Severe outbreak of bovine coronavirus infection in dairy cattle during the warmer season

Abstract

A severe outbreak of enteric and respiratory disease associated with bovine coronavirus (BCoV) infection is described. The outbreak occurred in a dairy herd of southern Italy in the first decade of September 2006, when summer temperatures were still recorded, affecting calves, heifers and adult cows, with a marked decrease in milk production. By virus isolation and RT-PCR targeting the S gene, BCoV was identified as the etiological agent of the outbreak, whereas bacteriological, parasitological and toxicological investigations failed to detect other causes of disease. BCoV strains with 99-100% nucleotide identity in the S gene were isolated from nasal, ocular and rectal swabs, thus proving the absence of separate clusters of virus on the basis of tissue tropism. Sequence analysis of the haemagglutination-esterase and spike proteins of the strain detected in one rectal sample (339/06) showed a high genetic relatedness with recent BCoV isolates (98-99% amino acid identity), with several unique amino acid substitutions in the S protein. The BCoV outbreak described in this paper presents interesting aspects: (i) the occurrence of a severe form of disease in the warmer season; (ii) the simultaneous presence of respiratory and enteric disease; (iii) the involvement of young as well as adult cattle.

Fig. 1

Cytopathic effect induced on HRT cells by a BCoV strain isolated from the outbreak.

Fig. 2

Neighbor-joining trees based on spike (a) and haemagglutinin-esterase (b) proteins of bovine coronaviruses. Accession numbers of the strains used for phylogeny are reported in Table 3. HCoV OC43 (accession number NC_005147) was used as outgroup. Bootstrap values were calculated and are indicated at each node. The scale bars represent 0.5 (a) or 1 (b) substitutions per 100 sequence positions.