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Tommy Leung
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Tommy Leung

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Of Chimps, Leopards, And Toxoplasma
Some of you may be familiar with the story about a little cat parasite call Toxoplasma gondii. It seems to be able to alter rodent behaviour so that they are more likely to be eaten by a cat, but it can also infect humans (and any warm-blooded vertebrate animal) and supposedly mess with human behaviour as well. Spoooooky. At least that's how the story goes. Like any other story, there is some grain of truth to it, but it is buried within a whole mass of (more sensationalised) dross. Any studies into Toxoplasma and host behaviour manipulation has the potential to go viral as it includes all the elements that makes a good headline - it contains cats, brain parasites, and zombies (in the form of host behaviour manipulation).

The literature on Toxoplasma and host behaviour is MASSIVE - some of it is good science, others are more like tabbies dressed as tigers. But for this post, I'm going to focusing on one story within a larger narrative, I want to talk about a paper recently published in Current Biology which had whipped the media into a frenzy (again) about how human behaviour is affected by Toxoplasma. http://www.cell.com/current-biology/abstract/S0960-9822%2815%2901517-1

Here's a tl;dr version of the study. The study found that compared with uninfected chimps, chimpanzees infected by Toxoplasma are not as averse to the odour of leopard (their natural predator) urine. The researchers concluded that this is because Toxoplasma is manipulating the chimps' behaviour so that they will be more likely to be eaten by a leopard (the final host for Toxoplasma are felines).

1) While the media coverage seems to be focused on how the parasite affects human behaviour, this experiment was done on chimps, and the media is extrapolating the conclusion of that study to humans. Humans and chimps may be genetically similar on some level, we have been separated by 5-7 million years of evolution, and our ancestors evolved in very different environments. There are some very key differences in the behaviour of chimps versus humans.
 
2) The study was not only correlative in nature, it was based on testing chimps for presence of Toxoplasma antibodies - not the parasites themselves, just a potential indicator of the parasites presence (having antibodies for something doesn't guarantee the presence of the said thing in the body). The researchers didn't confirm the presence of the parasites themselves. I understand they can't exactly do the latter for ethical reasons, in which case, maybe don't cannonball your way into such sensationalised conclusions?

3) The study tested how chimps response to the odour of urine and other big cats - the question is, just how much of a role does the sense of smell play in chimpanzees' predator avoidance repertoire? There is surprisingly little research on that. Is the sense of smell that important for predator avoidance compared with their other senses? Also, considering that chimpanzees are social animals, they would also rely upon other individuals in the group to warn of the presence of predators - you can't consider the vulnerability of a chimp to predation without the context of its social structure.

4) They mention potential behaviour variations between individuals (i.e. personalities) which may account for different level of aversion towards leopard urine odour which are pre-existing, regardless of the parasite. Good. But then, they just dismiss that possibility outright, by citing a single study that has found Toxoplasma is associated with disrupted fear response - in rat. Studies in other animals have shown that propensity for "recklessness" varies between individuals, even without the influence of parasites. So they're essentially saying Toxoplasma is the only possible explanation for why those chimps behaved slightly differently (in one aspects - response to leopard urine odour), even after bringing up the possibility that these behaviour variations exists regardless of parasitism, and discounting the dozens of other equally valid potential explanations. Not Wow.

5) Furthermore, when I dig into the methods, I found that the study was conducted on captive chimpanzees. Captive animals (especially behaviourally complex animals such as chimps) are known to exhibits behaviour which deviate significantly from their wild relatives. So we have no way of establishing whether such behaviour is representative of how they would behave in a natural setting (let alone extrapolating it to humans as the media has done). Once again, I understand that it would be extremely difficult to conduct such a study on wild chimps, in which case, the point I bring up in (2) still applies - don't jump to such sensationalised conclusions

6) Given the correlative nature of the study, we have no way of establishing how these chimps would have behaved before getting infected with Toxoplasma. So you can't rule out that maybe the chimps that behaved "oddly" are simply more likely to pick up Toxoplasma. They did mention this possibility, but they dismissed it just as quickly in the same manner as I described for (4).

7) The paper has 10 references in total (the supplementary material has 2 additional reference, but they were for methodological techniques), but did not cite a review recently published in 2014 in Advances in Parasitology which discussed at length the wide array of inconsistencies and seeming contradictory results from rodent-toxoplasmosis behavioural studies.
https://books.google.com.au/books?hl=en&lr=&id=ftnEAgAAQBAJ&oi=fnd&pg=PA109

And that's all I have to say about that. Peace out.
MFW I read another over-hyped "Toxoplasma gondii + host behaviour modification" paper pic.twitter.com/hOf8i62zWn · Tommy Leung – @The_Episiarch. I don't always subtweet, but when I do, it's about papers on Toxoplasma gondii and behavioural modification. Embedded image. 5:27 PM - 10 Feb 2016 ...
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That's exactly what is wrong with my neighborhood.
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Trematodes And Monster Girls
Some of you might have noticed that I have well and truly been bitten by the monster girl bug and I've been drawing some Parasite Monster Girls over the last 6 months. http://the-episiarch.deviantart.com/gallery/58399252/Parasite-MonMusu
Well, here's the latest - Maki the Trematode-infected Snail Monster Girl. Much like my last Parasite Monster Girl, I finished this a few days after I posted up new Parasite of the Day blog post, so the 3:1 ratio of scientific blog post about parasites versus monster girls based on parasites is still holding steady...
(more details on the inspiration for her design in the link below)
Here's another new Parasite Monster Girl! Introducing Maki - a snail monster girl that has been infected by a colony of parasitic flukes (trematodes). In a sense, she is quite similar to another Pa...
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I'm beginning to show some significant changes in the transformation of my life.
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Deep Sea Body-Snatchers
I have written a new Parasite of the Day blog post! This post is about a species of parasitic nematodes that infect deep sea amphipods. Over the last few decades, scientists have discovered that the inky, lightless realm of the abyss is home to a myriad of bizarre life forms. There is life even down in deep sea trenches, over 7000 metres below sea level, where there is no light, and the water pressure is crushing. Of course, where there is life, there will also be species that have evolved to be parasites - and this post about one such species!
This planet is full of parasites, and no matter what you are or where you live, there seems to be no escape from getting parasitised. A few years ago, I wrote a post about some microsporidian parasites which live in deep sea ...
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Hitchhiker Lice to the Louse Fly
I have written a new Parasite of the Day blog post! This post is about a species of louse fly - which is actually a type of fly, but it lives and looks kind of like a louse. But this post also features actual lice which hitch a ride on the louse fly. But not all lice are equally good at hitchhiking on a louse fly - see the post below to find out more!

#scienceeveryday  
Ever since birds and mammals have evolved to have feathers and fur respectively, many different orders of insects have also evolved to take advantage of the opportunities that they provide. Fleas, lice and some families of fl...
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 *Sea Monkeys, Tapeworms, And Arsenic*
I have written a new Parasite of the Day blog post! This post is about brine shrimps and tapeworms. While parasites are usually harmful to their host in some way, there might be times when the presence of parasites might be a good thing. For brine shrimps, it seems that being infected with tapeworm larvae might bring some unexpected to benefits. To find out more see the post below.

#scienceeveryday  
Most of the time, being infected with parasites is costly to the host in some way. But sometimes there might be circumstance when the presence of parasites might be a good thing. For brine shrimps (known to most as "sea monke...
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Title deliciously poetic without license:)
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Tapeworms And Monster Girls
Some of you might recall that towards the end of last year, I started drawing a some Parasite Monster Girls:
Luci the Zombie Snail Monster Girl
https://plus.google.com/+TommyLeung/posts/J2CiWHwHkvx
Cordelia the Zombie Ant Monster Girl
https://plus.google.com/+TommyLeung/posts/T9qsZTNm4RE
Well, I've been at it again, because actually, Frankenstein is the scientist. I, the person who keeps drawing Parasite Monster Girls, am the real monster.
Well, after a brief hiatus over Christmas and New Years, it looks like I'm back to drawing Parasite Monster Girls again. Previously it was Luci the Zombie Snail Monster Girl, and Cordelia the Zombi...
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Eat Jellies, Get Flukes
I've written a new Parasite of the Day blog post! This one is about parasitic flukes which infect jellyfish as a part of their complex life-cycles - but they don't infect all sea jellies equally, and their numbers also fluctuate over different seasons. To find out more, follow the link below!

#scienceeveryday  
Jellyfish are one of the most common inhabitants of the sea and while they are soft and squishy, their venomous stinging cells (call cnidocytes) can act as a deterrent for many potential predators. But not all predator though...
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Frogs vs Caecilians
I've written a new Parasite of the Day blog post! This one is about a parasite which infects Australian frogs - but it also infects the introduced cane toad. And in the study featured in this post, it seems to have also made the jump to colonise a group of legless amphibians call caecilians. But those legless amphibians are found in South America, so how did this parasite managed to infect them? Follow the link below to find out more!

#scienceeveryday  
Myxozoans are a group of very unusual parasites. Despite their simplified structure, latest research has shown that their closest living relatives are actually jellyfish (which means they are technically animals). They are fo...
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Parasites And Dinosaurs
The other day I was interview by Byran Crump of Radio NZ - the national public broadcaster of New Zealand. For the interview I talked about the what the (relatively sparse) fossil record of parasites can tell us about the evolution of parasitism, and the role the parasites play in the ecosystem. Follow the link below to listen to the full interview.

#scienceeveryday  
What does the fossil record reveal about the evolution of 'boneless' parasites? Dr. Tommy Leung from the School of Environmental & Rural Science at the University of New England explains.
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Nematodes And Monster Girls
Some of you might recall that in the last 6 months, I've been drawing some Parasite Monster Girls:
Tina the Tapeworm Queen
https://plus.google.com/+TommyLeung/posts/Cp95eJT7gfe
Cordelia the Zombie Ant Monster Girl
https://plus.google.com/+TommyLeung/posts/T9qsZTNm4RE
Luci the Zombie Snail Monster Girl
https://plus.google.com/+TommyLeung/posts/J2CiWHwHkvx
Well, here's another one (yay?) - Portia HIME the Nematode Princess. I don't think there's much else to say at this point except that I finished this on the same day as a new Parasite of the Day blog post, therefore so far this year, it's a 3:1 ratio of scientific blog post about parasites vs monster girls based on parasites.
¯\(ツ)/¯ Make what you will of that...
A new Parasite Monster Girl, this time, based on parasitic nematodes. Previously it was Luci the Zombie Snail Monster Girl, Cordelia the Zombie Ant Monster Girl, and Tina the Cestusa...
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Thanks +Kathy Rich!
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The Thousand Cercariae Itch
I have written a new Parasite of the Day blog post! This post is about a species of avian blood fluke. While this parasite normally infects ducks, it can cause a condition call "Swimmer's Itch" when the parasite's free-swimming larva tries to burrow under the skin of human swimmers. But of the thousands of larvae which are produced daily by the parasite's snail host, most do not reach their bird hosts. So what happens to them? Find out more in the post below. 

#scienceeveryday  
If you have ever gone for a swim in a lake and later found your arms and legs covered in red itchy welts resembling mosquito bites, it is quite likely that you have encounter parasites related to the one being featured today...
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+gabo montecino what about them?
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Slimy Saviour
I have written a new Parasite of the Day blog post! This post is about anisakid nematodes, a parasite commonly found in the body of fish and other marine animals, and the role that hagfish can play in their lifecycle. Follow the post below to find out more!

#scienceeveryday  
Raw fish are eaten all over the world. However, when preparing fish fillet for a meal, one might come across some parasitic worms, much to some people's shock and revulsion. Most of these parasitic worms are anisakid nematode...
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Nice 
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Tommy's Collections
Work
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Evolutionary biologist, parasitologist
Story
Tagline
Parasitologist, Evolutionary Biologist, Researcher, Lecturer
Introduction
Parasitologist and evolutionary biologist who also happen to write for a blog about parasites, and likes to draw things sometimes.

I am a biologist who conduct studies on various ecological and evolutionary biology aspects of parasitism/symbiosis. I also write for the Parasite of the Day blog, which I co-administrate with its founder, Susan Perkins of the American Natural History Museum.

Outside of my professional field, my favourite thing to do is drawing - some of which (but not all) are inspired by my scientific work. My drawings can be found on my dA account.
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Male