Toxoplasma gondii was discovered by scientists working in North Africa and 
Brazil around 100 years ago. The parasite has since been found to be capable of 
infecting all warm-blooded animals including humans making it one of the most 
successful parasitic organisms worldwide. The pathogenic potential of T. gondii 
was recognized in the 1920s and 1930s, in congenitally infected children 
presenting with the classic triad of symptoms, namely hydrocephalus, 
retinochoroiditis and encephalitis. In addition, around the same time T. gondii 
parasites were found to be associated with severe intraocular inflammation. In 
the 1980s, T. gondii emerged as a major cause of death in patients with acquired 
immunodeficiency syndrome, illustrating the importance of the immune system in 
controlling T. gondii infection. T. gondii was reported as a major cause of 
abortion in sheep in New Zealand in the 1950s, which raised questions about 
potential new transmission routes for the parasite. The discovery of the cat as 
the definitive host in the 1960s was a very important finding as it helped to 
complete our understanding of the parasite's life cycle, and the oocyst stage of 
T. gondii shed in the faeces of infected cats was found to be an important 
source of infection for many intermediate hosts and helped to explain infection 
in herbivorous animals and people with a vegetarian diet. In addition, this 
stage of the parasite was very robust and could survive in the environment, 
depending on the climatic conditions, for up to 12-18 months. Knowledge of the 
parasite's life cycle, transmission routes, risk groups and host immune 
responses has helped in the development of strategies to control the disease, 
reduce transmission of the parasite and limit environmental contamination.