Bovine Coronavirus

Also know as: Bovine Viral Scours — Bovine Winter Dysentry — Coronaviral Enteritis of Calves — Scours — Winter Dysentery

Introduction

Bovine coronavirus (BCV) is as a viral cause of calf enteritis. The virus infects the enteric and/or upper respiratory tract of calves and contributes to Enzootic pneumonia of calves. It is also the cause of Winter Dysentery in adult housed cattle.

Distribution

Bovine coronavirus has been found in cattle worldwide.

Wild ruminants are also infected with the virus. Even though other coronaviruses, it is an accepted rule that a coronavirus isolated from any species is named after that host.

The primary routes of entry for bovine coronavirus are via the faecal-oral route or the nasal cavity (Clark, 1993). Adult cattle are carriers and excrete the virus at low levels; however, during parturition, cows shed higher titres of the virus.

The incidence of BCV varies in different parts of the world but published and annual reports indicate that BCV causes 15-30% of all calf enteritis cases. Incidence may be underestimated because many laboratories around the world are not equipped with BCV antigen detection methods.

Signalment

Calves 1-week to 3-months-old are usually infected.

This condition affects cattle and zebu worldwide and can also affect wild ruminants such as deer.

In cattle where the disease causes Winter Dysentery, this occurs in autumn and winter when the cattle are housed.

In adult animals, the disease is usually sub-clinical, and the virus may be excreted intermittently at low levels..

Clinical Signs

Clinical signs include diarrhoea, sometimes with haematochezia or melaena, rumen atony, anorexia or a reduced appetite, weight loss or reduced weight gain, decreased milk yield and dehydration and depression.

Respiratory signs may include serous nasal discharge, progressing to purulent if secondary bacterial infection is present, coughing, dyspnoea and tachypnoea.

Diagnosis

History, signalment and clinical signs can be indicative of the disease.

Distinguishing between different BCV isolates with monoclonal antibodies is difficult. Most BCV isolates and wild ruminant strains can be distinguished on the basis of a haemagglutination inhibition test using mouse erythrocytes.

Enteric BCV infections generally are diagnosed by examination of faecal samples or intestinal contents by electron microscopy (EM) or ELISA.

No diagnostic tools are available for cow-side testing or in-office testing for veterinarians. When sending samples to diagnostic services it is important to include at least five sections from different parts of the gut, including the spiral colon because this is the common site of virus persistence

In respiratory disease, the viral antigen can easily be demonstrated in washed nasal epithelial cells by direct fluorescent antibody test. Demonstrating the antigen in the lower respiratory tract is difficult.

Serological tests, such as indirect fluorescent antibody, are used to monitor the presence of antibody in colostrum, serum, and intestinal contents. However, these are not yet commercially available.

Treatment

Treatment of BCV is generally symptomatic. Fluid therapy is given orally or intravenously. Astringents also are used to control diarrhoea. Additional feeding of fortified colostrum may be useful in preventing the clinical disease in newborn calves.

Control

A dam vaccine is available as a control measure for this disease. This should be given mid-late gestation to increased the number of BCV antibodies in the dams' colostrum. At birth, the calf must drink this colostrum for the vaccine to have been of any effect.

General husbandry measures such as ensuring good hygiene and ventillation in calving pens is important.

Bovine Coronavirus Learning Resources
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References

Clark, M. A (1993) Bovine coronavirus. Brit Vet J, 149(1):51-70;

Daginakatte, G. C., Chard-Bergstrom, C., Andrews, G. A., Sanjay, Kapil (1999) Production, characterization, and uses of monoclonal antibodies against recombinant nucleoprotein of elk coronavirus. Clinical & Diagnostic Laboratory Immunology, 6(3):341-344; 15.

Heckert, R. A., Saif, L. J., Myers, G. W., Agnes, A. G (1991) Epidemiologic factors and isotype-specific antibody responses in serum and mucosal secretions of dairy calves with bovine coronavirus respiratory tract and enteric tract infections. American J Vet Research, 52(6):845-851; 44.

Kapil, S., Pomeroy, K. A., Goyal, S. M., Trent, A. M (1991) Experimental infection with a virulent pneumoenteric isolate of bovine coronavirus. J Vet Diagnostic Investigation, 3(1):88-89; 6.

Majhdi, F., Minocha, H. C., Kapil, S (1997) Isolation and characterization of a coronavirus from elk calves with diarrhea. Journal of Clinical Microbiology, 35(11):2937-2942; 19.

Mebus, C. A., Stair, E. L., Rhodes, M. B., Twiehaus, M. J (1973) Pathology of neonatal calf diarrhoea induced by a coronavirus-like agent. Vet Pathol. 10:45-64.

Saif, L. J (1990) A review of evidence implicating bovine coronavirus in the aetiology of winter dysentery in cows: an enigma resolved? Cornell Vet, 80(4):303-311; 32.

Zhang, Z., Andrews, G. A., Chard-Bergstrom, C., Minocha, H. C., Kapil, S (1997) Application of immunohistochemistry and in situ hybridization for detection of bovine coronavirus in paraffin-embedded, formalin-fixed intestines. J Clinical Microbiology, 35(11):2964-2965; 11.