Factors affecting isolation and propagation of bovine coronavirus in human rectal tumor-18 cell line.

Abstract

Bovine coronavirus (BCV) is an important cause of calf enterocolitis and respiratory disease. It is the second major cause of viral diarrhea in calves, with rotavirus being the first. At the Wisconsin Animal Health Laboratory during 1993-1994, BCV was detected in 93 cases of calf scours out of 1,058 bovine fecal samples examined by direct electron microscopy. Electron microscopy is used commonly for the diagnosis of enteric viruses, including BCV. The advantages of electron microscopy are that diagnosis can be made rapidly and multiple pathogens, a common feature in enteritis, can be detected simultaneously. Using electron microscopy, more than a dozen novel enteric viruses have been described in the last 2 decades. However, electron microscopy has some limitations; approximately 1 million viral particles should be present to detect a virus by electron microscopy. Thus, it lacks sensitivity and can lead to false-negative results. In addition, some viruses, especially coronaviruses, can be confused morphologically with nonviral particles such as intestinal brush border epithelium and with other morphologically similar viruses, leading to false-positive results. Virus isolation is not commonly used for the diagnosis of BCV. However, 1 advantage is that the virus propagated in cell culture can be used for further antigenic and genomic characterization. To improve BCV isolation from clinical samples, factors affecting its isolation and propagation in human rectal tumor18 (HRT18) cell line were investigated. In a previous study, 10 HRT-18 was found to be a suitable cell line for BCV isolation. In this study, BCV propagated in vitro showed a change in hemagglutination pattern from that of the BCV from the original clinical samples. It is not known if this change correlates with changes in antigenicity and immunogenicity of the virus. HRT-18 and human colon tumor-8 (HCT-8) cells are derived from adenocarcinomas of human rectum and colon, respectively. 16 The 51 samples included in this study were provided by the Wisconsin Animal Health Laboratory (WAHL), Madison (n = 27), the California Veterinary Diagnostic Laboratory (CVDL), San Bernardino (n = 6), and another diagnostic laboratory (referred to as VDL for confidentiality) (n = 18). Samples were obtained as 20% fecal suspensions in phosphate-buffered saline (PBS) (pH 7.2), as