[Response of guinea pigs to vaccination with parainfluenza virus 3]

An inactivated vaccine was prepared with Parainfluenza-3 virus strain LQ-514 and strains of Pasteurella hemolytica and P. multocida, suspended in oil adjuvant. The virus had been isolated from 30-60 day old calves during an epidemic of Pneumonia. The vaccine was tested in guinea pigs aged 1 to 2 months. The antibody response and the virus titres in organs after the challenge were the parameters studied. Hemagglutination inhibition antibodies were first detected 14 days after vaccination and reached maximum titres at day 28. The challenge was done at day 34, and a secondary antibody response was observed 72 hours later, which reached its peak the following day. Virus could be isolated from lung samples of control animals at day 3, 4 and 5 after infection. Moreover, viral antigens and particles were observed in the same samples by immunofluorescence and electron microscopy, respectively. In contrast, all three methods failed to demonstrate the presence of virus in organs of immunized guinea pigs after the challenge.