Salmonella in Bovines

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Also Know As

Salmonellosis, Septicemic salmonellosis

Description

Salmonellosis is an infection of the digestive tract caused by the bacterium, Salmonella enterica. Salmonella enterica has over 2,000 strains. Fortunately cattle are usually clinically infected by less than 10 of them. The majority of Salmonella that infect cattle are in groups B (species example - S. Typhimurium), C (example - S. Montevideo), D (example - S. Dublin), or E (example - S. Anatum). The type that most commonly infects cattle in the Northeast is Salmonella Typhimurium.

Salmonella is widespread and can be found on a large number of dairy farms and in many species of animals, including mammals, birds, insects, reptiles and humans. It is often an opportunistic bacterium, meaning it infects an animal when its immune system is suppressed, when other competing gut bacteria are absent (common after antibiotic therapy), or when the animal is very young. It also infects healthy animals when they are exposed to high doses.

Infection with Salmonella  can produce diarrhea in animals of all ages, especially those that are stressed, closely stocked, or exposed to a heavily contaminated feed or water supply. In older animals, the disease is manifest by dysentery and toxemia, and mortality can be significant.

Infection can range from apparently “healthy” carrier animals to those that show acute signs of the infection. A spectrum of symptoms occur with Salmonella infection, from inapparent or subclinical infections to obvious or clinical disease. In calves, the disease most commonly affects colostrum- deprived or deficient calves, and may cause a fever (105°–107° F), diarrhea (yellow with or without flecks of blood and mucus), rapid dehydration and death within 24–48 hours.

In adult cattle, severe intestinal disease is often brought on by some stress factor(s). Clinical signs include: fever (104°–106° F), followed by going off feed, depression, and foul-smelling diarrhea with varying amounts of blood, mucus, and shreds of intestinal lining. In milking animals, milk production severely drops.

Abortions may occur in infected cattle.

Dehydration varies with the severity of disease. Temperatures typically rise 12 to 24 hours before other signs and may drop off again with the onset of diarrhea. Death rates vary depending on the serotype of Salmonella involved.

Clinical illness usually lasts 7–10 days, with recovery in 2 to 3 weeks. Some animals, however, never resume full production. Sick cows that recover may become carriers that shed Salmonella for varying periods of time (e.g., Salmonella Typhimurium is shed from 3 to 6+ months while Salmonella Dublin is shed for life).

In chronic cases, following an acute episode, fever (103°–104° F) is intermittent and watery diarrhea persists, resulting in progressive dehydration and weight loss. Recovery may be slow and death rates are difficult to predict because cattle are often culled due to unthriftiness and poor condition.

Signs

  • Fever
  • Dehydration
  • Diarrhea: may be severe and bloody
  • Depression
  • Discoloration of gums
  • Gas-caused abdominal distention
  • Bone and joint infections
  • Loss of appetite
  • Drop in milk production
  • Abortion

Causes

Salmonella is an opportunistic bacterium, meaning it infects an animal when its immune system is suppressed, when other competing gut bacteria are absent (common after antibiotic therapy), or when the animal is very young. It also infects healthy animals when they are exposed to high numbers of the bacterium.

Salmonella is a highly contagious bacteria that spreads primarily when animals consume contaminated feed or water. Salmonella can infect birds and mammals, including humans. As a result, manure from infected birds, rodents and other wild animals is a common source for contamination of the environment, water and feed.

Feed contamination can occur either in storage on the farm or on the premises of a feed vendor.

Large numbers of Salmonella are shed by clinically infected animals. Infected animals readily contaminate their surroundings, including feed, water troughs, barnyards, feeding equipment, and people who work around them. Most bacteria are shed in manure, but when systemic illness develops, the bacteria is also shed in saliva, nasal secretions, urine and milk.

Some animals, upon recovery, become carriers and continue to shed organisms for many months. They may not show outward signs of the disease, but are a continual, intermittent source of environmental contamination.

Outbreaks of this disease are often seen after episodes of flooding or runoff, when cattle feed or equipment is contaminated with flood waters carrying the organism. Salmonella bacteria love wet, dark environments. They have the remarkable ability to survive under adverse conditions, such as pH's between 4 and 8+, and temperatures between 46° and 113° F. Salmonella can survive in low oxygen environments, such as in manure lagoons and are known to survive for up to 4–7 months in water and soil.

Salmonella spread onto fields in manure may survive for weeks to months. Manure should be spread onto flat land, where it is exposed to the drying effects of wind and to the bactericidal effect of UV irradiation from the sun. Incorporate manure into soil in areas where runoff could be a problem. Manure should be spread onto cropland rather than onto pastures used for grazing. Recent investigations demonstrate manure disposal by composting and anaerobic digestion reduce organism numbers.

Salmonella are no more or less sensitive to the effects of commonly used disinfectants than are other fecal bacteria. Chlorine solutions, iodine, quaternary ammoniums and phenolic compounds are very good at killing Salmonella on surfaces.

However, it is very important to get rid of organic matter and bedding first, followed by wet cleaning with high pressure hot water/steam and then disinfection. Because Salmonella can "bloom" within a few hours in a warm, wet environment, disinfection should immediately follow cleaning.

Prevention

Management / biosecurity measures that reduce the risk of Salmonella infections in cattle include:

  • Avoid introducing potentially infected animals by maintaining a closed herd. Quarantine all introduced stock for at least four weeks.
  • Source new stock from other farms with high health status and not markets.
  • Avoid shared bulls and communal grazing areas.
  • Isolate sick animals in dedicated isolation boxes and not calving boxes.
  • Clean and disinfect buildings between occupancies. Provide good drainage and waste removal.
  • Maintain good fences to prevent straying of neighbouring stock.
  • Ensure that milk from ill cows (or cows that have been in contact with such cows) is not fed to calves.
  • Protect all feed stores from vermin including birds.
  • Only spread slurry on arable land wherever possible. Leave all grazing land at least three weeks after spreading slurry.
  • Insist visitors have clean boots and disinfect before entering and leaving the farm premises.

Consider herd vaccination where the problem persists despite the control measures listed above.

Treatment

Treatment response to all Salmonella infections is generally poor and prevention is much better than treatment. Treatment for neonatal calves involves the ingestion of colostrum from vaccinated dams (2 litres within the first 2-4 hours) is essential to reduce the risk of Salmonella septicaemia.

Supportive therapy, such as oral or intravenous electrolytes and fluids, are used to treat sick cows. While antibiotics are often used, they alone are seldom effective, especially if the disease has progressed to the diarrheal stage. One type of Salmonella, called Salmonella Typhimurium DT104, is often seen in sick cattle and is of particular concern to public health officials.

Salmonella Typhimurium DT104 is highly virulent, and causes severe symptoms in animals and people. Outbreaks due to this type have resulted in cattle deaths and severe illness in farm families, because it is resistant to a wide range of antibiotics and is quite difficult to treat.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.

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