Salmonellosis

Dairy cows with salmonellosis

What to look for

  • Fever and depression
  • Foul smelling diarrhoea which may contain shreds of intestinal lining and/or blood
  • Rapid dehydration, weight loss
  • High death rate in calves
  • Abortion in pregnant animals

Cause – a bacterial infection (various Salmonella species)

Salmonella infections occur in a huge range of animals, birds and reptiles, and can move from one animal species to another. It is often carried in the gut of animals and birds without causing disease. Contamination of feed stuffs and water with faecal material can cause large scale outbreaks. Outbreaks are sometimes related to stresses such as transport, temporary deprivation of feed or sudden onset of extreme weather events. The number of infected animals can vary from isolated cases to outbreaks involving large numbers of animals.

Animals likely to be affected

Most commonly seen in young calves (2-6 weeks of age) and lactating cows with high milk production.

Other diseases with similar signs - other causes of severe diarrhoea

In young animals (see Chapter 7 of Rearing Healthy Calves) these diseases include infection with rotavirus, cryptosporidia, Escherichia coli, coccidiosis, bovine viral diarrhoea, roundworms or Yersiniosis. In older animals you also need to consider conditions caused by trace element deficiencies (copper or selenium), plant toxicities or poisonings.

Confirming the diagnosis

The diagnosis is based on clinical examination, a thorough history of an outbreak and laboratory testing. Farmers that have experienced an outbreak of salmonellosis in adult cattle will be able to quickly recognise the clinical signs and should seek early assistance.

Spread of the disease

Salmonella can spread by movement of animals or by spreading of effluent on pastures. It can persist for months in a cool and moist environment and contamination can build up relatively quickly when an animal develops diarrhoea and excretes huge numbers of the organism. Prompt treatment and isolation of sick animals is therefore paramount.

Risks to people

Salmonella is one of the most important causes of gastroenteritis in people. Most cases occur after consumption of contaminated food but infection can be contracted directly from animals especially if they have clinical salmonellosis. In these circumstances it is very important to reduce exposure as much as possible and to practice high levels of personal hygiene. Do not drink unpasteurised milk from cows that may be infected with Salmonella.

Treatment

Cows and calves with serious cases of salmonellosis will deteriorate very quickly. Call your vet as quickly as possible to get a diagnosis and start appropriate treatment. They require prompt treatment with antibiotics and supporting therapy to save lives and slow spread of the disease.

Risk factors

  • introducing animals that have been mixed with animals of unknown origin, especially in stressful environments such as saleyards
  • introducing animals to the main herd before there has been time for any sick animals to identified
  • contact between susceptible animals and effluent on the home property or from neighbours
  • mixing agisted animals with other animals or transporting them in dirty trucks
  • rodent infestations

Prevention

A vaccine is available that cattle protects against the most important strains of salmonella found in Australia. It requires two doses about a month apart with an annual booster. Passive immunity in young calves can be boosted by feeding an adequate amount of colostrum from vaccinated cows in the first few hours of life.


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