Felis ISSN 2398-2950

Salmonella spp

Contributor(s): Richard Walker

Introduction

Classification

Taxonomy

  • Genus Salmonella.
  • Family Enterobacteriaceae.

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 gastrointestinal 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.

Transmission

  • Feco-oral.
  • Transovarian and egg transmission occurs in birds.
  • Infection via the mucous membranes of the upper respiratory tract and conjunctivae may occur.

Pathological effects

  • 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 occuring some weeks after recovery from acute S. Dublin disease.
  • Salmonella 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 virulent plasmid.

Factors

  • Normal gut flora usually inhibit growth and block access to attachment sites required (competative inhibition); 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.
  • Salmonella 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

Some of the diseases caused by Salmonella spp

  • Enteritis or septicemia in cattle, pigs, cats and birds.
  • Abortion in cattle, ewes and mares.
  • Meningitis, osteomyelitis, joint ill and terminal 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 - cattleS. pullorum- birds.

Control

Control via animal

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

Control via chemotherapies

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 hygiene procedures and methods of cooking food.
  • Observe hygienic precautions after handling animals and educate children to do so.
  • Adequate sanitation and supervision in abattoirs, food-processing plants, butchers' shops, etc.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Tauni M A & Osterlund A (2000) Outbreak of Salmonella typhimurium in cats and humans associated with infection in wild birds. JSAP 41(8), 339.
  • Lax A J, Barrow P A, Jones P W & Wallis T S (1995) Current perspectives in salmonellosis. Brit Vet J 151, 351-377.
  • Potter M E (1993) The changing face of foodbourne disease. JAVMA 201, 250-252.
  • Willard M D et al (1987) Gastrointestinal zoonoses. Vet Clin North Am Small Animal Pract 17(1), 145-178.

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