Outdoor cats suffer a much higher incidence of injury, parasites, and disease than cats kept indoors. Although some diseases are specific to cats—such as Feline Immunodeficiency Virus and Feline Leukemia Virus—others can afflict a wide variety of species, including people.
Toxoplasmosis is a disease caused by infection with the parasite Toxoplasma gondii. Although the parasite depends on cats (the definitive host) to complete its life cycle, it may infect all warm-blooded species (intermediate hosts).
Due to the potentially severe consequences of infection and potentially high levels of environmental contamination, toxoplasmosis is a serious concern and a neglected public health threat that impacts approximately one-third of humans globally.
The impacts of toxoplasmosis in people may be severe. As many as 1.26 million people in the United States have lesions on their eyes associated with toxoplasmosis.
Consequences of infection may also include deafness, seizures, mental retardation, blindness, schizophrenia, Alzheimer’s Disease, autism, obsessive compulsive disorder, memory loss, multi-organ failure, and even death.
Pregnant women and individuals with compromised immune systems are particularly susceptible to toxoplasmosis, and doctors have long advised against pregnant women cleaning litter boxes for this reason. New research, however, suggests that even adults with healthy immune systems are at risk.
People may become infected by T. gondii in several ways: ingestion or inhalation of infectious eggs (called oocysts), eating undercooked and infected meat, transmission from mother to child during pregnancy, blood transfusions, and organ transplants.
In the United States, infection via cat-excreted oocysts is likely the most common route. In fact, a study by Boyer et al. (2011) found that 78 percent of mothers of infants infected during pregnancy were exposed to this disease from oocysts.
Felines are the only animals known to distribute oocysts, and a cat infected with T. gondii may expel hundreds of millions of infectious oocysts into the environment through its feces. These oocysts are incredibly resistant to degradation and may remain viable for years in soil or water.
As many as 74 percent of all domestic cats in the United States will be infected by T. gondii during their lifetimes. With an estimated 60 to 160 million free-roaming domestic cats in the United States, the potential exists for large-scale environmental contamination.
A study by Torrey and Yolken (2013) concluded: “Because cats are now so ubiquitous in the environment, one may become infected by neighboring cats which defecate in one’s garden or play area, or by playing in public areas such as parks or school grounds. Indeed, as cats increasingly contaminate public areas with T. gondii oocysts it will become progressively more difficult to avoid exposure.”
By keeping cats indoors, people can substantially reduce their own and their community’s risk of exposure to this potentially fatal disease. They can also protect the many wild species that live around our homes and are equally at risk from toxoplasmosis.
Rabies is a viral disease that impacts mammals and, if left untreated, is almost always fatal. The virus may be transmitted through a bite or saliva that contacts an open wound or mucous membrane.
In the United States, wildlife species account for the majority of reported rabid animals, but domestic cats represent a disproportionate risk for potential human exposures, in part because people are more likely to interact with them.
Cats are the top carrier of rabies among domestic animals in the United States and have outpaced dogs for decades. Since 2000, the proportion of reported rabid cats to dogs has ranged from 2.2 (in 2000) to 4.4 (in 2010). While required mass vaccination, aggressive control of strays, and restrictions against running at large have significantly reduced rabies prevalence in dogs, these policies are scarce for cats.
The post-exposure prophylaxis (PEP), which is used to treat people after exposure to rabies, has been critical to preventing human deaths from disease, but it is dangerous and costly to rely on PEP administration for protection. PEP is administered only after an exposure to rabies has been identified and, therefore, is only as effective as the identification process. If left untreated, rabies is fatal.
PEP treatments are not cheap, typically in excess of $1,000 per exposure. Well over 6,000 people receive PEP every year in the U.S. due to potential exposure from cats, and these costs add up. PEP for a single New Hampshire mass exposure event in 1994 caused by a single rabid kitten cost over $1.1 million.
The surest and cheapest way of protecting cats and people from rabies is to prevent exposures from occurring. This means making sure that all cats have current vaccinations and are kept safely separated from wildlife, whether on a leash, in an enclosure, or kept exclusively indoors.