Toxoplasmosis

Toxoplasma gondii(tŏk'sə-plāz'mə gŏn'dē-ī') is anobligate,intracellular,parasiticprotozoanthat causes the diseasetoxoplasmosis.[1]

Found worldwide,T. gondiiis capable of infecting virtually allwarm-bloodedanimals.[2]In humans, it is one of the most common parasites;[3]serologicalstudies estimate that up to a third of the global population has been exposed to and may be chronically infected withT. gondii, although infection rates differ significantly from country to country.[4]Although mild, flu-like symptoms occasionally occur during the first few weeks following exposure, infection withT. gondiigenerally produces no symptoms in healthy human adults.[5][6]However, in infants,HIV/AIDSpatients, and others withweakened immunity, infection can cause serious and occasionally fatal illness (toxoplasmosis).[5][6]

Infection in humans and other warm-blooded animals can occur

1. by consuming raw or undercooked meat containingT. gondiitissue cysts[7]
2. by ingesting water, soil, vegetables, or anything contaminated withoocystsshed in thefecesof an infected animal[7]
3. from ablood transfusionororgan transplant
4. ortransplacentaltransmissionfrom mother tofetus, particularly whenT. gondiiis contracted duringpregnancy[7]

AlthoughT. gondiican infect, be transmitted by, andasexually reproducewithin humans and virtually all other warm-blooded animals, the parasite cansexually reproduceonly within theintestinesof members of thecat family (felids).[8]Felids are therefore defined as thedefinitive hostsofT. gondii, with all other hosts defined as intermediate hosts.

T. gondiihas been shown to alter the behavior of infectedrodentsin ways thought to increase the rodents' chances of beingpreyedupon by cats.[9][10][11]Because cats are the only hosts within whichT. gondiican sexually reproduce to complete and begin its lifecycle, such behavioral manipulations are thought to beevolutionary adaptationsto increase the parasite'sreproductive success,[11]in one of the manifestations the evolutionary biologistRichard Dawkinsattributes to the "extended phenotype". Although numerous hypotheses exist and are being investigated, the mechanism ofT. gondii–induced behavioral changes in rodents remains unknown.[12]

A number of studies have suggested subtle behavioral or personality changes may occur in infected humans,[13]and infection with the parasite has recently been associated with a number ofneurological disorders, particularlyschizophrenia.[10]However, evidence forcausalrelationships remains limited.[10]