Detection and subtyping (H5 and H7) of avian type A influenza virus by reverse transcription-PCR and PCR-ELISA.

Avian influenza virus infections are a major cause of morbidity and rapid identification of the virus has important clinical, economical and epidemiological implications. We have developed a one-tube Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) for the rapid diagnosis of avian influenza A. A panel of reference influenza strains from various hosts including avian species, human, swine and horse were evaluated in a one tube RT-PCR using primers designed for the amplification of a 218 bp fragment of the NP gene. The PCR products were detected by PCR-ELISA by use of an internal catching probe confirming the NP influenza A origin. The PCR-ELISA was about 100 times more sensitive than detection of PCR products by agarose gel electrophoresis. RT-PCR and detection by PCR-ELISA is comparable in sensitivity to virus propagation in eggs. We also designed primers for the detection of the influenza. A subtypes H5 and H7 shown to have pathogenic potential in poultry. The H5 primers cover the cleavage site of the HA gene and specifically amplify influenza A subtype H5. The H7 primers also cover the HA cleavage site and detected all H7 reference strains investigated. In addition, the H7 primers also amplified very weak and/or additional bands on an agarose gel from other subtypes. However, the H7 origin and the pathogenic potential defined by the presence or absence of basic amino acids at the cleavage site can be determined by sequencing of the PCR product. As far as we know this is the first demonstration of RT-PCR detection on a panel of H7 strains using only one primer set.