Page 97 - Avian Virology: Current Research and Future Trends

90 | Paldurai and Samal

production in turkeys (Shortridge et al., 1980; Saif et al., 1997; for haemagglutination (HA) activity. All negative samples should
Warke et al., 2008b). However, APMV-6 and APMV-7 viruses be passaged twice more before discarding. Viruses of APMV-5
have been shown not to cause any apparent disease in chickens do not grow in the allantoic cavity. These viruses are isolated by
by experimental infection (Shortridge et al., 1980; Xiao et al., inoculating materials into the amniotic cavity of 9- to -11-day-old
2009). APMV-8 and APMV-9 isolates rarely cause clinical signs embryonated chicken eggs or into the yolk sac of 6- to -7-day-old
in poultry (Alexander et al., 1983a; Stallknecht et al., 1991; Mal- embryonated chicken eggs. A positive result by the HA test will
donado et al., 1994; Capua et al., 2004). Hence, it seems that only indicate that the agent could be an APMV or an AIV. Negative
APMV-2 and APMV-3 viruses are capable of causing significant results by HI testing with NDV-specific and AIV-specific anti-
disease and economic impact on poultry production. APMV-10 sera will suggest that the virus is an APMV serotype other than
to APMV-21 have been isolated exclusively from wild birds APMV-1. Further HI testing against a range of specific antisera
which have no evidence of any disease. APMV-12 and APMV-13 representing all other APMV serotypes is performed to identify
were found to be avirulent for chickens (Terregino et al., 2013; the serotype of APMV. However, APMV-5 do not cause HA
Yamamoto et al., 2015). Serological survey showed presence of with RBCs of chicken or any other known species (Nerome et
antibodies to different APMVs in commercial poultry in the U.S., al., 1978; Samuel et al., 2010). There has also been a report of an
indicating inapparent APMV infection (Warke et al., 2008a). APMV-4 (Wang et al., 2013) and an APMV-6 (Chen et al., 2018)
Experimental infection of chickens or turkeys with APMV-2 to isolated from China that are HA-negative. Therefore, it is recom-
APMV-9 have produced mild respiratory disease (Warke et al., mended that sequence analysis in addition to a HA test should be
2008b; Kumar et al., 2010a; Subbiah et al., 2010b). Intracerebral performed.
pathogenicity indices of all other APMV serotypes (including APMV serotypes 1 to 10 and APMV-13 replicate in avian and
the novel serotypes recently isolated) in one-day-old chicks have mammalian cells. APMV-14 grows only in CEF cells. APMV-20
been very low, indicating that they are avirulent to chickens. does not replicate in cell culture. Some of the APMV serotypes
The replication and pathogenicity of APMV-2 to APMV-9 require the addition of trypsin (1 µg/ml) or 10% fresh allantoic
in non-avian species has also been studied (Samuel et al., 2011; fluid to facilitate growth. In general, APMVs grow most efficiently
Khattar et al., 2011, 2013; Bui et al., 2017). Experimental infection in chicken fibroblast (DF-1) cells, followed by Vero and BHK-21
of hamsters and mice by intranasal route with prototype strains of cells. The CPE varies among APMV serotypes. Some of the
APMV-1 to APMV-9 showed that each of the viruses replicated APMV serotypes cause cell rounding and detachment and do not
in hamsters and mice and produced mild or inapparent clinical cause syncytia formation, a hallmark of paramyxovirus infection.
signs (Khattar et al., 2011; Samuel et al., 2011). Recently, it was Whereas APMV-1, APMV-3 strain Netherlands and APMV-13
reported that two strains of APMV-6 replicated in respiratory tis- strain Shimane/67 cause syncytia formation. Inoculation of
sues of infected mice and induced respiratory disease, sometimes embryonated chicken eggs is the most sensitive method for isola-
resulting in death of the mice (Bui et al., 2017). Experimental tion of APMVs.
infection of Rhesus macaques (Macaca mulatta) by intranasal
and intratracheal routes showed that APMV-1 to APMV-9 except
APMV-5 induced a virus-specific serum antibody response in General virion structure and replication
all infected animals. None of the animals exhibited any clinical strategy
disease signs (Khattar et al., 2013). These results indicate that The general molecular biologic characteristics of all paramyxo-
APMVs are competent to infect primates in nature but are not viruses are very similar. Although the structure and replication
likely to cause any significant disease. strategies of other APMV serotypes are not well studied, it is
probably very similar to those of NDV. Therefore, the readers are
advised to refer the chapter on NDV for a detail understanding of
Isolation and identification of APMVs the molecular biology of other APMV serotypes.
The most successful samples for virus isolation have been fresh
faeces or faecal swabs. The next important sample for virus isola- Virion morphology
tion has been tracheal swabs. Additional samples can be collected The morphology of other APMV serotypes is indistinguishable
from organs of dead birds. Swabs are placed in medium contain- from that of APMV-1 by electron microscopy (Fig. 3.1). The avian
ing high levels of antibiotics. Isolation should be performed as paramyxoviruses are enveloped, pleomorphic, 100 to 500 nm
rapidly as possible. Freezing or storing at 4ºC of the samples may in diameter, and it can be filamentous. The envelope is derived
cause loss of virus infectivity as these viruses are present in very from the plasma membrane of the host cell. Inserted into the
low quantity and are highly fragile. Tissue suspensions or swab envelope are viral glycoprotein spikes that extend ≈ 15 nm from
washings are centrifuged at 1000 × g for 10 minutes. The isola- the surface of the virion. All APMVs contain two types of glyco-
tion of APMVs is most commonly accomplished by inoculation protein spikes, fusion (F) and haemagglutinin-neuraminidase
of 0.1 to 0.2 ml of sample supernatant into the allantoic cavity of (HN), but APMV-6 contains an additional envelope protein,
three to five 9- to -11-day-old specific pathogen-free embryonated small hydrophobic (SH) protein. Underneath the envelope lies
chicken eggs. The inoculated eggs are placed at 37°C and candled the matrix (M) protein. Inside the envelope is the nucleocapsid
daily. Eggs with dead embryos and all eggs after 5 to 7 days of core (also called as ribonucleoprotein [RNP] core). In avian and
inoculation are chilled to 4°C and the allantoic fluids are tested all other paramyxoviruses, the nucleocapsid core consists of a