Bovine Rotavirus

Rotaviruses are the most common cause of neonatal diarrhoea in calves.

Bovine rotavirus is a non-enveloped RNA virus that belongs to the family Reoviridae. The virus is present in most cattle herds and typically causes diarrhoea in calves between 5 to 14 days old. Clinical disease in calves older than one month is rare. However, periodic asymptomatic re-infection and shedding occurs in older cows and calves.

Pathogenesis and Clinical Signs

Calves become infected via the faecal-oral route. Virus is excreted into the environment after an incubation period that varies from 15 hours to five days.

Many infections are subclinical but a proportion result in diarrhoea. The severity and duration of disease are variable. Disease onset can be triggered by antibody in the intestinal lumen dropping below protective levels. Clinical signs may last for four to eight days.

The virus invades the surface epithelial cells of the small intestinal villi. Loss of the epithelial cells results in shortened villi, which become covered by immature cells arising from the villous crypts. The immature cells and the loss of surface area dramatically reduce the absorptive capacity of the gut and the secretion of normal digestive enzymes. The result is a dramatic increase in fluid, containing contains undigested and unabsorbed nutrients, in the gut lumen. There is increased microbial activity and the osmotic imbalance draws more water into the intestine. The subsequent diarrhoea causes dehydration, acidosis and hypoglycaemia. In severe cases death may occur.

Electromicrograph of a rotavirus particle