Winter dysentery in dairy cattle herds caused by bovine coronavirus

During late winter and early spring in 1997 and 1998, an epizootic diarrhea prevailed among cattle over six months in dairy herds of two regions of Hungary. The disorder showed marked resemblance to the disease literally named 'winter dysentery' that is caused by Bovine Coronavirus (BCV). This disease had never been diagnosed in Hungary before. Investigations were carried out on 4 large and 7 small scale farms. The disease spread very quickly both among and within herds with a sudden onset of symptoms in affected herds. On large scale farms, the infection progressed in 3-4 days and appeared on animals kept in other buildings in 1-2 weeks. In large herds the morbidity was 80 per cent, while in small farms it could reach 100%. The affected animals showed anorexia and fever followed by a watery diarrhea, that became bloody or blood-stripped after 2-3 days. In milking cows, milk production decreased by 50-100 per cent, i.e. there was an overall decrease in excess of 50 per cent at farm level The severity of symptoms decreased after about 5-6 days with the gradual disappearance of the diarrhea. Milk production returned to normal in 2-4 weeks depending on the size of the herd. In a large herd, losses were between 110-750 liter milk daily during the phase of diarrhea, totaling over 3000 USD. In another herd, the number of cows observed to be in heat decreased from the normal 6,3 to 2,9 per day during the course of the disease. Fecal and blood samples were sent for laboratory investigation from the affected farms. Feces and paired blood samples were tested from 5 herds showing acute symptoms. BCV was detected in feces samples from all five herds, however, only 22 out of 43 samples were positive with a direct ELISA method. Since blood samples were taken at the onset of infection, only three of these 22 BCV positive were positive for BCV antibodies by the HAI method. However, sero-conversion or rising titers specific to BCV were demonstrated in 39 of the 48 paired blood samples. HAI titers of 1:32-greater than or equal to 512 were found in 37 of the 40 reconvalescent sera from a total of 7 herds. These results indicate the causative role of BCV in epizootic diarrhea of adult cattle in Hungary.