PARTNER FEATURE ▶▶▶
Influenza and its presence in European pig herds
European domestic pig populations appear to be an emerging reservoir of potentially zoonotic influenza A viruses. Recently, a study was published to support this theory. What exactly does that discovery mean and how can it influence vaccination programmes?
BY PROF TIMM HARDER* S 100 75 50
wine influenza virus (SIV) infections appear to be widespread in European domestic swine popula- tions. In a recent study by German, British, Finnish and American scientists, published in the peer-re-
viewed journal Cell Host & Microbe, a high incidence of infec- tion was evident in pigs with respiratory disease. The virus apparently acts as a component of a mixture of different co-pathogens. The study was designed as a passive surveil- lance driven by sample submissions from holdings affected by respiratory problems. Hence, the results were not meant to be representative.
Prevalence in the EU pig population Up to 50% of holdings with respiratory problems housed pigs with SIV infections, and up to 30% of individual pigs showing
Figure 1 - Proportional distribution of haemagglutinin (HA) over were detected.
H1av H1hu H1pdm H3
respiratory clinical signs tested positive for the virus. In total, four main lineages of SIV were identified: H1avN1av, H1huN2, H3N2, H1pdmN1pdm. Their prevalence differed widely between regions and countries in Europe. In addition, eight further subtype reassortants of these strains were iden- tified at different, usually lower, frequency. Often those reas- sortants have a local origin (e.g. H1pdmN2 in northwestern Germany; H1avN2 in Denmark, etc.) and a few show spread- ing tendencies. There was a dynamic fluctuation over time of the composition of circulating SIV in a country. The frequency of these strains varied between different coun- tries. Often, they shared 5–15% of the total SIV load in a country. H1pdm-like strains were detected at higher frequen- cy in the UK and Ireland compared to on the continent. In the research, up to four major SIV lineages showed up in farms. Some farms had a single prevailing strain of SIV, but there were also holdings from which different lineages were isolated consecutively over time. In few farms, the simultane- ous presence of two or three of the major lineages was evident.
In total 31 different genotypes The study described 31 distinct genotypes. The majority origi- nated from reassortment events between older SIV lineages and the human pandemic H1N1 virus introduced to the swine population in 2009. Similar increasing reassortment ac- tivity has also been observed in the Americas and in Asia. In North America since 2011, several series of regional out- breaks of human infections with SIV have been due to SIV re- assortants which carried at least the matrix genome segment (M) of the human H1pdm virus. The reassortants detected in Europe, however, were different from those that have caused the outbreaks in the US. Never- theless, the incursion of the human H1pdm virus into the swine population further increases viral variability and may create increased zoonotic potential in SIV reassortants.
25 0 2016 Year (months)
A viruses, Cell Host & Microbe, 2020.
10 2017
The risk of strains as reservoirs Antigenic diversification of human influenza A virus (IAV) strains after transmission to and spread in swine populations is one of the risks of reverse-zoonotic IAV spillover events. An- tigenic cartography as used in the study is a versatile tool to assess the antigenic relationship of different IAV strains. Evi- dence was found indeed for extended circulation in domestic
▶PIG PROGRESS | Volume 36, No. 7, 2020
positive samples (%)
PHOTO: DR ALEX RAMIREZ
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