Zoonoses transmitted by cats highlight importance of proper care

April 2008

On July 14, 2007, a softball coach from a North Carolina team found an apparently healthy and alert kitten in a barrel-shaped garbage bin located near one of the playing fields in Spartanburg County, South Carolina, where a four-state tournament was held.

The kitten was later brought to at least six different games played at two recreational facilities that same day and later transported by the coach to her home in Buncombe County, North Carolina.

On July 15, 2007, the kitten began behaving abnormally and became lethargic. The coach’s housemate brought it to an emergency animal hospital in Buncombe County for care. After evaluation indicated that the kitten was severely ill, it was euthanized and held for cremation, planned for July 18, 2007. Rabies was not suspected by the attending veterinarian; testing for rabies was not planned because the person who brought it had signed a routine release form indicating the kitten had not bitten anyone during the preceding 10 days.

The same day of the euthanization, the mother of a softball player from North Carolina, after learning from the coach that the kitten had become ill and was subsequently euthanized, contacted the emergency animal hospital and asked whether the kitten had been tested for rabies.

The mother — who had been bitten while trying to feed the kitten during the tournament – went to the clinic and took the cat’s body in her private vehicle to her local health department.

On July 23, 2007, the kitten had rabies diagnosed by direct fluorescent antibody testing. The North Carolina Division of Public Health immediately notified the South Carolina Department of Health and Environmental Control; both obtained a roster of teams from the tournament organizer and discovered that Georgia, North Carolina, South Carolina and Tennessee all had teams participating in the tournament. They contacted CDC and state public health authorities in Georgia and Tennessee. All four states subsequently initiated contact investigations.

Eventually, 27 people from three states were identified as “actual exposures” to the kitten’s saliva that warranted postexposure prophylaxis. According to the report “Public Health Response to a Rabid Kitten — Four States, 2007” in CDC’s Morbidity and Mortality Weekly Report of Jan. 4, 2008, from which the above data have been derived, eventually none of the contacts developed rabies.

Obviously, exposures to rabid cats may have worse outcome. During the last 25 years, four human rabies cases have been reported in Israel. Three of these cases were transmitted by unidentified nocturnal animals; the fourth and last case in May 2003 involved a 58-year-old woman attacked by a stray cat six weeks earlier. Though clinically treated, PEP was not applied. She died two weeks after hospitalization.

Economic implications

In addition to the risk for rabies, exposure to rabid cats carries substantial economic implications for exposed people, health insurance companies, and health departments.

For example, in New Hampshire in 1994, approximately 600 people received PEP after potential exposure to a single rabid cat, at a cost of approximately $1 million for biologics alone. Between 1995 and 2000, cats accounted for 523, or 24%, of 2,216 animal rabies exposures requiring PEP reported by four counties in upstate New York.

Cats have become the industrialized world’s most popular pet. Cats co-occupy one-third of all residences in the United States (an estimated 57 million pet cats). Though cats can transmit an array of diseases to their owners, ranging from trivial to fatal ailments, if kept indoors and provided with the appropriate veterinary care, owners and their pets can live together with little risk of disease transmission. The situation is strikingly different concerning stray cats, as clearly demonstrated by the above and similar incidents, worldwide.

Rabies, though the oldest known and most lethal cat-transmitted zoonotic disease, is only one of more than 30 bacterial, rickettsial, viral, protozoan, exo- and endoparasitic and fungal disease entities recognized as transmissible from cat to man.

In a 2004 review (see reference), those entities were divided into six groups according to their respective infection routes:

1. Inhalation: Bordetella, plague, Q fever.
2. Vector-borne: Ehrlichiosis, Cat scratch disease (CSD), Bacillary angiomatosis, flea-borne spotted fever.
3. Fecal-oral: Campylobacter, Helicobacteriosis, Cryptosporidiosis, Toxoplasmosis, Salmonella, Anaerobiospirillum thomasii, Yersinia pseudotuberculosis-gastroenteritis, Toxocariasis, Opisthorchiasis and Dipylidiasis.
4. Bite, Scratch or Puncture: Rabies, Erysipelothrix infection, anthrax, Pasteurella multocida, Mixed aerobe and anaerobe bacterial infections (causing cat-bite cellulitis), sporothricosis, feline orthopox (cowpox virus) and tularemia.
5. Soilborne: Histoplasmosis.
6. Direct contact: Dermatophilosis, Scabies, Cheyletiella mite infestation, Dermatophytosis (epidermophyton, microsporum, trichophyton).

Since 2004, highly pathogenic avian influenza H5N1, which has spread throughout three continents in the eastern hemisphere following its initial outbreak in southeast Asia, has been found as capable of infecting felines. Clinical disease and mortalities have been reported in wild feline species as well as in domestic cats. Even though all human cases of this zoonosis seem to have contracted their infections exclusively from birds, predominantly domestic poultry, cats should be taken into consideration as potential sources of human infection. This relates particularly to bird predator stray cats.

Another emerging zoonotic disease, SARS, caused by a coronavirus, was initially regarded to be transmitted to man by civet cats (family Viverridae). Later, domestic cats were shown to be susceptible to experimental infection and capable of transmitting the virus to other cats. However, according to current knowledge, the natural reservoir of SARS are bats.

Toxoplasmosis and CSD

This concise overview does not allow a full-scale discussion of all mentioned pathogens; further reading is recommended. Here, we shall briefly address two of them, toxoplasmosis and CSD.

Cats are the definitive hosts of Toxoplasma gondii, which undergo replication in their intestinal tract. Unsporulated oocysts are excreted in the feces and sporulate in the environment. Infections are particularly common in strays and less prevalent in pets. Orally infected humans undergo an incubation period of five to 20 days after exposure to infected cats.

In immunocompetent non-pregnant individuals, infection with T. gondii is usually asymptomatic. Approximately 10% to 20% of patients develop lymphadenitis or a mild, flulike syndrome. The symptoms, in most cases, resolve without treatment within weeks to months. Ocular toxoplasmosis with uveitis can be seen in adolescents and young adults.

Infections acquired during pregnancy can lead to congenital toxoplasmosis of the infant, affecting the developing brain and/or retina. The spectrum of disease varies from severe congenital toxoplasmosis affecting CNS and the eye, to mild cases with only slightly diminished vision. A study, conducted from 1986-1992 in New England, reported one case per 10,000 live births. Other sources suggest a rate of one per 4,000 live births.

Toxoplasmosis is often severe in immunosuppressed patients, with neurologic disease as the most common sign. Encephalitis may lead to coma and death. Chorioretinitis, myocarditis and pneumonitis also occur.

Cat scratch disease, caused by Bartonella henslae, is usually self-limiting and benign in immunocompetent individuals. Most people, including those with neurologic involvement, recover; deaths are extremely rare. An estimated 22,000 to 24,000 cases of CSD are thought to occur in the United States each year; 3.6% to 6% of the general population has antibodies to B. henselae.

B. henselae causes bacillary angiomatosis and peliosis hepatitis, mainly in immunocompromised individuals.

According to the 2007 Guidelines for the Vaccination of Cats, issued by the World Small Animal Veterinary Association, “In a geographical area in which rabies is endemic, all cats should be routinely vaccinated for the protection of both the pet and human populations.” CDC’s annual report for 2006 noted 6,940 cases of rabies in wild or domesticated animals, of which 318 were cats, representing 4.6% of all cases, an 18% increase from 2005.

Unvaccinated cats are a life-threatening risk in rabies-affected areas. The fact that, contrary to owned, housed cats, they remain also unvaccinated against the main feline infectious diseases, exposes them to severe cat-health threats, suffering and cruel death. In addition, their infections compromise the health of the housed pets.

Many diseases are more likely to be encountered by outdoor cats. In fact, free-roaming strays are the linkage between their infected prey and human contacts. Indoor cats are significantly less likely to be sources of human infections. From both public health and animal health/welfare considerations, the feeding and nurturing of strays should be discouraged, probably with the exception of well-managed colonies of vaccinated cats within defined boundaries.

Simple preventive measures, such as washing hands before eating, using gloves when gardening, changing the litter daily and thoroughly cooking all meat, can reduce the risk of acquiring diseases from a housed cat. Also, routine veterinary care, including appropriate vaccinations, deworming, and care for sick animals, should reduce the risk of disease transmission. Cats should not be thought of as vectors for disease transmission but as sources of joy for their owners.

For more information:

• Arnon Shimshony, DVM, is Associate Professor at the Koret School of Veterinary Medicine Hebrew University of Jerusalem, Rehovot, and is the ProMED-mail Animal Diseases and Zoonoses Moderator. Dr. Shimshony was Chief Veterinary Officer, State of Israel, from 1974 to 1999.
• Goldstein E. & Green C. Chapter 6 “Around cats”, in Infections of leisure, ed D.Schlosberg, ASM Press, 3rd edition, 2004. Pp. 179-196.
• Disease fact sheets, the Center for Food Security and Public Health, Iowa State University www.cfsph.iastate.edu/DiseaseInfo/factsheets.htm