Toxoplasmosis

Toxoplasmosis is a protozoan parasite that spreads through food or water contaminated with oocysts, infected meat, or contact with oocysts from feline faeces.

Acute infection is usually asymptomatic, and once acquired, parasites remain in human tissues lifelong.

Symptomatic disease can be seen in patients who are immunocompromised with re-activation of latent infection or with acquisition of new infection.

Symptomatic eye disease can be seen in both patients who are immunocompromised and patients who are immunocompetent.

Primary infection during pregnancy is often asymptomatic in the mother but can result in congenital disease in the fetus.

Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii. Cats are the definitive hosts for the parasite and can excrete millions of oocysts that survive in the environment for months. Humans are intermediate hosts, and become infected by ingesting uncooked meat infected with tissue cysts (bradyzoites), by ingestion of other food or water contaminated with oocysts, or by transplacental spread of tachyzoites.[1]Tenter AM, Heckeroth AR, Weiss LM. Toxoplasma gondii: from animals to humans. Int J Parasitol. 2000 Nov;30(12-13):1217-58. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3109627 http://www.ncbi.nlm.nih.gov/pubmed/11113252?tool=bestpractice.com ​ Once bradyzoites or oocysts are ingested, or tachyzoites have spread through the placenta to a fetus, T gondii rapidly travels to tissues and organs where it encysts and remains permanently. Infection in humans is lifelong and often asymptomatic, unless a patient becomes immunosuppressed.

In Europe and North America, there are three main strains of T gondii, types I, II, and III, with type I being the most virulent and type III the least virulent. Type II is the most frequent strain seen in human disease in Europe and North America.[2]Howe D, Sibley LD. Toxoplasma gondii comprises three clonal lineages: correlation of parasite genotype with human disease. J Infect Dis. 1995 Dec;172(6):1561-6. http://www.ncbi.nlm.nih.gov/pubmed/7594717?tool=bestpractice.com ​ Parasites with a more diverse genetic background cause human disease in South America, Africa, and Asia.[3]Zhou P, Zhang H, Lin RQ, et al. Genetic characterization of Toxoplasma gondii isolates from China. Parasitol Int. 2009 Jun;58(2):193-5. http://www.ncbi.nlm.nih.gov/pubmed/19567233?tool=bestpractice.com [4]Ferreira Ade M, Vitor RW, Gazzinelli RT, et al. Genetic analysis of natural recombinant Brazilian Toxoplasma gondii strains by multilocus PCR-RFLP. Infect Genet Evol. 2006 Jan;6(1):22-31. http://www.ncbi.nlm.nih.gov/pubmed/16376837?tool=bestpractice.com [5]Boughattas S, Ben-Abdallah R, Siala E, et al. Direct genotypic characterization of Toxoplasma gondii strains associated with congenital toxoplasmosis in Tunisia (North Africa). Am J Trop Med Hyg. 2010 Jun;82(6):1041-6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877409 http://www.ncbi.nlm.nih.gov/pubmed/20519598?tool=bestpractice.com ​​​