S-91. The role for PCR in Influenza virus detection and surveillance

The Influenza virus is a RNA virus and its genome consists of 8 segments. It is an enveloped virus with haemagglutinin and neuraminidase spikes. There are 3 types namely A, B, and C based on RNP, of which type A undergoes antigenic shift and drift, type B undergoes antigenic drift only but type C is relatively stable. Influenza A virus undergoes antigenic shifts and antigenic drifts with the haemagglutinin and neuraminidase proteins and it is the antigenic shifts of the haemagglutinin that results in pandemics whereas antigenic drifts in the H and N proteins result in epidemics. Influenza A virus subtype H5N1, also known as A (H5N1) or simply H5N1, is a subtype of the Influenza A virus which can cause illness in humans and many other animal species. A bird-adapted strain of H5N1, called HPAI A(H5N1) for “highly pathogenic avian influenza virus of type A of subtype H5N1”, is the causative agent of H5N1 flu, commonly known as “avian influenza” or “bird flu”. It is endemic in many bird populations, especially in Southeast Asia. One strain of HPAI A(H5N1) is spreading globally after first appearing in Asia. It is epizootic (an epidemic in nonhumans) and panzootic (affecting animals of many species, especially over a wide area), killing tens of millions of birds. The laboratory diagnosis can be achieved today by number of means: 1.Detection of Antigen - a rapid diagnosis can be made by the detection of influenza antigen from nasopharyngeal aspirates and throat washings by IFT and ELISA. 2. Virus Isolation - virus may be readily isolated from nasopharyngeal aspirates and throat swabs in MDCK cell line usually within 5 days of inoculation (a second passage may be necessary for some wild strains). Serology achieves a retrospective diagnosis, the CFT & HAI are useful but for detection the latter is most widely used. EIA may be used for type-specific antibody detection. This information is useful for epidemiological purposes. In recent years there is an emphasis on developing conventional and real-time PCR for influenza A virus especially the avian virus. It is shown to be considerably more rapid and sensitive than cell culture. The primers are for gene sequences of the matrix, haemagglutinin or neuraminidase proteins. This talk will emphasize on this aspect of influenza diagnosis and surveillance.