Immunofluorescence in the serological diagnosis of parainfluenza type 3 and respiratory syncytial virus infection in calves.

The fluorescent antibody (FA) test is compared with the haemagglutination inhibition (HI) test for parainfluenza virus type 3 (PI-3) and virus neutralisation (VN) test for respiratory syncytial (RS) virus for detection and titration of virus-specific antibodies. In experimentally inoculated calves PI-3 and RS virus FA tests detected seroconversion at the same time as HI and VN tests, however, in serially diluted sera, the FA test was positive to higher dilution. In studies with paired samples from calves from four farms with respiratory problems, the FA test gave similar results to PI-3 HI and RS virus VN tests. Large increases in antibody titre to RS virus detected by FA and VN tests indicated this was the problem on two of the farms. Individual animals showed large rises to PI-3 by FA and HI test on three farms. It is concluded that the FA test provides a rapid and sensitive alternative to the more conventional serological tests for respiratory viruses.