Studies on viral infections of the respiratory tract in cattle

Abstract

A severe respiratory tract infection of cattle characterized by respiratory and nervous symptoms occurred in the Edinburgh area in the period Mid -December 1966 to January 1967. During the early phase of the outbreak, nine viral isolates were recovered from post mortem material at the Veterinary Investigation Centre, Edinburgh. These included isolates from the brain, frontal sinus and trachea. Four further isolates from the nasal passages were made from cattle during this time at the farm.

1. Virus was isolated from two of four convalescing animals ( 7F42 and 7F73 ) brought to the institute for neuropathological examination. Isolations of virus were made exclusively from the respiratory passages of these two animals.

2. Three of the isolates, 02/66 a neurogenic strain and two respiratory strains C1/66 and 7F73/1 recovered from animals involved in this outbreak were characterized. They were lipid sensitive, acid labile and showed enhanced inactivation to heat at 500C for 1 hour in the presence of 1M MgCl2. The structure of the virus particles was similar to the virion of herpes simplex and IBR virus. The three isolates produced a similar cytopathic effect in calf kidney cells consisting of rounding of cells and intranuclear inclusions. Antigenically they were similar to the Oxford strain of IBR. virus. It was concluded that the Edinburgh strains were strains of IBR virus.

3. Paired serum samples and single serum samples collected from cattle in the affected farm were assayed for IBR neutralizing antibody, by tube neutralization and plaque neutralization methods.

a) Neutralizing antibody titres were low < 1:4 to 1:13.3 when tested by the conventional tube neutralization method. b) No significant rises of antibody were observed in the paired serum samples tested.

4. Neutralizing antibody in three of the same paired serum samples and 3 single serum samples were examined by the plaque neutralization method. It was found that: a) This method was more sensitive for detecting neutralizing antibody to this virus. b) A slowly rising antibody was observed in 1 paired serum sample.