Rotavirus infections in calves.

Rotaviruses are now established as a major cause of neonatal enteritis and diarrhoea in calves. Laboratory diagnosis is usually based on detection of the virus or virus antigens in faeces by direct electron microscopy or tests such as ELISA and IEOP. Rotaviruses are resistant to inactivation and are normally present in large numbers in faeces, so that environmental contamination is both heavy and persistent. Infection is transmitted primarily by faecal-oral contact. Calves are usually protected from infection for the first few days of life by colostral antibody. When this disappears from the gut the calf is totally susceptible to infection and maximum virus excretion normally occurs around the end of the first week of life. The disease has a high morbidity, but clinically is of mild to moderate severity. Many infections are subclinical. The virus infects and destroys mature villous enterocytes in the small intestine, resulting in villous atrophy and replacement of mature epithelial cells by undifferentiated immature cells. Diarrhoea probably results from malabsorption and net water secretion. Control is based on management systems designed to decrease the amount of infection to which the calf is exposed and on increasing the specific resistance of the calf to infection e.g. by feeding immune colostrum or by vaccination. Vaccination of the dam with adjuvanted, inactivated vaccines has given promising results, but this work is still at an early stage.