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 Bacterial Diseases - SALMONELLOSIS

(Salmonella food poisoning, enteric paratyphosis) A common bacterial cause of food-poisoning worldwide. Over 1800 food-poisoning serotypes of salmonella (bacterium) exist. The prevalence of individual serotypes constantly changes. In the U.S., 5 million cases are diagnosed annually. S. typhi, the cause of Typhoid Fever, rarely occurs in the U.S. and is not discussed here.

RESERVOIR AND MODE OF TRANSMISSION:

Salmonellas are common commensals of all animals and birds and are excreted in feces. Host-adapted strains may cause serious illness (e.g., S. dublin in cattle, S. pullorum in chickens), but most human food-poisoning salmonellas do not cause clinical signs in animals. The main reservoirs for human infection are poultry, cattle, sheep and pigs. Infection in animals is maintained by recycling slaughterhouse waste as animal feed, fecal oral spread and fecal contamination of hatching eggs. Transmission occurs when organisms, introduced into the kitchen in poultry carcasses, meat or unpasteurized milk, multiply in food owing to inadequate cooking, cross-contamination of cooked foods and inadequate storage. Person-to-person spread is common in institutions such as hospitals. The organism inhabits the intestinal tract of many animals including birds, cattle, sheep, pigs, lab. animals (rats, mice, hamsters, guinea pigs, nonhuman primates) and humans. Salmonella occurs worldwide. The house mouse may also be a reservoir of the infection and may play a role in human and animal salmonellosis. Humans, rarely, and animals may be carriers and asymptomatic shedders of the organism. Salmonella prevalence in the U.S. canine population may be 10% or more. Prevalence data from 8 studies conducted worldwide indicated that a wide range (0.6-27%) of cats were culture-positive for Salmonella. Salmonella carriers in newly imported Rhesus and Cynomolgus monkeys exceeded 20% in some shipments. Birds, reptiles, and turtles are especially dangerous sources of Salmonellosis. 94% of all reptiles harbor Salmonella. Turtles alone in 1970 may have caused 280,000 human cases of Salmonellosis. In 1975 the FDA ruled it illegal to sell a. Viable Turtle eggs b. Live turtles with a carapace length <10.2cm (4 inches) c. Exceptions Educational & scientific institutions and marine turtles. d. Marine turtles have not been shown to be a reservoir of Salmonella

TRANSMISSION:

Indirect transmission via contaminated food and water are the most common sources but transmission may also be by direct contact. It is a common contaminant of sewage. Found in many environmental water sources. Environmental contamination continues to be a potential source of infection for lab animals and secondarily for personnel handling those animals. Animal feed containing animal by products continues to be a source of Salmonella contamination, especially if the diets consist of raw meal and have not undergone the pelleting process.

INCUBATION PERIOD:

Humans. 12-72 hours. Animals. 1-5 days.

CLINICAL FEATURES:

Humans. The presence and severity of symptoms depends on the infecting dose. Typically there is watery diarrhea for about ten days, possibly leading to dehydration, with abdominal pain and low-grade fever. Septicemia and abscess formation are rare.

Animals. Subclinical infection is common and many animals may be intermittent or persistent carriers. However, cows may suffer with fever, diarrhea and abortion. Calves undergo epizootic outbreaks of diarrhea with high mortality. In pigs, fever and diarrhea are less common than in cattle. Infected sheep, goats and poultry usually show no signs of infection.

PATHOLOGY:

Humans. Enteritis is a feature. Extraintestinal infection may cause abscesses.

Animals. Penetration of the infection into the mucosa is followed by inflammation, especially ileitis, progressing to inflamed mesenteric lymph nodes in the mesentery, possibly progressing to septicemia and pneumonia especially in calves. Dehydration and rapid loss of weight are due to stimulation of chloride excretion and inhibition of sodium absorption. Abortion in cattle is caused by massive proliferation of salmonella in the placenta leading to placental necrosis.

DIAGNOSIS:

Humans. Isolate salmonella from feces and suspected foods using selective media followed by serotyping and, if appropriate, phage typing.

Animals. Culture feces, postmortem tissues and foods of animal origin. Serological tests are of limited value as many noninfected animals have titers from past infections.

Humans. Usually only a self-limiting illness occurs. Deaths from dehydration or septicemia are rare and occur usually in infants, or debilitated or elderly patients.

Animals. There is abortion in cattle and endometritis with temporary infertility. In calves, dehydration and septicemia may lead to death.

PREVENTION:

Humans. Educate food handlers in good kitchen hygiene. Ensure thorough cooking of meat, refrigerate cooked foods and prevent cross-contamination. Pasteurize all milk. Ensure personal hygiene. Reduce contamination of poultry carcasses at abattoirs. Irradiation of meat and other foods before purchase will reduce contamination.

Animals. This is difficult and often impractical because there are many sources of infection. Principles of control include the following: maintain closed herds and flocks; keep animals in small groups; purchase replacements direct from the farm of origin; avoid mixing animals from different sources; sterilize ingredients of animal feed; provide mains drinking water for grazing livestock; prevent access of wild birds and rodents to animal houses; completely destock animals and thoroughly cleanse and disinfect housing between batches; monitor poultry breeding stock and remove excreters; disinfect hatching eggs and fumigate incubators.

TREATMENT:

Humans. Treatment of uncomplicated enterocolitis is symptomatic only. Young, malnourished, or immunocompromised infants, severely ill patients, those with sickle cell disease, and those with suspected bacteremia should be treated for 3-5 days with trimethoprim-sulfamethoxazole (one double-strength tablet twice a day), Ampicillin (100 mg/kg IV or orally), or ciprofloxacin 9750 mg twice daily).

Animals. Treatment with antibiotics and sulfonamides immediately diarrhea and fever occur reduces mortality but is contraindicated in healthy carriers in which treatment may prolong the carrier state.

VACCINATION:

Humans. None.

Animals. Vaccines are available against S. dublin and S. typhimurium in calves. A live vaccine prepared from a rough strain of S. dublin gives good protection in calves against both S. dublin and S. typhimurium.

LEGISLATION:

Humans. The disease is notifiable specifically in the USA, Australia, New Zealand and several European countries, or as food-poisoning as in the UK. Animals. Notification of infection in food animals is obligatory in some countries, including the UK, with statutory sampling of animal protein for animal feed. Heat treatment of waste food applies in the UK. A slaughter policy is claimed in Luxembourg, Germany and Czechoslovakia.