Thesis (Ph.D.)--Chulalongkorn University, 2008

Severe respiratory illness can be caused by several factors. The important factor is viral infection especially influenza A virus infection. Influenza A virus can cause severe respiratory illness in every age which makes patient has high fever, cough, sneeze including pneumonia particulary in children or elderly people. In this thesis, the molecular genetics of influenza A virus in Thailand were studied. There were influenza A virus subtype H1N1, H1N2, H3N2 and also H5N1 which spread among avian species in Thailand since 2004 and cross species to infect human. The studies consisted of firstly, the H5N1 influenza virus from human plasma was isolated and proved that the virus can replicate in the cell culture experiment. Secondly, Oseltamivir resistant detection of H5N1 influenza virus was designed using 2 specific TaqMan probes. This method can detect the mixture of both wild type and oseltamivir resistant virus which could be the advantage for monitoring the change of virus in patient during Oseltamivir treatment. Thirdly, the 2 distinct genotypes, genotype Z and V H5N1 influenza virus spreading in Thailand were identified and characterized which showed the difference in the sensitivity of Amantadine drug. Fourthly, influenza A virus, H1N1 and H3N2, infants and children who admitted to Chulalongkorn memorial hospital since 2006-2007 were detected. The sequences of HA and NA gene were characterized for comparing the receptor binding and antigenic site of each subtype. In addition, they were compared with H1N1 and H3N2 vaccine strain from Northern hemisphere 2007-2008, the finding showed the isolated subtypes were not different from vaccine strain. As a final, subtypes of swine influenza virus were isolated. Three subtypes, H1N1, H1N2 and H3N2, are described. Phylogenetic analysis of the SIV hemagglutinin and neuraminidase genes shows individual clusters with swine, human or avian influenza virus at various global locations.