Genomic sequence of an antigenic variant Newcastle disease virus isolated in Korea

In Korea, extensive Newcastle disease (ND) vaccine programs have been implemented, but ND outbreaks continue to occur occasionally, even in well-vaccinated farms. KBNP-4152 is a virulent ND virus, which has been isolated from vaccinated chickens in Korea. In this study, we conducted a comparison of the antigenicity of KBNP-4152 with that of a vaccine strain, La Sota, via virus-neutralization (VN) and cross haemagglutination-inhibition (HI) tests, and analyzed the genomic sequences. The antigenicity of KBNP-4152 was distinct from La Sota, and the expected genome size was 15,192 nt, as was the case with other recent virulent ND viruses analyzed. Based on the partial F gene, the strain was phylogenetically classified into the VIId genotype, but was distinct from other VII viruses due to amino acid changes at (E347K) and proximal to (M354K), the major linear epitope of HN, as well as relatively low amino acid similarity of the V protein, and a truncated W protein (203 aa vs. 227 aa). Therefore, KBNP-4152 is unique among genotype VII.     

Whole genome sequencing and biological characterization of Duck/JS/10, a new lentogenic class I Newcastle disease virus

A lentogenic Newcastle disease virus (NDV), Duck/JS/10 (JS10), was isolated from an unvaccinated duck in China. The complete genome of the virus contained 15,198 nucleotides. Based on length of the genome and a partial sequence of the F gene, the virus was classified as a class I genotype 4 NDV. The antigenicity of the virus was compared with that of NDV strain La Sota via hemagglutination inhibition (HI), virus neutralization (VN) assay and animal experiments. Our results show that JS10 generates higher HI and VN titers than La Sota against both class I and II virulent NDV strains. Experiments on animals demonstrate that virus shedding from chickens vaccinated with JS10 is significantly reduced when compared to those vaccinated with La Sota. Overall, this study strongly suggests that JS10 may qualify as a new vaccine candidate against Newcastle disease.     

Effect of phylogenetic diversity of velogenic Newcastle disease virus challenge on virus shedding post homologous and heterologous DNA vaccination in chickens

Newcastle disease (ND) is a highly devastating disease for the poultry industry as it causes high economic losses. In this present study, a DNA vaccine containing the F and HN surface antigens of a highly virulent Newcastle disease virus (NDV), NDV/1/Chicken/2005 (FJ939313), was successfully generated. Cell transfection test indicated that the vaccine expressed the F and HN genes in Hep-2 cells. The main objective of this study was to compare the extent of protection induced by DNA vaccination after homologous and heterologous NDV-challenge as determined by the amount of NDV shedding after challenge. NDV-antibody-negative chickens were vaccinated either once, twice or thrice intramuscularly at 7, 14 and 21 days old and were challenged 14 days post vaccination with either homologous virus (vaccine-matched velogenic viscerotropic Newcastle disease virus (vvNDV) strain, FJ939313), phylogenetically related to group VII, or a phylogenetically divergent heterologous virus (unmatched vvNDV strain, AY968809), which belongs to genogroup VI and shows 84.1% nucleotide similarity to the NDV-sequences of the DNA vaccine. Our data indicate that birds, which received a single dose of the DNA vaccine were poorly protected, and only 30–40% of these birds survived after challenge with high virus shedding titre. Multiple administration of the DNA vaccine induced high protection rates of 70–90% with reduced virus shedding compared to the non-vaccinated and challenged birds. Generally, homologous challenge led to reduced tracheal and cloacal shedding compared to the heterologous vvNDV strain. This study provides a promising approach for the control of ND in chickens using DNA vaccines, which are phylogenetically closely related to the circulating field strains.     

Recombinant Newcastle disease virus (NDV) La Sota expressing the haemagglutinin–neuraminidase protein of genotype VII NDV shows improved protection efficacy against NDV challenge

Intensive vaccination strategies against Newcastle disease (ND) have been implemented in many countries for a long time, but ND outbreaks still occur frequently, with most isolates belonging to genotype VII of Newcastle disease virus (NDV). Many researchers have revealed that vaccines closely matched to epidemic viruses provide better protection. Therefore, using a previously established reverse genetics system, we generated a recombinant NDV vaccine strain (rLa Sota-HN) based on the La Sota vaccine strain expressing the haemagglutinin–neuraminidase (HN) protein of genotype VII NDV. The pathogenicity of the recombinant virus was confirmed by the mean death time in 9-day-old specific-pathogen-free embryonated chicken eggs and the intracerebral pathogenicity index in 1-day-old specific-pathogen-free chickens. Subsequently, 1-day-old chickens were immunized with commercial vaccine La Sota and recombinant virus rLa Sota-HN and then challenged with virulent genotype VII NDV strain. The results indicated that recombinant virus rLa Sota-HN provided increased protection of vaccinated chickens from morbidity and mortality, and inhibited the shedding of virulent virus after challenging with genotype VII virus, compared with the conventional vaccine La Sota. Our findings indicated that rLa Sota-HN is a promising vaccine candidate to improve the protection efficiency against ND in chickens, thereby preventing frequent outbreaks of this disease.     

Characterization of newly emerging Newcastle disease virus isolates from the People's Republic of China and Taiwan

Seven Newcastle disease (ND) virus (NDV) isolates which were recovered from ND outbreaks in chicken and pigeon flocks in China and Taiwan between 1996 and 2000 were genotypically and pathotypically characterized. By phylogenetic analysis of the fusion protein genes, isolates Ch-A7/96, Ch/98-3, Ch/99, Ch/2000, and TW/2000 were placed into two novel subgenotypes, VIIc and VIId. Isolate Ch/98-1 was grouped into subgenotype VIb, while Ch-W6/96 was proven to be a mixture of isolates Ch-A7/96 and Ch/98-1. These isolates were pathotyped as viscerotropic velogenic for Ch/98-3, Ch/99, Ch/2000, and TW/2000; neurotropic velogenic for Ch-A7/96; and mesogenic for Ch/98-1. Three separate, comparative, genetic analyses of the F genes, including genetic distance measurement, phylogenetic tree analysis, and residue substitution analysis, were performed with our isolates and selected NDV strains from GenBank. Results showed that the close genetic similarity provided evidence for the epidemiological linkage between the outbreaks in China and Taiwan and that the 1990s outbreaks in Asia, the Middle East, Africa, and Europe constituted the fourth panzootic of ND. In combination with epidemiological analysis, an evolutionary model of the NDV strains, representative of the direction of transmission within the NDV strains, was proposed, and epidemiology of NDV transmission was evaluated with emphasis on molecular aspects. Finally, a cross-protective experiment indicated that at least one strain (Ch-A7/96) among our NDV isolates was an antigenic variant, responsible for recent outbreaks of ND in vaccinated chicken flocks.     

Phylogenetic and Pathotypic Characterization of Newcastle Disease Viruses Circulating in West Africa and Efficacy of a Current Vaccine

Newcastle disease (ND) is a deadly avian disease worldwide. In Africa, ND is enzootic and causes large economic losses, but little is known about the Newcastle disease virus (NDV) strains circulating in African countries. In this study, 27 NDV isolates collected from apparently healthy chickens in live-bird markets of the West African countries Benin and Togo in 2009 were characterized. All isolates had polybasic fusion (F)-protein cleavage sites and were shown to be highly virulent in standard pathogenicity assays. Infection of 2-week-old chickens with two of the isolates resulted in 100% mortality within 4 days. Phylogenetic analysis of the 27 isolates based on a partial F-protein gene sequence identified three clusters: one containing all the isolates from Togo and one from Benin (cluster 2), one containing most isolates from Benin (cluster 3), and an outlier isolate from Benin (cluster 1). All the three clusters are related to genotype VII strains of NDV. In addition, the cluster of viruses from Togo contained a recently identified 6-nucleotide insert between the hemagglutinin-neuraminidase (HN) and large polymerase (L) genes in a complete genome of an NDV isolate from this geographical region. Multiple strains that include this novel element suggest local emergence of a new genome length class. These results reveal genetic diversity within and among local NDV populations in Africa. Sequence analysis showed that the F and HN proteins of six West African isolates share 83.2 to 86.6% and 86.5 to 87.9% identities, respectively, with vaccine strain LaSota, indicative of considerable diversity. A vaccine efficacy study showed that the LaSota vaccine protected birds from morbidity and mortality but did not prevent shedding of West African challenge viruses.     

Newcastle disease virus: is an updated attenuated vaccine needed?

Newcastle disease virus (NDV) is a major cause of infectious mortality and morbidity in poultry worldwide. It is an enveloped virus with two outer-membrane proteins—haemagglutinin-neuraminidase (HN) and fusion protein (F)—that induce neutralizing antibodies. All NDV strains belong to one serotype. Yet, NDV vaccines, derived from genotype II, do not fully prevent infection or shedding of viruses from other genotypes. The aim of this study was to test if an updated vaccine is required. For this purpose, NDVs isolated from infected, albeit heavily vaccinated, flocks were genetically and immunologically characterized. Amino acid differences in F and HN protein sequences were identified between the vaccine strain and each of the isolates, some specifically at the neutralization sites. Whereas all tested isolates showed similar haemagglutination-inhibition (HI) titres, 100–100,000 times higher antibody-to-virus ratios were needed to neutralize viral propagation in embryos by the field isolates versus the vaccine strain. As a result, a model and an equation were developed to explain the phenomenon of escape in one-serotype viruses and to calculate the HI values needed for protection, depending on variation rate at key positions. In conclusion, to confer full protection against NDVs that differ from the vaccine strain at the neutralizing epitopes, very high levels of antibodies should be raised and maintained to compensate for the reduction in the number of effective epitopes; alternatively, an adjusted attenuated vaccine should be developed—a task made possible in the current era of reverse vaccinology.     

Characterization of a novel VIIl sub-genotype of Newcastle disease virus circulating in Iran

Newcastle disease is an economically important and highly contagious disease affecting wild and domestic avian species. Despite extensive vaccination efforts within the poultry industry, Newcastle disease virus (NDV) outbreaks causing significant economic losses still occur. Rural chickens may act as a potential reservoir of NDVs for commercial poultry due to poor biosecurity and inadequate vaccination. The aim of this study was to investigate the phylogenetic relationship and molecular characterization of eight NDVs isolated from backyard poultry in Iran during 2011–2013. The complete coding sequence of fusion (F) and haemagglutinin-neuraminidase (HN) genes of eight NDVs were determined and compared with other published NDVs. Based on inter-population distances and phylogenetic topology between available NDV categories, Iranian isolates formed a novel VIIl sub-genotype distinct from previous groups designated in genotype VII. Furthermore, both F and HN genes of the Iranian isolates shared high nucleotide sequence similarity with viruses isolated in China. All viruses analysed contained a polybasic cleavage site motif (¹¹¹G/RRRQKR↓F¹¹⁷), indicating that all isolates could be categorized as a virulent pathotype. No mutation was observed in the neutralizing epitopes of the F protein. Analysis of amino acids associated with neutralizing antigenic sites within the HN protein revealed that all isolates exhibited a unique amino acid (Q) at position 347. These results emphasize the need for strengthening the biosecurity measures implemented on village flocks and practicing a mandatory vaccination programme for local poultry. Moreover, continuous monitoring of NDVs in different species of birds can help to gain more knowledge about the evolution of this virus and prevent future panzootics.     

Newcastle disease virus: An evolving pathogen?

Australia experienced outbreaks of virulent Newcastle disease (ND) in chickens in the state of New South Wales in the years 1998, 1999 and 2000. The disease had occurred previously in Australia in 1930 and 1932 but the country was free of it until the recent outbreaks. Avirulent strains of Newcastle disease virus (NDV) were detected in 1966 and, during the next two to three decades, strains (so-called lentogenic strains) able to induce mild respiratory disease equivalent to that induced by vaccine strains such as LaSota were also detected. Nucleotide sequence analysis of the genes encoding the haemagglutinin and fusion proteins of Australian isolates of the virus during this time demonstrated that Australian chicken strains of NDV could be differentiated from NDV isolated elsewhere. Analysis in this way demonstrated that NDV isolates causing the recent outbreaks of virulent disease were Australian viruses that were so closely related to a recognized Australian lentogenic strain, termed the Peat's Ridge strain, that it was considered to be the precursor of the virulent virus. The outbreaks of virulent disease in 1998 and 1999 were controlled by an official "stamping out" eradication campaign. This was subsequently replaced by strategic use of ND vaccines when virulent virus was again detected on some farms that had been restocked following depopulation. The national situation with regard to ND is now being assessed through a structured national survey of ND viruses, particularly to determine the distribution of the precursor strain. No new outbreaks of virulent ND have been recognized since February 2000, although immunization of flocks in areas where the disease was recognized has occurred.     

Genomic characterisation of a lentogenic Newcastle disease virus strain HX01 isolated from sick pigs in China

This paper describes the complete genome sequence of HX01, an isolate of the Newcastle disease virus (NDV) collected from a swine disease outbreak. The genome is 15,186 nt long and consists of six genes in the order of 3′-NP-P-M-F-HN-L-5′. This genome has the same length as the old NDV genotypes (I–IV), whereas the new NDV genotypes (V–IX) are 15,192 nt long. Compared with the genomic sequences of the reference NDV strains, the HX01 genome is highly similar to the genome of other NDV strains. However, some unique features of the HN gene were found in HX01. HX01 possesses the motif ¹¹²G-R-Q-G-R-L¹¹⁷ at the fusion protein cleavage site, which is typical of lentogenic strains. Pathogenicity tests based on the mean death time and the intracerebral pathogenicity index also revealed the isolate’s lentogenic character. Phylogenetic analysis based on the variable region of the F gene (nt 47–420) revealed that HX01 was clustered to genotype II within class II NDV. Genetically, HX01 has a high similarity with the La Sota vaccine strain based on the single gene or complete genomic but is far different from the prevalent genotype VIId NDV which circulates in fowls and waterfowls in mainland China.     

Complete genome sequence of highly virulent neurotropic Newcastle disease virus strain Texas GB

Newcastle disease virus (NDV) strain Texas GB is a highly virulent neurotropic virus that is used as a standard vaccine challenge virus in the U.S. In this study, the complete genome sequence of strain Texas GB was determined and compared with the complete genome sequences of other NDV strains. The genome is 15,186 nucleotides (nt) long and consists of six genes in the order of 3′leader-N-P-M-F-HN-L-5′trailer. The genome contains a 55-nt leader sequence at the 3′ end and a 114-nt trailer sequence at the 5′ end. The intergenic sequences are 2, 1, 1, 31, and 47 nt between N/P, P/M, M/F, F/HN, and HN/L genes, respectively. The putative cleavage site of fusion protein showed amino acid sequence of R-R-Q-K-R↓F in position 112 to 117, which corresponds to those of virulent NDV strains. The phylogenetic analysis showed that strain Texas GB is closely related to the neurovirulent mesogenic strain Beaudette C (BC) and to NDV viruses isolated in China and Egypt than to other strains of NDV.     

Pathotypical and genotypical characterization of strains of <Emphasis Type="Italic">Newcastle disease virus</Emphasis> isolated from outbreaks in chicken and goose flocks in some regions of China during 1985–2001

Summary.  Twenty-nine strains of Newcastle disease virus (NDV) isolated from outbreaks in chicken and goose flocks in several regions of China during 1985–2001 were characterized pathotypically and genotypically. All except one of these strains were velogenic. For genotyping, phylogenetic tree analysis (nt 47–420), restriction site mapping (nt 334–1682) and residue substitution analysis (residues 4–124) of the F gene were performed using sequences of our isolates and sequences of selected NDV strains from GenBank. The results revealed that most of these newly characterized strains belonged to six novel genetic groups that were designated as VIf, VIg, VIIc, VIId, VIIe and IX. The genotype IX viruses, to which the China challenge strain F48E8 used for vaccine evaluation belonged, were found only in China and still induced sporadic infections in certain areas. Isolates belonging to group VIf and VIg were distinct from previously reported members of genotype VI, with genetic distance from 2.5 to 12.1%. Subgenotype VIIc, VIId and VIIe viruses, which were distributed in clusters in the phylogenetic tree distinct from members of subgenotypes VIIa and VIIb, were responsible for disease outbreaks in chicken and goose flocks and circulated predominantly in southern China in recent years. Finally, cross-protective testing showed that specific-pathogen free (SPF) chickens vaccinated with La Sota vaccines can be fully protected against challenge by strains from genetic groups VIb, VIg, VIId and IX, indicating that the antigenic differences between strains of various genotypes are insufficient to change the cross-protection conferred by the commonly used vaccine. Received August 16, 2002; accepted January 6, 2003 Published online April 28, 2003     

Simultaneous vaccination of day-old chickens against Newcastle and Marek's diseases

Commercial day-old chicks vaccinated against Marek's disease (MD) with turkey herpesvirus (HVT) were tested for their ability to respond to a live Newcastle disease vaccine (NDV) - La Sota strain - administered by different routes. Simultaneous vaccination of day-old birds with HVT and NDV did not affect the immune response to NDV nor the viraemia induced by HVT vaccination. MD and ND vaccinations performed together, the first by the intramuscular route and the second by beak dipping, gave a valuable protection in flocks exposed to the two diseases.     

Emergence of a virulent genotype VIIi of Newcastle disease virus in Iran

Newcastle disease (ND) is a contagious viral disease affecting numerous avian species, particularly domestic poultry, and causes devastating outbreaks. In spite of its endemicity and importance in Iran, data on the genetic characterization of ND virus (NDV) are scarce. An alarming issue that has just been raised is the occurrence of ND outbreaks with unexpected high mortality and severe clinical signs. The present study was conducted to characterize the emerging NDV genetically. An NDV strain, isolated in 2017 from commercial broilers showing severe nervous and enteric signs, was completely sequenced and found to be 15,192 nucleotides in length. The phylogenetic analysis demonstrated that the virus belonged to subgenotype VIIi, a subgenotype with potential panzootic features which has recently emerged in the Middle East and Asia. The supporting genetic pattern obtained from the complete genome, fusion and haemagglutinin gene analysis showed close relationship of the isolate with Pakistani VIIi NDVs. The analysis of the F protein showed a polybasic amino acid motif and a phenylalanine at position 117 at the cleavage site, which is a characteristic of virulent strains. The isolate showed significant differences from the previously characterized NDV strains from commercial and rural chickens in Iran. This may describe the importance of the illegal trade of pet birds from neighbouring countries leading to the emergence of new genotypes. This study introduces a newly emerging NDV VIIi subgenotype in Iran. This investigation emphasizes the necessity of effective control strategies.     

Molecular Characterization of Virulent Newcastle Disease Virus Isolates from Chickens during the 1998 NDV Outbreak in Kazakhstan

Newcastle disease virus (NDV) infects domesticated and wild birds throughout the world and has the possibility to cause outbreaks in chicken flocks in future. To assess the evolutionary characteristics of 10 NDV strains isolated from chickens in Kazakhstan during 1998 we investigated the phylogenetic relationships among these viruses and viruses described previously. For genotyping, fusion (F) gene phylogenetic analysis (nucleotide number 47-421) was performed using sequences of Kazakhstanian isolates as compared to sequences of selected NDV strains from GenBank. Phylogenetic analysis showed that all newly characterized strains belonged to the genetic group designated as VIIb. All strains possessed a virulent fusion cleavage site (RRQRR/F) belonging to velogenic or mesogenic pathotypes with intracerebral pathogenicity indexes (ICPI) varying from 1.05 to 1.87.     

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.     

Assembly and immunological properties of a bivalent virus-like particle (VLP) for avian influenza and Newcastle disease

Avian influenza virus (AIV) and Newcastle disease virus (NDV) are both important pathogens in poultry worldwide. The protection of poultry from avian influenza and Newcastle disease can be achieved through vaccination. We embarked on the development of a bivalent vaccine that would allow for a single immunization against both avian influenza and Newcastle disease. We constructed a chimeric virus-like particle (VLP) that is composed of the M1 protein and HA protein of avian influenza virus and a chimeric protein containing the cytoplasmic and transmembrane domains of AIV neuraminidase protein (NA) and the ectodomain of the NDV hemagglutinin-neuraminidase (HN) protein (NA/HN). The single immunization of chickens with the chimeric VLP vaccine induced both AIV H5- and NDV-specific antibodies. The HI titers and specific antibodies elicited by the chimeric VLPs were statistically similar to those elicited in animals vaccinated with the corresponding commercial monovalent vaccines. Chickens vaccinated with chimeric VLP vaccine and then challenged with the Newcastle disease F48E9 virus displayed complete protection. Overall, the chimeric VLP vaccine elicits strong immunity and can protect against Newcastle disease virus challenge.     

Characterization of Malaysian velogenic NDV strain AF2240-I genomic sequence: a comparative study

Newcastle disease virus (NDV) strain AF2240 is a viscerotropic velogenic strain that is used as a vaccine challenge virus in Malaysia. The identification of the full length genome will be a crucial platform for further studies of this isolate. In this study, we fully sequenced the genome of a derivative of this strain named AF2240-I. The 15,192 nt long genome contains a 55-nt leader sequence at the 3′ whereas the trailer region consists of 114 nt at the 5′. The intergenic sequences between the NP-P, P-M, M-F, F-HN, and HN-L genes comprise 1, 1, 1, 31, and 47 nt, respectively. The acknowledged cleavage site of fusion protein showed amino acid sequence of 112-R-R-Q-K-R-F-117, which corresponds to those of virulent NDV strains. Phylogenetic analysis of the whole virus genome shows that the strain AF2240-I belongs to genotype VIII and is more closely related to velogenic strains QH1, QH4, Fontana, Largo, and Italienas compared to other strains of NDV. Differences are noticed in the hemagglutinin-neuraminidase (HN) and matrix (M) gene between AF2240 and its derivative AF2240-I. This is the first report of a complete genome sequence of an NDV strain isolated in Malaysia.     

Multiplex RT-PCR for rapid detection and differentiation of class I and class II Newcastle disease viruses

A multiplex RT-PCR was developed for detection and differentiation of class I and class II strains of Newcastle disease virus (NDV). The method was shown to have high specificity and sensitivity. The results obtained from the multiplex RT-PCR for a total of 67 NDV field isolates obtained in 2009 were consistent with those obtained by nucleotide sequencing and phylogenetic analysis. A phylogenetic tree based on the partial sequences of the F gene revealed that the 67 field isolates of NDV could be divided into two classes. Twenty-seven NDV isolates were grouped into class I, and two genotypes were identified. Most of the class I isolates were determined to be of genotype 3, with the exception of isolate NDV09-034, which belonged to genotype 2. Forty class II NDV isolates were divided into three genotypes, namely genotype VII (27 isolates), genotype I (2 isolates) and genotype II (11 isolates). Isolates of genotypes I and II in class II were shown to be related to commercial vaccine strains used commonly in China. All isolates of genotype VII were predicted to be virulent, on the basis of the sequence motif at the cleavage site of the F gene. This genotype has become predominantly responsible for most outbreaks of ND in China in recent years. In conclusion, this multiplex RT-PCR provides a new assay for rapid detection and differentiation of both classes of NDV isolates.     

Sequence variation in the Newcastle disease virus genome

Full-length genome sequences of five virulent and five avirulent strains of Newcastle disease virus isolated between 1998 and 2002 in Victoria and New South Wales, Australia were determined. Comparisons between these strains revealed that coding sequence variability in the haemagglutinin-neuraminidase (HN), matrix (M) and phosphoprotein (P) gene sequences appeared to be more variable than in the fusion (F), nucleocapsid (N) and RNA dependent-RNA replicase (L) genes. Sequence analysis of a number of other isolates made during the recent virulent NDV outbreaks, also identified the presence of a number of variants with altered F gene cleavage sites, which resulted in altered biological properties of those viruses. Quasispecies analysis of a number of field isolates indicated the presence of virulent virus in one particular isolate. Gene sequence analysis of the progenitor virus isolated in 1998 showed very little sequence variation when compared to that of a progenitor-like virus isolated in 2001, demonstrating that in the field, viral genome sequence variation appears to be biologically restricted to that of a consensus sequence.