Prevalence, genetics, and transmissibility in ferrets of Eurasian avian-like H1N1 swine influenza viruses

Abstract

Pigs are important intermediate hosts for generating novel influenza viruses. The Eurasian avian-like H1N1 (EAH1N1) swine influenza viruses (SIVs) have circulated in pigs since 1979, and human cases associated with EAH1N1 SIVs have been reported in several countries. However, the biologic properties of EAH1N1 SIVs are largely unknown. Here, we performed extensive influenza surveillance in pigs in China and isolated 228 influenza viruses from 36,417 pigs. We found that 139 of the 228 strains from pigs in 10 provinces in China belong to the EAH1N1 lineage. These viruses formed five genotypes, with two distinct antigenic groups, represented by A/swine/Guangxi/18/2011 and A/swine/Guangdong/104/2013, both of which are antigenically and genetically distinct from the current human H1N1 viruses. Importantly, the EAH1N1 SIVs preferentially bound to human-type receptors, and 9 of the 10 tested viruses transmitted in ferrets by respiratory droplet. We found that 3.6% of children (≤10 y old), 0% of adults, and 13.4% of elderly adults (≥60 y old) had neutralization antibodies (titers ≥40 in children and ≥80 in adults) against the EAH1N1 A/swine/Guangxi/18/2011 virus, but none of them had such neutralization antibodies against the EAH1N1 A/swine/Guangdong/104/2013 virus. Our study shows the potential of EAH1N1 SIVs to transmit efficiently in humans and suggests that immediate action is needed to prevent the efficient transmission of EAH1N1 SIVs to humans.

Influenza A Viruses of Swine (IAV-S) in Vietnam from 2010 to 2015: Multiple Introductions of A(H1N1)pdm09 Viruses into the Pig Population and Diversifying Genetic Constellations of Enzootic IAV-S

“…In contrast, 3 of the remaining 5 genotypes (that is, genotypes 4, 12, and 13) are also found in China, but they are unlikely to have been introduced into Vietnam from China. The EA-like IAV-S lineage has been constantly isolated in the Chinese pig population since 2002 (11,12), and long-term serological surveillance suggests that the EA-like IAV-S lineage had been predominant in China since 2003 (40). Nonetheless, neither EA-like IAV-S nor IAV-S containing EA-like genes have been found in Vietnam to date.…”

“…EA-like IAV-S and its reassortant with a human seasonal influenza virus have been endemic in Europe since the 1980s (9). Thereafter, EA-like IAV-S have spread to Thailand (10) and China (11,12).…”

Protective efficacy of an inactivated Eurasian avian-like H1N1 swine influenza vaccine against homologous H1N1 and heterologous H1N1 and H1N2 viruses in mice

“…These viruses were previously isolated from pigs during surveillance activities conducted in China between 2009 and 2013 for swine influenza [6,7,13], and were used as challenge viruses in this study. These viruses were propagated in specific pathogen-free (SPF) embryonated chicken eggs and titrated to determine the 50% egg infective dose (EID 50 ) by the method of Reed and Muench [17].…”

“…Since 2009, an intensive surveillance program for swine influenza has been carried out in more than 20 provinces in China. This program found that EA H1N1 viruses were the predominant circulating viruses in pigs and formed two antigenic groups distinct from the classical swine H1N1 (CS H1N1) and the 2009/H1N1 viruses [6][7][8].…”

“…Moreover, our recent study showed that the EA H1N1 viruses have obtained traits that could cause a human influenza pandemic after long-term evolution in pigs [6]. Pigs, which are considered to be an intermediate host for potential pandemic influenza viruses, thus represent a source of a new threat to public health.…”