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Synonyms
Type of zoonosis
Definition
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Salmonellosis is a direct anthrapozoonosis, caused by Salmonella spp., is characterized by either intestinal or septicemic salmonellosis. The septicemic form is usually caused by the human adapted serotypes (Salmonella typhi and Salmonella paratyphi). The zoonotic salmonellosis is mainly caused by non-typhoid serotypes. Mostly the Salmonella of animal origin causes an intestinal infection in man, is characterized by fever, myalgia, cephalalgia and malaise.
Etiology
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It is caused by Salmonella spp., which belong to the family Enterobacteriaceae. They are Gram negative, motile, facultative anaerobic bacteria.
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They do not survive at temperature above 70oC (at pasteurization temperature for 15 seconds destroys Salmonella in milk).
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They resist dehydration for a very long time, both in faeces and foods.
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They survive well in salinity (20%) and products with a high protein and fat content (sausage).
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They resist smoking and survive for a long time in soil and water.
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Kauffman-White scheme divides Salmonella in to serotypes (~2,200 serotypes), based on "O" somatic, "H" flagellar and "Vi" capsular antigens.
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Virulence factors in Salmonella are lipopolysaccharides, pili, flagella, cytotoxin and enterotoxin.
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Salmonella spp. in animals are:
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Cattle: Salmonella dublin and Salmonella typhimurium
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Swine: Salmonella choleraesuis, Salmonella enteritidis and Salmonella typhimurium
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Sheep and goats: Salmonella abortus ovis and Salmonella typhimurium
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Horses: Salmonella abortus equi and Salmonella typhimurium
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Fowl: Salmonella pullorum and Salmonella gallinarum
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Dogs and cats: Asymptomatic carriers for many species of Salmonella
Reservoir and incidence
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Poultry, cattle, sheep and pigs mainly act as reservoirs for human salmonellosis. However, all animals are reservoirs for Salmonella.
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Salmonella spp. are common commensals of all animals and birds.
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Only host-adapted strains of Salmonella spp. cause clinical disease in animals.
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Food-poisoning Salmonella spp. of humans do not cause clinical signs in animals.
- Salmonella inhabits the intestinal tract of animals and humans, and excreted in faeces.
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Infection in animals is maintained by feeding of animals with slaughterhouse waste, faecal-oral spread and faecal contamination of hatching eggs.
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All domestic animals, wild animals, birds and humans are asymptomatic carriers / latent carriers. They harbour the pathogens in its lymph nodes and eliminate in its faeces intermittently or persistently.
Transmission
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Faecal-oral transmission.
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Ingestion of contaminated food and water (poultry carcasses, meat or unpasteurized milk, inadequatly cooked food, cross-contamination of cooked foods and inadequately storage).
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Environmental contamination (water sources and sewage) is a potential source of infection.
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Nosocomial infection: Person-to-person spread is common in hospitals.
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Mechanical transmission by flies (environmental contamination).
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Animal-to-animal transmission due to over-crowding.
Disease in animals
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Subclinical infection is common and many animals may be intermittent or persistent carriers.
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In cows, it may cause clinical infection with increased fever, diarrhoea and abortion (leading to placental necrosis).
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In calves, it causes diarrhoea with high mortality.
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In pigs, it may cause increased fever and diarrhoea.
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Sheep, goats and poultry usually show no signs of infection.
Disease in humans
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Incubation period is short, which ranges from 12 to 72 hours. Usually it is a self-limiting illness.
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The severity of clinical infection depends on the level of infecting dose.
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Clinical signs include watery diarrhoea for about ten days, nausea and vomiting, which leads to dehydration, with abdominal pain and low-grade fever.
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Enteritis is a feature (called as "enteric fever").
Diagnosis
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Based on clinical signs and history of gastroenteritis
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Isolation and identification from faeces and suspected foods, followed by serotyping, phage typing and plasmid profiling.
Treatment
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Zoonotic Salmonella usually heal without complications.
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Symptomatic treatment is highly essential with antibiotic administration based on antibiogram. This is to avoid development of multiple antibiotic resistance.
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Antibiotics such as trimethoprim-sulfamethoxazole, ampicillin, ciprofloxacin or amoxicillin can be given to severely ill patients for 3 to 5 days with supportive treatment.
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Multiple drug resistance Salmonella have reported in nurseries and pediatric clinics with complications such as septicemia or meningitis with high mortality.
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Sulfonamides can be given to animals to reduce mortality due to enteric salmonellosis, but is contraindicated in healthy carriers in which treatment may prolong the carrier state.
Prevention and control
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Existing food processing practices, by which it is difficult to obtain salmonella-free foods of animal origin. But, control of salmonellosis in man is currently based on reducing its prevalence in animals. So, veterinary meat and poultry production inspection at slaughter houses and supervision of milk pasteurization and egg production are important for consumer protection.
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Education of food handlers, about correct cooking, refrigeration practices of foods of animal origin, pasteurization of milk and about personal and environmental hygiene.
- Prevent cross-contamination of food materials.
- Prevent contamination of poultry carcasses at abattoirs.
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Irradiation of meat and other foods before purchase will reduce contamination.
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In animals, general cleanliness should be followed. It includes avoiding mixing animals from different sources, providing clean drinking water, prevention of access of wild birds and rodents to animal houses, thorough cleaning and disinfection of animal houses before restocking of animals, regular removal of excreta of poultry, disinfection of hatching eggs and fumigation of egg incubators.
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