"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

July 27, 2012

Special Report: #ASP2012 (American) - Part I: What's a Parasite? Zombie Ants, and Bidding Wars

The 2012 American Society of Parasitology meetings were held July 13-16 in Richmond, Virginia. There were over 150 papers presented and an additional 50 or so posters and being just one person, I obviously couldn't see all of them! Here are a few of the highlights of the meeting from the ones I did see, though. The first talk I saw was my Ron Fayer of the USDA, who studies Blastocystis in livestock. Seems that the prevalence of this parasite can be quite high, but detection methods have improved a lot, making its prevention and control more hopeful. Heather Stigge then gave a nice talk about how digeneans (like this one) choose sites in their frog hosts - apparently no one likes bullfrog mouths! This was followed by another digenean talk by Stephen Greiman, who presented data on pathogenic bacteria being transmitted by these parasites in some cases. At the end of this first afternoon, there was a new feature of the meetings - shorter talks by more junior grad students who presented their ideas and plans for Ph.D. projects in order to solicit some feedback from us sage old members. It was very impressive to me how many of the faculty forewent dinner in order to do this. The next morning started rather somberly - it was the final editorial breakfast for Jerry Esch, who has been at the helm of the Journal of Parasitology for 19 years (more on that to come). The President's Symposium followed and that was great fun. ASP President Armand Kuris kicked it off with a summary of the patterns of evolution of parasitism and a search for unifying themes in ecological modeling. His presentation began some debate in that he narrowly defined "parasite" and perhaps prompted a few later speakers to justify why they were at a Parasitology meeting! David Hughes then wowed us with his work on "zombie ants" - behaviorally modified ants who are infected with fungal parasites. It is really elegant, systems-biology-style work that looks at manipulation from many different angles, including ecological, neurological, and phylogenetic. Ryan Hechinger, a former student of Kuris's, finished up the symposium with a great talk highlighting how large a role that parasites plan in understanding energy fluxes in ecosystems. There were some other nice talks in the afternoon in the parallel sessions. A current student of Kuris, Sarah Weinstein, set the place abuzz when her analyses suggested that parasitism as a lifestyle has evolved 175 times and then a few talks on gregraines by the Clopton and Cook labs set my mind adrift to Dr. Seuss characters. That evening, we held our annual Live and Silent Auctions to raise money to support the student travel grants and once again had a slew of really fun donations by the creative community. Highlights are always paintings that Bill Campbell has done - they fetch hundreds of dollars - but Kristin Jensen's felted iPhone and iPad covers have also grown in popularity (and I was thrilled to win one again this year!). The high-drama auction item of the night turned out to be a pair of hand-painted wine glasses with snails and cercariae, done by author and artist (oh, and parasitologist), John Janovy, Jr.

July 24, 2012

Special Report: #ASP2012 (Australia) Part IV: Swimming with the Parasites

This post is part 4 (and final) of my special report on the #ASP2012 (Australia) meeting at Launceston, Tasmania - see part 1 here, part 2 here, and part 3 here.

Photo by Kate Hutson
The last day of the conference was a bumper day for marine parasitology so I will just write as briefly as I can on what I saw to cover some highlights. The day kicked off with a series of plenary lectures on; sea lice on farmed salmonids in British Columbia, the history of using parasites as biological markers to identify stock and age of orange roughy (Hoplostethus atlanticus), and an overview of the various parasitic infections that pose a threat to aquaculture by Prof. Barbara Nowak.

But out of those, the presentation which stood out as being most relevant to the original mission of this blog was a talk by Terry Miller - a research officer from the Queensland Museum. He discussed the outcome (so far) of a project to explore to categorise the diversity and genetics of parasites found in fishes of Lizard Island and Heron Island on the Great Barrier Reef, as well as Ningaloo Reef on Western Australia as a part of the Census of Marine Life project. The sheer biodiversity of parasites was the reason why this blog was started and a subject that we discussed in an essay at the end of 2010 - Terry Miller, with his many collaborators, have certainly been busy finding, describing, and classifying this overlooked wealth of biodiversity. They found all manners of myxozoans, flukes, tapeworms, and roundworms, and have already described 56 new species so far. But there are still many unanswered questions relating to biogeography, life-cycles, phylogenetics of these parasites and their significance for fisheries. With 2000 species of parasitic flukes (not counting other fish parasites) estimated to be in the fishes of Australia alone - that's a lot of species descriptions to come!

Photos and drawings used with permission from Leonie Barnett
Speaking of the weird and wonderful, Leonie Barnett from Central Queensland University presented a poster on the molecular phylogeny of a family of parasitic flukes call acanthocolpids which have very odd-looking and remarkably ornate cercariae (the free-living stage which emerge form the first host in the fluke life-cycle). Most cercariae simply look like microscopic tadpoles, with a leaf-shaped body followed by a tapered tail. Leonie has given those acanthocolpid "funky cercariae" nicknames such as "Ducks" and "Starship Enterprise"(see photo on the right). The question must be asked (which at this point can only be rhetorical) - why produce such remarkably elaborate-looking larvae when the majority of them will die after a day or two? What hosts do these parasites infect which warrant such amazing extravagance?

There were a number of presentations thorough the day which were relevant to the fisheries and aquaculture industry, including talks on the detection and treatment of blood-flukes in ranched tuna, identifying and characterising anisakid nematode larvae (which normally infect marine mammals but can cause disease in human if accidentally ingested) from fishes in Australasian waters, and a presentation by Kate Hutson on assessing risks pose to barramundi and mulloway aquaculture by various parasites.

Different Philophthalmus sp. rediae morphs
(insert: specialised morph attacking
the sporocysts of a rival species)
Ian Whittington started off the afternoon session with some videos of monogeneans and to follow that, I talked about potential caste formation and eusocial-like traits amongst the asexual stage of Philophthalmus sp. and how these specialised morphs may in fact be playing a in interspecific competition (see photo on the right or my alternative rendering here)

Sarah Catalano from the Hutson lab talked about a bizarre and little-known group of parasite called the dicyemids which are found in the kidneys of cephalopods (octopus, squid, cuttlefish). These parasites have a very simple body structure, but a very complicated life-cycle. They are astonishingly diverse and also display high levels of host specificity with each species occurs exclusively in a single host species. Because of their specificity they can also be used as a biological marker to reveal different host species where before they were simply considered as subpopulations.

Also from the Hutson lab was Alex Brazenor who presented a study looking at the effects of different water temperature and salinity levels on Neobenedenia - the little worm mentioned in the previous post which is capable of consecutive bouts of self-fertilisation and kick off an outbreak on its own. Alex found that at higher water temperature, Neobendenia lived a faster life -  whereas it took 18 days to reach sexual maturity at 22°C, it only took 10 days to reached that stage at 30°C. Their eggs are more likely to hatch successfully at the higher temperature and salinity level, although if the temperature reached beyond 32°C they start suffering detrimental effects.

Well, that does it for my reports on the #ASP2012 (Australia) conference. Overall, I had a great time - I got to catch up with some colleagues I haven't seen for a while,we talked about a lot of interesting science, and I saw some great presentations and posters - just about all that you can ask for at a conference really. So for me, it's back to writing up blog posts about new papers being published on all manners of interesting parasites - and I already have quite a few lined up...

July 17, 2012

Special Report: #ASP2012 (Australia) Part III: Sleepy Lizards, Painted Dogs

This post is part 3 of my special report on the #ASP2012 (Australia) meeting at Launceston, see part 1 here and part 2 here.

Photo by Caroline Wohlfeil
There were a number of interesting talks from the wildlife session, first up was a talk by Caroline Wohlfeil - a student from Michael Bull's lab. She gave a talk on sleepy lizards (see right) and the reptile tick, Bothriocroton hydrosauri. These ticks go through 3 stages in their life-cycle, alternating between feeding on a lizard and dropping off in a sheltered area to develop once they are fully engorged. It is in this latter stage that there ticks are transmitted - when lizards take shelter at refuges that have previously been used by infected lizards, they pick up ticks that were dropped off from the previous lizard. Using GPS loggers which continuously recorded the lizard's activity and location, Caroline was able to use that data to work out how often each of the tracked lizard had opportunities for infection. Her network analysis revealed that lizards that are highly-connected also had higher tick loads.

This was followed with a talk by Luz Botero Gomez, a student at Murdoch University, on trypanosome infections in little marsupial call the Brushed-Tail Bettong or Woylie. We have previously covered trypanosomes in another marsupials on this blog, namely the koala, but as it turns out, there is a great diversity of Trypanosoma in native marsupials - most of it still unknown. Woylie are known to be infected with 3 species - T. cruzi (the species which causes Chagas disease), T. copemani, and an as yet unnamed clade of Trypanosoma. Some of those Trypanosoma species are also found in other Australian marsupials but only the woylie is known to carry all three. Much like the koala-infecting trypanosome, T. copemani seems to only cause problem when it occurs in mixed infection with other Trypanosoma species - such co-infections can leads to inflammations and lesions in the tissue. In addition, these different trypanosomes also seem to have varying degrees of tissue specificity, with some species occurring in the blood, while other in muscle tissues, but overall mixed infections are more likely to occur in organs and muscles. Given the Woylie is currently critically endangered, it is very important to know what kind of diseases are induced by these trypanosomes and how it is affected by whether they are single or mixed infections.

Photo from Wikipedia by Helenabella
For a change of pace from parasites threatening a critically endangered mammal, Amanda Ash (also from Murdoch University) presented a talk call "Parasite: embrace not erase" which praised the important functional roles played by parasites in various ecosystems, and discussed the results of a study she conducted looking at the inestinal parasites of African Painted Dogs. She collected fecal samples from captive and wild Painted Dogs and compared the types of parasite eggs and cysts found in those sample. She found that the intestinal fauna of captive dogs was comparatively depauperated, populated only by Giardia whereas the wild dogs had a more eclectic mix of tapeworms, hookworms, and various protozoan parasites - in addition Giardia. Another stark contrast between the captive and wild dogs is that whereas parasitic infection was ubiquitous in the wild population, with 99% had some sort of parasite, only 15% of the captive dogs carried intestinal parasites of some sort.

This has enormous implications for conservation measures such as captive breeding programs - animals which have not been exposed to a wide range of parasites and pathogens can grow up to become immunologically naive so that when they are release into the wild, they may not be able to cope with the wide range of parasites they encounter. In addition, it is unknown what other physiological side-effects may result from lack of exposure to parasites. According to the hygiene hypothesis, the numerous types of allergies and auto-immune diseases which afflict some of us living in western societies have result from the lack of exposure to parasitic worms which are masters at manipulating and modulating our immune system. By limiting both the prevalence and variety of parasitic infections in those captive African Painted Dogs, are we consigning them to the same fate?

During the poster presentation, we saw some students who have come up with creative ways of presenting a 2 min talk - a student from James Cook University read a poem about whether wild dingoes pose a threat to the health of Indigenous communities in Queensland, while a student from University of Western Australia was literally singing the praises of using volatile chemicals for malaria parasite detection. Some of the most fascinating poster talks may present nightmarish scenarios to some people, but for different reasons.

Photo by Kate Hutson
For non-parasitologists, the tongue-biter seems like a one-off freak of nature. But in fact there are actually many species of tongue-biting isopods and other parasitic crustaceans which inhabit the mouth, gills, and branchial cavity of fish. One genus of tongue-biter isopod - Ceratothoa - encompasses 29 known species worldwide, 6 of which are found in Australia waters. However, a new study by Melissa Martin from University of Tasmania revealed that there at least 12 species of Ceratothoa (from 7 families of fish), and 4 of them are new to science.

Dinh Hoai Truong, a student from the Hutson lab at James Cook University presented a horror of a different kind - less visceral than having a parasite in your mouth, but more of a biosecurity nightmare to aquaculturists. He presented a poster on Neobenedenia - a hermaphroditic monogenean which infects the skin of Barramundi. His experiment showed that a single Neobenedenia is able produce eggs through self-fertilisation for consecutive generations without suffering any deleterious effects of inbreeding - each consecutive generation of inbred Neobenedenia are just as infective as the last. This means that even a single worm can start an entire sustained infestation at a fish farm. Unlike the widespread monogenean Gyrodactylus - a notorious aquacuture pest which has the viviparous "Russian Doll"-style "worm-within-a-worm" reproductive set-up (which allows them to swarm a fish like aphids on a rose bush) - Neobenedenia does what most monogeneans do and simply produce eggs. However because they are able to self-fertilise and have very short generation time, they can still become a serious pest to aquaculture.

In the next and final post on #ASP2012 (Australia), we will talk about how environmental factors can affect the generation time of Neobenedenia, and meet many other weird and wonderful marine parasites.

Next post: Swimming with the Parasites

July 11, 2012

Special Report: #ASP2012 (Australia) Part II: Parasites Gone Wild!

 This is Part 2 of my special report on #ASP2012 (Australia) - for part 1 see here.

The presentation on DFTD as the "perfect parasite" was followed with a talk by Andrew Thompson who holds a Chair in Parasitology at Murdoch University. He talked about how the presence of humans and our activities have often exposed wildlife to various infectious diseases. Wildlife are usually seen as a source of potentially harmful infectious diseases, and are often treated as the "bad guys" when it comes to pathogens. But in fact, sometimes wildlife have more to fear from us, and they act as sentinels, sinks, and sufferers of emerging infectious diseases which had been brought about through human action.

Tapeworm cysts in wallaby lung (photo from here)
For example, since the introduction of dogs and domestic livestock, macropods such as kangaroos and wallaby have become host to cysts of hydatid tapeworms (which Carl Zimmer wrote a post on about a month ago and was among the first batch of parasites to be featured on this blog). Hydatid infections in macropods come from eggs which are deposited in the environment by farm dogs which have the adult tapeworms living in their intestine. The dogs themselves acquire the worm from feeding on offal of infected livestock. Thus our canine companions are acting as the conduit for hydatid to jump from livestocks (one of their original hosts) to the likes of Skippy.

Bandicoot photo by JJ Harrison
from the Wikipedia
But hydatids are not the only introduced parasites which is afflicting Australia's marsupial fauna. Everyone's favourite cat parasite - Toxoplasma gondii - can also end up infecting the brain of bandicoots. However, this did not result from bandicoots coming into in close contact with cats (or rather, their feces). Instead, being such cute little mammals, people often leave food out for bandicoots in their backyard, and encourage them to enter into urban environments where they are more likely to be exposed to infective cysts.

In addition to introduced parasites, Australia's marsupials are home to all manner of little known vector-borne infections. There are multiple species of trypanosomes found in native marsupials (which I will discuss in more details in the next post), but there is very little information on their ecology and vectors. The vector for Trypanosoma cruzi (which causes Chagas disease) is a triatomine bug, but next to nothing is known about the Australian species and their potential role in vectoring those parasites. Thompson also discussed what appears to be a unique species of Leishmania in red kangaroos - which is transmitted via a midge (photo below right) instead of sandflies like other Leishmania.
Photo from this paper

Speaking of little known parasite fauna of Australian animals, Prof. Ian Beveridge - who is an absolute goldmine of knowledge on parasite biodiversity - gave a talk on that very topic. A fact he presented during his talk, which got retweeted a few times during the livestream, was that the average kangaroo is carrying 60000 nematode worms inside them. What I did not tweet at the time was that some individual kangaroos can be infected with up to half a million nematodes. Beveridge estimated that there are about 300 species of nematodes found in macropods. Traditionally horses and other equine are considered as particular "wormy" hosts (Sorry about that Bronies, but your Ponies be loaded with Wormies), harbouring a great diversity of nematode parasites - something which was remarked upon by Hippocrates. However, Beveridge estimated that macropods may in fact be equally "wormy" if not more so - there are so many nematode species which are yet to be found and described, and many host species which have not been properly examined for parasites (Beveridge mentioned road kills as an opportunistic sources of parasite samples - something which I have done on occasions.)

Even with the worms that are already known, it could be that they are even more diverse than we initially expected. Beveridge talked about a case where nematodes from rock wallabies which have previously been classified as 3 species (based on their morphological features) were later revealed by DNA analyses to be composed of 15 distinct genetic lineages (we have previously posted about cryptic species complex on this blog here and here).

And just bring it full circle and refer back to the previous post - the Tassie Devil is host to some unique parasites itself. Out of the two species of flukes, two species of tapeworms, and three species of nematode that it hosts, one of the flukes and two of the tapeworms are unique to the Tassie Devil and found in no other animals. If we lose the devils thanks to DFTD, we will lose those one-of-a-kind parasites too. Sometimes parasite extinctions can be brought about through the best of intentions (see the case of the Californian Condor) - when the devils are brought in for captive breeding or as an "insurance population", the vets treat them for parasites - so good-bye special worms! However, Dasyurotaenia robusta - a species of tapeworm unique to the Tassie Devil - is actually covered by the Threatened Species Protection Act in Tasmania.

Save the devil, save the D. robusta!

Coming up in the next part: Sleepy Lizards, Painted Dogs.

July 8, 2012

Special Report: #ASP2012 (Australia) Part I: Better the Devil you (get to) know

This post is the first in a series of special reports that I will be writing based on my recent experience at the Australian Society of Parasitology conference in Launceston, Tasmania (some of you might have noticed my tweets from the event tagged with #ASP2012). As a disclaimer, I will only be writing about the talks and posters which I personally saw, thus they will be those which reflect my interest in natural history, evolutionary biology, ecology, and wildlife diseases. Those also happens to be the type of post which appears on this blog anyway, so if you are a long-time reader of Parasite of the Day, it might as well be business as usual.

The conference started off with a series of free-to-public talk. The first was a presentation by Greg Woods, an associate professor from University of Tasmania, on the Devil Facial Transmissible Tumour as the "perfect" parasites - keep in mind I have emphasised many times on this blog (directly or indirectly) that there is no such thing as "perfect" in evolution. I first encountered the concept of DFTD as a parasite in an abstract I read from the program of the eleventh ICOPA (International Conference of Parasitology) held at Glasgow in 2006. Ever since I have been intrigued by the idea of cancerous cell lines becoming infectious and transmissible between different individual hosts/carriers (DFTD is not a lone anomaly - see also the Canine Transmissible Venereal Tumour and reticulum cell sarcoma of the Syrian hamster). According to Woods, based on current evidence, the DFTD cell line currently being circulating in the devil population had originated in 1996 from the mutated Schwann cells of a female devil (the "DFTD Eve" I guess). The original function of Schwann cells is to protect and maintain the peripheral nerve cells. The cells of DFTD are heavily modified from their ancestral form both in appearance and function, which made it difficult to identify their origin.

During the audience Q&A session, Woods also mentioned that during the course of research on DFTD, scientists were able to co-opt the background knowledge and pre-existing tools we already have for the study of human cancer cells to understand the biology of the DFTD cell line. In turn, molecular tools which were subsequently developed specifically for identifying and elucidating DFTD cells have also become useful for studying human cancer cells. Those parallel cancer research programs have proved to be a far more mutualistic relationship than that between the Tassie Devil and the DFTD cells.

Woods discussed some of the criteria which qualifies DFTD a parasite including their ability to produce immunological suppression factor, allowing them to escape the host's immune system. While some may object to calling the facial tumour cell line a "parasite" because it eventually kills their host - many parasites eventually kill their host, whether by accident or as a part of their life-cycle (as we have written about many times on this blog) - there is no universal parasite creed that goes "thou shalt not kill your host" - if parasites did have a creed it would read more like "thou shalt use the host in whatever way you see fit and get away with".

In a review on DFTD published in Trends in Ecology and Evolution, Prof Hamish McCallum wrote that the cell causing DFTD is "...essentially a clonally reproducing mammal that is an obligate parasite." which may seen radical, but once you get over the preconceived notions you may have about what a "parasite" ought to be (or what a mammal, or a "species" or "life" ought to be), it makes biological sense. After all, there are stranger things which exists in nature and biology. Those who want to read more about DFTD should see this article here. Apart from learning about DFTD, thanks to the appearance of a special guest (see right) we also found out that the infamous Tasmanian Devil is nowhere near as aggressive as most people might think...

Coming up in the next part: Parasites Gone Wild!