Host Manipulation by Toxoplasma gondii

Abstract

Many parasites have evolved adaptive mechanisms for manipulation of host phenotypes, including behavior, to increase their chances of transmission from infected to noninfected hosts (Holmes J, Bethel WM. Modification of intermidiate host behaviour by parasites. In: Canning EU, Wright CA (eds) Behavioural aspects of parasite transmission. Academic Press, New York, p 123–149, 1972). Very conspicuous behavioral changes are induced by parasites that are transmitted from intermediate to definitive host by predation because induced behavioral patterns increase biological fitness of the manipulating parasite but decrease fitness of the carrier – the infected animal. An already classical model for studying manipulative activity of parasites is the heteroxenous coccidian Toxoplasma gondii, whose life cycle includes transmission from intermediate host (any warm blooded animal) to definitive host (any feline species) by predation. Toxoplasma is known to modify not only the behavior of its intermediate animal hosts but also the behavior and personality of infected humans. The mechanisms most probably responsible for the observed behavioral changes are increase of dopamine, increase of testosterone in males and hypomethylation of certain regulatory elements of key genes in amygdala of infected hosts.