Swine influenza viruses in Northern Vietnam in 2013–2014

Abstract

Swine are an important intermediate host for emergence of pandemic influenza. Vietnam is the largest swine producer in South East Asia. Systematic virological and serological surveillance of swine influenza viruses was carried out in Northern Vietnam from May 2013 to June 2014 with monthly sampling of pigs in local and large collective slaughterhouses and in a live pig market. Influenza A seroprevalence in the local slaughterhouses and in the large collective slaughterhouse was 48.7% and 29.1%, respectively. Seventy-seven influenza A viruses were isolated, all from the large collective slaughterhouse. Genetic analysis revealed six virus genotypes including H1N1 2009 pandemic (H1N1pdm09) viruses, H1N2 with H1 of human origin, H3N2 and H1N1pdm09 reassortants, and triple-reassortant H3N2 viruses. Phylogenetic analysis of swine and human H1N1pdm09 viruses showed evidence of repeated spill-over from humans to swine rather than the establishment of H1N1pdm09 as long-term distinct lineage in swine. Surveillance at the large collective slaughterhouse proved to be the most efficient, cost-effective, and sustainable method of surveillance for swine influenza viruses in Vietnam.

Surveillance of swine influenza viruses in sentinel familial farms in Hung Yen province in Northern Vietnam in 2013–2014

“…Data on the swine industry in these areas were obtained by interviewing staff at the Department of Agriculture in Van Giang and Van Lam districts. Surveillance of SIV in slaughterhouses and a weaner market in Hanoi and Hung Yen province was carried out at the same time, and the findings have been reported elsewhere (Baudon et al, , ) (Figure ). In each commune, one large (≥10 sows) and one small (<10 sows) farrow‐to‐finish family‐run farms were selected for one production cycle.…”

“…The infecting virus was clearly H1N1/pdm in litters du1 and du4 but there was antibody to both H1N1/pdm and H1N1/EA in litter Du5. The latter results were likely due to cross‐reactivity between the H1 viruses, since no evidence of H1N1/EA lineage viruses has been reported in Vietnam (Baudon et al, ). Thus, it is likely that litter Du5 was also infected with H1N1/pdm.…”

“…Laboratory analyses have been previously described in detail (Baudon et al, ). In brief, virus isolation from nasal swabs was performed by inoculation onto Madin Darby Canine Kidney (MDCK) cells grown in minimum essential medium with trypsin (2 µg/ml) in 24‐well tissue culture plates.…”

“…When CPE or hemagglutinin activity was observed, the result was confirmed by testing with a rapid antigen detection test DirectigenTM EZ, Flu A + B (Becton, Dickinson and Company). Any positive isolates would be stored at −80°C and have sequencing of the virus hemagglutinin carried out for virus subtyping as previously described (Baudon et al, ).…”

“…In contrast, there has been less surveillance of SIV in Vietnam, the second largest pig producer in the region after China (FAO, ; Takemae et al, ). In parallel with surveillance of SIV in abattoirs (Baudon et al, , ), we implemented a study in family‐run swine farms in North Vietnam. The main objectives of these studies were to improve our knowledge of SIV epizootiology in the smallholder swine husbandry sector in Northern Vietnam and to compare swine influenza virus (SIV) lineages circulating in this sector with those found at the central abattoirs.…”