Detection of West Nile virus in the tissues of specific pathogen free chickens and serological response to laboratory infection: a comparative study.

Using an isolate of West Nile virus (WNV) from lineage 1 (Goose/Israel 1998), groups of specific pathogen free chickens were experimentally infected via the subcutaneous or intravenous routes. To evaluate the relative efficiency of detecting the virus in the infected chickens, samples from a range of tissues and organs were examined by virus isolation tests in tissue culture, including Vero, primary chicken embryo liver and fibroblast cells, and polymerase chain reaction (PCR) analyses. Additionally, in order to investigate the serological response of the chickens and produce WNV monospecific antibodies, serum samples were collected from the birds during the trial and analysed for antibodies by virus neutralization (VN) and the plaque-reduction neutralization test (PRNT). No clinical signs or gross pathological changes were seen in any of the inoculated chickens throughout the study. The nested PCR used in the study appeared to be significantly more sensitive at detecting the presence of the virus in both the tissues and the inoculated Vero cell cultures compared with the detection of gross cytopathic changes as observed in infected Vero cell culture. No cytopathic changes were seen in the inoculated avian cell cultures. Following primary inoculation of the chickens there was a weak antibody response 15 days post-inoculation. However, following re-inoculation with inactivated WNV and adjuvant there was a substantial increase in the neutralizing antibody titres when tested 2 weeks later. The results obtained suggested that the PRNT was more sensitive than the conventional VN test. Based on detection of virus and serology there was no evidence of viral transmission to the close contact controls. It can be concluded that the PCR used in this study was more sensitive than virus isolation for the detection of WNV while the PRNT also appeared more sensitive than the conventional VN test.