Page 93 - Avian Virology: Current Research and Future Trends

86 | Paldurai and Samal

also a possibility of lack of haemagglutination activity in some test (Alexander et al., 1979; Nayak et al., 2012). This is a par-
of the future serotypes, as found in APMV-5 (Nerome et al., ticular concern when attempting to exclude APMV-1 by HI test.
1978) and in a strain of APMV-4 (Wang et al., 2013). To estab- APMV-1 also shows some cross-reaction with APMV-9 (Nayak et
lish a classification method that can be applied consistently, the al., 2012). APMV-10 was found to show some cross-reaction with
International Committee on Taxonomy of Viruses (ICTV) has APMV-2 and APMV-8 (Miller et al., 2010). APMV-12 was also
categorized the APMVs based on the topology of the phyloge- found to have some cross-reaction with APMV-1 and APMV-9
netic tree derived using deduced complete amino acid sequences (Terregino et al., 2013). One-way antigenic cross-reaction has
of the RNA-dependent RNA polymerase (RdRp), also called the been observed between APMV-1 and APMV-13 (Yamamoto et
large polymerase (L) protein, into three genera, Orthoavulavirus al., 2015). Viruses within an APMV serotype also show antigenic
(OAvV), Metaavulavirus (MAvV), and Paraavulavirus (PAvV) variation. It has been suggested that APMV-2, APMV-3 and
under the subfamily Avulavirinae (ICTV, 2019). APMV-6 each contain at least two antigenic subtypes (Kumar et
The genus Orthoavulavirus includes eight species, Avian al., 2010b; Subbiah et al., 2010a; Xiao et al., 2010). Traditionally,
orthoavulavirus 1 (AOAvV-1), AOAvV-9, AOAvV-12, AOAvV-13, antigenic analysis is carried out by a cross-HI test, the results of
AOAvV-16, AOAvV-17, AOAvV-18, and AOAvV-19 containing which are very much influenced by the source of antisera. The
APMV-1, APMV-9, APMV-12, APMV-13, APMV-16, APMV- antisera raised by multiple infections usually induce broadly
17, APMV-18 and APMV-19, respectively. The latest APMV cross-reactive antibodies. It is recommended that antisera should
isolate Cheonsu/1510 (putative APMV-21) clusters alongside be raised in chickens by a single infection through the natural
other orthoavulaviruses but it is yet to be officially recognized by route (Miller et al., 2010). The results of a HI test sometimes do
the ICTV. The genus Metaavulavirus includes 10 species, Avian not agree with the results of virus neutralization (VN) test. For
metaavulavirus 2 (AMAvV-2), AMAvV-5, AMAvV-6, AMAvV-7, example, anti-APMV-1 serum reacts with high titres to APMV-8
AMAvV-8, AMAvV-10, AMAvV-11, AMAvV-14, AMAvV-15, and by HI test, but with low titres by the VN test (Tsunekuni et al.,
AMAvV-20 containing APMV-2, APMV-5, APMV-6, APMV- 2014). The reason could be that the antibodies against the HN
7, APMV-8, APMV-10, APMV-11, APMV-14, APMV-15 and protein of APMV-1 contribute less to virus neutralization than
APMV-20, respectively. The genus Paraavulavirus includes two antibodies to the F protein (Kumar et al., 2011; Kim et al., 2013).
species, Avian paraavulavirus 3 (APAvV-3) and APAvV-4 contain- The antigenic cross-reactivity by HI test does not always depend
ing APMV-3 and APMV-4, respectively. on the amino acid (aa) sequence identity of the HN protein but
Since 2017, eight APMV serotypes (APMV-14 to -21) have depends upon conservation of the epitope involved in HA activ-
been reported (Jeong et al., 2018; Karamendin et al., 2017; Lee et ity of the protein. For example, APMV-3 significantly cross-reacts
al., 2017; Neira et al., 2017; Thampaisarn et al., 2017; Thomazelli by the HI test with APMV-1 but shares only 34.9% aa identity
et al., 2017), among which APMV-14 to -20 have been officially with the HN protein of APMV-1 (Nayak et al., 2012).
recognized (Tables 3.1 and 3.2). Cross-protection studies have shown that prior immuniza-
tion with APMV-3 provides a high level of protection against
NDV (Alexander et al., 1979; Nayak et al., 2012). This observa-
Antigenic relationships tion indicates that some of the epitopes involved in protection
Antigenic cross-reaction has been observed between APMV sero- are conserved between the two APMV serotypes. However, our
types by HI test (Alexander et al., 1979; Lipkind and Shihmanter, unpublished results indicate that protection offered by APMV-3
1986; Miller et al., 2010; Nayak et al., 2012). The data from vari- against NDV only occurs at lower challenge virus doses. Prior
ous studies show that in general APMV-2 to APMV-21 have little immunization with other APMV serotypes confers little or no
or no serological cross-reactivity with APMV-1, except APMV-3 protection against NDV (Alexander et al., 1979; Nayak et al., 2012;
which shows significant cross-reactivity with APMV-1 by HI Grund et al., 2014; Tsunekuni et al., 2014). It was found that the

Table 3.1 Recently reported APMV serotypes
Date or year of collection or
APMV Original virus isolate isolation GenBank accession number Reference
APMV-14 duck/Japan/11OG0352/2011 10/28/2011 KX258200 Thampaisarn et al. (2017)
APMV-15 Calidris fuscicollis/Brazil/ 04/2012 KX932454 Thomazelli et al. (2017)
RS-1177/2012
APMV-16 WB/Kr/UPO216/2014 2014 KY511044 Lee et al. (2017)
APMV-17 Antarctic Penguin Virus A 2014 KY452442 Neira et al. (2017)
APMV-18 Antarctic Penguin Virus B 2014 KY452443 Neira et al. (2017)
APMV-19 Antarctic Penguin Virus C 2014 KY452444 Neira et al. (2017)
APMV-20 gull/Kazakhstan/5976/2014 2014 MF033136 Karamendin et al. (2017)
APMV-21 a wild birds/Cheonsu1510/2015 10/15/2015 MF594598 Jeong et al. (2018)
a Putative APMV serotype awaiting official recognition from the ICTV.