Bovine coronavirus infection

Bovine coronavirus infection

Bovine coronavirus infection

Previous Authors: L J SAIF

Current Authors:
L J SAIF - Professor, MS, PhD, Food Animal Health Research Program, CFAES and CVM, OARDC, Ohio State University, 1680 Madison Ave, Wooster, Ohio, OH 44691, USA
M A ALHAMO - Research, DVM, MSc, OARDC Food Animal Health Research Program, Ohio State University, 1680 Madison Avenue, Wooster, Ohio, OH 44691, USA

Introduction

Bovine coronavirus (BCV) was first recognized in 1972 in the USA as a cause of neonatal calf diarrhoea.47 Since then, it has been implicated in winter dysentery in adult dairy cattle 2, 17, 57, 61, 62, 70, 73, 74 and in respiratory infections of cattle of various ages.11, 28, 34, 39, 41, 45, 52, 55, 56, 64, 65, 68, 79 In addition, coronaviruses (CoVs) antigenically indistinguishable from BCV have been isolated from wild ruminants,44, 71 including cases of bloody diarrhoea resembling winter dysentery of cattle.71 Bovine coronavirus enteric or respiratory infections are found in cattle worldwide,4, 8, 52, 53, 56, 58, 79 leading to major health and economic losses to beef and dairy farms. Among other domestic ruminants, BCVs have also been isolated from water buffaloes.14, 49 Studies of wild white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus),71 and caribou (Rangifer tarandus caribou),18 in North America have indicated BCV antibody seroprevalence rates of 7 to 14 per cent, suggesting that BCV infections may be endemic in wild native ruminants.56, 71 Captive wild ruminants in the USA have been identified as a source of BCV infections, including sambar deer (Rusa unicolor), white-tailed deer, waterbuck (Kobus ellipsiprymnus), elk or wapiti (Cervus elephus), and giraffe (Giraffa camelopardalis).5, 26, 44, 71 In addition, betacoronaviruses (clade A, like BCVs), were detected from faeces or nasal swabs of camelids, namely alpacas (Vicugna pacos), llamas (Lama glama), and, in the United Arab Emirates (UAE), from dromedary camels (Camelus dromedarius).78 Analysis of a French calf BCV strain revealed 99.1 per cent nucleotide similarity in the orf1ab gene with the dromedary camel strain (HKU23–23-362F) from the UAE.35 To date, the coronaviruses isolated and characterized from both enteric and respiratory infections of cattle and enteric infections of wild ruminants are genetically, 1 biologically and antigenically similar and comprise a single serotype of BCV,4, 13, 16, 28, 52, 56, 71, 72 although two to three subtypes or subclades of BCV have been identified.21, 28, 72 However, experimental inoculation of calves with these different BCV strains cross-protected against disease, but not virus shedding.17

Aetiology

Bovine coronavirus (BCV) belongs to the Betacoronavirus genus (clade A) of the family Coronaviridae, in the order Nidovirales.33, 36, 78 Bovine coronavirus is an enveloped, pleomorphic virus ranging in diameter from 65 to 210 nm, with a double layer of surface projections, the shorter projections (~11 nm) consisting of the haemagglutinin and the longer projections (~25 nm) comprising the spike (S) glycoprotein.8, 56, 58 (Figure 1) The BCV contains a single-stranded, positive sense RNA genome of 27 to 32 kb. The virus is composed of four major structural proteins, three of which are glycosylated, whereas the fourth, the nucleocapsid (N) protein (50 kDa) that surrounds the viral RNA, is not. The glycoproteins include the 25 kDa integral membrane (M) protein, the 190 kDa S protein, which is cleaved into 90 and 100 kDa subunits (S1 and S2), and the haemagglutinin esterase (HE), which is a disulphide-linked dimer of 120 to 140 kDa.8, 58 These last two proteins are responsible for the haemagglutination (HA) of BCV with chicken, mouse, rat and hamster erythrocytes.28, 29 The HA protein also acts as a receptor-destroying enzyme (RDE), serving as an esterase to reverse haemagglutination. 8, 58 Although some variability exists among BCV strains in patterns of HA or RDE activity with erythrocytes from different species, these differences are unrelated to the clinical origin (enteric versus respiratory) of the BCV strains.28, 29, 72

Both the S and HA proteins are involved in viral attachment to host cells and induce the formation of neutralizing antibodies to BCV.8, 29, 58 Monoclonal antibodies (MAbs) to the S or HA proteins of BCV prevent villous atrophy in vivo in intestinal loops of calves,12 suggesting that either or both proteins are important for inducing immunity to BCV.58

As in other enveloped viruses, BCV is sensitive to detergents and lipid solvents such as ether and chloroform.8, 56, 58 It is also inactivated by formalin (0,02 per cent at 37 °C for 24 hours) and heating (50 °C for 1 hour), but is relatively stable at pH 3,0.

To date only one serotype of BCV is recognized.4, 8, 56, 58 Some antigenic variability exists among BCV isolates as demonstrated using two-way virus neutralization (VN) or haemagglutination inhibition (HI) assays with polyclonal antibodies or MAbs to BCV,13, 16, 28, 29, 72 and two to three subtypes of BCV have been described.28, 72 This variability, however, is unrelated to the age of the infected animal (calf diarrhoea versus winter dysentery in adults) or to the clinical source of the isolate (enteric versus respiratory).28, 72 The BCV is antigenically and genetically related to the betacoronaviruses, clade A, which include murine hepatitis virus, human coronavirus OC43, porcine...

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