ClinQuiz: Increase your zoonotic parasite prowess, answer 2A
Many cats have been exposed to T. gondii and are seropositive. While paired serum samples can be used to detect recent or active infection, serologic tests cannot predict oocyst shedding in cats nor indicate past shedding. Seropositive cats are unlikely to be shedding oocysts or to be a source of human infection. Cats shed oocysts for only seven to 21 days after infection, and most apparently never shed again, even upon reexposure to infected prey,4 although reshedding upon a second exposure has been shown experimentally in some cats.5
While it is true that oocysts in feces from the entire local cat population may contaminate the environment, creating a risk of infection for people and other animals, individual pet cats are not a major concern as a source of infection in people, particularly adult cats kept indoors.4 Less than 1% of cats are shedding oocysts at any point, and the rate would be expected to be much lower in adult cats kept inside.6,7 Indeed, infection with T. gondii in people is not associated with cat ownership or exposure to cats8,9; thus, prevention advice must be more comprehensive.