Keep pet cats inside, stop feeding strays, cook meat sufficiently and reconsider the way the veterinary profession and public health agencies think - and teach - about the zoonotic pathogen Toxoplasma gondii.
Such are the recommendations of Milton M. McAllister, a professor of pathobiology in the College of Veterinary Medicine at the University of Illinois at Urbana-Champaign. He delivered that message in Christchurch, New Zealand, at the 20th International Conference of the World Association for the Advancement of Veterinary Parasitology.
McAllister, also a clinical professor of pathology in the U. of I. College of Medicine at Urbana-Champaign, made his case based on his review of numerous studies on the animal-carried pathogen during the past decade. His review, prepared for the conference, appeared in the Sept. 30 issue of the journal Veterinary Parasitology.
"Our profession needs to come to grip with the accumulating body of evidence about the tremendous burden wrought on society by toxoplasmosis," McAllister wrote. "Further research is needed to clarify the association between toxoplasmosis and mental health, but until such time that this association may be refuted, it is my opinion that the current evidence is strong enough to warrant an assumption of validity."
Toxoplasma can infect most warm-blooded animals, as well as humans and birds. Domestic cats and some wild cats are the only animals that can transmit the parasite by shedding the organism in feces. Other animals become infected when they consume the organisms shed by cats. This method of parasite transmission is called fecal-oral, but it doesn't actually mean that feces are directly ingested.
The organisms survive in soil long after feces have decomposed. Dust contaminates paws, fingers, feedstuffs and water, ultimately leading to ingestion by animals and people.
McAllister and colleagues are beginning to work on a new vaccine, which, if successful, would be administered to cats orally, possibly incorporated into a treat. The vaccine would be used to prevent cats from shedding toxoplasma.
"Cats usually become infected with toxoplasma by ingesting an infected animal, or raw meat from an infected animal," he said. "So a cat gets infected by catching and eating mice or birds, or by eating meat scraps from such things as poultry, pork, lamb or game."
In his review, McAllister noted a long list of maladies made worse by toxoplasma infection in people with suppressed immunity, and he cited a growing list of studies that link problems in people whose immune systems are not impaired. Among the latter problems are fever, enlarged lymph nodes, weakness and debilitation, damaged vision, or multi-systemic infections with serious complications such as pneumonia and hepatitis. Toxoplasma also is a causative agent of encephalitis in AIDS patients.
People can get infections either by fecal-oral transmission -- even through inhaling oocysts in dusty conditions -- or by eating undercooked infected meat. Oocysts, the egg-like forms of a parasite, can survive for more than a year in soil, dust or water, McAllister said.
"Cats that remain indoors have a low potential to become infected if they don't have access to mice and if they are not fed raw meat or meat products," McAllister said. Owners can safely keep an indoor cat simply by practicing good hygiene with the litter box and washing hands after daily cleanings, he added.
Infected mice, he noted, show altered behavior, including being less aware of cats in an area, leaving the mice open to predation that renews the parasite's life cycle. Mice may not be the only creatures susceptible to behavioral changes from infections, he said.