Niigata Chuo Livestock Hygiene Service Center, Hataya 686, Nishikan, Niigata, Niigata 9590423, Japan.
Arch Virol. 2012 Mar;157(3):423-31. doi: 10.1007/s00705-011-1183-9. Epub 2011 Dec 14.
Bovine torovirus (BToV) is recognized as an enteric pathogen of calves, but its etiological role in diarrhea and epidemiological characterization in adult cows remain unclear. In 2007-2008, three outbreaks of epidemic diarrhea occurred in adult cows at three dairy farms in Niigata Prefecture, Japan. BToV was the only enteric pathogen detected in these outbreaks, as determined by electron microscopy, reverse transcription-PCR, bacteria and parasite tests of fecal samples, and antibody tests with paired sera. The epidemiological features of the three outbreaks were similar to those of bovine coronavirus infection, except for the absence of bloody diarrhea, with diarrhea spreading among most adult cows, but not in calves, within several days and diarrhea lasting for 3-5 days with anorexia. Decreased milk production and mild respiratory symptoms were also observed in two of the outbreaks. Nucleotide sequence analysis of the BToV nucleocapsid, spike, and hemagglutinin-esterase (HE) genes revealed a close relatedness among the detected BToV strains from each outbreak and those of Japanese BToV strain Aichi/2004. Furthermore, we isolated a BToV strain, designated Niigata (TC), from a fecal sample using a human rectal tumor cell line. Sequence analysis of this isolate and Aichi/2004 indicated that both strains have truncated HE genes with deletions in the 3' region that occurred through cell culture-adaptation. The short projections that are believed to be formed by the HE protein on virus particles were not observed in these cultured strains by electron microscopy. Taken together, these results suggest that BToV causes epidemic diarrhea in adult cows and should be included in the differential diagnosis of diarrhea in adult cows. In addition, our findings indicate that the HE protein of BToV may not be necessary for viral replication.
牛传染性冠状病毒（BToV）被认为是犊牛的一种肠道病原体，但它在成年牛腹泻中的病因作用及其流行病学特征尚不清楚。2007-2008 年，日本新泻县三个奶牛场的成年奶牛发生了三次流行性腹泻暴发。通过电镜检查、逆转录-PCR、粪便细菌和寄生虫检测以及配对血清抗体检测，确定这些暴发中唯一的肠道病原体是 BToV。这三次暴发的流行病学特征与牛冠状病毒感染相似，只是没有血性腹泻，大多数成年奶牛在几天内腹泻，3-5 天内出现厌食、腹泻持续时间长，而犊牛不受影响。其中两次暴发还观察到产奶量减少和轻度呼吸症状。对从每个暴发中检测到的 BToV 毒株的核衣壳、刺突和血凝素-酯酶（HE）基因的核苷酸序列分析表明，所检测到的 BToV 株与日本 Aichi/2004 株密切相关。此外，我们还从粪便样本中使用人直肠肿瘤细胞系分离到一株 BToV 株，命名为 Niigata（TC）。该分离株与 Aichi/2004 的序列分析表明，两株均具有 3'区缺失的截短 HE 基因，这是通过细胞培养适应而发生的。电镜观察到，在这些培养的菌株中，病毒颗粒上由 HE 蛋白形成的短突起没有观察到。综上所述，这些结果表明 BToV 可引起成年奶牛流行性腹泻，应纳入成年奶牛腹泻的鉴别诊断。此外，我们的研究结果表明，BToV 的 HE 蛋白可能不是病毒复制所必需的。
