria. Gregarines parasitize all sorts of invertebrates, such as oysters, beetles, earthworms, harvestmen, and a variety of insects. There are very likely tens of thousands, if not more, undiscovered species of gregarines in nature. For example, we recently found a new species of gregarine in the Eastern fork-tail damselfly in upstate New York, shown in this image. The star-like structure, the epimerite, is used to attach to the intestinal wall. We are now working on describing this new species.

Post and photo contributed by Crystal Wiles and Florian Reyda.

July 4 - Babesia uriae

Recently, you met Babesia microti, an Apicomplexan parasite that is sometimes affectionately referred to as "Montauk malaria" because of it's presence in the Northeast and the fact that it causes a disease much like malaria in people who become infected via tick bites. Today's parasite is Babesia uriae, a species that infect birds - in this case, the murre, from California. Two birds were found to be infected after having been brought into wildlife rehabilitation centers. The parasites appear to cause pathology in these birds and based on both morphological differences and molecular data were determined to be a new species. This was the first time that a species of Babesia was found in the family Alcidae (the auks). Currently, the vectors are not known.

Photo by Michael Yabsley, one of the discoverers of this species.

June 18 - Plasmodium mexicanum

Plasmodium mexicanum is, without a doubt, the best-studied species of lizard malaria parasite, and that is thanks to decades of work by Dr. Joseph Schall and his students. This parasite infects western fence lizards (Sceloporus occidentalis), in northern California and Oregon, but unlike most other Plasmodium species, it doesn't use a mosquito as its vector; it uses a phlebotomine sandfly. Work by Schall and others demonstrated that this parasite does have fitness consequences for its hosts - females lay fewer eggs and males have trouble defending a territory from other males. The parasite also seems to affect the bright coloring on the bellies of these lizards.

Photo by Schall himself.

Happy birthday, Joe.

June 8 - Plasmodium floridense

In January, you read about Plasmodium minuoviride, a malaria parasite of lizards, and learned that over 100 malaria parasites use lizard hosts. Today’s parasite – Plasmodium floridense – is another of these lizard parasites. As you might have guessed from its species name, it was first described in Florida, but its distribution includes the southern United States, most of the Caribbean, as well as parts of Central America. It is known from roughly 30 lizard species (a high host number for this kind of parasite), with most of these belonging to the lizard genus Anolis.

Prevalence (the percentage of animals infected) of P. floridense varies greatly among these hosts, ranging 5 to 50%. The cause of this variation is unknown. Differences in host ecology might affect prevalence, because – for example – some lizard species occur in open areas and infected lizards might use heat from the sun to raise their body temperature (i.e., a “behavioral fever”). Likewise, a vector species may encounter some lizard species more frequently than others, based on differences in these lizards’ roosting preferences, thereby skewing the rates of infection. These and several other potential factors could be causing the variation in prevalence of P. floridense.

Anolis lizards make good subjects in which evaluate the factors affecting parasite prevalence. They have undergone a repeated pattern of adaptive evolution in the Greater Antilles, and based on their behavior, morphology, and ecology, these lizards can be categorized into one of several “ecomorph” types. The pattern on each island is very similar, as near to a replicated experimental design as an evolutionary biologist could hope. Preliminary research on Hispaniola has shown that P. floridense infections are found primarily in lizards of one ecomorph type, and ongoing work will determine if this pattern is consistent across other islands (Falk et al., unpublished).

Contributed by Bryan Falk.