Lapis ISSN 2398-2969

Salmonella spp

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

Introduction

Classification

Taxonomy

  • Order: Enterobacterales.
  • Family: Enterobacteriaceae.
  • GenusSalmonella.

Etymology

  • Genus discovered by American biologist, Theobald Smith; named after his laboratory chief and co-author, Daniel 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 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 alternative 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 inhibits 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.
  • Concurrent infection with other pathogens, eg Aeromonas and Eimeria spp, has been recorded in intestinal content of rabbits with clinical history of enteric disease.
  • 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 Salmonellosis.
  • 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 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 - 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, butcher shops, etc.

Vaccination

  • Although vaccinations are available for some species, eg poultry, against Salmonella enterica serovar Typhi, these are usually not effective against other serovars.
  • Rabbits are commonly used as animal models for salmonellosis, including in vaccine research.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • García-Rubio V G, Bautista-Gómez L G, Martínez-Castañeda J S & Romero-Núñez C (2017) Multicausal etiology of the enteric syndrome in rabbits from Mexico. Rev Argent Microbiol 49 (2), 132-138 PubMed
  • Higginson E E, Simon R & Tennant S M (2016) Animal models for salmonellosis: applications in vaccine research. Clin Vaccine Immunol 23 (9), 746-756 PubMed.
  • 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.

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