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Swine influenza virus infection in different age groups of pigs in farrow-to-finish farms in Thailand

Nobuhiro Takemae12, Sujira Parchariyanon3, Ruttapong Ruttanapumma3, Yasuaki Hiromoto12, Tsuyoshi Hayashi12, Yuko Uchida12 and Takehiko Saito12*

Author Affiliations

1 Thailand-Japan Zoonotic Diseases Collaboration Center, Kasetklang, Chatuchak, Bangkok 10900, Thailand

2 Research Team for Zoonotic Diseases, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan

3 National Institute of Animal Health, Kasetklang, Chatuchak, Bangkok, 10900, Thailand

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Virology Journal 2011, 8:537  doi:10.1186/1743-422X-8-537

Published: 14 December 2011

Abstract

Background

Understanding swine influenza virus (SIV) ecology has become more and more important from both the pig industry and public health points of views. However, the mechanism whereby SIV occurs in pig farms is not well understood. The purpose of this study was to develop a proper strategy for SIV surveillance.

Findings

We conducted longitudinal monitoring in 6 farrow-to-finish farms in the central region of Thailand from 2008 to 2009. Nasal swabs and serum samples were collected periodically from clinically healthy pigs consisting of sows, fattening pigs, weaned piglets and pigs transferred from other farms. A total of 731 nasal swabs were subjected to virus isolation and 641 serum samples were subjected to detection of SIV antibodies against H1 and H3 subtypes using the hemagglutination inhibition test and ELISA. Twelve SIVs were isolated in this study and eleven were from piglets aged 4 and 8 weeks. Phylogenetical analysis revealed that SIVs isolated from different farms shared a common ancestor. Antibodies against SIVs were detected in fattening pigs on farms with no SIV isolation in the respective periods studied. These observations suggested that piglets aged 8 weeks or younger could be a main target for SIV isolation. Farm-to-farm transmission was suggested for farms where pigs from other farms are introduced periodically. In addition, antibodies against SIVs detected in fattening pigs could be a marker for SIV infection in a farm.

Conclusions

The present study provided important information on SIV surveillance that will enable better understanding of SIV ecology in farrow-to-finish farms.

Keywords:
Influenza virus; Pig; Surveillance; Farrow-to-finish pig farm