History of Toxoplasmosis

Toxoplasma gondii also known as toxoplasmosis is a protozoan parasite first discovered in 1908 and named a year later. Its medical importance remained unknown until 1939 when Toxoplasma gondii was identified in tissues of a congenitally infected infant, and veterinary importance became known when it was found to cause abortions in sheep in 1957. The discovery of Sabin-Feldman dye test, a toxoplasma gondii specific antibody test, in 1948 led to the recognition that Toxoplasma gondii is a common parasite of warm-blooded hosts with a worldwide distribution. Until 1970 its life cycle was unknown then it was discovered that felids are its definitive host and an environmentally resistant stage (oocyst) is excreted in feces of infected cats. The recent discovery of its common infection in certain marine wildlife (sea otters) indicates contamination of our seas with T. gondii oocysts washed from land.

Toxoplasma gondii is a tissue protozoan with three life stages – tachyzoites, bradyzoites and sporozoites. Tachyzoites is the rapidly dividing stage of the organism that disseminate in the blood or lymph during active infection and that can infect almost all tissues. The tachyzoites replicate intracellularly until the infected cell is destroyed, releasing the organism.
Cats are the only species able to complete the coccidian life cycle of T. gondii in the intestinal tract. After cats ingest bradyzoites (that are encysted in tissues of prey animals) intestinal epithelial cells are infected and several rounds of asexual replication occur followed by the sexual cycle. Sporulated oocysts are passed in the feces; at this stage they are non-infectious. Sporozoites develop in the oocysts after one to five days of exposure to oxygen in conjunction with appropriate environmental temperatures and humidity.

Toxoplasmosis is found in humans worldwide, and in many species of animals and birds. Cats are the definitive host of the parasite.
Human infection may result from:
• Blood