Salmonella

Salmonella are ubiquitous human and animal pathogens, and salmonellosis, a disease that affects an estimated 2 million Americans each year, is common throughout the world. Salmonellosis in humans usually takes the form of a self-limiting food poisoning (gastroenteritis), but occasionally manifests as a serious systemic infection (enteric fever) which requires prompt antibiotic treatment. In general, more serious infections occur in infants, in adults over the age of 50, and in subjects with debilitating illnesses. In addition, salmonellosis causes substantial losses of livestock 8.

Salmonella is a genus of Gram-negative, facultatively anaerobic, rod-shaped bacteria (bacilli) of the family Enterobacteriaceae. The bacteria are named for the American pathologist Salmon, who first isolated Salmonella choleraesuis from a pig's intestine. Organisms within this genus are separated on the basis of antigenic characteristics, sugar fermentation patterns, and bacteriophage susceptibility 1. All Salmonella organisms, except those causing human typhoid fever (S. typhi and S. paratyphi) infect humans and animals.

Salmonella species cause a wide range of disease in wild and domestic animals. For example, S. arizonae commonly harbored by lizards and snakes, may cause enteric, bone, and joint infections in humans. The bacteria have also been isolated from a wide range of wild birds including seagulls, parrots, raptors, and water birds. The most frequent bird isolate is S. typhimurium, a serotype of Salmonella enterica that is a frequent agent of Salmonella gastroenteritis in humans. The majority of isolations have been from healthy birds 5.

SalmonellaSalmonella Source: CDC/ James Archer

Four Types of Diseases Caused by Salmonella

The most common clinical syndromes caused by Salmonella are gastroenteritis, enteric fever (including typhoid fever), bacteremia, and localized infection. All four syndromes may have neurologic manifestations 6.

Most persons infected with Salmonella develop gastroenteritis characterized by diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most persons recover without treatment. However, in some persons, the diarrhea may be so severe that the patient needs to be hospitalized. Some patients may develop bacteremia and meningitis, especially children 6.



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Enteric fevers are severe systemic forms of salmonellosis. The best studied enteric fever is typhoid fever, the form caused by S typhi, but any species of Salmonella may cause this type of disease. Enteric fever caused by S. typhi is called typhoid fever, when it is caused by other Salmonella species, it is called paratyphoid fever. Typhoid fever is a particularly serious condition with a fatality rate of 10%, and from which it can take up to 8 weeks to recover. Salmonella bacteremia, or fever associated with gastroenteritis, is particularly common in AIDS patients. Intracranial abscesses and miningitis occur in about 10% of patients with Salmonella bacteremia. 6.

Localized infections caused by Salmonella include endocarditis, pericarditis, mycotic aneurysm, myocardial abscess, septic thrombophlebitis, necrotizing enetrocolitis, appendicitis, abdominal abscess, cholecystitis, urinary tract infection, arthritis, osteomyelitis, Reiter's syndrome, pharyngeal abscess, pneumonia, and endophthalmitis 7.

Public Health Risks

Salmonella are able to survive in numerous animal hosts, on vegetables and fruits, insects, raw animal products, soil, water, an ability that has made transmission of this organism difficult to control. Dogs and horses have the greatest zoonotic potential for those with occupational exposure. Reptiles and amphibians are most frequently incriminated in pet-associated cases. Contacts with contaminated pet food products have been an important source of exposure for humans, especially young children 4,2.

Contaminated food is the major mode of transmission for non-typhoidal Salmonella. Because of the ability of the organism to survive in meats and animal products that are not thoroughly cooked, animal products are the main vehicle of transmission 8. There is no vaccine to prevent salmonellosis.

References

  1. Medical Subject Headings
  2. Greene Infectious Diseases of the Dog and Cat. Craig E. Greene, DVM, MS, DACVIM
  3. Salmonella
  4. Steffen Porwollik (editor). Salmonella: From Genome to Function
  5. Philip Ladd (editor). Pathology of Australian Native Wildlife
  6. Neil R. Miller. Walsh And Hoyt's Clinical Neuro-Ophthalmology, Volume 3
  7. Russell W. Steele. Clinical Handbook of Pediatric Infectious Disease
  8. S. Baron (editor). Medical Microbiology. 4th edition

 

 

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