Surveillance of avirulent Newcastle disease viruses at live bird markets in Eastern China during 2008-2012 reveals a new sub-genotype of class I virus

Surveillance of Class I Newcastle Disease Virus at Live Bird Markets in China and Identification of Variants with Increased Virulence and Replication Capacity

In this study, 232 class I Newcastle disease viruses (NDVs) were identified from multiple bird species at nationwide live bird markets (LBMs) from 2017 to 2019 in China. Phylogenetic analysis indicated that all 232 isolates were clustered into genotype 1.1.2 of class I on the basis of the fusion (F) gene sequences, which were distinct from the genotypes identified in other countries. Most of the isolates (212/232) were shown to have the typical F gene molecular characteristics of class I NDVs, while a few (20/232) contained mutations at the site of the conventional start codon of the F gene, which resulted in open reading frames (ORFs) altered in length. The isolates with ACG, CTA, and ATA mutations showed different levels of increased virulence and replication capacity, suggesting that these viruses may be transitional types during the evolution of class I NDVs from avirulent to virulent. Further evaluation of biological characteristics with recombinant viruses obtained by reverse genetics demonstrated that the ATG located at genomic positions 4523 to 4525 was the authentic start codon in the F gene of class I NDV, and the specific ATA mutations which contributed to the expression of F protein on the surface of infected cells were the key determinants of increased replication capacity and virulence. Interestingly, the mutation at the corresponding site of genotype II LaSota of class II had no effects on the virulence and replication capacity in chickens. Our results suggest that the alteration of virulence and replication capacity caused by specific mutations in the F gene could be a specific characteristic of class I NDVs and indicate the possibility of the emergence of virulent NDVs due to the persistent circulation of class I NDVs. IMPORTANCE The available information on the distribution, genetic diversity, evolution, and biological characteristics of class I Newcastle disease viruses (NDVs) in domestic poultry is currently very limited. Here, identification of class I NDVs at nationwide live bird markets (LBMs) in China was performed and representative isolates were characterized. A widespread distribution of genotype 1.1.2 of class I NDVs was found in multiple bird species at LBMs in China. Though most isolates demonstrated typical molecular characteristics of class I NDVs, a few that contained specific mutations at the site of the conventional start codon of the fusion gene with increased virulence and replication capacity were identified for the first time. Our findings indicate that the virulence of class I NDVs could have evolved, and the widespread transmission and circulation of class I NDVs may represent a potential threat for disease outbreaks in poultry.

The chicken-derived velogenic Newcastle disease virus can acquire high pathogenicity in domestic ducks via serial passaging

Velogenic Newcastle disease virus (NDV) strains, which show high mortality in chickens, generally do not cause severe disease in waterfowl such as ducks. To elucidate the difference in the pathogenic mechanisms of NDV between chickens and ducks, a chicken-derived velogenic strain (9a5b) was passaged in domestic ducks five times in their air sacs, followed by 20 times in their brains. Eventually, 9a5b acquired higher intracerebral and intranasal pathogenicity in ducks. The intracerebral pathogenicity index (ICPI) value increased from 1.10 to 1.88. All one-week-old ducks intranasally inoculated with the passaged virus (d5a20b) died by 5 days post-inoculation, whereas 70% of the ducks inoculated with parental 9a5b survived for 8 days. The d5a20b strain replicated in broader systemic tissues in ducks compared with the 9a5b strain. The velogenic profile of 9a5b in chickens was maintained after passaging in ducks. The d5a20b suppressed IFN-β gene expression in duck embryo fibroblasts and replicated more rapidly than 9a5b. A total of 11 amino acid substitutions were found in the P, V, M, F, HN, and L proteins of d5a20b. These results suggest that chicken-derived velogenic NDVs have the potential to become virulent in both chickens and ducks during circulation in domesticated waterfowl populations. RESEARCH HIGHLIGHTSChicken-derived NDV acquired high pathogenicity in ducks with serial passaging.The passaged NDV showed intracerebral and intranasal pathogenicity in ducks.The passaged NDV efficiently replicated in systemic tissues in ducks.Of 11 amino acid substitutions some or all are likely involved in pathogenicity.

Evolutionary dynamics and transmission patterns of Newcastle disease virus in China through Bayesian phylogeographical analysis

The Chinese poultry industry has experienced outbreaks of Newcastle disease (ND) dating back to the 1920s. However, the epidemic has exhibited a downtrend in recent years. In this study, both observational and genetic data [fusion (F) and haemagglutinin-neuraminidase genes (HN)] were analyzed, and phylogeographic analysis based on prevalent genotypes of Newcastle disease virus (NDV) was conducted for better understanding of the evolution and spatiotemporal dynamics of ND in China. In line with the observed trend of epidemic outbreaks, the effective population size of F and HN genes of circulating NDV is no longer growing since 2000, which is supported by 95% highest posterior diversity (HPD) intervals. Phylogeographic analysis indicated that the two eastern coastal provinces, Shandong and Jiangsu were the most relevant hubs for NDV migration, and the geographical regions with active NDV diffusion seemed to be constrained to southern and eastern China. The live poultry trade may play an important role in viral spread. Interestingly, no migration links from wild birds to poultry received Bayes factor support (BF > 3), while the migration links from poultry to wild birds accounted for 64% in all effective migrations. This may indicate that the sporadic cases of ND in wild bird likely spillover events from poultry. These findings contribute to predictive models of NDV transmission, and potentially help in the prevention of future outbreaks.

Phylodynamic analyses of class I Newcastle disease virus isolated in China

Newcastle disease virus (NDV), the pathogen of Newcastle disease, has caused significant losses to the poultry industry worldwide. However, owing to its avirulence, class I NDVs have not been studied as much as class II NDVs. We aimed to epidemiologically monitor the spread of class I NDVs in China. We isolated 104 class I NDV strains from poultry in live poultry markets (LPMs) of Guangdong Province, south China, between January 2016 and December 2018. Genetic analysis revealed that all 104 isolates and most of the strains isolated from China were clustered into genotype 1.1.2 of class I NDVs. Bayesian analysis revealed that, although the United States may be the source, east and south China may be the epicentres of class I NDVs in China. In addition, in China, class I NDVs are presumably transmitted by chickens and domestic ducks as the virus is mostly prevalent in these birds. These novel findings demonstrated that class I NDVs are prevalent in south China, and it is important to perform routine surveillance and limit the numbers of different birds in different areas of LPMs to decrease the risk of intra- and interspecies transmission of NDVs.

Comparative pathogenicity of two closely related Newcastle disease virus isolates from chicken and pigeon respectively

Newcastle disease (ND), caused by virulent Newcastle disease virus (NDV), is a highly contagious disease that has led to tremendous economic losses worldwide. Pigeon paramyxovirus type 1 (PPMV-1) is an antigenic and host variant of NDV. However, limited in-depth studies are available concerning side-by-side comparison of pathogenicity of PPMV-1 and its phylogenetically close NDV both in chickens and pigeons. To this end, two phylogenetically closely related NDV isolates, Kuwait 256 and JS/07/04/Pi from chicken and pigeon respectively were pathotypically and genotypically characterized in this study. The results indicated that Kuwait 256 was a velogenic strain, while JS/07/04/Pi was a mesogenic strain based on the mean death time of chick embryos (MDT) and intracerebral pathogenicity index in 1-day-old chicks (ICPI). Pathogenicity tests showed that Kuwait 256 caused severe clinical signs and 100 % mortality, while JS/07/04/Pi caused no apparent disease in chickens. Interestingly, both Kuwait 256 and JS/07/04/Pi caused morbidity and mortality in pigeons. Notably, pigeons infected with JS/07/04/Pi exhibited viral shedding for longer time compared to Kuwait 256-infected pigeons. Collectively, the findings of this study suggested that PPMV-1 decreased the pathogenicity in chickens but gained a survival advantage over NDV of chicken origin after its adaptive variation in pigeons based on the previous evidence that PPMV-1 originated from chicken-origin viruses. This study laid the foundation for the elucidation of the molecularmechanism underlying difference in pathogenicity of PPMV-1 and chicken-origin NDV in chickens.

Comparison between class I NDV and class II NDV in aerosol transmission under experimental condition

Recent epidemiological surveys have shown that class I Newcastle disease virus (NDV) is widely distributed in China. However, little is currently known about its transmission. Therefore, in this study, we compared the transmission of class I and class II NDV. Specific-pathogen-free chickens were divided into a class I NDV inoculation group and an aerosol-exposed infection group and kept in 2 separate isolators (A and B, respectively) that were connected with an airtight plastic pipe. After inoculation, air samples were collected regularly with an All-Glass Impinger-30 (Liaoyang, China), and the airborne virus contents were analyzed using the plaque count method. In addition, oral and cloacal swabs were collected regularly to detect virus shedding using quantitative reverse transcription PCR. Similar trials were conducted simultaneously with class II NDV in isolators C and D. We consistently detected class I NDV aerosols in both isolators A and B up to 40 D post-inoculation (dpi). The aerosol concentration reached a maximum of 13.81 × 103 plague-forming units per cubic meter of air at 18 dpi and was significantly higher than that of class II NDV at 21 and 24 dpi. We also detected class I virus shedding from 2 to 40 dpi in the inoculated chickens and from 7 to 40 D post-aerosol-exposed infection in the aerosol-exposed chickens. This phenomenon may explain why class I NDV has been the primary epidemic strain of NDV in recent years.

A class Ⅰ lentogenic newcastle disease virus strain confers effective protection against the prevalent strains

The traditional vaccine strains, such as LaSota, do not completely prevent the shedding of NDV. An ideal vaccine which could not only prevent the clinical signs, but significantly reduce the shedding of NDV is urgently needed for the eradication of ND. In this study, an NDV isolate APMV-1/Chicken/China (SC)/PT3/2016 (hereafter referred as PT3) was identified as a class Ⅰ NDV and a lentogenic strain. The antigenic relationship between PT3 and 3 other NDV strains, including vaccine strain LaSota and 2 prevalent genotype Ⅶd and Ⅵb strains were analyzed. The protective efficacy of PT3 and LaSota against challenge with genotype Ⅶd and Ⅵb strains were assessed. The antigenic analysis result showed that 4 strains belong to the single serotype and the PT3 antiserum exhibited the highest HI titer against 3 other NDV strains. The results of protective efficacy showed that both of LaSota and PT3 could provide 100% survivability for infected chickens. However, PT3 performed better in inducing higher humoral responses and reducing virus shedding than the LaSota strain. Lentogenic strains from Class I NDV appear to be promising vaccine candidates for the control of ND, and allows for the easy discrimination of field NDV and vaccine strains.

Evaluation of transmission potential and pathobiological characteristics of mallard originated Avian orthoavulavirus 1 (sub-genotype VII.2) in commercial broilers

Newcastle disease (ND), caused by Avian orthoavulavirus 1 (AOAV-1), affects multiple avian species around the globe. Frequent disease outbreaks are not uncommon even in vaccinates despite routine vaccination and, in this regards, viruses of diverse genotypes originating from natural reservoirs (migratory waterfowls) play an important role in a disease endemic setting. Though genomic characterization of waterfowl originated viruses has been well-elucidated previously, there is a paucity of data on clinico-pathological assessment of mallard-originated sub-genotype VII.2 in commercial chickens. Hence, the current study was designed to evaluate its transmission potential, tissue tropism and micro- and macroscopic lesions in commercial broilers. Based on complete genome and complete F gene, phylogenetic analysis clustered the study isolate within genotype VII and sub-genotype VII.2 in close association with those reported previously from multiple avian species worldwide. The study strain was found to be velogenic on the basis of typical residue pattern in the F-protein cleavage site (¹¹²R-RQ-K-R↓F¹¹⁷), sever disease induction in chicken, tissue tropism and subsequent clinico-pathological characteristics. Giving a clear evidence of horizontal transmission, a 100% mortality was observed by 4^th and 6^th day post infection (dpi) in chickens challenged with the virus and those kept with the challenged birds (contact birds), respectively. The observed clinical signs, particularly the greenish diarrhea, and macroscopic lesions such as pinpoint hemorrhages in proventriculus and caecal tonsils were typical of the infection caused by an AOAV-1 in chickens. The virus exhibited a broad tissue tropism where genomic RNA corresponding to study virus was detected in all of the tissues collected from recently mortile and necropsied birds. The study concludes that mallard-originated Avian orthoavulavirus 1 is highly velogenic to commercial chicken and therefore ascertain continuous disease monitoring and surveillance of migratory/aquatic fowls to better elucidate infection epidemiology and subsequent potential impacts on commercial poultry.

Characterization of a Novel Avian Avulavirus 1 of Class I isolated from a Mute Swan (Cygnus Olor) in Macedonia in 2012

Avian avulavirus type 1 (AAvV-1) belongs to the family Paramyxoviridae, genus Avulavirus. Even though belonging to a single serotype, there is great genetic variability between these viruses. On the basis of the available complete fusion (F) gene and whole genome sequences and using the genotype classification system, AAvV-1 viruses are divided in two major groups: class I and class II. Class I viruses are predominantly avirulent viruses and majority of the isolations come from waterfowl and domestic poultry from live bird markets in USA and China although isolations from wild birds are reported globally. In our study we used classical, molecular and phylogenetic tools to characterize an AAvV-1 isolated from a mute swan in Macedonia. Based on the complete F gene sequence, we have concluded that the virus designated as AAvV-1/mute swan/Macedonia/546/2012 (KP123431) belongs to the class I of AAvV-1 with an avirulent cleavage site motif 112ERQER*L117. The virus could not be assigned to any of the four currently existing subgenotypes (1a, 1b, 1c or 1d) of the single genotype 1 of class I viruses. Two distant viruses, isolated from goose in Alaska in 1991 and from goose in Ohio in 1987, shared the highest nucleotide sequence identity of the complete F gene with the isolate in our study: 92.7% and 92.8%, respectively. This is the first report of isolation of class I AAvV-1 in Southeastern Europe. The asymptomatic nature and the underreporting of sequences from the class I viruses impede the understanding of the molecular epidemiology and evolution of this group of viruses.

Phylogeny, pathogenicity and transmissibility of a genotype XII Newcastle disease virus in chicken and goose

Although Newcastle disease virus (NDV) has a worldwide distribution, some NDV genotypes have more regional geographical ranges within continents. In this study, we isolated a subgenotype XIIb NDV strain, Goose/CH/GD/E115/2017 (E115), from geese in Guangdong province, Southern China, in 2017. Phylogenetic analysis showed that E115 and six other NDVs from geese in China were grouped under subgenotype XIIb and were distinct from subgenotype XIIa, isolated from chickens in South Africa, and subgenotype XIId, isolated from chickens in Vietnam. To better understand the pathogenicity and transmission of the subgenotype XIIb NDVs from geese in Guangdong province, we inoculated chickens and geese with 10⁶ EID₅₀ of the E115 virus. Eight hours after inoculation, three naïve chickens and three naïve geese were co-housed with the infected chickens or geese to assess intraspecific and interspecific horizontal transmission of the E115 virus. The E115 virus induced significant clinical signs without mortality in chickens, while it was not pathogenic to geese. Intraspecific and interspecific horizontal transmission of the E115 virus was observed among chickens and geese via direct contact. Furthermore, although the current vaccines provided complete protection against disease in chickens after challenging them with the E115 virus, the virus could also be transmitted from vaccinated chickens to naïve contact chickens. Collectively, our findings highlight the need for avoiding the mixing of different bird species to reduce cross-species transmission and for surveillance of NDV in waterfowl.

Complete Genome Sequence of a Class I Newcastle Disease Virus Strain Isolate from a Breeding Chicken Flock in Sichuan, China

A Newcastle disease virus (NDV) strain, APMV-1/Chicken/China(SC)/PT3/2016, was isolated from asymptomatic chickens at a breeding farm in China. The PT3 strain has a genome length of 15,198 nucleotides and is classified as subgenotype 1b of class I. Pathogenicity tests demonstrated that PT3 is a lentogenic strain.

Viral infection detection using metagenomics technology in six poultry farms of eastern China

With rapidly increasing animal pathogen surveillance requirements, new technologies are needed for a comprehensive understanding of the roles of pathogens in the occurrence and development of animal diseases. We applied metagenomic technology to avian virus surveillance to study the main viruses infecting six poultry farms in two provinces in eastern China. Cloacal/throat double swabs were collected from 60 birds at each farm according to a random sampling method. The results showed that the method could simultaneously detect major viruses infecting farms, including avian influenza virus, infectious bronchitis virus, Newcastle disease virus, rotavirus G, duck hepatitis B virus, and avian leukemia virus subgroup J in several farms. The test results were consistent with the results from traditional polymerase chain reaction (PCR) or reverse transcription-PCR analyses. Five H9N2 and one H3N8 avian influenza viruses were detected at the farms and were identified as low pathogenic avian influenza viruses according to HA cleavage sites analysis. One detected Newcastle disease virus was classified as Class II genotype I and avirulent type according to F0 cleavage sites analysis. Three avian infectious bronchitis viruses were identified as 4/91, CK/CH/LSC/99I and TC07-2 genotypes by phylogenetic analysis of S1 genes. The viral infection surveillance method using metagenomics technology enables the monitoring of multiple viral infections, which allows the detection of main infectious viruses.

Molecular characterization, pathogenicity, and protection efficacy analysis of 2 wild-type lentogenic class I Newcastle disease viruses from chickens in China

In this study, 2 wild-type Newcastle disease viruses (NDVs), designated as CK/GX/65/15 and CK/GX/26/15, were isolated from asymptomatic chickens in Guangxi province, China. They were identified as lentogenic NDV with mean death time (MDT) above 90 and intracerebral pathogenicity index (ICPI) below 0.7. The results of complete genome sequence analysis show that the 2 NDV strains are members of class I genotype 3 with the length 15,198 nt, which followed the "rule of six" and the order 3'-NP-P-M-F-HN-L-5'. In addition, 8 amino acid substitutions were identified in the functional domains of fusion protein (F) of CK/GX/65/15 and 9 in CK/GX/26/15, whose amino acid sequences of F protein cleavage site are 112E-R-Q-E-R-L117. The isolates were found to be apathogenic in specific pathogen free (SPF) chickens and ducks without morbidity or mortality. Furthermore, the protection study shows that isolates can provide the same effective protection against a major NDV virulent strain in China (class II genotype VII) as the commercial vaccine LaSota. Moreover, vaccination with isolates reduced number of chickens shedding virus compared to those vaccinated with LaSota. In conclusion, 2 wild-type NDV strains exhibited fine protection efficacy against genotype VII NDV in poultry and can be considered as candidate vaccines against NDV.

Pathobiology of Avian avulavirus 1: special focus on waterfowl

Avian avulaviruses serotype 1 (abbreviated as APMV-1 for the historical name avian paramyxovirus 1) are capable of infecting a wide spectrum of avian species with variable clinical symptoms and outcomes. Ease of transmission has allowed the virus to spread worldwide with varying degrees of virulence depending upon the virus strain and host species. The emergence of new virulent genotypes from global epizootics, and the year-to-year genomic changes in low and high virulence APMV-1 imply that distinct genotypes of APMV-1 are simultaneously evolving at different geographic locations across the globe. This vast genomic diversity may be favoured by large variety of avian species susceptibility to APMV-1 infection, and by the availability of highly mobile wild birds. It has long been considered that waterfowls are not sensitive to APMV-1 and are unable to show any clinical signs, however, outbreaks from the 90's contradict these concepts. The APMV-1 isolates are increasingly reported from the waterfowl. Waterfowl have strong innate immune responses, which minimize the impact of virus infection, however, are unable to prevent the viral shedding. Numerous APMV-1 are carried by domestic waterfowl intermingling with terrestrial poultry. Therefore, commercial ducks and geese should be vaccinated against APMV-1 to minimize the virus shedding and for the prevention the transmission. Genetic diversity within APMV-1 demonstrates the need for continual monitoring of viral evolution and periodic updates of vaccine seed-strains to achieve efficient control and eradication of APMV-1 in waterfowls.

Recombinant Newcastle disease virus (NDV) expressing Duck Tembusu virus (DTMUV) pre-membrane and envelope proteins protects ducks against DTMUV and NDV challenge

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Firstly generated a NDV-vectored Duck Tembusu Virus (DTMUV) bivalent vaccine that expressing the pre-membrane and envelope proteins of DTMUV.

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Evaluated the efficacy of the NDV-vectored Duck Tembusu Virus bivalent vaccine.

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Provided a new method for NDV and DTMUV controlling in waterfowl.

The newly emerged Duck Tembusu virus (DTMUV) is responsible for considerable economic loss in waterfowl-raising areas in China since 2010. Meanwhile, the virulent Newcastle disease virus (NDV) has also caused sporadic outbreaks in waterfowl. The individual vaccines against both diseases are available, however, there is no bivalent or combined vaccine for either disease. Here, we constructed a recombinant NDV-vectored vaccine candidate that expresses the pre-membrane (prM) and envelope (E) genes from DTMUV, designated as aGM/prM + E. The foreign prM and E proteins were stably expressed in aGM/prM + E and exhibited similar pathogenicity but higher growth kinetics than those of the parental virus. The aGM/prM + E carries a fusion cleavage site in accordance with avirulent viruses that have been frequently isolated from waterfowl, and induced remarkably (p < 0.001) higher NDV-specific hemagglutination inhibition (HI) titers than commercially available live NDV vaccines (LaSota strain). The aGM/prM + E also elicited significantly higher (p < 0.05) virus neutralization (VN) titers than commercially available DTMUV inactivated vaccines (HB strain). The aGM/prM + E not only provided complete protection against NDV challenge but also reduced the gross lesions on ovarian folliculi and provided 80% protection against DTMUV in ducks. We note that the aGM/prM + E vaccine can prevent challenged ducks from shedding of NDV and DTMUV. Our results suggest that the candidate vaccine aGM/prM + E would help decrease NDV and DTMUV transmissions in waterfowl raising areas in China.

Spillover of Newcastle disease viruses from poultry to wild birds in Guangdong province, southern China

Despite intensive vaccination programs in many countries, including China, Newcastle disease has been reported sporadically and is still a significant threat to the poultry industry in China. Newcastle disease virus (NDV) is infectious for at least 250 bird species, but the role of wild birds in virus epidemiology remains largely unknown. Fourteen NDV isolates were obtained from 2040 samples collected from wild birds or the environment in Guangdong province, southern China, from 2013 to 2015. The isolation rate was the highest in the period of wintering and lowest during the periods of spring migration, nesting, and postnesting. A maximum clade credibility phylogenetic analysis revealed that at least four genotypes circulate in southern China: three class II genotypes (II, VI, and IX) and one class I (1b). We also demonstrated that most isolates from wild birds were highly similar to isolates from poultry, and two isolates were linked to viruses from wild birds in northern China. These data suggested that wild birds could disseminate NDV and poultry-derived viruses may spillover to wild birds. Accordingly, vaccine development and poultry management strategies should be considered to prevent future NDV outbreaks, particularly given the strength of the poultry industry in developing countries, such as China.

Genomic Characterizations of a Newcastle Disease Virus Isolated from Ducks in Live Bird Markets in China

One class I Newcastle disease virus (NDV), designated as duck/Guangxi/1261/2015 (GX1261), was isolated from asymptomatic ducks in live bird markets (LBM) from southern China during the national active surveillance for NDVs in 2015. The complete genome length of GX1261 isolate was 15,198 nucleotides with the gene order of 3'-NP-P-M-F-HN-L-5'. The motif at the cleavage site of F protein was 112ERQER/L117, which was typical of low virulence NDV. Several mutations were identified in the functional domains of F and HN proteins, including fusion peptide, heptad repeat region, transmembrane domains and neutralizing epitopes. Phylogenetic analysis based on the complete F gene revealed that the isolate was clustered into sub-genotype 1c in class I, and showed a high level of similarity with the strains isolated from waterfowl in the United States of America. This is the first report of this kind of virus in the mainland of China. These results demonstrated that GX1261-like viruses might exist in asymptomatic waterfowl, and remain undetected or unidentified. Thus, more investigation needs to be done in order to identify the source of the virus. This study revealed the genetic and phylogenetic characteristics of GX1261 isolate and could help us to better understand the epidemiological context of class I NDV in China.

Phylogenetic and Pathotypic Characterization of Newcastle Disease Viruses Circulating in South China and Transmission in Different Birds

Although Newcastle disease virus (NDV) with high pathogenicity has frequently been isolated in poultry in China since 1948, the mode of its transmission among avian species remains largely unknown. Given that various wild bird species have been implicated as sources of transmission, in this study we genotypically and pathotypically characterized 23 NDV isolates collected from chickens, ducks, and pigeons in live bird markets (LBMs) in South China as part of an H7N9 surveillance program during December 2013–February 2014. To simulate the natural transmission of different kinds of animals in LBMs, we selected three representative NDVs—namely, GM, YF18, and GZ289—isolated from different birds to evaluate the pathogenicity and transmission of the indicated viruses in chickens, ducks, and pigeons. Furthermore, to investigate the replication and shedding of NDV in poultry, we inoculated the chickens, ducks, and pigeons with 10⁶ EID₅₀ of each virus via intraocular and intranasal routes. Eight hour after infection, the naïve contact groups were housed with those inoculated with each of the viruses as a means to monitor contact transmission. Our results indicated that genetically diverse viruses circulate in LBMs in South China's Guangdong Province and that NDV from different birds have different tissue tropisms and host ranges when transmitted in different birds. We therefore propose the continuous epidemiological surveillance of LBMs to support the prevention of the spread of these viruses in different birds, especially chickens, and highlight the need for studies of the virus–host relationship.

High Genetic Diversity of Newcastle Disease Virus in Wild and Domestic Birds in Northeastern China from 2013 to 2015 Reveals Potential Epidemic Trends

Newcastle disease (ND), caused by the virulent Newcastle disease virus (NDV), is one of the most important viral diseases of birds globally, but little is currently known regarding enzootic trends of NDV in northeastern China, especially for class I viruses. Thus, we performed a surveillance study for NDV in northeastern China from 2013 to 2015. A total 755 samples from wild and domestic birds in wetlands and live bird markets (LBMs) were collected, and 10 isolates of NDV were identified. Genetic and phylogenetic analyses showed that five isolates from LBMs belong to class I subgenotype 1b, two (one from wild birds and one from LBMs) belong to the vaccine-like class II genotype II, and three (all from wild birds) belong to class II subgenotype Ib. Interestingly, the five class I isolates had epidemiological connections with viruses from southern, eastern, and southeastern China. Our findings, together with recent prevalence trends of class I and virulent class II NDV in China, suggest possible virus transmission between wild and domestic birds and the potential for an NDV epidemic in the future.

Genetic characterization and evolutionary analysis of Newcastle disease virus isolated from domestic duck in South Korea

Domestic ducks are considered a potential reservoir of Newcastle disease virus. In the study, a Newcastle disease virus (NDV) isolated from a domestic duck during surveillance in South Korea was characterized. The complete genome of the NDV isolate was sequenced, and the phylogenetic relationship to reference strains was studied. Phylogenetic analysis revealed that the strain clustered in genotype I of Class II ND viruses, has highly phylogenetic similarity to NDV strains isolated from waterfowl in China, but was distant from the viruses isolated in chickens and vaccine strains used in South Korea. Pathogenicity experiment in chickens revealed it to be a lentogenic virus. The deduced amino acid sequence of the cleavage site of the fusion (F) protein confirmed that the isolate contained the avirulent motif (112)GKQGRL(117) at the cleavage site and caused no apparent disease in chickens and ducks. With phylogeographic analysis based on fusion gene, we estimate the origin of an ancestral virus of the isolate and its sister strain located in China around 1998. It highlights the need of continuous surveillance to enhance current understanding of the molecular epidemiology and evolution of the pathogenic strains.

Evolution of Newcastle Disease Virus Quasispecies Diversity and Enhanced Virulence after Passage through Chicken Air Sacs

It has been reported that lentogenic Newcastle disease virus (NDV) isolates have the potential to become velogenic after their transmission and circulation in chickens, but the underlying mechanism is unclear. In this study, a highly velogenic NDV variant, JS10-A10, was generated from the duck-origin lentogenic isolate JS10 through 10 consecutive passages in chicken air sacs. The velogenic properties of this selected variant were determined using mean death time (MDT) assays, intracerebral pathogenicity index (ICPI), the intravenous pathogenicity index (IVPI), histopathology, and the analysis of host tissue tropism. In contrast, JS10 remained lentogenic after 20 serial passages in chicken eggs (JS10-E20). The JS10, JS10-A10, and JS10-E20 genomes were sequenced and found to be nearly identical, suggesting that both JS10-A10 and JS10-E20 were directly generated from JS10. To investigate the mechanism for virulence enhancement, the partial genome covering the F0 cleavage site of JS10 and its variants were analyzed using ultradeep pyrosequencing (UDPS) and the proportions of virulence-related genomes in the quasispecies were calculated. Velogenic NDV genomes accumulated as a function of JS10 passaging through chicken air sacs. Our data suggest that lentogenic NDV strains circulating among poultry might be a risk factor to future potential velogenic NDV outbreaks in chickens.

IMPORTANCE

An avirulent isolate, JS10, was passaged through chicken air sacs and embryos, and the pathogenicity of the variants was assessed. A virulent variant, JS10-A10, was generated from consecutive passage in air sacs. We developed a deep-sequencing approach to detect low-frequency viral variants across the NDV genome. We observed that virulence enhancement of JS10 was due to the selective accumulation of velogenic quasispecies and the concomitant disappearance of lentogenic quasispecies. Our results suggest that because it is difficult to avoid contact between natural waterfowl reservoirs and sensitive poultry operations, circulating lentogenic NDV strains may represent a potential reservoir for emergent velogenic NDV strains that could cause outbreaks in chickens.