Date of Award
Doctor of Philosophy (PhD)
Veterinary Medical Sciences - Pathobiological Sciences
A total of 411 G clone cell-dependent virus strains recently were isolated from nasal, trachea and lung samples in etiological investigations of acute respiratory tract diseases of vaccinated cattle, including shipping fever pneumonia. The virus infectivity titers reached up to 1.2 x 10 7 plaque forming units per gram of lung tissues of fatal cases. These viral agents were isolated in the 1st G clone cell passage without trypsin enhancement, and induced cell fusion. They have a restricted hemagglutination pattern, agglutinating only rat and mouse erythrocytes. Majority of them has receptor-destroying enzyme activities. They are round and enveloped with a diameter of 80 nm. Based on these features and the site of infections, these virus isolates were identified as respiratory bovine coronaviruses (RBCV). The RBCV were previously not recognized to be associated with acute respiratory tract diseases of cattle. Tests on serum samples from RBCV-positive cattle during a shipping fever epizootic revealed characteristic primary immune responses with specific antibodies to hemagglutinin-esterase and spike. The RBCV-positive cattle that died had only IgM responses to RBCV infections. High level of opsonic and virus-neutralizing IgG2 apparently protected cattle from RBCV infections and respiratory tract disease. These cattle entered this experiment with high antibodies against hemagglutinin-esterase and spike. The G clone cells had maximal susceptibility to RBCV infections from apical domains. Asymmetric release of RBCV occurred through the apical surfaces of the cells. The RBCV-induced polykaryons had intact plasma membranes and degenerated nuclei and resulted from expression of spike on cytoplasmic membrane and RBCV replication, indicating fusion from within. The purified RBCV particles showed higher acetylesterase activity at 37°C than at 39°C, while the purified enteropathogenic BCV (EBCV) particles retained full acetylesterase activity at both 37°C and 39°C. Transiently expressed hemagglutinin-esterase of RBCV exhibited a drastic reduction in acetylesterase activity after 40 min at 37°C while the acetylesterase activity of the transiently expressed hemagglutinin-esterase of EBCV remained stable beyond the 40 min threshold. The deduced amino acid sequences of hemagglutinin-esterase specified by RBCV strains contained specific amino acid changes in comparison to the wild-type EBCV strain, which may be responsible for the observed enzymatic differences.
Lin, Xiaoqing, "Isolation and Characterization of Newly Emerging Coronaviruses in Acute Respiratory Tract Diseases of Cattle." (2000). LSU Historical Dissertations and Theses. 7207.