Toxoplasma gondii

Toxoplasma gondii is a protozoan with worldwide geographic distribution, reaching up to 60% of the population in certain countries; however, cases of illness are less frequent. It is a very frequent zoonosis in several species of mammals and birds. The cat and other felids are the definitive or complete hosts and humans, among other animals, can be the intermediate or incomplete host.

Source: Toxoplasma gondii, AJ Cann from UK

This sporozoan, Toxoplasma gondii, is the causative agent of toxoplasmosis, an infection caused by indirect contagion, since, although there are no vectors or transmitters for the contamination, it is not directly transmitted from a sick individual to a healthy one. The parasite, during its life cycle, goes through a stage of reproduction by sporogony, in the definitive host (cats and other non-immune felids), and through an asexual reproduction stage (schizogony), in the tissues of various hosts, including cats and of man.

Source: Servier Medical Art, 2021

Various tissues and cells (except red blood cells) and organic fluids such as saliva, milk, sperm, etc. can be the habitat of T. gondii. In non-immune felids, forms of the sexual cycle can be found in the intestinal epithelium and also in the external environment, along with the feces (this being the resistant form, called oocyst).

Lesson on Toxoplasmosis: Acquired vs Congenital, signs and symptoms, how to diagnose and what can be used to treat it. Toxoplasmosis is caused by an infection with the protozoa toxoplasma gondii, which resides in hosts including cats and livestock.

Contamination can occur through ingestion of oocysts present in gardens, contaminated food or objects; ingestion of cysts present in undercooked meat, especially pork and lamb; and also congenital or placental transmission.

“Crazy cat lady” stereotypes or not, there could be some actual psychological risks from hanging around so many kitties… if just one of them is harboring the parasite Toxoplasma gondii.

The disease manifests itself with constant fever, rash (reddened punctate spots on the skin), enlarged ganglia, enlarged liver and spleen, which can be complicated by pneumonia and encephalitis. In the congenital form of toxoplasmosis, in which the pregnant woman with the disease serves as a means of contamination, the parasite crosses the placental barrier and reaches the fetus, causing severe eye damage, blindness or injuries to the skull and brain, which can cause abortion, or premature birth.

Source: Toxoplasma gondii AIDS Brain Perivascular cuffing. Michael Wunderli, 2021.

There is still no effective drug against toxoplasmosis. The drugs used act against proliferative forms, but not against cysts. As most people with positive serology do not have the disease and the drugs used are toxic in prolonged doses, it is recommended to treat only acute cases, ocular toxoplasmosis and contaminated immunodeficient individuals.


Dubey, J. P. (2011). Toxoplasma gondii.

Lyons, R. E., McLeod, R., & Roberts, C. W. (2002). Toxoplasma gondii tachyzoite–bradyzoite interconversion. Trends in parasitology18(5), 198-201.

Dubey, Jitender P. “The history of Toxoplasma gondii—the first 100 years.” Journal of Eukaryotic Microbiology 55, no. 6 (2008): 467-475.

Tenter, Astrid M., Anja R. Heckeroth, and Louis M. Weiss. “Toxoplasma gondii: from animals to humans.” International journal for parasitology 30, no. 12-13 (2000): 1217-1258.

Hill, D., and J. P. Dubey. “Toxoplasma gondii: transmission, diagnosis and prevention.” Clinical microbiology and infection 8, no. 10 (2002): 634-640.

Innes, E. A. “A brief history and overview of Toxoplasma gondii.” Zoonoses and public health 57, no. 1 (2010): 1-7.

Gajria, Bindu, Amit Bahl, John Brestelli, Jennifer Dommer, Steve Fischer, Xin Gao, Mark Heiges et al. “ToxoDB: an integrated Toxoplasma gondii database resource.” Nucleic acids research 36, no. suppl_1 (2007): D553-D556.

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