Bovine Coronavirus

Coronavirus infection is usually seen in calves between one and three weeks old, although disease may occur up to three months of age. Combined rotavirus and coronavirus infections are common.

Etiology

Coronavirus is an RNA virus that has three major proteins in the viral envelope (S, HE and M) with a fourth protein (N) associated with the nucleocapsid.

Pathogenesis

Coronavirus infection occurs orally or nasally. The virus initially infects cells in the proximal small intestine, and then spreads throughout the small intestine and colon. Pathogenesis and clinical signs are similar to that of rotavirus; the surface epithelial cells of the intestinal villi are destroyed. Coronavirus affects both the small and large intestine. As with rotavirus infection, epithelial cells are replaced by immature cells from the villous crypts, with a subsequent loss of absorptive capacity, dramatic increase in the gut fluid volume and osmotic imbalance.

Clinical signs

Coronavirus diarrhoea is generally more watery and of greater severity than rotavirus diarrhoea, leading rapidly to dehydration and acidosis. Initially fluid yellow diarrhoea is seen, later milk clots and mucous are passed and the diarrhoea becomes very watery. Depression, fever and anorexia are seen. Clinical signs of disease usually last four to five days.

Subclinical or recurrent infections are common and virus excretion from these cattle contaminates the environment. Adult cows are frequently carriers of Coronavirus the rate of virus excretion increases during the winter months and at parturition.