Salmonellosis is caused by the infection of bacteria of the genus Salmonella (family Enterobacteriacecae). These are gram-negative bacteria, there are three recognized species with over 1400 known serotypes (Microsoft Encarta Online Encyclopedia, 2003).

Although clinical signs of salmonellosis are uncommon, the bacteria is frequently isolated from the feces dogs, cats (Birchard and Sherding, 2000), reptiles, amphibians (Frye, 1991), and livestock including cows, pigs and poultry (Merck Veterinary Manual, 2003).

Salmonella bacteria live in the intestinal lining of the host (they may eventually migrate to the bloodstream), and are often shed in the animal's feces and milk (Birchard and Sherding, 2000; Peralta, 2003). The disease is transmitted by the feco-oral route, either by direct ingestion of infected fecal matter, or (more commonly) by ingesting contaminated food or water. Transmission by contact with other objects where the bacteria can live is possible, as they are able to live outside of the host for long periods of time (Birchard and Sherding, 2000). Symptoms usually appear within a day or two after ingestion, as the incubation period for these bacteria is from 4-48 hours (Microsoft Encarta Online Encyclopedia, 2003).

After they have been ingested, the bacteria colonize in the intestinal tract (the ileum and colon). They soon invade the epithelial lining of these areas, and reproduce within the lymphoid follicles and epithelium. This will cause acute inflammation of the epithelium, which will initiate fluid production and induce diarrhea in the host (Giannella, 2003; Pender, 2003). The bacteria prompting the production of cytotoxin and enterotoxin may also induce diarrhea and contribute to intestinal damage (Merck Veterinary Manual, 2003). In more serious cases of infection, after multiplying the bacteria spread to mesenteric lymph nodes and throughout the body via systemic circulation (the bloodstream). They can further invade the reticuloendothelial system, and depending on the serotype, it may then infect the liver, spleen, gallbladder, bones, meninges, and other organs. However, in humans most Salmonella serotypes are killed quickly outside of the intestine (Giannella, 2003).

The risk of becoming seriously infected by Salmonella depends on the age and defense factors of the host, competition from established flora in the gut (the "good bacteria"), the infectivity of the serotype, and size of the inoculum (Birchard and Sherding, 2000; Giannella, 2003). Infection rates are the highest in overcrowded, confined groups of young animals with poor sanitation (Birchard and Sherding, 2000).

A Salmonella infection may go unnoticed, as many non-human carriers are asymptomatic (Birchard and Sherding, 2000; Grognet, 2002), especially reptiles and amphibians (Frye, 1991). An infection may be categorized into one of three syndromes: the subclinical carrier state, enterocolitis, and enterocolitis with bacteremia (Birchard and Sherding, 2000). Animals with mucousy and/or bloody diarrhea (Birchard and Sherding, 2000; Pender, 2003), tenesmus, anorexia, lethargy, abdominal pain, dehydration, or fever (varies with host species) may be infected if there are suspected, identifiable risk factors, such as young or old age, immune deficiency, another debilitating sickness or disease, housing in overcrowded or unsanitary conditions, or known or probably exposure to contaminated fomite (Birchard and Sherding, 2000; Grognet, 1998; Merck Veterinary Manual, 2003).

More severe cases where the bacteria have successfully invaded the bloodstream (bacteremia and endotoxemia) may yield symptoms such as shock, dehydration, high fever or hypothermia, electrolyte imbalances, azotemia, hypoproteinemia, hypoglycemia, neutropenia or coagulopathy (Birchard and Sherding, 2000; Merck Veterinary Manual, 2003). Abortion in pregnant animals as well as dry gangrene of the extremities may occur (Merck Veterinary Manual, 2003).

The clinical signs are similar to some other diseases (such as Escherichia coli infection), so the diagnosis is best confirmed by isolating Salmonella from feces, or blood in the case of bacteremic animals (Birchard and Sherding, 2000; Merck Veterinary Manual, 2003; Center For Disease Control, 2003).

People with salmonellosis usually experience diarrhea, vomiting, fever, muscle aches, nausea and abdominal pain. More severe infections may seriously dehydrate the host (Center For Disease Control, 2003; Peralta, 2003). A very small percentage of people will develop Reiter's syndrome: Pain in joints, irritation of the eyes and painful urination. This can contribute to chronic arthritis, and symptoms may last for months to years (Center For Disease Control, 2003).

Replacing lost fluids and electrolytes, as well as identifying and correcting the cause or source of the infection are key aspects of treatment in any animal affected with salmonellosis. Most animals and people recover naturally within 2-7 days (Center For Disease Control, 2003; Peralta, 2003). Antibiotic treatment is not recommended unless the host is affected by bacteremia or endotoxemia, when the disease can be fatal (Center For Disease Control, 2003). Oral antibiotics may negatively alter the intestinal microflora and prolong the shedding of the Salmonella through the feces (Birchard and Sherding, 2000; Center For Disease Control, 2003). Antibiotic-resistant strains of Salmonella may eventually be produced (Merck Veterinary Manual, 2003). Resistance in some serotypes has already been observed (Headrick et al., 2001; Pender, 2003; Poppe et al., 1998).

If treatment is necessary, oral antibiotics are selected based on culture and sensitivity testing. Most Salmonella bacteria are susceptible to enrofloxacin (Bayer; Baytril) or trimethoprimsulfa. The antibiotics are typically administered for 7 to 10 days, and the feces are re-tested 1 week and 4 weeks after the treatment is finished (Birchard and Sherding, 2000). Treatment for humans is recommended on the same basis as for other animals, the antibiotics are selected the same way (Center For Disease Control, 2003).

Prevention of salmonellosis varies with the species it affects. Livestock should be kept in sanitary conditions that are not overcrowded, and new animals should be isolated for at least one week to determine if they are a host. Carriers should be culled or treated to prevent spreading the pathogen. Food and water should be protected from being contaminated by feces (Merck Veterinary Manual, 2003). Dogs, cats, birds and small mammals should be kept in sanitary conditions and monitored for illness (Birchard and Sherding, 2000). Reptiles and amphibians are often carriers, however they are rarely affected by the bacteria, prevention is for the most part unnecessary.

Salmonellosis is rather easily prevented in humans. Excellent hygiene should be practiced around all animals, especially suspected carriers or animals at risk of being infected (due to known infection risks). This includes washing hands and forearms thoroughly with warm water and antibacterial soap after handling any animals or any objects that could have been in contact with the animals or their feces, and by refraining from eating, drinking or smoking while working with these possible vectors. Food items such as eggs (and foods that may contain raw eggs), poultry and meat should be avoided or thoroughly cooked (Center For Disease Control, 2003).

Works Cited:

BIRCHARD and Sherding. 2000."Saunders Manual of Small Animal Practice" (2nd ed.). Philadephia, Pennsylvania: W. B. Saunders Company.

Center For Disease Control. 2003. "DBMD - Salmonellosis - General Information." <www.cdc.gov/ncidod/dbmd/diseaseinfo/salmonellosis_g.htm> (September 17, 2003).

FRYE, F. L. (1991). "Reptile Care: An Atlas of Diseases and Treatments, Volume 1." New Jersey: T. F. H. Publications, Inc.

GIANELLA, R. A. 2003. "Salmonella." < gsbs.utmb.edu/microbook/ch021.htm> (November 8, 2003).

GROGNET, J. 2002. Salmonellosis. Dogs In Canada, 93 (8), 20.

HEADRICK, M. L., L. A. Walker and P. J. Fedorka-Cray. 2001. Antimicrobial resistance in salmonella isolates from exotic animals,

NARMS 1997-1999. Poster from NARMS Scientific Meeting held March 15-16, 2001 (Rockville, MD).

Merck. 2003. "Merck Vet. Edition - Salmonellosis." < www.merckvetmanual.com/mvm/htm/bc/20400.htm> (September 20, 2003).

PENDER, A. B. 2003. Salmonellosis in a herd of beef cows. Can Vet J, 44 (4), 319-320.

PERALTA, J. M. 2003. "Reducing the Risk: Salmonellosis." < web.vet.cornell.edu/crar/OHP/SALMON.html> (September 20, 2003).

POPPE, C., N. Smart, R. Khakhria, W. Johnson, J. Spika, J. Prescott. 1998. Salmonella typhimurium DT104: A virulent and drug-resistant pathogen. Can Vet J, 39 (1), 559-565.

"Salmonella." Microsoft Encarta Online Encyclopedia. The Microsoft Corporation. 2003. <encarta.msn.com/encyclopedia_761566118/Salmonella.html> (September 23, 2003).