Salmonellosis, caused by the Salmonella bacterium, is a cause of diarrhoea in both neonatal and adult cattle. It causes infection of the gut but this can develop into systemic illness. There are two main strains of Salmonella bacterium – Salmonella dublin and Salmonella typhimurium. Within these strains there are many serotypes of the bacteria.
Salmonellosis is acquired by ingestion of the bacteria, which then invade and destroy the cells lining the gut. Following damage to the gut wall, the bacteria migrate to the local lymphoid tissue (Peyers patches and mesenteric lymph nodes) where they can invade lymphoid cells. Because the bacteria lives inside host cells, they are protected to some extent from antibiotics. The bacteria also release a toxin (endotoxin) which can also cause damage in the host and cause the systemic signs of illness. Calves aged 1-2 months old are most susceptible, but the infection can also occur in older cattle, especially those that are debilitated, suffering from other illness or are very old. The bacteria is able to inhabit some animals without causing disease, but these animals still shed Salmonella in the faeces and in milk, and can transmit the disease to other individuals. Animals that are in crowded or stressful conditions are more prone to acquiring the disease. Failure of passive transfer (due to low volume or quality of colostrum intake), hygiene and a high protein diet are all important factors that can increase the risk of disease. The disease is diagnosed based on clinical signs and by culturing the faeces to show the presence of Salmonella bacteria. However, culture is not easy and a lot of faecal samples may be needed to successfully grow the bacteria in the laboratory. Salmonella is therefore only usually definitively eliminated as a cause of diarrhoea if faecal samples from 5 consecutive days fail to demonstrate the bacteria.
Clinical Signs
Calves
- Enteric disease manifesting as brown, watery to mucoid diarrhoea that contains blood
- Fever
- Extreme weakness
- Dehydration
- Septicaemia – may be fatal
- Septicaemia-associated signs, including anorexia, meningitis, depression, polyarthritis, pneumonia, sudden death
Adults
- Acute disease is seen as fever and severe, watery to mucoid diarrhoea containing blood and fibrin
- Chronic disease is seen as persistent diarrhoea and failure to thrive
- Abortion may occur
Treatment
Treatment of Salmonella includes use of an appropriate antibiotic such as trimethoprim sulfadiazine. Use of a non-steroidal anti-inflammatory drug such as flunixin meglumine is appropriate as the disease is likely to be painful. If the animal is dehydrated, administration of fluids with an electrolyte restoration solution is indicated. Prognosis in calves in generally poor, and many succumb to the disease. Prognosis is adults is fair if appropriate treatment is used.