Answer and Discussion of Quiz Set: C-002

1.    Which one of the followings is the definitive host of toxoplasma?

A.  Human

B.  Pig

C.  Sheep

D.  Snail

E.  Cat

Answer and Discussion: The answer is (E). Toxoplasma gondii is an intracellular parasite in the phylum Apicomplexa. It can infect a wide variety of warm blooded  animals including. However, the members of family Felidae (domestic cats and their relatives) are the definitive host and the sexual phase of this organism is in cats. The three form of T. gondii are oocysts, tachyzoites, and bradyzoites. Infection of human or other intermediate hosts are acquired by ingesting the oocysts that are passed in feces of infected cats. The oocysts will develop into tachyzoites which are the rapidly multiplying form that divide rapidly in cells. Transplancental spread of tachyzoites causes congential infection or still birth of fetus. Tachyzoites will eventually convert into tissue cyst or bradyzoites. This conversion is thought to be a response to the immune reaction of the host. Ingestion of meat contaminated with bradyzoites is also a source of infection. Toxoplasma is an important cause of mobidity in immunecomprised host such as AIDS patients.

Further Reading:

1.    Life cycle of Toxoplasma gondii: http://www.dpd.cdc.gov/dpdx/html/Toxoplasmosis.htm

2.    Life cycle and general information of Toxoplasma gondii: http://www.stanford.edu/class/humbio103/ParaSites2006/Toxoplasmosis/lifecycle.html