Study Finds Free-Roaming Cats Pose Threat from "Serious Public Health Diseases"

Cat with American Coot by Debbie Shearwater
Cat with American Coot by Debi Shearwater

(Washington, D.C., September 18, 2012) A study published in the peer-reviewed public health journal, Zoonoses and Public Health, has found that free-roaming cats pose a threat from “serious public health diseases” to humans, domestic animals, and wildlife.

The paper was authored by R.W. Gerhold of the University of Tennessee's Center for Wildlife Health, Department of Forestry, Wildlife and Fisheries, and by D.A. Jessup, retired from the California Department of Fish and Game.

Among the key findings of the paper are:

  • Free roaming cats are an important source of animal-transmitted, serious diseases such as rabies, toxoplasmosis, and plague.
  • Free roaming cats account for the most cases of human rabies exposure among domestic animals, and are the source for one-third of rabies post-exposure treatments in the United States. Because of inconsistent incident reporting, that number is likely an underestimate of the actual cases of rabies exposure.
  • Trap, neuter, and release (TNR) programs may lead to increased, un-inoculated populations of cats that can serve as a source of transmittable serious diseases.

The study found that since 1988, rabies has been detected more frequently in cats than in dogs; in 2008, the number of cats detected with rabies was four times higher than dogs.  In 2010, rabies cases declined for all domestic animals except cats, which comprised 62 percent of all rabies cases for domestic animals.

“This is a significant study that documents serious wildlife and public health issues associated with 125 million outdoor cats in the United States.  Decision-making officials need to start looking at the unintended impacts these animals have on both the environment and human health when they consider arguments to sanction Trap, Neuter, and Return (TNR) cat colonies. These colonies are highly detrimental to cats, wildlife, and people, and only serve to exacerbate the cat overpopulation problem,” said Darin Schroeder, Vice President for Conservation Advocacy at American Bird Conservancy.

According to the study, which cites numerous specific examples of rabies exposures from cats,  “…….human exposure to rabies is largely associated with free-roaming cats because of people being more likely to come into contact with cats, [the existence of] large free-roaming cat populations and lack of stringent rabies vaccination programs.”

Importantly, the study also seems to directly contradict notions that TNR programs lead to smaller sizes of cat colonies and that they pose no health risk. Those programs purport to capture all the cats in a colony, neuter and vaccinate them, and return them to a colony that is fed and by volunteers.

“….neutered groups (colonies) increased significantly compared to [sexually] intact groups because of higher immigration and lower emigration. ………sexually intact adult cats immigrated into the neutered groups at a significantly higher rate than [they did to the] sexually intact group.  ………immigrating sexually intact females had increased fertility along with increased survivorship of kittens as a population compensation response to neutered individuals.”

The authors report that the data suggest that neutered cat groups act as an attractant of sexually intact free-roaming cats, thus negating the belief that TNR programs lead to decreases in free-roaming cat populations. This attraction and subsequent movement of unneutered and un-inoculated cats into cat colonies “…may severely limit the protection offered by vaccination of TNR processed cats and would not abate the [transmittable disease] threat of rabies in these groups.”

The report also cited the dangers associated with TNR feeding stations in attracting raccoons, skunks, foxes, and other wild animals associated with rabies. The feeding stations not only increase the likelihood of contact between humans and rabies-exposed animals, they also increase the human and wildlife exposure to a potentially fatal parasite, raccoon roundworm, harbored by raccoons that is being seen in ever-increasing parts of the country.  The danger to wildlife was illustrated in a 2008 study that found that five Florida panthers were killed as a result of a single such infected cat.

Another significant disease threat cited by the study concerns is a parasite frequently found in water or soil contaminated by cat feces.  This parasite is responsible for causing the disease toxoplasmosis.  Consequences of contracting this parasitic infection are most serious if you are either pregnant, HIV positive, or are undergoing chemo-therapy treatment, and range from significant to severe to fatal. The report cited a 2011 study that found that 63 percent of the patients with acute toxoplasmosis had become infected through cat feces.

The authors conclude by saying that their study “…highlights the serious public health diseases associated with free-roaming cats and underscores the need for increased public health attention directed towards free-roaming cats.” The fact that rabies exposure in humans is disproportionately associated with free-roaming cats “…should be of paramount concern to health officials because of the high mortality rate of clinical rabies…”