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Newcastle Disease Virus | 45

AMAvV-6, AMAvV-7, AMAvV-8, AMAvV-10, AMAvV-11, the cup shaped heads is approximately 6 nm, while the diameter
AMAvV-14, AMAvV-15, and AMAvV-20. The genus Orthoa- of the stalk is approximately 2 nm (Mast and Demeestere, 2009).
vulavirus has eight species, Avian orthoavulavirus 1 (AOAvV-1), Beneath the envelope lies a non-glycosylated membrane protein
AOAvV-9, AOAvV-12, AOAvV-13, AOAvV-16, AOAvV-17, called matrix (M) protein which is tightly associated with the
AOAvV-18, and AOAvV-19. The genus Paraavulavirus contains phospholipid membrane. Inside the viral envelope lies the nucle-
two species, Avian paraavulavirus 3 (APAvV-3) and APAvV-4. The ocapsid. The nucleocapsid consists of the RNA genome that is
species AOAvV-1 contains all strains of APMV-1, that includes tightly encapsidated with the nucleocapsid (N) protein, which
NDV and PPMV-1. According to the World Organization for has the classical herringbone morphology with a mean diameter
Animal Health (OIE), only those strains of APMV-1 that fulfil the of 17 nm, a central canal of approximately 5 nm and a pitch of 1
OIE definition of a virulent virus are called NDV. All other aviru- rotation per 5 nm. Within the central canal lies the viral genomic
lent and low virulence strains are called APMV-1. OIE defines or antigenomic RNA. The viral nucleocapsid is associated with
an APMV-1 strain virulent if the virus has an ICPI value of 0.7 the phosphoprotein (P), and the large polymerase protein (L). A
or greater (2.0 is maximum) and/or presence of multiple basic majority of NDV virions (approximately three-quarters) contain
amino acids (aa) in the fusion protein cleavage site and phenyla- a single functional genome, while a minority of virions contain
lanine at position 117 (OIE, 2012). Since NDV is an important two, three, or more functional genomes (Goff et al., 2012). A
poultry pathogen, AOAvV-1 is the most extensively studied spe- schematic of the virion is shown in Fig. 2.2.
cies in the subfamily Avulavirinae. In this chapter, for easy reading,
the name NDV will be used to represent all APMV-1 strains. Propagation
NDV is easily propagated in the laboratory, which has made it a
Virion morphology virus of choice for molecular biologic studies. NDV grows to high
9
10
Virions are 100 to 500 nm in diameter, pleomorphic, but mostly titres (10 to 10 ) in embryonated chicken eggs (ECE). ECE are
spherical in shape (Fig. 2.1). Occasionally, filamentous particles used for both virus isolation and for virus production. NDV is
of variable length are present. The virion is enveloped with a lipid commonly grown in 9- to 11-day-old specific pathogen free ECE
membrane derived from the host cell plasma membrane. The 14 to by inoculation into the allantoic cavity. NDV can also replicate in
18 nm wide envelope contains two transmembrane glycoproteins primary cells and cell lines of multiple animal species. However,
– the fusion (F) and the haemagglutinin-neuraminidase (HN) some NDV strains may require several passages to adapt them
proteins. These proteins are present as homo-oligomers and form to cell culture systems. Some of the commonly used cells for
densely packed spike-like projections on the outer surface of the virus propagation are primary chicken embryo fibroblasts (CEF)
virion. These glycoprotein spikes are 17 nm tall. The diameter of and chicken embryo kidney (CEK) cells, chicken fibroblast cell

A B

Figure 2.1 Negative contrast electron micrograph of intact Newcastle disease virus particle. (A) Central part of the virion. Bar: 100 nm. (B)
The envelope showing fusion (F) and haemagglutinin-neuraminidase (HN) proteins. Bar: 10 nm. The image is reproduced from Mast and
Figure 1
Demeestere (2009) published by BioMed Central Ltd, part of Springer Nature.