Toxoplasma gondii Presentations at the 10th International Workshops on Opportunistic Protists: 100 Years and Counting

Toxoplasma gondii, an apicomplexan parasite of mammals, was first identified over 100 years ago (in 1908) by Nicolle and Manceaux, who isolated tachyzoites from the gundi, a North African rodent (34). Splendore also identified this parasite in the tissue of a rabbit in 1908 (46). The genus Toxoplasma was named for its bow-like shape (from the Greek “toxo,” for bow or arc, and “plasma,” for creature). The presence of a tissue cyst (bradyzoite) life stage was rapidly recognized, but it was not until almost 60 years later that this organism was recognized to be a coccidian and that felines were identified as being the definitive hosts by several groups working independently, including Dubey and Frenkel in 1970 (16). The association of T. gondii with food-borne and waterborne transmission has resulted in its classification as a National Institute of Allergy and Infectious Diseases (NIAID) category B priority agent. Due to the extensive repertoire of applicable experimental techniques available for this pathogen, it has become a model organism for the study of intracellular pathogens. Research on T. gondii continues to move rapidly, and this review will address information related to recent advances in our understanding of the biology of T. gondii presented at the IWOP-10 held in Boston, MA, 28 to 31 May 2008, and the symposium entitled “Centenary Celebration of Toxoplasma Discovery” held at that meeting. History, epidemiology, and life cycle. The details of the history of the discovery of T. gondii were reviewed at IWOP-10 by Dubey (15) and were also described in recent reviews (1, 14). T. gondii is estimated to infect about one-third of the world’s human population and is a significant zoonotic and veterinary pathogen. In humans and veterinary hosts, T. gondii is frequently associated with congenital infection and abortion. This parasite can be transmitted by the vertical transmission of the rapidly growing tachyzoite form if an immunologically naive mother acquires a new infection during pregnancy. In addition, T. gondii is an opportunistic pathogen associated with encephalitis or systemic infections in immunocompromised hosts such as individuals with advanced human immunodeficiency virus infection (i.e., AIDS). Tachyzoites divide rapidly within host cells and are thought to be responsible for the clinical manifestations of infection. In humans, T. gondii is most commonly acquired by the oral