Salmonella typhi and paratyphi (as well as Shigella) are strictly human pathogens and domestic animals play no role in the epidemiology of these infections (although non-human primates may be infected and serve as a source for their handlers). All of the other "non-typhoid" Salmonella spp. (Salmonella enterica) are ubiquitously present in the environment and reside in the GI tracts of animals. As such, animals are the ultimate source for virtually all Salmonella. The vast majority of human cases of salmonellosis are, however, acquired not through direct contact with animals, but rather by ingestion of contaminated foods. For example:

• Salmonella enteritidis from undercooked eggs
• Salmonella typhimurium from undercooked meats or fecal contamination of a variety of foods.
  • One study of 200 meat samples from grocery stores in the Washington, D.C. area found that 20% contained Salmonella bacteria, and 84% of these Salmonella strains were resistant to at least one antibiotic. However, overall rates of Salmonella contamination of meats in the U.S. have been dropping in recent years, from 10.65% in 1998 to 3.6% in 2003 (USDA data).

Salmonellosis in humans:

• Salmonellosis is an extremely common disease among humans. There were 41,901 reported cases in the U.S. in 1997, which probably only represents the "tip of the iceberg" of an estimated 1.4 million cases/year of non-typhoidal Salmonella infections, with ~16,000 hospitalizations and 600 deaths.
• Following a 12-36 hour incubation period, symptoms of fever, headache, diarrhea, abdominal pain, nausea and dehydration develop, which may lead to fulminant septicemia/endotoxemia.

Salmonellosis in dogs and cats:

The severity of salmonellosis in dogs and cats varies:

• subclinical carrier state (most common)
• acute enterocolitis
  • fever, anorexia, lethargy
  • diarrhea, possibly with mucus or blood
  • abdominal pain (infection is often associated with mesenteric lymphadenitis)
    • Cats may present with prolonged periods of fever and anorexia without diarrhea.
• septicemia/endotoxemia
  • Salmonellosis in cats has also been caused "song bird fever," reflecting association with predation on infected migratory birds.

The role of dogs and cats in zoonotic transmission:

• Salmonella infections in dogs and cats deserve special comment for several reasons related to zoonotic transmission:
  • Salmonella spp. can be isolated from healthy dogs and cats at rates of up to 36% and 18%, respectively.
  • Dogs and cats tend to shed Salmonella organisms for very prolonged periods of time after infection.
  • Dogs and especially cats can shed Salmonella organisms in both their feces and saliva, meaning that transmission can occur via licking.
  • Pig ear dog treats may be a source of Salmonella infection for both dogs and humans that handle the treats.
  • Dogs and cats may suffer salmonellosis as a "reverse zoonosis," with infection transmitted from human-to-dog and subsequently back to other humans.
    • Similarly, outbreaks of Salmonella infections in large animal teaching hospitals have been linked to the introduction of bacteria from infected human personnel, with subsequent spread to animals and then back to other human workers.

The role of other domestic animals:

• The feces of virtually any animal may be a potential source of Salmonella.
  • As such, ill and/or hospitalized horses and cattle must be considered as potential sources of Salmonella for veterinary clinicians and students. In one study, Salmonella could be isolated from 5.5% of hospitalized horses.
• Recognizing the potential for pigs to serve as a source of Salmonella is particularly important since human infection with S. cholerae-suis is associated with a 20% mortality rate!
• A recent report highlighted the potential for inadvertent contamination of household carpets with Salmonella when residents had occupational exposure to cattle on farms or cats in veterinary clinics (Rice et al., 2003).

The role of exotic pets and wild animals:

• Salmonellosis is well recognized as a zoonosis associated with many species of reptiles. In the 1970s, it was estimated that 280,000 human cases of salmonellosis/year were associated with reptiles, leading to the ban on turtles with carapace lenghts < 4 inches (i.e. would fit in a child's mouth). This led to a substantial reduction in pediatric cases of salmonellosis, but a recent study has suggested that 6% of all sporadic human cases of Salmonella infection are still associated with reptiles.
• In 2002, there was even a report of a reptile owner who donated blood products and two transfusion recipients became infected with a strain of Salmonella matching that of the donor's snake.
• Salmonellosis has also been associated with ritual consumption of raw marine mammal blubber or meat.
• Links are increasingly being recognized between specific animals and unusual serotypes of Salmonella, e.g.:

Diagnosis of Salmonella infections:

• fecal culture

Treatment - the use of antibiotics?:

• Simple gastroenteritis should be treated with supportive therapy, fluids, etc.
• Treatment with antibiotics should probably be restricted to those animals that develop evidence of systemic spread of infection.
  • There is an on-going debate as to whether antibiotics truly prolong shedding of Salmonella, as historically suggested. However, the use of antibiotics should also be restricted because of the ease with which Salmonella spp. acquire antibiotic resistance.
• A recent report suggests that bleach is the most effective disinfectant in veterinary hospital settings.

For specific infromation about Salmonella typhimurium DT104, go to: http://www.vetmed.wisc.edu/pbs/zoonoses/O157DT104/O157DT104index.html

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