Equis ISSN 2398-2977

Salmonella spp

Contributor(s): Sarah Binns, Susan Dawson, Richard Walker

Introduction

Classification

Taxonomy

  • Family: Enterobacteriaceae.
  • GenusSalmonella.

Etymology

  • Genus discovered by American biologist, Theobald Smith; named after his laboratory chief and co-author, D E Salmon.

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Clinical Effects

Epidemiology

Habitat

  • Reservoir is the gastrointestianl tract of warm- and cold-blooded animals.
  • Sources of infection include:
    • Contaminated soil.
    • Vegetation.
    • Water.
    • Components of animal feeds, eg bone meal, meat meal and fish meal.
    • Foods containing milk, meat or eggs.

Lifecycle

  • Salmonellae adhere to and invade cells in the distal small and proximal large intestine.
  • Multiplication occurs here or in the macrophages of the liver and spleen if septicemia occurs.
  • Multiplication results in endotoxemia Endotoxemia: overview.

Transmission

  • Feco-oral.
  • Transovarian and egg transmission occurs in birds.
  • Also endogenous infection following alterations of intestinal microenvironment.
  • Infection via the mucous membranes of the upper respiratory tract and conjunctiva may occur but is rare.

Pathological effects

  • Specific local antibodies prevent attachment.
  • Circulating antibodies encourage phagocytosis.
  • Endotoxin-mediated damage to blood vessels and activation of blood-clotting mechanism together with alternate complement pathway → disseminated intravascular coagulation, eg ischemic necrosis of distal limbs, ears and tail of calves occurring some weeks after recovery from acute S. dublin disease.
  • Salmonellae fimbriae → attachment to cells of distal small intestine → disease.
  • Some strains produce exotoxins → enteritis and diarrhea.
  • Invasive strains → multiply within macrophage → escape destruction → septicemia.
  • The invasiveness of some strains of S. typhimurium is increased by genes carried on a plasmid.

Factors

  • Normal gut flora usually inhibit growth and block access to attachment sites required; host's susceptibility to infection increased by disruption of normal flora, eg by antibiotics or deprivation of food and water.
  • Stress → decreased peristalsis → allows multiplication of organisms in intestine.
  • Major pathogens of animals.
  • Animals may be healthy excretors following infection.

Zoonotic salmonellosis

  • Salmonellosis is an important zoonosis.
  • Contaminated food, mainly of animal origin, is the predominant source.
  • Salmonellea strains cause a wide range of human enteric disease:
    • Mild self-limiting gastroenteritis.
    • Severe gastroenteritis with or without bacteremia.
    • Typhoid fever - severe, debilitating and potentially fatal.

Other Host Effects

  • Carried subclinically in approximately 3% of horses.

Some of the diseases caused by Salmonella spp

  • Diarrhea and/or septicemia in adult horses, more rarely in neonates. Predisposed to by colic, intestinal surgery or antimicrobial therapy. S. typhimurium and S. anatum most commonly implicated. Infection often acquired in veterinary hospitals.
  • Enteritis or septicemia in cattle, pigs and birds.
  • Abortion in cattle, ewes and mares.
  • Meningitis, osteomyelitis, joint ill and terminal appendage ischemia in calves.
  • Fowl typhoid, fowl paratyphoid and other severe infections in birds may be egg transmitted.
  • Some Salmonella serotypes are host-adapted, eg S. typhi - humans, S. dublin - cattle, S. pullorum - birds.

Control

Control via animal

  • Avoidance of stress helps reduce colonization of the gastrointestinal tract.

Control via chemotherapies

  • Antibiotic Therapeutics: antimicrobials treatment of the invasive diseases is indicated in conjunction with antimicrobial susceptibility testing.

Control via environment

  • Salmonellosis is controlled through protocols designed to inhibit spread to susceptible animals and people.
  • Food handlers and the public should be educated in hygienic procedures and through cooking of food.
  • Observe hygienic precautions after handling animals and educate children to do do.
  • Adequate sanitation and supervision in abattoirs, food-processing plants, butchers' shops, etc.

Vaccination

  • Bacterins have been tried, but with only limited success.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Kim L M, Morley P S, Traub-Dargatz J L, Salmon M D & Gentry-Weeks C (2001) Factors associated with Salmonella shedding among equine colic patients at a veterinary teaching hospital. JAVMA 218 (5), 740 PubMed.
  • Hartmann F A, Callan R J, McGuirk S M & West S E H (1996) Control of an outbreak of salmonellosis caused by drug-resistant Salmonella anatum in horses at a veterinary hospital and measures to prevent future infections. JAVMA 209 (3), 629 PubMed.
  • Walker R L, Deperalta T L, Villanueva M R et al (1995) Genotypic and fenotypic analysis of Salmonella strains associated with an outbreak of equine neonatal salmonellosis. Vet Microbiol 43 (2-3), 143-150 PubMed.
  • Lax A J, Barrow P A, Jones P W & Wallis T S (1995) Current perspectives in salmonellosis. Br Vet J 151 (4), 351-377 PubMed.
  • Vanduijkeren E et al (1994) Equine salmonellosis in a Dutch veterinary teaching hospital. Vet Rec 135 (11), 248-250 PubMed.
  • Potter M E (1992) The changing face of foodbourne disease. JAVMA 201 (2), 250-252 PubMed.

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