Field study using sentinel birds and ELISA for differentiating infected from vaccinated animals (DIVA) in chicken flocks vaccinated with inactivated avian influenza H5 vaccines

This study used unvaccinated sentinels plus Avian Influenza Virus (AIV) specific ELISA for differentiating infected from vaccinated animals (DIVA). Birds assessed were from 10 broiler flocks (F1-F10), three layer (F11-F13) and two breeder flocks (F14 and F15) vaccinated with inactivated whole virus H5 vaccines. These 'sentinels' were monitored for clinical signs, mortality and post-mortem (PM) lesions specific for HPAI H5 virus infection. Seroconversion was measured by HI assay and virologically monitored by real-time PCR testing. The AIV antibody ELISA kit (IDEXX AI AB kit) was evaluated as a possible DIVA tool in these chicken flocks by testing the vaccinated birds only.2. Three broiler flocks (F3, F6 and F7) and one layer flock (F11) were infected by highly pathogenic avian influenza virus (HPAIV) H5N1. This was observed by sudden deaths and high mortality with pathognomonic clinical signs and PM lesions which confirmed by molecular testing. Sentinel birds in H5N1 infected flocks showed positive HI titres ~3 ×log2 in the majority of tested birds while noninfected sentinels showed negative results.3. Broiler flocks exposed to H5N1 infection (F3, F6 and F7) showed positive ELISA titres (at least 75%), while, noninfected broiler flocks showed negative results. This indicated that, even without using sentinels, ELISA kits for AIV M and NP could be used as a DIVA tool. However, flocks vaccinated with H5 inactivated whole virus vaccines showed negative ELISA titres at 30 d old after single vaccination, while after booster dose(s), positive ELISA titres were observed.4. The trial demonstrated the unsuitability of ELISA kits for influenza A as DIVA tool in flocks vaccinated several times like layer and breeder flocks. However, sentinel birds could be considered as possible DIVA strategy for longer-lived birds, such as layer and breeder flocks.