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.