Bovine Coronavirus

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

Introduction

Bovine coronavirus (BCV) was characterized as a viral cause of calf enteritis by Mebus et al. (1973) and is now recognized as a leading cause of calf enteritis around the world. The virus infects the enteric and/or upper respiratory tract of calves that are 1-week to 3-months-old and contributes to Enzootic pneumonia of calves. In adult animals, the disease is usually sub-clinical, and the virus may be excreted intermittently at low titre (Schoenthaler and Kapil, 1999). Bovine coronavirus has also been identified as the etiological agent of Winter dysentery in adult cows (Saif, 1990). The incidence of BCV varies in different parts of the world but published and annual reports indicate that BCV causes 15-30% of calf enteritis cases (Langpap et al., 1979). The incidence of diarrhoea from bovine coronavirus may be underestimated because many laboratories around the world are not equipped with BCV antigen detection methods such as electron microscopy and BCV ELISA; also the isolation of BCV in tissue culture is difficult (Kapil et al., 1996). Bovine coronavirus infection occurs in combination with other enteric viral, bacterial, parasitic, and protozoal pathogens.
Bovine coronavirus has been found in cattle worldwide. Wild ruminants are also infected with the virus. Even though wild ruminant coronavirus may be antigenically, genetically, and biologically very close to coronaviruses, it is an accepted rule that a coronavirus isolated from any species is named after that host. Elk coronavirus has been found to be related closely to BCV both genetically (Majhdi et al., 1997) and antigenically (Daginakatte et al., 1999). 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.

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

Signalment

This condition affects cattle and zebu worldwide and can also affect wild ruminants such as deer. Calves are usually affected around 2 weeks of age. In cattle where the disease causes winter dysentry, this occurs in autumn and winter when the cattle are housed.

Clinical Signs

Clinical signs include diarrhoea, sometimes with haematochezia or melena, rumen atony, anorexia or a reduced appetite, weight loss or reduced weight gain, decreased milk yield and dehydration and depression.
Respiratory signs may include serious 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.
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 (Kapil et al., 1994a; Kapil et al., 1994b).
In respiratory coronavirus disease the viral antigen can easily be demonstrated in washed nasal epithelial cells by direct fluorescent antibody test using conjugate obtained from National Veterinary Services Laboratory (Kapil et al., 1991). Demonstrating the antigen in the lower respiratory tract is difficult. In the future, diagnosis could be made more specific, if antibodies against spike protein (protective antigen) are monitored through a sub-unit ELISA. 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 and Control

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 (Murakami et al., 1986). It is suggested that milk containing high amounts of coronavirus specific antibodies be fed to calves for the first 14 days of life to reduce the incidence and duration of viral shedding (Heckert et al., 1991). Addition of the neutralizing monoclonal antibody (Z3A5) against the spike protein to immune colostrum might also provide protection, but it is not yet commercially available. It has also been reported that in vitro Hygromycin B inhibits the replication of virus in cell culture (Zhang et al., 1997); however, the drug has not been tested in calves.

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.

References

Clark MA, 1993. Bovine coronavirus. British Veterinary Journal, 149(1):51-70; many ref.
Daginakatte GC, Chard-Bergstrom C, Andrews GA, Sanjay Kapil, 1999. Production, characterization, and uses of monoclonal antibodies against recombinant nucleoprotein of elk coronavirus. Clinical and Diagnostic Laboratory Immunology, 6(3):341-344; 15 ref.
Heckert RA, Saif LJ, Myers GW, Agnes AG, 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 Journal of Veterinary Research, 52(6):845-851; 44 ref.
Kapil S, Pomeroy KA, Goyal SM, Trent AM, 1991. Experimental infection with a virulent pneumoenteric isolate of bovine coronavirus. Journal of Veterinary Diagnostic Investigation, 3(1):88-89; 6 ref.
Kapil S, Goyal SM, Trent AM, 1994. Cellular immune status of coronavirus-infected neonatal calves. Comparative Immunology, Microbiology and Infectious Diseases, 17(2):133-138; 16 ref.
Kapil S, Trent AM, Goyal SM, 1994. Antibody responses in spiral colon, ileum, and jejunum of bovine coronavirus-infected neonatal calves. Comparative Immunology, Microbiology and Infectious Diseases, 17(2):139-149; 13 ref.
Langpap TJ, Bergeland ME, Reed DE, 1979. Coronalviral enteritis of young calves: Virologic and pathologic findings in naturally occurring infections. Am. J. Vet. Res., 40:1476-1478.
Majhdi F, Minocha HC, Kapil S, 1997. Isolation and characterization of a coronavirus from elk calves with diarrhea. Journal of Clinical Microbiology, 35(11):2937-2942; 19 ref.
Mebus CA, Stair EL, Rhodes MB, Twiehaus MJ, 1973. Pathology of neonatal calf diarrhoea induced by a coronavirus-like agent. Vet Pathol. 10:45-64.
Murakami T, Hirano N, Inoue A, Tsuchiya K, Chitose K, Ono K, Yanagihara T, 1986. Prevention of calf diarrhea with an immunoglobulin diet in beef herds. Japanese Journal of Veterinary Science, 48(5):879-885; 19 ref.
Saif LJ, 1990. A review of evidence implicating bovine coronavirus in the aetiology of winter dysentery in cows: an enigma resolved ?. Cornell Veterinarian, 80(4):303-311; 32 ref.
Schoenthaler SL, Kapil S, 1999. Development and applications of a bovine coronavirus antigen detection enzyme-linked immunosorbent assay. Clinical and Diagnostic Laboratory Immunology, 6(1):130-132; 13 ref.
Zhang Z, Andrews GA, Chard-Bergstrom C, Minocha HC, Kapil S, 1997. Application of immunohistochemistry and in situ hybridization for detection of bovine coronavirus in paraffin-embedded, formalin-fixed intestines. Journal of Clinical Microbiology, 35(11):2964-2965; 11 ref.