Evaluation of a commercial ELISA kit (IDEXX) to differentiate AI virus-infected poultry from AI-vaccinated poultry (DIVA)

Vaccination programs for the control of avian influenza (AI) in poultry have limitations due to the problem of differentiating between vaccinated and virus-infected birds. The use of AI vaccination in poultry would have greater worldwide acceptance if reliable tests that clearly discriminated between naturally infected and vaccinated-only animals (DIVA) were available. In this study, to differentiate avian influenza virus (AIV)-infected chickens vs. chickens immunized with inactivated avian influenza virus, a commercial ELISA Kit (IDEXX) was used. Using HI as the reference method, the sensitivity of the commercial ELISA kit was 100% and its specificity was 100%. In the present study, we demonstrated that, 3 weeks after infection or vaccination, sera from both infected and vaccinated groups were tested positive and the difference in mean optical density between vaccinated and challenged birds, as detected by a commercial ELISA kit (IDEXX), was very small. Therefore, this assay cannot distinguish infected from vaccinated poultry.(AU)

Isolation and characterization of an H9N2 influenza virus isolated in Argentina.

As part of our ongoing efforts on animal influenza surveillance in Argentina, an H9N2 virus was isolated from a wild aquatic bird (Netta peposaca), A/rosy-billed pochard/Argentina/CIP051-559/2007 (H9N2) - herein referred to as 559/H9N2. Due to the important role that H9N2 viruses play in the ecology of influenza in nature, the 559/H9N2 isolate was characterized molecularly and biologically. Phylogenetic analysis of the HA gene revealed that the 559/H9N2 virus maintained an independent evolutionary pathway and shared a sister-group relationship with North American viruses, suggesting a common ancestor. The rest of the genome segments clustered with viruses from South America. Experimental inoculation of the 559/H9N2 in chickens and quail revealed efficient replication and transmission only in quail. Our results add to the notion of the unique evolutionary trend of avian influenza viruses in South America. Our study increases our understanding of H9N2 viruses in nature and emphasizes the importance of expanding animal influenza surveillance efforts to better define the ecology of influenza viruses at a global scale.