Interaction between genomes of infectious bronchitis and Newcastle disease viruses studied by reverse transcription-polymerase chain reaction.

Reverse transcription-polymerase chain reaction (RT-PCR) with specific primers for the S1 gene of IBV and for the fusion protein cleavage site of NDV was used for detection of Infectious bronchitis virus (IBV, the family Coronaviridae) and Newcastle disease virus (NDV) genomes. The sensitivity of IBV and NDV RT-PCR was 10(3.7) and 10(3.0) EID50, respectively. Although a multiplex RT-PCR could detect and differentiate NDV and IBV genomes present in the same sample, there was a slight inhibition of the IBV PCR if a high amount of NDV genome was present in the sample. To overcome this problem a separate PCR for each virus was used to assess the interaction between vaccine IBV and NDV either inoculated singly or together into chickens. In the group vaccinated with the Newcastle disease (ND) vaccine alone, the viral genome was detected on days 2, 4 and 7 post vaccination (p.v.), while in the chickens given the infectious bronchitis (IB) vaccine alone, the viral genome was detected only on day 4 p.v. In the group inoculated with both vaccine viruses there was a 10(3)-fold reduction in the cDNA dilution factor on day 4 p.v. for both IBV and NDV genomes. This demonstrated clearly that when both these vaccines are administered there is a transient reduction in the replication of both viruses, probably due to their competition for the same target epithelial cells in the respiratory tract.