Development of Neuraminidase Inhibition test for subtyping avian influenza viruse Neuraminidase, in Razi Vaccine and Serum Research Institute

Detection and identification of influenza A viruses hemagglutinin is done with serological or molecular techniques and the neuraminidase (NA) subtyping is also necessary in purpose of epidemiological studies specially in H5 or H7 (highly pathogenic/ low pathogenic) outbreaks and/or endemic areas. Subtype Identification of NA usually is performed by molecular tests such as RT-PCR. Since 1971, WHO has suggested that the surface glycoprotein neuraminidase of avian influenza viruses could be divided in different subtypes serologically by Neuraminidase Inhibition test (NI). In reference or specialized laboratories like OIE licensed labs, NI test is running routinely. Considering the importance of this valuable test, an experimental study was conducted to develop the classic NI test according to OIE protocol. RT-PCR test with subtype-specific primers was used as a control for evaluation of test accuracy. According to our results, NI test can detect and distinguish various NA subtypes in serum or viral samples. In conclusion, the NI test is a practical tool in diagnostic and research trials, especially in differentiation of vaccinated from unvaccinated birds (DIVA) in endemic areas with vaccination strategy or in validated reference laboratories such as Razi Vaccine and Serum Research Institute.