JOIN USToxoplasma gondii, a highly contagious protozoa, infects more than half the world's population, and most people's immune systems are unable to purge them.
"Toxoplasma is an especially promiscuous parasite. It infects nearly all warm-blooded species, most nucleated cell types and much of the human population," said Eric Denkers, professor of immunology at Cornell University.
Infections related to Toxoplasma gondii have been linked to behavioural and personality shifts and schizophrenia among humans, the journal Public Library of Science Pathogens reported.
Similarly, it has been shown to alter rodent brain chemistry so that they fearlessly pursue cats. Cats eat the rodents, delivering the parasites to their breeding ground in feline intestines, according to a Cornell statement.
"The infection can seriously harm people with weak immune systems, yet most hosts experience no overt symptoms because Toxoplasma has found a way to coerce cooperation," added Denkers.
"We found that Toxoplasma quiet(en)s its host's alarm system by blocking immune cells from producing certain cytokines, proteins that stimulate inflammation," said Denkers.
"Cytokines are double-edged swords: They summon the immune system's reinforcements, but if too many accumulate they can damage the body they're trying to defend. An unregulated immune response can kill you."