Lapis ISSN 2398-2969

Salmonella spp

Contributor(s): Vetstream Ltd, Susan Dawson, Molly Varga

Introduction

Classification

Taxonomy

  • Order: Enterobacteriales.
  • Family: Enterobacteriaceae.
  • Genus:Salmonella.

Etymology

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

Active Forms

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

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 target 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

  • Fecal-oral route.
  • 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 acuteS. dublindisease.
  • 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 ofS. typhimuriumis 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.
  • Salmonellastrains 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 bySalmonellaspp
  • Enteritis or septicemia in cattle, pigs 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.
  • SomeSalmonellaserotypes are host-adapted, egS. typhi- humans,S. dublin - cattle,S. pullorum- birds.

Control

Control via animal

  • Avoidance of stress helps reduce colonization of the gastrointestinal tract.
  • Provision of suitable diet to promote healthy gut bacteria.

Control via chemotherapies

  • Antibiotic treatment of the invasive diseases is indicated in conjunction with sensitivity 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 thorough cooking of 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

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Lax A J, Barrow P A, Jones P W et al (1995) Current perspectives in salmonellosis. Brit Vet J 151 (4), 351-77 PubMed.
  • Potter M E (1992) The changing face of foodborne disease. JAVMA 201 (2), 250-253 PubMed.

ADDED