The long view: a selective review of 40 years of Newcastle disease research

This review is written for the series celebrating the 40th year since the first issue of Avian Pathology. The aim of the authors was to cover the developments in Newcastle disease (ND) research over the last 40 years that they considered significant. During those 40 years there have been several panzootics of this serious disease in poultry and for the last 30 years there has been a continuing panzootic in domestic pigeons, which has spread to wild birds and poultry. The 40-year period began with worldwide outbreaks of severe ND, which served as an important impetus for ND research work. Although early work was concerned with controlling the disease, specifically by improving and developing new vaccines and vaccine regimens, even prior to the 1970s ND virus was seen as a useful laboratory virus for replication and virulence studies. This review covers the historical developments in the following areas: understanding the molecular basis of virulence; epidemiology and relatedness of different ND strains, both antigenically and genetically; the emergence of virulent strains and their relationship with viruses of low virulence; sequencing and understanding the viral genome and genes; the development of rapid molecular-based diagnostic tests; and the phylogeny and molecular taxonomy of ND virus. The authors suggest areas in which future research could or should be undertaken.     

Immune responses of poultry to Newcastle disease virus

Newcastle disease (ND) remains a constant threat to poultry producers worldwide, in spite of the availability and global employment of ND vaccinations since the 1950s. Strains of Newcastle disease virus (NDV) belong to the order Mononegavirales, family Paramyxoviridae, and genus Avulavirus, are contained in one serotype and are also known as avian paramyxovirus serotype-1 (APMV-1). They are pleomorphic in shape and are single-stranded, non-segmented, negative sense RNA viruses. The virus has been reported to infect most orders of birds and thus has a wide host range. Isolates are characterized by virulence in chickens and the presence of basic amino acids at the fusion protein cleavage site. Low virulent NDV typically produce subclinical disease with some morbidity, whereas virulent isolates can result in rapid, high mortality of birds. Virulent NDV are listed pathogens that require immediate notification to the Office of International Epizootics and outbreaks typically result in trade embargos. Protection against NDV is through the use of vaccines generated with low virulent NDV strains. Immunity is derived from neutralizing antibodies formed against the viral hemagglutinin and fusion glycoproteins, which are responsible for attachment and spread of the virus. However, new techniques and technologies have also allowed for more in depth analysis of the innate and cell-mediated immunity of poultry to NDV. Gene profiling experiments have led to the discovery of novel host genes modulated immediately after infection. Differences in virus virulence alter host gene response patterns have been demonstrated. Furthermore, the timing and contributions of cell-mediated immune responses appear to decrease disease and transmission potential. In view of recent reports of vaccine failure from many countries on the ability of classical NDV vaccines to stop spread of disease, renewed interest in a more complete understanding of the global immune response of poultry to NDV will be critical to developing new control strategies and intervention programs for the future.     

Phylogenetic Relationships among Highly Virulent Newcastle Disease Virus Isolates Obtained from Exotic Birds and Poultry from 1989 to 1996

Newcastle disease virus {NDV (avian paramyxovirus type 1 [APMV1])} isolates were recovered from imported exotic birds confiscated following importation into the United States, from waterbirds in the United States, and from poultry. The exotic birds probably originated from Central and South America, Asia, and Africa. The NDV isolates were initially characterized as highly virulent because of a short mean death time in embryonated chicken eggs. The isolates were typed as neurotropic or viscerotropic velogenic by intracloacal inoculation of adult chickens. Intracerebral pathogenicity index values for the virulent NDV isolates ranged from 1.54 to 1.90, compared to a possible maximum value of 2.0. These isolates had a dibasic amino acid motif in the fusion protein cleavage site sequence required for host systemic replication. Sequence differences were detected surrounding the fusion protein cleavage site and the matrix protein nuclear localization signal, indicating evolution of highly virulent NDV. Phylogenetically, these isolates were categorized with other highly virulent NDV strains that caused outbreaks in southern California poultry during 1972 and in cormorants in the north central United States and southern Canada during 1990 and 1992. These isolates are related to NDV that may have the APMV1 strain chicken/Australia/AV/32 or a related virus as a possible progenitor. Recent virulent NDV isolates and those recovered during disease outbreaks since the 1970s are phylogenetically distinct from current vaccine viruses and standard challenge strains.     

Intracontinental and intercontinental dissemination of Asian H5 highly pathogenic avian influenza virus (clade 2.3.4.4) in the winter of 2014–2015

Asian H5 highly pathogenic avian influenza viruses (HPAIVs) that possess the clade 2.3.4.4 HA gene have been identified in wild birds and poultry since late 2014 in both Europe and North America (N. America). Clade 2.3.4.4 H5 HPAIVs of the H5N8 subtype have been isolated in both regions, whereas reassortment viruses with NA N1 and N2 subtypes of the North American (N. American). avian lineage have only been identified in N. America. The HA genes of those isolates were closely related to genes of the HPAIVs that have caused massive outbreaks in poultry in Korea since January 2014. The outbreaks caused by those viruses and the genetic relatedness of their HA and NA genes are reviewed in this study. Although the illegal movement of poultry and poultry products cannot be ruled out as a cause of intercontinental and intracontinental dissemination of clade 2.3.4.4 H5 HPAIVs during the winter of 2014–2015, transmission of the viruses by infected migratory birds appears to be a more plausible mechanism for their dissemination. In particular, the involvement of migratory birds in HPAIV transmission between Asia and N. America is highly likely because of the reassortments between H5N8 HPAIV and the N. American lineage avian influenza viruses. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of two pigeon paramyxovirus type 1 isolates in China

For over three decades, there has been a continuing panzootic caused by a virulent variant avian paramyxovirus type 1 strain, the so-called pigeon paramyxovirus type 1. It is found primarily in racing pigeons, but it has also spread to wild birds and poultry. In this study, two pigeon paramyxovirus type 1 strains, SD12 and BJ13, obtained from diseased pigeons in China, were characterized. Phylogenetic analysis based on complete sequences allowed characterization of both strains as genotype VI, class II. Further phylogenetic analysis of a 374-nucleotide section of the fusion gene showed that SD12 fell into lineage VIbii-d and BJ13 into VIbii-f. The deduced amino acid sequence of the cleavage site of the fusion protein confirmed that both isolates contained the virulent motif ¹¹²K/RRQKR↓F¹¹⁷ at the cleavage site. Nevertheless, the values of intracerebral pathogenicity indices showed the SD12 isolate to be a velogenic strain and BJ13 isolate to be a mesogenic strain. The SD12 isolate was further investigated via clinical observation, RNA detection, histopathology and viral serology in experimentally infected 3-week-old chickens. It showed a mild pathological phenotype in chickens, with viral replication restricted to a few tissues. The molecular mechanism for the SD12 isolate to have a virulent motif but low levels of virulence for chickens requires further study.     

Molecular characterization of the glycoprotein genes of H5N1 influenza A viruses isolated in Israel and the Gaza Strip during 2006 outbreaks

Highly pathogenic H5N1 avian influenza A viruses (AIV) have caused outbreaks among domestic poultry and wild aquatic birds in many Asian, European, and African countries since 1997. In March 2006 an avian H5N1 influenza A virus was isolated from poultry in Israel. In the present study we molecularly characterized the hemagglutinin (HA) and neuraminidase (NA) genes of eleven H5N1 viruses isolated from domestic poultry in Israel and Gaza in March–April 2006. Phylogenetic analysis of the HA and NA genes showed that the Israeli and Gazian viruses were closely related to viruses isolated in Egypt in 2006.     

Presence of Newcastle disease viruses of sub-genotypes Vc and VIn in backyard chickens and in apparently healthy wild birds from Mexico in 2017

Virulent Newcastle disease viruses (NDV) have been present in Mexico since 1946, and recently, multiple outbreaks have been reported in the country. Here, we characterized eleven NDV isolated from apparently healthy wild birds and backyard chickens in three different locations of Jalisco, Mexico in 2017. Total RNA from NDV was reverse-transcribed, and 1285 nucleotides, which includes 3/4 of the fusion gene, was amplified and sequenced using a long-read MinION sequencing method. The sequences were 99.99–100% identical to the corresponding region obtained using the Illumina MiSeq. Phylogenetic analysis using MinION sequences demonstrated that nine virulent NDV from wild birds belonged to sub-genotypes Vc and VIn, and two backyard chicken isolates were of sub-genotype Vc. The sub-genotype Vc viruses had nucleotide sequence identity that ranged from 97.7 to 98% to a virus of the same sub-genotype isolated from a chicken in Mexico in 2010. Three viruses from pigeons had 96.3–98.7% nucleotide identity to sub-genotype VIn pigeon viruses, commonly referred to as pigeon paramyxovirus, isolated in the USA during 2000–2016. This study demonstrates that viruses of sub-genotype Vc are still present in Mexico, and the detection of this sub-genotype in both chickens and wild birds suggests that transmission among these species may represent a biosecurity risk. This is the first detection and complete genome sequencing of genotype VI NDV from Mexico. In addition, the utilization of an optimized long-read sequencing method for rapid virulence and genotype identification using the Oxford nanopore MinION system is demonstrated.

     

Molecular Epidemiology of Outbreak-Associated and Wild-Waterfowl-Derived Newcastle Disease Virus Strains in Finland,Including a Novel Class I Genotype

Newcastle disease (ND) is a highly contagious, severe disease of poultry caused by pathogenic strains of Newcastle disease virus (NDV; or avian paramyxovirus-1). NDV is endemic in wild birds worldwide and one of the economically most important poultry pathogens. Most of the published strains are outbreak-associated strains, while the apathogenic NDV strains that occur in wild birds, posing a constant threat to poultry with their capability to convert into more virulent forms, have remained less studied. We screened for NDV RNA in cloacal and oropharyngeal samples from wild waterfowl in Finland during the years 2006 to 2010: 39 of 715 birds were positive (prevalence, 5.5%). The partial or full-length F genes of 37 strains were sequenced for phylogenetic purposes. We also characterized viruses derived from three NDV outbreaks in Finland and discuss the relationships between these outbreak-associated and the wild-bird-associated strains. We found that all waterfowl NDV isolates were lentogenic strains of class I or class II genotype I. We also isolated a genetically distinct class I strain (teal/Finland/13111/2008) grouping phylogenetically together with only strain HIECK87191, isolated in Northern Ireland in 1987. Together they seem to form a novel class I genotype genetically differing from other known NDVs by at least 12%.     

Newcastle Disease Viruses Causing Recent Outbreaks Worldwide Show Unexpectedly High Genetic Similarity to Historical Virulent Isolates from the 1940s

Virulent strains of Newcastle disease virus (NDV) cause Newcastle disease (ND), a devastating disease of poultry and wild birds. Phylogenetic analyses clearly distinguish historical isolates (obtained prior to 1960) from currently circulating viruses of class II genotypes V, VI, VII, and XII through XVIII. Here, partial and complete genomic sequences of recent virulent isolates of genotypes II and IX from China, Egypt, and India were found to be nearly identical to those of historical viruses isolated in the 1940s. Phylogenetic analysis, nucleotide distances, and rates of change demonstrate that these recent isolates have not evolved significantly from the most closely related ancestors from the 1940s. The low rates of change for these virulent viruses (7.05 × 10⁻⁵ and 2.05 × 10⁻⁵ per year, respectively) and the minimal genetic distances existing between these and historical viruses (0.3 to 1.2%) of the same genotypes indicate an unnatural origin. As with any other RNA virus, Newcastle disease virus is expected to evolve naturally; thus, these findings suggest that some recent field isolates should be excluded from evolutionary studies. Furthermore, phylogenetic analyses show that these recent virulent isolates are more closely related to virulent strains isolated during the 1940s, which have been and continue to be used in laboratory and experimental challenge studies. Since the preservation of viable viruses in the environment for over 6 decades is highly unlikely, it is possible that the source of some of the recent virulent viruses isolated from poultry and wild birds might be laboratory viruses.     

The epidemiology of Newcastle disease in rural poultry: A review

Rural poultry are the dominant form of poultry kept in the developing world. They are a natural resource whose potential is not fully exploited for the welfare of rural populations. The most devastating disease of rural poultry is Newcastle disease (ND). ND is an epidemic disease in intensive poultry and is responsible for high economic losses. Its epidemiology in intensive poultry is well understood, but little has been published on its behaviour in village poultry populations. Some research has been carried out during the past few years and it now appears that rural poultry are receiving increasing support for research and development from many government and international funding agencies throughout the world. All strains of Newcastle disease virus (NDV) occur in rural poultry, but velogenic strains are reported to be more common. Serological surveys in conjunction with isolation studies have shown that velogenic NDV strains are endemic in rural poultry populations even in isolated villages and possibly in isolated flocks. Although NDV is endemic in village poultry, the clinical disease usually follows an epidemic pattern. ND outbreaks often occur once or twice a year at regular intervals affirming the endemicity of the virus, however, 'mini' outbreaks in individual flocks and sporadic cases in individual birds may occur. Epidemics usually occur at times of climatic stress, leading to seasonal occurrence. The spread of NDV within and between village poultry populations is relatively slow due to a low contact rate. The major mode of transmission appears to be by the faecal-oral route. The respiratory route may also play a role in flocks where close bird-to-bird associations exist. Other poultry species, wild and feral birds, wild animals, communal water reservoirs and domestic animals may play a role in transmission; however, their role has not been properly investigated. In non-immune, intensively reared poultry, introduction of a sufficient quantity of virulent NDV is sufficient to cause severe outbreaks, but in rural poultry epidemic disease depends upon a number of factors. These include NDV pathotype, age structure and immunity of the host population, breed susceptibility, concurrent disease and seasonal influences. Although ND is endemic in rural poultry, many aspects of the epidemiology and economics of ND have not been fully understood. Well-designed, longitudinal studies made within a socio-economic framework are required to improve our understanding of the main problems of rural poultry systems.     

Susceptibility of wild passerines to subtype H5N1 highly pathogenic avian influenza viruses

Highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype have spread throughout many areas of Asia, Europe and Africa, and numerous cases of HPAI outbreaks in domestic and wild birds have been reported. Although recent studies suggest that the dissemination of H5N1 viruses is closely linked to the migration of wild birds, information on the potential for viral infection in species other than poultry and waterfowl is relatively limited. To investigate the susceptibility of terrestrial wild birds to infection with H5N1 HPAI viruses, common reed buntings (Emberiza schoeniclus), pale thrushes (Turdus pallidus) and brown-eared bulbuls (Hypsipetes amaurotis) were infected with A/mountain hawk-eagle/Kumamoto/1/07(H5N1) and A/whooper swan/Aomori/1/08(H5N1). The results showed that common reed buntings and brown-eared bulbuls were severely affected by both virus strains (100% mortality). While pale thrushes did not exhibit any clinical signs, seroconversion was confirmed. In common reed buntings, intraspecies-transmission of A/whooper swan/Aomori/1/08 to contact birds was also confirmed. The findings show that three passerine species; common reed buntings, brown-eared bulbuls and pale thrushes are susceptible to infection by H5N1 HPAI viruses, which emphasizes that continued surveillance of species other than waterfowl is crucial for effective monitoring of H5N1 HPAI virus outbreaks.     

Newcastle disease in ostriches (Struthio camelus) — a review

Newcastle disease (ND) in ostriches was first reported in zoo birds in the 1950s. An outbreak of ND in commercial ostriches in Israel was reported in 1989, but of more significance were the ND infections of ostriches in southern Africa during the 1990s as a result of assumed spread from commercial domestic fowl. The latter outbreaks were of particular concern due to the boom in international trade in ostriches and their products at that time. ND virus appeared to spread only slowly through affected ostrich flocks, and the clinical signs and mortality seen varied considerably with age. In field and experimental infections, morbidity, mainly in the form of nervous signs, and mortality could be extremely high in young birds but low or absent in adults. Characterization of ND viruses isolated during outbreaks in ostriches has shown them to be indistinguishable from viruses infecting chickens in the locality. Experimental challenge has shown ND poultry vaccines to be protective in ostriches, and several workers have proposed vaccine regimens employing both live and inactivated vaccines, usually given more frequently and employing much higher doses than recommended for chickens. Indirect and blocking enzyme-linked immunosorbent assay (ELISA) tests have been developed for the detection of ND antibodies in ostrich sera. Although some reports have suggested problems using the haemagglutination inhibition(HI)tests, others have recorded good correlation between ELISA, HI and virus neutralization tests. Because of their size and, as a consequence, the method of rearing, ostriches are quite different to conventional poultry and respond differently, in terms of disease and spread, when infected with ND virus. However, at present, for the international control of ND, there would appear to be little alternative to treating ostriches as poultry for the purposes of trade.     

Genetic diversity and mutation of avian paramyxovirus serotype 1 (Newcastle disease virus) in wild birds and evidence for intercontinental spread

Avian paramyxovirus serotype 1 (APMV-1), or Newcastle disease virus, is the causative agent of Newcastle disease, one of the most economically important diseases for poultry production worldwide and a cause of periodic epizootics in wild birds in North America. In this study, we examined the genetic diversity of APMV-1 isolated from migratory birds sampled in Alaska, Japan, and Russia and assessed the evidence for intercontinental virus spread using phylogenetic methods. Additionally, we predicted viral virulence using deduced amino acid residues for the fusion protein cleavage site and estimated mutation rates for the fusion gene of class I and class II migratory bird isolates. All 73 isolates sequenced as part of this study were most closely related to virus genotypes previously reported for wild birds; however, five class II genotype I isolates formed a monophyletic clade exhibiting previously unreported genetic diversity, which met criteria for the designation of a new sub-genotype. Phylogenetic analysis of wild-bird isolates provided evidence for intercontinental virus spread, specifically viral lineages of APMV-1 class II genotype I sub-genotypes Ib and Ic. This result supports migratory bird movement as a possible mechanism for the redistribution of APMV-1. None of the predicted deduced amino acid motifs for the fusion protein cleavage site of APMV-1 strains isolated from migratory birds in Alaska, Japan, and Russia were consistent with those of previously identified virulent viruses. These data therefore provide no support for these strains contributing to the emergence of avian pathogens. The estimated mutation rates for fusion genes of class I and class II wild-bird isolates were faster than those reported previously for non-virulent APMV-1 strains. Collectively, these findings provide new insight into the diversity, spread, and evolution of APMV-1 in wild birds.     

Pandemic threat posed by avian influenza A viruses

Influenza pandemics, defined as global outbreaks of the disease due to viruses with new antigenic subtypes, have exacted high death tolls from human populations. The last two pandemics were caused by hybrid viruses, or reassortants, that harbored a combination of avian and human viral genes. Avian influenza viruses are therefore key contributors to the emergence of human influenza pandemics. In 1997, an H5N1 influenza virus was directly transmitted from birds in live poultry markets in Hong Kong to humans. Eighteen people were infected in this outbreak, six of whom died. This avian virus exhibited high virulence in both avian and mammalian species, causing systemic infection in both chickens and mice. Subsequently, another avian virus with the H9N2 subtype was directly transmitted from birds to humans in Hong Kong. Interestingly, the genes encoding the internal proteins of the H9N2 virus are genetically highly related to those of the H5N1 virus, suggesting a unique property of these gene products. The identification of avian viruses in humans underscores the potential of these and similar strains to produce devastating influenza outbreaks in major population centers. Although highly pathogenic avian influenza viruses had been identified before the 1997 outbreak in Hong Kong, their devastating effects had been confined to poultry. With the Hong Kong outbreak, it became clear that the virulence potential of these viruses extended to humans.     

Characterization of a highly pathogenic H5N1 avian influenza virus isolated from ducks in Eastern China in 2011

This study describes the characterization of seven H5N1 avian influenza viruses from domestic ducks in Eastern China in 2011. Phylogenetic analysis showed these viruses were closely related to an H5N1 virus circulating in wild birds in Hong Kong. Some characteristics of these viruses were similar to those of an H5N1 strain that circulated in China and Vietnam (2003-2004). The virulence of three isolates was examined in chickens and mice, and they were found to be highly pathogenic in chickens but showed low pathogenicity in mice. These results suggest that continued H5N1 surveillance in poultry should be used as an early warning system for avian influenza outbreaks.     

Effect of host selective pressure on Newcastle disease virus virulence

Newcastle disease virus (NDV) causes an economically important disease that can vary from clinically inapparent to highly virulent forms. Generally, NDV strains isolated from wild birds are non-pathogenic for chicken. However, there are evidences supporting the fact that avirulent viruses maintained in feral birds could have caused outbreaks of virulent NDV in poultry. The strain-specific difference in virulence is determined by structural variations on the fusion glycoprotein (F). More basic amino acids are present in the F cleavage site of virulent strains. Nevertheless, other regions have been involved in virulence determination. When we subjected an avirulent NDV isolated from a wild bird to a host change we found that the virus arose was virulent for chicken. Nucleotide changes in the F protein cleavage site amino acid sequence and in the hemagglutinin-neuraminidase protein sequence are reported.     

Genetic characterization and pathogenicity assessment of highly pathogenic H5N1 avian influenza viruses isolated from migratory wild birds in 2011, South Korea

The continued spread of a highly pathogenic avian influenza (HPAI) H5N1 virus among wild birds and poultry has posed a potential threat to human public health. In the present study, we report the isolation of HPAI H5N1 viruses (A/Md/Korea/W401/11 and A/Md/Korea/W404/11) from fecal samples of migratory birds. Genetic and phlyogenetic analyses demonstrated that these viruses are genetically identical possessing gene segments from avian virus origin and showing highest sequence similarities (as high as 99.8%) to A/Ws/Hokkaido/4/11 and 2009-2010 Mongolian-like clade 2.3.2 isolates rather than previous Korean H5N1 viruses. Both viruses possess the polybasic motif (QRERRRK/R) in HA but other genes did not bear additional virulence markers. Pathogenicity of A/Md/Korea/W401/11 was assessed and compared with a 2006 clade 2.2 HPAI H5N1 migratory bird isolate (A/EM/Korea/W149/06) in chickens, ducks, mice and ferrets. Experimental infection in these hosts showed that both viruses have high pathogenic potential in chickens (2.3-3.0 LD(50)s) and mice (3.3-3.9 LD(50)s), but A/Md/Korea/W401/11 was less pathogenic in duck and ferret models. Despite recovery of both infection viruses in the upper respiratory tract, efficient ferret-to-ferret transmission was not observed. These data suggest that the 2011 Korean HPAI wild bird H5N1 virus could replicate in mammalian hosts without pre-adaptation but could not sustain subsequent infection. This study highlights the role of migratory birds in the perpetuation and spread of HPAI H5N1 viruses in Far-East Asia. With the changing pathobiology caused by H5N1 viruses among wild and poultry birds, continued surveillance of influenza viruses among migratory bird species remains crucial for effective monitoring of high-pathogenicity or pandemic influenza viruses.     

Emerging influenza.

In 1918 the Spanish influenza pandemic, caused by an avian H1N1 virus, resulted in over 50 million deaths worldwide. Several outbreaks of H7 influenza A viruses have resulted in human cases, including one fatal case. Since 1997, the outbreaks of highly pathogenic avian influenza (HPAI) of the H5N1 subtype have affected a wide variety of mammals in addition to poultry and wild birds. Here, we give an overview of the current knowledge of the determinants of pathogenicity of these three subtypes of avian influenza A virus in mammals. Common mechanisms for acquisition of virulence and replication of these avian influenza viruses in mammals are becoming apparent. Therefore, monitoring these and additional genetic changes upon zoonotic infections is important. Identification of genetic changes responsible for transmission between mammals will be an important task for the near future.     

A molecular epidemiological investigation of avian paramyxovirus type 1 viruses isolated from game birds of the order Galliformes

The partial (370 nucleotides) fusion gene sequences of 55 avian paramyxovirus type 1 (APMV-1) isolates were obtained. Included were 41 published sequences, of which 16 were from strains of APMV-1 of previously determined lineages included as markers for the data analysed and 25 were from APMV-1 viruses isolated from game birds of the order Galliformes. In addition, we sequenced a further 14 game bird isolates obtained from the repository at the Veterinary Laboratories Agency. The game bird isolates had been obtained from 17 countries, and spanned four decades. Earlier studies have shown that class II APMV-1 viruses can be divided into at least 15 lineages and sub-lineages. Phylogenetic analysis revealed that the 39 game bird isolates were distributed across 12 of these sub-lineages. We conclude that no single lineage of Newcastle disease viruses appears to be prevalent in game birds, and the isolates obtained from these hosts reflected the prevailing, both geographically and temporally, viruses in poultry, pigeons or wild birds.     

Complete genome and clinicopathological characterization of a virulent Newcastle disease virus isolate from South America

Newcastle disease (ND) is one of the most important diseases of poultry, negatively affecting poultry production worldwide. The disease is caused by Newcastle disease virus (NDV) or avian paramyxovirus type 1 (APMV-1), a negative-sense single-stranded RNA virus of the genus Avulavirus, family Paramyxoviridae. Although all NDV isolates characterized to date belong to a single serotype of APMV-1, significant genetic diversity has been described between different NDV isolates. Here we present the complete genome sequence and the clinicopathological characterization of a virulent Newcastle disease virus isolate (NDV-Peru/08) obtained from poultry during an outbreak of ND in Peru in 2008. Phylogenetic reconstruction and analysis of the evolutionary distances between NDV-Peru/08 and other isolates representing established NDV genotypes revealed the existence of large genomic and amino differences that clearly distinguish this isolate from viruses of typical NDV genotypes. Although NDV-Peru/08 is a genetically distinct virus, pathogenesis studies conducted with chickens revealed that NDV-Peru/08 infection results in clinical signs characteristic of velogenic viscerotropic NDV strains. Additionally, vaccination studies have shown that an inactivated NDV-LaSota/46 vaccine conferred full protection from NDV-Peru/08-induced clinical disease and mortality. This represents the first complete characterization of a virulent NDV isolate from South America.