Introduction
Avian influenza viruses (AIVs) in birds can be divided into H1-H16 subtypes and N1-N9 subtypes according to the antigenic characteristics of their two surface proteins, Haemagglutinin (HA) and Neuraminidase (NA) (Webster et al., 1992). Wild birds are considered to be the natural hosts of a variety of AIVs of different subtypes (Kawaoka et al., 1988), especially Charadriiformes and Anseriformes distributed all over the world (Brown et al., 2007; Guan et al., 2019). Some HA subtypes of AIVs are potentially associated with species susceptibility, such as H5, H7 and H9 subtypes are most endemic in poultry (Lee et al., 2010), while the H4, H11 and H13 subtypes are mostly from shorebirds and gulls (Krauss et al., 2004; Latorre-Margalef et al., 2014), H3 and H6 subtypes are prevalent in waterfowl (Munster et al., 2007).
The H10-H12 subtypes are also usually associated with “waterfowl-associated” subtypes and are detected very infrequently in nature, but as part of the influenza A virus pool, they can highly reassort with other subtypes of AIVs (Wille et al., 2018). It has been reported that the H10 viruses can spillover to humans and mammal animals (Vachieri et al., 2014; Zohari et al., 2014). The H10N4 virus was detected from farmed mink in Sweden in 1984 (Klingeborn et al., 1985), which was the first example of a disease in mammals caused by the H10 subtype. The H10N4 virus was closely to the circulating avian influenza virus and the migratory waterfowls probably could spread the subtype of virus (Koehler et al., 2008; Wille et al., 2018). Subsequently, H10N7 virus was observed to cause mass deaths among harbor seals in Sweden in 2014 (Zohari et al., 2014). In late 2013, the human infections with a novel reassortant avian influenza A H10N8 virus was identified in Jiangxi, China (Chen et al., 2014). All of these indicate that the H10 subtype viruses could cause disease in a broad host range. Unlike the H10 subtype, there was no evidence demonstrate that the H11 subtype viruses could directly cause the human infection at present, but it could provide gene donors for other subtype viruses, such as the recent human infections with H7N9 virus revealed that H11N9 virus was the NA gene donors for them (Lam et al., 2013). H12N1 was first reported in Canada in 1983 (Velarde et al., 2010) and then H12 subtype viruses were occasionally reported in wild birds (Bui et al., 2015; Wongphatcharachai et al., 2012). According to current research, there was little research has been done on the H12 subtypes (Latorre-Margalef et al., 2014; Wilcox et al., 2011), and their ecology and phylogenetic analysis were largely unknown.
Waterfowls play an important role in transmitting the viruses, since faeces from infected birds were excreted into the water, and the viruses could be further transmitted by migratory birds and even caused infection in other birds and mammals by cross the interspecies barrier (Appel et al., 1991; Huang et al.; Sharp et al., 1997). Shanghai as a city in Yangtze River estuary on China’s east coast, is located on the East Asian-Australian Flyway and is an important stopover and wintering site for migratory birds. During our routine surveillance in wild birds in recent years, we found that a small amount of H10-H12 subtype viruses could be detected in this region. In order to expand our understanding of the ecological distribution and evolution of these rare AIV subtypes in China, we studied the characteristic of these H10-H12 subtypes AIVs in wild birds in Shanghai from 2016 to 2019.