Avian influenza is a viral infection which affects mainly the respiratory system of birds. The H7N3 subtype influenza viruses were isolated for the first time in 1994 from breeder flock in northern areas of Pakistan. A second wave of avian influenza outbreak was detected in 1999. The causative agent of this outbreak was H9N2. The H9N2 considered as low pathogenic avian influenza (LPAI) virus and continuously circulating in poultry flocks causing enormous economic losses to poultry industry of Pakistan. This showed that avian influenza viruses are present in commercial poultry. Most of the efforts to isolate avian influenza A viruses are from commercial poultry and these isolations are outbreak based. That is why we have mad’ an effon to isolate and identify H9 subtype avian influenza viruses from apparently healthy live desi and zoo birds (Lahore, Pakistan). We have successfully isolate H9 subtype influenza viruses from these birds during our study.
As these viruses have RNA genome and their RNA polymerase enzyme lacks proof reading activity which resulted in spontaneous mutation in surface glycoproteins (HA and NA) and reassortment of their genomic segments results in escape from host immune response produced by the vaccine. This is the reason that
every year we require a new candidate virus for vaccine preparation. We have made
an effort to isolate and identify avian influenza viruses from live desi and zoo birds of
Lahore and performed antigenic characterization. In this way, we have been able to
know the exact status of avian influenza virus strains present in the desi and zoo birds.
We also have seen that the imported vaccine have less interaction with the local strains and gives less protective titer although it gives best titers when we raise antisera against imported vaccine. The local vaccines although gives a little bit less titer when we raise the antisera against these vaccines but their antisera have more interaction with the local H9 subtype antigen so it gives better protective immune response. By this study we have seen that antisera obtained from infected chicken give more antibody titer as compare to antibody raised in the rabbits. Infected chicken antisera are more reactive as compare to rabbit antisera. This shows that our isolates have highest similarity with the currently circulating viruses.
All above results helped us to devise a new control strategy against avian influenza viral infections present in these local birds. The antigenic characterization of these avian influenza isolates helped us to see the antigenic differences between the isolates of this study and H9 subtype avian influenza viruses used in vaccines. Therefore, this study clearly suggests that a new local H9 subtype avian influenza virus should be used as vaccinal candidate every year for the effective control of influenza viral infections of poultry.