History

Toxoplasma gondii is a coccidium, with the domestic cat and other felids as its definitive host and a wide range of birds and mammals as intermediate hosts. It was first detected by Nicolle and Manceaux (1908, 1909) in a rodent Ctenodactylus gondi, and by Splendore (1908) in a rabbit. The name Toxoplasma is derived from the crescent shape of the tachyzoite (in Greek: toxo = arc, plasma = form). Knowledge of the full lifecycle of T. gondii was not completed until 1970, when the sexual phase of the lifecycle was identified in the intestine of the cat, by demonstrating oocysts in cat faeces and characterizing them biologically and morphologically (Dubey et al. 1970a, b).

Taxonomy

Toxoplasma gondii is placed in the phylum Apicomplexa (Levine 1970), class Sporozoasida (Leukart 1879), subclass Coccidiasina (Leukart 1879). Traditionally, all coccidia until 1970 were classified in the family Eimeriidae. After the discovery of the coccidian cycle of T. gondii in 1970, T. gondii has been placed by different authorities in the families Eimeriidae, Sarcocystidae or Toxoplasmatidae. Phylogenetic analysis of T. gondii and order Apicomplexa is shown in Figure 1.1.

Lifecycle

The definitive host is the domestic cat and other Felidae (Frenkel et al. 1970; Jewell et al. 1972), where the sexual cycle takes place in the intestinal epithelial cells. Infected cats excrete oocysts which are infectious to virtually all warm-blooded animals.