Molecular characterization of three new virulent Newcastle disease virus variants isolated in China

Comparison of genomic and antigenic properties of Newcastle Disease virus genotypes II, XXI and VII from Egypt do not point to antigenic drift as selection marker

Newcastle disease (ND), caused by avian orthoavulavirus type-1 (NDV), is endemic in poultry in many regions of the world and causes continuing outbreaks in poultry populations. In the Middle East, genotype XXI, used to be present in poultry in Egypt but has been replaced by genotype VII. We investigated whether virus evolution contributed to superseding and focussed on the antigenic sites within the hemagglutinin-neuraminidase (HN) spike protein. Full-length sequences of an NDV genotype VII isolate currently circulating in Egypt was compared to a genotype XXI isolate that was present as co-infection with vaccine-type viruses (II) in a historical virus isolated in 2011. Amino acid differences in the HN glycoprotein for both XXI and VII viruses amounted to 11.7% and 11.9%, respectively, compared to the La Sota vaccine type. However, mutations within the globular head (aa 126-570), bearing relevant antigenic sites, were underrepresented (a divergence of 8.8% and 8.1% compared to 22.4% and 25.6% within the protein domains encompassing cytoplasmic tail, transmembrane part and stalk regions (aa 1-125) for genotypes XXI and VII, respectively). Nevertheless, reaction patterns of HN-specific monoclonal antibodies inhibiting receptor binding revealed differences between vaccine-type viruses and genotype XXI and VII viruses for epitopes located in the head domain. Accordingly, compared to Egyptian vaccine-type isolates and the La Sota vaccine reference strain, single aa substitutions in 6 of 10 described neutralizing epitopes of HN were found. However, the same alterations in neutralization sensitive epitopes were present in old genotype XXI as well as in newly emerged genotype VII isolates. In addition, isolates were indistinguishable by polyclonal chicken sera raised against different genotypes including vaccine viruses. These findings suggest that factors other than antigenic differences within the HN protein account for facilitating the spread of genotype VII versus genotype XXI viruses in Egypt.

Generation and evaluation of a vaccine candidate of attenuated and heat-resistant genotype VIII Newcastle disease virus

Newcastle disease, which is a highly contagious and fatal disease caused by the Newcastle disease virus (NDV), has harmed the poultry industry for decades. The administration of effective vaccines can control most outbreaks and epidemics of Newcastle disease in the world. However, vaccination failures of live attenuated vaccines becasue of storage and transportation problems have been reported. Hence, thermostable live vaccine strains, such as V4 and I-2 strains, are being used and welcomed in tropical regions such as Africa and Southeast Asia. In this study, a thermostable, attenuated vaccine candidate strain NDV/rHR09 was generated using the genotype VIII heat-resistant virulent NDV strain HR09 by the reverse genetics system. The results of the determination of the mean death time and intracerebral pathogenicity index indicated that NDV/rHR09 is lentogenic even after 15 serial passages in embryonated chicken eggs. The thermostability assessment showed that the NDV/rHR09 strain exhibited hemagglutination activity and infectivity when exposed to 56°C for 60 min. Compared with the commercially available La Sota and V4 vaccines, the NDV/rHR09 induced higher antibody titers in specific pathogen-free chickens. In addition, NDV/rHR09 conferred complete protection against virulent genotype VII NDV challenge and virus shedding from vaccinated chickens. These results suggest that NDV/rHR09 is a promising thermostable vaccine candidate strain.

Molecular and biological characterization of some circulating strains of Newcastle disease virus in broiler chickens from Eastern Saudi Arabia in 2012-2014

Background and Aim:

Newcastle disease (ND) is a worldwide poultry disease that is historically known to cause severe losses in the poultry industry. In the present study, attempts were made to characterize ND virus (NDV) recovered from broiler chickens in the Eastern Region of Saudi Arabia from January 2012 to March 2014.

Materials and Methods:

Reverse transcription-polymerase chain reaction was used for the detection of NDV followed by partial sequencing of the fusion (F) gene. The intracerebral pathogenicity index (ICPI), mean death time (MDT), and complete sequencing of the hemagglutinin-neuraminidase (HN) gene were also used for further biological and molecular characterization.

Results:

NDV was detected at a rate of 9.6% (11/115) of the tested flocks, most of which were vaccinated against ND. F gene-based phylogeny and motifs of the fusion protein cleavage site (FPCS) showed segregation of Saudi isolates into two groups. The first group contained 10 isolates and was located in genotype II with the lentogenic motif ¹¹²GRQGRL¹¹⁷ at the FPCS. The second group contained one isolate and was located in genotype VII with velogenic motif ¹¹²RRQKRF¹¹⁷. Further characterization using the ICPI and MDT of two representative isolates showed virulence of both tested isolates. Phylogenetic analysis of the HN gene showed close nucleotide identity between the two isolates. A BLAST search for sequences similar to HN gene sequences showed high identity with isolates from the surrounding region.

Conclusion:

The present findings showed a low detection rate of NDV, possibly due to the wide application of vaccines, and the circulation of at least two NDV genotypes, II and VII, in the Eastern Region of Saudi Arabia. The present Saudi isolates may share common ancestors with isolates from the surrounding region.

Disparate thermostability profiles and HN gene domains of field isolates of Newcastle disease virus from live bird markets and waterfowl in Uganda

Background

Uganda poultry production is still faced with frequent outbreaks of Newcastle disease (ND) in the backyard free-range systems despite the accessibility of cross protective vaccines. Live bird markets and waterfowl has long been reported as a major source of disease spread as well as potential sources of avirulent strains that may mutate to virulent strains. ND-virus has been reported enzootic in Ugandan poultry but limited studies have been conducted to ascertain thermostability phenotypes of the Ugandan ND-virus strains and to understand how these relate to vaccine strains.

Methods

This study evaluated thermostability of 168 ND-virus field isolates recovered from live bird markets and waterfowls in Uganda compared to two live commercial vaccine strains (I₂ and LaSota) by standard thermostability procedures and Hemagglutinin-Neuraminidase (HN) gene domains. The known pathotypes with thermostability profiles were compared at HN amino acid sequences.

Results

Field isolates displayed disparate heat stability and HN gene domains. Thermolabile isolates were inactivated within 15 min, while the most thermostable isolates were inactivated in 120 min. Four thermostable isolates had more than 2 log₂ heamaglutinin (HA) titers during heat treatment and the infectivity of 9.8 geometric mean of log₁₀ EID_{50 %} in embryonated eggs. One isolate from this study exhibited a comparable thermostability and stable infectivity titers after serial passages, to that of reference commercial vaccine was recommended for immunogenicity and protection studies.

Conclusion

The occurrence of ND-virus strains in waterfowl and live bird markets with disparate thermostability and varying HN gene domains indicate circulation of different thermostable and thermolabile ND-virus pathotypes in the country.

Evaluation of the contributions of individual viral genes to newcastle disease virus virulence and pathogenesis

Naturally occurring Newcastle disease virus (NDV) strains vary greatly in virulence. The presence of multibasic residues at the proteolytic cleavage site of the fusion (F) protein has been shown to be a primary determinant differentiating virulent versus avirulent strains. However, there is wide variation in virulence among virulent strains. There also are examples of incongruity between cleavage site sequence and virulence. These observations suggest that additional viral factors contribute to virulence. In this study, we evaluated the contribution of each viral gene to virulence individually and in different combinations by exchanging genes between velogenic (highly virulent) strain GB Texas (GBT) and mesogenic (moderately virulent) strain Beaudette C (BC). These two strains are phylogenetically closely related, and their F proteins contain identical cleavage site sequences, (112)RRQKR↓F(117). A total of 20 chimeric viruses were constructed and evaluated in vitro, in 1-day-old chicks, and in 2-week-old chickens. The results showed that both the envelope-associated and polymerase-associated proteins contribute to the difference in virulence between rBC and rGBT, with the envelope-associated proteins playing the greater role. The F protein was the major individual contributor and was sometimes augmented by the homologous M and HN proteins. The dramatic effect of F was independent of its cleavage site sequence since that was identical in the two strains. The polymerase L protein was the next major individual contributor and was sometimes augmented by the homologous N and P proteins. The leader and trailer regions did not appear to contribute to the difference in virulence between BC and GBT.

IMPORTANCE

This study is the first comprehensive and systematic study of NDV virulence and pathogenesis. Genetic exchanges between a mesogenic and a velogenic strain revealed that the fusion glycoprotein is the major virulence determinant regardless of the identical virulence protease cleavage site sequence present in both strains. The contribution of the large polymerase protein to NDV virulence is second only to that of the fusion glycoprotein. The identification of virulence determinants is of considerable importance, because of the potential to generate better live attenuated NDV vaccines. It may also be possible to apply these findings to other paramyxoviruses.

Genetic diversity of Newcastle disease virus in Pakistan: a countrywide perspective

Background

Newcastle disease (ND) is one of the most deadly diseases of poultry around the globe. The disease is endemic in Pakistan and recurrent outbreaks are being reported regularly in wild captive, rural and commercial poultry flocks. Though, efforts have been made to characterize the causative agent in some of parts of the country, the genetic nature of strains circulating throughout Pakistan is currently lacking.

Material and methods

To ascertain the genetics of NDV, 452 blood samples were collected from 113 flocks, originating from all the provinces of Pakistan, showing high mortality (30–80%). The samples represented domesticated poultry (broiler, layer and rural) as well as wild captive birds (pigeons, turkeys, pheasants and peacock). Samples were screened with real-time PCR for both matrix and fusion genes (1792 bp), positive samples were subjected to amplification of full fusion gene and subsequent sequencing and phylogenetic analysis.

Results

The deduced amino acid sequence of the fusion protein cleavage site indicated the presence of motif (¹¹²RK/RQRR↓F¹¹⁷) typical for velogenic strains of NDV. Phylogenetic analysis of hypervariable region of the fusion gene indicated that all the isolates belong to lineage 5 of NDV except isolates collected from Khyber Pakhtunkhwa (KPK) province. A higher resolution of the phylogenetic analysis of lineage 5 showed the distribution of Pakistani NDV strains to 5b. However, the isolates from KPK belonged to lineage 4c; the first report of such lineage from this province.

Conclusions

Taken together, data indicated the prevalence of multiple lineages of NDV in different poultry population including wild captive birds. Such understanding is crucial to underpin the nature of circulating strains of NDV, their potential for interspecies transmission and disease diagnosis and control strategies.

Complete genome sequencing and analysis of an anti-tumor Newcastle disease virus strain

HBNU/LSRC/F3, a Newcastle disease virus (NDV) strain stored in our lab, exhibited an anti-tumor ability in our previous studies. Nonetheless, very little is known about its genome sequence, which is vital for further study. Here, the complete HBNU/LSRC/F3 genome was fully sequenced and compared with other NDV sequences. Its genome contained 15,192 nucleotides (nt) consisting of two termini and six genes in the following order: 3'-Le-NP-P-M-F-HN-L-Tr-5'. Phylogenetic analysis indicated that this NDV strain belonged to the Class II genotype IX group. A multibasic amino acid (aa) sequence was found at the cleavage site ((112)RRQRR↓F(117)) within the fusion (F) protein, and a 6 nt insertion was present in the 5' non-coding region of the NP gene. The whole genome sequence was highly similar to other genotype IX NDV genomes reported in China. Overall, this study provides insight into the sequence characteristics of genotype IX NDVs, which will be useful for subsequent investigations.

Enhanced reliability of avian influenza virus (AIV) and Newcastle disease virus (NDV) identification using matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS)

In-solution enzymatic and nonenzymatic digestion methods have been successfully implemented in matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS)-based virus identification, extending to typing/subtyping of deadly influenza viruses. However, these methods are inefficient in obtaining more precise information on surface proteins of myxovirus particles, not only the hemagglutinin and neuraminidase of influenza virus but also the hemagglutinin-neuraminidase of Newcastle disease virus (NDV). Imbalances in viral protein composition cause ion suppression of tryptic fragments from low-abundant target proteins (surface proteins), adversely affecting reproducibility of mass spectra. Additionally, the coexistence of tryptic peptides from several proteins requires sophisticated statistical solutions for precise result interpretations. To circumvent these, we apply detergent-based (gel-free) partitioning of whole viruses into soluble surface proteins and insoluble virus materials, using differential centrifugation. MALDI-TOF or MALDI-TOF/TOF MS was applied to analyze tryptic peptides from separated viral proteins. In this study, we achieved type/subtype of avian influenza virus (AIV) within 5 h, based on 4 major proteins, by significantly reducing ion suppression and signal overlap from various protein sources. Hence, our approach can both yield dependable results and allow Web-based search engines to be directly employed, obviating the need for additional statistical strategy. Additionally, we demonstrate the utility of the method using NDV.

The effect of vaccination on the evolution and population dynamics of avian paramyxovirus-1

Newcastle Disease Virus (NDV) is a pathogenic strain of avian paramyxovirus (aPMV-1) that is among the most serious of disease threats to the poultry industry worldwide. Viral diversity is high in aPMV-1; eight genotypes are recognized based on phylogenetic reconstruction of gene sequences. Modified live vaccines have been developed to decrease the economic losses caused by this virus. Vaccines derived from avirulent genotype II strains were developed in the 1950s and are in use globally, whereas Australian strains belonging to genotype I were developed as vaccines in the 1970s and are used mainly in Asia. In this study, we evaluated the consequences of attenuated live virus vaccination on the evolution of aPMV-1 genotypes. There was phylogenetic incongruence among trees based on individual genes and complete coding region of 54 full length aPMV-1 genomes, suggesting that recombinant sequences were present in the data set. Subsequently, five recombinant genomes were identified, four of which contained sequences from either genotype I or II. The population history of vaccine-related genotype II strains was distinct from other aPMV-1 genotypes; genotype II emerged in the late 19^th century and is evolving more slowly than other genotypes, which emerged in the 1960s. Despite vaccination efforts, genotype II viruses have experienced constant population growth to the present. In contrast, other contemporary genotypes showed population declines in the late 1990s. Additionally, genotype I and II viruses, which are circulating in the presence of homotypic vaccine pressure, have unique selection profiles compared to nonvaccine-related strains. Collectively, these data show that vaccination with live attenuated viruses has changed the evolution of aPMV-1 by maintaining a large effective population size of a vaccine-related genotype, allowing for coinfection and recombination of vaccine and wild type strains, and by applying unique selective pressures on viral glycoproteins.

Modified live virus (MLV) vaccines have been effective in reducing disease burden and economic loss caused by Newcastle Disease (ND) in domestic poultry. Because the vaccine is a live virus, it is transmissible among birds. Thus, vaccination strategies have the potential to impact the evolutionary genetics of wild type strains of aPMV-1 including those that cause ND. In this report, we provided evidence that viruses isolated from wild and domestic birds have recombined with vaccine strains, because vaccinated birds are protected from disease but not infection with other strains of aPMV-1. Despite the use of vaccines since the 1950s, the population size of the strain from which the most widely used vaccine was derived has steadily increased. In contrast, other contemporary genotypes, which emerged in the 1960s, experienced a decline in population size in 1998, which may reflect a change in poultry farming practices or disease. Vaccination imposed a unique selection profile on the genotypes derived from the vaccine-related strains when compared with nonvaccine-related strains. Although modified live viruses are important for controlling Newcastle Disease, the potential of vaccination strategies to change viral diversity and population dynamics should be considered.