| Toxoplasma gondii |
|Parasite that can rewire brain behavior to make host do things that everything in their fiber normally tells them not to do, especially in cats, but also humans. The U.S military has shown interest.|
Toxoplasma gondii (T. gondii) is an obligate intracellular parasitic protozoan eukaryote that causes the infectious disease toxoplasmosis. Found worldwide, T. gondii is capable of infecting virtually all warm-blooded animals, but felids, such as domestic cats, are the only known definitive hosts in which the parasite may undergo sexual reproduction.
T. gondii has been shown to alter the behavior of infected rodents in ways that increase the rodents' chances of being preyed upon by felids. Support for this "manipulation hypothesis" stems from studies showing that T. gondii-infected rats have a decreased aversion to cat urine. Because cats are the only hosts within which T. gondii can sexually reproduce to complete and begin its lifecycle, such behavioral manipulations are thought to be evolutionary adaptations that increase the parasite's reproductive success. Rats that do not avoid cats' habitations will more likely become cat prey.
The primary mechanisms of T. gondii–induced behavioral changes in rodents are now known to occur through epigenetic remodeling in neurons that govern the relevant behaviors.
Toxoplasmosis is usually spread by eating poorly cooked food that contains cysts, exposure to infected cat feces, and from an infected mother to her baby during pregnancy. Rarely, the disease may be spread by blood transfusion. It is not otherwise spread between people. However, it can infect most types of warm-blooded animals, including humans. Diagnosis is typically by testing blood for antibodies or by testing the amniotic fluid in pregnant women for the parasite's DNA.
Mild, flu-like symptoms occasionally occur during the first few weeks following exposure; otherwise, symptoms are not readily observable in healthy human adults. This asymptomatic state of infection is referred to as a latent infection, and it has recently been associated with numerous subtle, yet adverse or pathological, behavioral alterations in humans.
“You want to know something terrifying? Here's something terrifying and not surprising. The U.S. military knows about Toxo and its effect on behavior. They're interested in Toxo. They're officially intrigued. An I would think they would be intrigued, studying a parasite that makes mammals perhaps do things that everything in their fiber normally tells them not to do because it's dangerous. But suddenly, with this parasite on board, the mammal is a little more likely to go and do it. Who knows? But they're aware of Toxo.”
Professor in neurology and neurosurgery Robert Sapolsky (2 December 2009) 
- Life, the leading edge of Evolutionary Biology,Genetics,Anthropology and Environmental Science; Harper Perennial 2016, page 356