Longitudinal survey of swine influenza virus infection in a pig farm in Thailand, 2017-2018

Abstract

Swine influenza cause by influenza A virus, is the one of the most important zoonotic disease of pigs. Swine influenza virus (SIV) infection in pigs causes both economic loss in pig production and public health problem. SIVs subtypes H1N1, H1N2 and H3N2 cause respiratory disease in pigs worldwide. The objectives of this thesis were to determine the dynamic of swine influenza virus subtypes circulation in a pig farm in 2017-2018 and to monitor genetic diversity of swine influenza virus in a pig farm. During January 2017 to November 2018, the nasal swab samples (n=436) and blood samples (n=436) were collected from 4-10 weeks-old pigs from a pig farm. For influenza A virus detection, the nasal swabs were tested for influenza A virus by real-time RT-PCR. Our result showed that 38.76% (169/436) were positive and suspected for influenza A virus. Subsequently, 13.07% (57/436) could be isolated for influenza A virus. For serological test, 37.23% (140/436), 18.35% (69/436) and 27.13% (102/436) of pigs had antibodies against SIV-H3N2, SIV-H1N1 and pdmH1N1 viruses, respectively. For SIV characterization, 24 SIVs were characterized by whole genome sequencing using next-generation sequencing. Our result showed that SIVs can be subtyped as SIV-H1N1 (n=18) and SIV-H3N2 (n=6). The SIV-H1N1 can be classified into 2 genotypes,rH1N1 (pdm+2) and rH1N1 (pdm+1), and SIV-H3N2 can be classified into 1 genotype, rH3N2 (pdm+2). Genotype rH1N1 (pdm+2) contained HA and NA genes from endemic Thai SIV-H1N1, and internal genes from pandemic H1N1-2009. Genotype rH1N1 (pdm+1) contained HA gene from endemic H1N1, while NA and internal genes from pandemic H1N1-2009. Genotype rH3N2 (pdm+2) contained HA and NA genes from human-like swine from endemic Thai-SIV and the internal genes from pandemic H1N1-2009. It is noted that genotype rH1N1 (pdm+1) is the novel genotype which never been reported in Thailand. While the rH1N1 (pdm+2) and rH3N3 (pdm+2) were previously observed in Thailand. The results of genetic analysis showed that SIVs in this thesis possessed most human-like characteristics and some avian-like characteristics. Base on our result, it could be speculated that pandemic H1N1-2009 was circulating in a pig farm for a period of time, Thus, zoonotic and reverse zoonotic infection between workers and pigs in the pig farm is common. Thus, monitoring of SIVs in pigs and workers is important and should be routinely conducted. Good practice and management in pig farm including personal hygiene and personal protective equipment (PPE) should be practiced and used in the farm for prevention and control of influenza virus transmission in pigs and humans.