About 30% of the world's population is infected by the Toxoplasma parasite but in most people the infection appears to be asymptomatic and the parasite remains as a small cyst in the brain and muscle. However, if the infected person is immunosuppressed by pregnancy or diseases such as HIV/AIDS, the Toxoplasma infection can have serious consequences. In sheep and goats throughout the world it is an important cause of abortion.

From the early part of the 20th century, it was known that people could become infected from eating under-cooked or raw meat from an infected animal. However, it was not known how herbivores or vegetarians became infected.

Pioneering work by William Hutchison in 1965 showed that the domestic cat was an important vector of the disease by passing the parasite in its faeces. Furthermore, he showed that the parasite (in the form of oocysts) could survive in the environment for up to one year.

William Hutchison

"The only living material observed, apart from bacteria, were the oocysts of Isospora and the ova of T. cati."

This discovery had universal health implications. Because there are no drugs which are effective against the tissue forms (cysts) of the parasite his findings led to a series of recommended public health measures. These were aimed at creating greater public awareness of the problem and advising people to reduce contact with cat faeces, especially if they are pregnant women or people infected with immunosuppressive illnesses.

In 1970, Hutchison was awarded the Robert Koch medal, the first British Scientist to receive this award.