In Thailand, pathogenesis of SIV subtype H1N1 and H3N2 infection in swine has never been studied. Since
different subtypes of the influenza type A viruses isolated from pigs are found to cause different pathogenic levels in
pigs, the objective of this study is to investigate the pathogenesis of SIV (Thai isolates) subtype H1N1 (A/swine/
Thailand/HF6/05) and H3N2 (A/swine/Thailand/S1/05) in weanling SPF pigs. Genetic characterization of the HA gene of both studied viruses were also performed in this report. The results of this study may assist in the prevention and control of SIV infection in Thailand, especially for H1N1 and H3N2 subtypes. Based on the percentages of cranioventral
pneumonic lesion and times of virus shedding, the H1N1 virus might play a major role in respiratory diseases
in weanling pigs in that farm. More works are needed in the co-infection model with other respiratory pathogens
and in the prevention and control of the SIV-related diseases in Thailand. In this study, investigations on virus
transmissibility between sentinel animals housing together with infected animals were not performed. Therefore, whether these Thai H1N1 and H3N2 subtypes will be transmitted efficiently in the field situation requires further experimental and epidemiologic studies.

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