U.S. researchers say more than a quarter of the world's population is infected with a feline parasite related to malaria and which causes personality changes.
The Toxoplasma-gondii is spread by cats to humans and other animal species, including rats, and can lead to suicidal tendencies, said Dr. Kevin Lafferty, of the University of California at Santa Barbara in the journal Proceedings of the Royal Society, Biology.
"In populations where this parasite is very common, mass personality modification could result in cultural change," Lafferty wrote.
His study said about 7 percent of Britain's population had the parasite in their brains, while almost 70 percent of people in Brazil were affected.
Lafferty wrote that an infected rat's behavior changes and becomes more active, less cautious and therefore more likely to be caught by a cat.
Earlier research at Imperial College London said the same parasite may trigger schizophrenia, The Telegraph reported.
Copyright 2006 by United Press International
Explore further: Britain to offer all infants meningitis B vaccine