Interaction between a live avian pneumovirus vaccine and two different Newcastle disease virus vaccines in broiler chickens with maternal antibodies to Newcastle disease virus

Overview & Synopsis

Broiler chicks with maternal antibodies to Newcastle disease virus (NDV) but none to avian pneumovirus (APV) were divided into six groups. One group was kept as an unvaccinated control group. Three of the other groups were vaccinated at one-day old with live APV vaccine or one of two live NDV vaccines (VG/GA or HB1). The remaining two groups received the APV vaccine in combination with either of the two NDV vaccines at one day old. At intervals after vaccination for up to 42 days, distribution of the viruses in the tissues was monitored, together with humoral antibody responses. Few NDV isolations were made from any NDV-vaccinated chicks probably due to the presence of NDV-maternal antibodies. In both dual vaccinated groups, APV persisted longer [up to 21 days post vaccination (d.p.v.)] than in the single vaccinates (up to 14 d.p.v.). After 14 d.p.v., antibody titres against APV in both dual vaccinated groups remained higher than the single APV vaccinates. For NDV haemagglutination inhibition (HI) antibodies, similar titres were found in the single and dual NDV VG/GA vaccinates. However, for chickens dually vaccinated with NDV HB1 and APV, HI titres were significantly higher at 21 and 28 d.p.v. than the single HB1 vaccinates. These differences reflect that the NDV HI titres may depend on the NDV vaccines used.