Aroonprasert D, Fagerland J A, Kelso N E, Zheng S, Woode G N
College of Veterinary Medicine, Texas A&M University, College Station 77843-4467.
Vet Microbiol. 1989 Feb;19(2):113-25. doi: 10.1016/0378-1135(89)90077-1.
Bovine astrovirus serotype 2 (US2) was adapted to primary neonatal kidney cell (NBK) cultures by the addition of 50 micrograms ml-1 of trypsin in the medium. Infectious virus was released from the cells within 7 days post-infection in early passages and within 3 days in later passages. In the absence of trypsin, neither passage of infected cells nor release of infectious virus occurred. The virus was shown to be similar to the fecal astrovirus by a neutralization test and by ultrastructural studies of infected cells. Primary embryo bovine kidney (EBK) and NBK cell cultures supported infection with both fecal and tissue culture adapted (TCA) astrovirus. The time-related development of infection, as studied by immunofluorescence, was similar for both fecal and TCA astrovirus and for both cell culture types. The first indication of viral infection and expression of viral antigens occurred at 7 h post-infection and was characterized by the appearance of a diffuse faint immunofluorescence (IF) of the cytoplasm. Soon after, two or three brilliant IF granules were observed in the nucleus, which appeared to involve the nucleoli. Subsequently, dense granular IF was seen in the perinuclear region of the cytoplasm, which later extended to involve all the cytoplasmic area. In both EBK and NBK cultures infected with either fecal or tissue culture adapted astrovirus, only a minority of cells became infected, even when the multiplicity of infection exceeded one. Occasionally 10-20% of cells were infected, but in most cultures the proportion did not exceed 2% and in NBK cultures, from 3/9 calves, no infected cells were observed. The virus did not infect bovine cell lines. Infectivity of the virus was not removed by treatment with chloroform, and iododeoxyuridine and actinomycin D when added to the medium, did not block replication. Masses of virions were observed by electron microscopy in discrete areas in the cytoplasm, with similar distributions as the viral antigen foci as seen by IF. The mean diameter of the virions was 34 nm. In conclusion, bovine astrovirus lacks both essential lipids and an envelope, probably has an RNA genome, may have a nuclear phase of replication involving the nucleoli which is not blocked by DNA inhibitors, and has a selective cell tropism.
牛星状病毒2型（US2）通过在培养基中添加50微克/毫升的胰蛋白酶适应原代新生牛肾细胞（NBK）培养。在早期传代中，感染后7天内细胞释放出感染性病毒，后期传代中在3天内释放。在没有胰蛋白酶的情况下，感染细胞既不传代也不释放感染性病毒。通过中和试验和对感染细胞的超微结构研究表明，该病毒与粪便星状病毒相似。原代牛胚胎肾（EBK）和NBK细胞培养物支持粪便型和组织培养适应型（TCA）星状病毒的感染。通过免疫荧光研究，粪便型和TCA星状病毒以及两种细胞培养类型的感染时间相关发展相似。病毒感染和病毒抗原表达的第一个迹象出现在感染后7小时，其特征是细胞质出现弥漫性微弱免疫荧光（IF）。此后不久，在细胞核中观察到两三个明亮的IF颗粒，似乎涉及核仁。随后，在细胞质的核周区域看到密集的颗粒状IF，随后扩展到整个细胞质区域。在感染粪便型或组织培养适应型星状病毒的EBK和NBK培养物中，即使感染复数超过1，也只有少数细胞被感染。偶尔有10 - 20%的细胞被感染，但在大多数培养物中，这一比例不超过2%，在来自3/9头小牛的NBK培养物中，未观察到感染细胞。该病毒不感染牛细胞系。用氯仿处理不能去除病毒的感染性，向培养基中添加碘脱氧尿苷和放线菌素D也不阻断复制。通过电子显微镜在细胞质的离散区域观察到大量病毒粒子，其分布与IF所见的病毒抗原灶相似。病毒粒子的平均直径为34纳米。总之，牛星状病毒既缺乏必需脂质也没有包膜，可能具有RNA基因组，可能有涉及核仁的核复制阶段，该阶段不受DNA抑制剂的阻断，并且具有选择性细胞嗜性。
