Patrick L. McDonough, M.S., Ph.D.
Professor of Microbiology,
Assistant Director, Microbiology/Mycology Section
College of Veterinary Medicine, Cornell University
The salmonellae comprise nearly two thousand different serotypes of the genus Salmonella, bacteria found throughout the environment, in wild and domestic animals. Salmonella bacteria are responsible for a spectrum of maladies ranging from uncomplicated intestinal disease and diarrhea, to life-threatening systemic illness. Clinical salmonellosis in cats is relatively uncommon and few references to it exist in the scientific literature. Surveys conducted by sampling feces or rectal swabs of "normal," nondiarrheic cats have revealed a salmonella carrier rate ranging from zero up to 14 percent (it is likely that these surveys underestimate the true numbers of infected carrier cats because not all cats carrying the organism shed it at the time they are tested). Stray cats, shelter cats, and hunter cats are more likely to be carriers and to be excreting salmonellae in feces than are housebound pet cats.
Cats appear to be highly resistant to salmonella infection unless they are stressed by overcrowding, dietary changes, transport, hospitalization, antimicrobial therapy, or concurrent illness at the time of salmonella exposure. The source of the salmonellae is most likely to be either contaminated feed, water, or carrier animals (whether clinically ill or healthy). Contamination can arise from rodent or bird feces, raw or undercooked or contaminated meat and table scraps, or commercially prepared foods that are contaminated during processing.
Cats usually acquire salmonellosis by ingestion. Once ingested, the bacteria can cause a spectrum of clinical signs. Salmonellae that survive the acidity of the stomach go on to invade the small intestine and local lymph nodes. From this point, the bacteria either are contained by the body's defenses or proceed to invade the bloodstream, from which they reach other tissues such as the liver and spleen. Because of their fastidious grooming habits, infected cats quickly contaminate their fur and environment with salmonellae. Clinically ill animals often shed large numbers of bacteria in feces and sometimes in saliva.
Clinical signs of salmonellosis in cats are seen after a two- to four-day incubation period and can include, in the gastrointestinal form, fever, poor appetite, diarrhea, vomiting, and abdominal pain. More severely ill cats may be profoundly depressed and lethargic. Cats may also exhibit a more systemic form of salmonellosis characterized by persistent fever, anorexia, and malaise, but without any gastrointestinal signs of diarrhea. Diagnosis must be based on the history and physical examination, bacterial cultures of rectal swabs or fresh feces, blood cultures (when indicated), cytology (for presence of inflammatory cells in feces), and hematology (CBC. Evidence of some "stress" as outlined above is also usually in the patient's recent history.
The treatment of salmonellosis is a subject of some controversy. In cases of uncomplicated salmonella enteritis (intestinal inflammation) with diarrhea, but without signs of systemic illness, it is best to treat symptomatically by replacing fluids and electrolytes lost through vomiting and diarrhea. Antibiotic usage is not encouraged in such cases because of the risk of producing antibiotic-resistant salmonellae and because the antibiotic may eliminate normal intestinal bacteria that serve to protect the cat from harmful microorganisms. In cases of systemic illness, however, when a threat to the life of the patient is perceived, antibiotic therapy should be instituted.
Salmonellosis is of great public health significance because salmonellae can infect not only pets but pet owners as well. Cats-especially if very young, very old, immunosuppressed, or recently treated with an antibiotic-should be regarded with some caution when showing signs of diarrhea, fever, depression, vomiting, and inappetence. Diarrhea may not always be present, but rather the cat may have vague nonspecific signs of lethargy and fever. Salmonellosis is transmitted by the fecal-oral route; anything that can be done to break that cycle of infection will help to limit spread of the bacteria. Hands should be washed often, especially after handling the ill cat, its toys, food dishes, or other possibly contaminated materials. All litter should be bagged and disposed of promptly and properly. Disinfectants, such as diluted chlorine bleach, should be used to clean floors and other surfaces where the cat eats and sleeps and where the litter box is kept. Food and water bowls should be cleaned as often as possible. Young children, older adults, and immunocompromised individuals (e.g., by AIDS or immunosuppressive therapy) should be kept away from the affected cat, especially for the first few weeks postinfection, until the numbers of salmonellae shed by the cat have declined. The cat's feces should be cultured periodically by the veterinarian to assess the level of excretion of the bacteria. if a recovered animal subsequently shows signs of vomiting and diarrhea, especially after some obvious stress factor (e.g., antibiotic treatment, travel, vaccination, diet change), the veterinarian should be notified. If anyone in the family becomes ill with diarrhea, vomiting, severe abdominal pain, and fever, a physician should be consulted as soon as possible. it should be explained to the physician that a pet in the household has been diagnosed as a salmonella carrier. The physician should then contact the attending veterinarian for specific details about the case.
Unfortunately, there are no vaccines available to protect cats against salmonellosis. Because salmonellae are ubiquitous in nature, it is very unlikely that the disease will be eradicated. most cases of feline salmonellosis can be prevented, however, by maintaining a high level of household hygiene, by not feeding raw or undercooked meat to cats, and by having a cat checked promptly by a veterinarian if any clinical signs suggestive of salmonellosis are observed. A caveat: Cats that hunt are more likely to contact infected prey animals (rodents, birds) than are cats that remain housebound-an important consideration.