Introduction

Classification

Taxonomy

• 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

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, but is rare.

Pathological effects

• Endotoxin-mediated damage to blood vessels and activation of blood clotting mechanism together with alternate complement pathway → disseminated intravascular coagulation 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 Diarrhea: chronic.
• Invasive strains → multiply within macrophage → escape destruction → septicemia.
• The invasiveness of some strains of S. typhimurium is increased by genes carried on a virulence plasmid.

Factors

• Normal gut flora usually inhibit growth and block access to attachment sites required (competitive 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 serotypes

• Enteritis or septicemia in cattle, pigs, cats and birds.
• Abortion in cattle, ewes and mares.
• Meningitis Meningitis , osteomyelitis 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, 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: antimicrobial drug 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 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

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Philbey A W, Mather H A, Gibbons J F et al (2014) Serovars, bacteriophage types and antimicrobial sensitivities associated with salmonellosis in dogs in the UK (1954-2012). Vet Rec 174 (4), 94 PubMed.
• Lax A J, Barrow P A, Jones P W et al (1995) Current perspectives in salmonellosis. Brit Vet J 151 (4), 351-377 PubMed.
• Potter M E (1992) The changing face of foodborne disease. JAVMA 201 (2), 250-253 PubMed.
• Calvert C A (1985) Salmonella infections in hospitalized dogs - epizootiology, diagnosis and prognosis. JAAHA 21, 499.