Winter dysentery is an acute, highly contagious GI disorder that affects housed adult dairy cattle, primarily during winter. Clinical features include explosive diarrhea (sometimes accompanied by dysentery), a profound drop in milk production, variable anorexia and depression, and mild respiratory signs such as coughing. The disease has a high morbidity but low mortality, and spontaneous recovery within a few days is typical.
Transmission, Epidemiology, and Pathogenesis:
Bovine Corona Virus is transmitted via the fecal-oral route through ingestion of feed or water contaminated with feces from clinical cases or clinically normal carrier animals. Viral particles present in respiratory secretions of affected animals may further enhance transmission. Transmission of disease is promoted by close confinement. Winter dysentery is highly contagious and easily introduced to barns by visitors, carrier animals, and fomites. Winter dysentery is common in northern climates where animals are housed indoors for extended periods during the winter months.
Coronaviruses survive best at low temperatures and at low ultraviolet light intensities, which can lead to a buildup of virus in the environment during the colder months. Adult lactating cows that have recently calved are most severely affected, but the disease can affect younger or older animals and males. Mortality rates associated with winter dysentery are generally low (1-2%), but morbidity in affected herds is high, with 20-50% of the animals in a herd exhibiting clinical signs within a few days and close to 100% of animals in the herd exhibiting signs within a week. Some degree of immunity to winter dysentery appears to develop because recurrences, if seen in the same herd, are noted at 1- to 5-yr intervals.
The clinical syndrome is characterized by an acute onset of fluid diarrhea and a profound decrease in milk production (25-95% production loss). Feces are liquid and homogenous with little odor, dark green to black, and rarely contain blood or mucus. A sweet, musty, unpleasant odor is reported in barns with large numbers of affected cattle. Nasolacrimal discharge or cough may accompany or precede the diarrhea. Other signs include mild colic, dehydration, depression, a brief period of anorexia, and some decrease in body condition. Occasionally, animals exhibit more severe signs such as passage of feces with variable amounts of blood, severe dehydration, and weakness. Fatalities are rare. Diarrhea in individual animals has a short course, and feces return to normal in 2-3 days in most animals. Disease in the herd typically subsides in 1-2 wk, but milk production may take weeks to months to return to normal.
Differential diagnoses for acute diarrhea in adult cattle include bovine viral diarrhea (BVD), coccidiosis, and enteric salmonellosis. These diseases can be ruled out by absence of mucosal lesions (BVD), negative fecal cultures ( Salmonella spp ), and negative fecal flotation (coccidiosis), as well as by the characteristic clinical presentation of winter dysentery (rapid onset of diarrheal disease of short duration in a herd with high morbidity but low mortality).
Treatment and Control:
Most affected cattle recover spontaneously. Fresh water, palatable feed, and free-choice salt should be available at all times. IV fluid therapy or blood transfusions may be required in severely affected cattle.
There is no vaccine for winter dysentery. Isolation of newly introduced cattle for 2 wk and isolation of any adult cow with diarrhea is advised to decrease the likelihood of disease introduction into a herd. In an outbreak, access to the premises should be restricted, and all persons in contact with affected cattle should ensure that their footwear and clothing are clean before leaving an affected farm.