Although the incidence of toxoplasmosis among humans probably has not changed significantly over the years, awareness and concern about the disease have increased within the medical and veterinary communities. It has been estimated that 30 to 50 percent of the world's human population has been infected with Toxoplasma and harbors the clinically inapparent cyst form. This encysted form is important because, if given the opportunity, it can produce disease in immunocompromised patients. For this reason veterinarians are often called on to clarify the role that cats play in the transmission of Toxoplasma to humans. The organism may also on occasion be present in some unpasteurized dairy products, such as goat's milk.
Congenital infection is of greatest concern in humans.
The vast majority of women infected during pregnancy have no symptoms of the infection themselves. It has been estimated that Toxoplasma is responsible for over three thousand human congenital infections in the United States each year, most of which are symptomless. Freezing and thawing, salting, smoking, or pickling will not reliably destroy cysts in meat. Restricting the access of pet cats to rodents and birds and offering them only cooked meat, commercially prepared cat food, and pasteurized dairy products should prevent most transmission. Scavenging can be discouraged by placing secure lids on all garbage cans.