Parasite gives wolves what it takes to be pack leaders

Amazing stuff! So what parasites have which behavioral effects on humans (actually the Wikipedia on Toxoplasmosis mentions a few known prominent cases)? 

Maybe one day we will find out that Putin the Terrible was also infected by Toxoplasmosis! 😊

This study is based on a very unique dataset on the wolf population in the Yellowstone National Park for over 27 years.

"Wolves infected with a common parasite are more likely than uninfected animals to lead a pack, according to an analysis of more than 200 North American wolves. Infected animals are also more likely to leave their home packs and strike out on their own. ...
Warm-blooded mammals can catch the parasite by eating an infected animal or ingesting forms of T. gondii shed in the faeces of infected cats. After a period of acute infection, semi-dormant cysts form in muscle and brain tissue, and persist for the rest of the host’s life. Up to one-third of humans might be chronically infected. ...
a rare opportunity to link infection with behaviour in wild wolves: data on grey wolves (Canis lupus) collected intensively in Yellowstone National Park, Wyoming, over nearly 27 years. ...
The team looked at 256 blood samples from 229 wolves, which had been carefully watched throughout their lives, and had their life histories and social status recorded. ... found that infected wolves were 11 times more likely than uninfected ones to leave their birth family to start a new pack, and 46 times more likely to become pack leaders — often the only wolves in the pack that breed. ..."

From the abstract:

"Toxoplasma gondii is a protozoan parasite capable of infecting any warm-blooded species and can increase risk-taking in intermediate hosts. Despite extensive laboratory research on the effects of T. gondii infection on behaviour, little is understood about the effects of toxoplasmosis on wild intermediate host behavior. Yellowstone National Park, Wyoming, USA, has a diverse carnivore community including gray wolves (Canis lupus) and cougars (Puma concolor), intermediate and definitive hosts of T. gondii, respectively. Here, we used 26 years of wolf behavioural, spatial, and serological data to show that wolf territory overlap with areas of high cougar density was an important predictor of infection. In addition, seropositive wolves were more likely to make high-risk decisions such as dispersing and becoming a pack leader, both factors critical to individual fitness and wolf vital rates. Due to the social hierarchy within a wolf pack, we hypothesize that the behavioural effects of toxoplasmosis may create a feedback loop that increases spatial overlap and disease transmission between wolves and cougars. These findings demonstrate that parasites have important implications for intermediate hosts, beyond acute infections, through behavioural impacts. Particularly in a social species, these impacts can surge beyond individuals to affect groups, populations, and even ecosystem processes."

Parasite gives wolves what it takes to be pack leaders Study is one of the few to show the behavioural effects of Toxoplasma gondii in wild animals.

Parasitic infection increases risk-taking in a social, intermediate host carnivore (open access)

Fig. 1: Map of cougar density and T. gondii seroprevalence in wolves in Yellowstone National Park (YNP).