Page 51 - Avian Virology: Current Research and Future Trends

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Geographic distribution and sparrows. The disease is least severe in waterfowl, koels, shags,
Virulent strains of NDV are enzootic in most parts of the world, gulls, coots, and cranes. Ducks and geese are generally thought
but an exact assessment of the true geographic distribution of ND to be natural reservoirs of NDV, and resistant to ND (Alexander
is difficult because in some countries the presence of ND in vil- and Senne, 2008). However, since the late 1990s, frequent out-
lage chickens or backyard flocks is not always reported. Currently, breaks of ND have occurred in geese throughout China, causing
ND is present on at least six of the seven continents of the world devastating economic losses (Chen et al., 2015). Although ducks
and is either enzootic or cause of frequent outbreaks throughout are more resistant to ND compared with geese, many natural
Africa, Asia, the Middle East, Mexico, Central and South America. outbreaks were associated with NDV (Dai et al., 2014). These
The countries of Oceania are relatively free from ND, probably findings suggest that geese and ducks may not be just reservoirs
because of effective quarantine and geographic isolation. of NDV but are also becoming susceptible to ND.
ND has been controlled in the USA, Canada and most coun- Although avian species are the natural host for NDV, many
tries in Europe. In the USA, the disease is referred to as virulent non-avian species have also been shown to be naturally or
Newcastle disease (vND), formerly known as exotic Newcastle experimentally susceptible to infection with NDV. Both avirulent
disease, and was first reported in California in 1950. Since then, and virulent strains of NDV can infect and cause clinical signs
virulent NDV has been introduced into the USA on several occa- of disease in humans (Chang, 1981). The virus usually causes
sions, but each outbreak was subsequently eradicated. The latest only mild, transient conjunctivitis or flu-like symptoms. Natural
outbreak of vND was reported in backyard exhibition chickens in human infection with NDV is extremely rare. To date, only two
California in 2018. Prior to this, the outbreak of vND occurred fatal cases of NDV infection in humans have been reported, one
in California in 2002–2003, and approximately 3.5 million birds in the USA (Goebel et al., 2007) and the other in the Netherlands
were depopulated to eradicate the disease. The California vND (Kuiken et al., 2018). Both the patients had immunosuppres-
virus was most closely related to viruses isolated from ND out- sive conditions and both the virus isolates were typed as pigeon
breaks in Mexico and Central America (Pedersen et al., 2004). paramyxovirus type 1 (PPMV-1), which is a variant of NDV. It
Historically, virulent NDV has been introduced into the USA is not known whether all PPMV-1 isolates or only those isolates
through the importation of exotic avian species (Utterback and from fatal human cases are virulent for immunosuppressive
Schwartz, 1973; Senne et al., 1983; Bruning-Fann et al., 1992; people. However, ND is now recognized as an occupational
Panigrahy et al., 1993) and water birds (Wobeser et al., 1993; health hazard to those people associated with poultry farming,
Banerjee et al., 1994). In the USA, virulent NDV is listed as a production of vaccines and laboratory personnel. There is no
USDA Select Agent as it is a pathogen of national concern. In report of human-to-human transmission. NDV has also been
Europe, sporadic epizootics of ND regularly occur in many coun- shown to experimentally infect calves, swine, sheep, mice, guinea
tries despite widespread vaccination programs. From 1932 to pigs, rabbits, ferrets, hamsters and non-human primates such as
1998, Australia has been free of virulent NDV. However, six out- monkeys (Reagan et al., 1947; DiNapoli et al., 2007a,b; Subbiah et
breaks caused by virulent NDV occurred between 1998 and 2002 al., 2008). However, some non-avian species are more susceptible
in localized areas of New South Wales. In each case, the NDV is than others. For example, guinea pigs are more susceptible than
thought to have evolved from certain low-virulence Australian mice and hamsters (Khattar et al., 2011a,b; Samuel et al., 2011).
strains. There is no evidence that Australian outbreaks have been
caused by viruses introduced from overseas (Westbury, 2001).
Although NDV is prevalent in domestic and wild birds Infectious agent
worldwide, the genetic and antigenic characteristics of the NDV
strain varies with the host species and/or geographic region. For Virus classification
example, the NDV strains circulating in Africa are genetically NDV is a member of the genus Orthoavulavirus of subfamily
and antigenically different than the strains circulating in South Avulavirinae, family Paramyxoviridae, order Mononegavirales
America. Similarly, the NDV strains circulating in pigeons are (Amarasinghe et al., 2017; ICTV, 2019). The subfamily Avulaviri-
genetically and antigenically different than the strains circulating nae is one of the four subfamilies of family Paramyxoviridae (the
in chickens. other subfamilies are Metaparamyxovirinae, Orthoparamyxovirinae
and Rubulavirinae). The subfamily Avulavirinae contains viruses
isolated from avian species and members of this subfamily have
Natural and experimental host range haemagglutinin and neuraminidase activities. They share greater
NDV infections have been reported in at least 241 species of birds sequence relatedness among them than with members of other
representing 27 of the 50 orders of birds (Kaleta and Baldauf, subfamilies. The subfamily Avulavirinae has 20 species distributed
1988). It is probable that all species of birds are susceptible to among three genera, Metaavulavirus (MAvV), Orthoavulavirus
NDV infection. However, the disease varies greatly depending (OAvV) and Paraavulavirus (PAvV) based on the phylogenetic
upon the virus strain and host species. Infection in most avian tree derived using deduced complete amino acid sequences of the
species do not result in disease. The disease is most severe in large polymerase (L) protein (ICTV, 2019). Each Avulavirinae
chickens, peafowls, guinea fowl, pheasants, ostrich, psittacines, species has a single member virus, called APMV-1 to APMV-20
quails, and pigeons (Kaleta and Baldauf, 1988). A somewhat less for species 1 to species 20, respectively. The genus Metaavulavirus
severe disease occurs in turkeys, penguins, owls, falcons, eagles has ten species, Avian metaavulavirus 2 (AMAvV-2), AMAvV-5,