Exactly one hundred years ago, the first description of Toxoplasma gondii was recorded but a further 60 years were to elapse before the final identification of the cat family as the definitive host was made. The heteroxenous nature of the parasite, its ability to infect any warm-blooded creature, the territorial range of its hosts (especially birds) and the production of tissue cysts that can survive for many years have contributed to the world-wide dissemination of the infection. Indeed, it is reasonable to conclude that perhaps T.gondii is one of the most successful parasites on Earth. About one billion people throughout the world are infected though the prevalence of infection shows consideration geographical variation.

Transmission of infection is by ingestion of either oocysts as a result of environmental contamination or tissue cysts in raw or undercooked meat. It is probable that the favoured route of transmission varies in different parts of the world – the epidemiology of the infection is still not completely known. It is also possible that other vectors, for example water and aerosols, may be involved.

Toxoplasma infection can be acute, chronic, latent/quiescent or re-activated, while the clinical presentation, investigation and management can vary according to the specific patient group involved. Infection in the immunocompetent, though very common, is generally regarded as a trivial event though there are suggestions that it may in fact be a more debilitating illness than was previously supposed.