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.