Genetic and Antigenic Variation of Shedding Viruses from Vaccinated Chickens After Challenge with Virulent Newcastle Disease Virus

Efficacy of Newcastle disease LaSota vaccine-induced hemagglutination inhibition antibodies against challenges with heterologous virulent strains of genotypes VII and IX

Newcastle disease (ND), caused by virulent Newcastle disease virus (NDV), still remains one of the most important avian diseases affecting the poultry industry worldwide, despite intensive vaccination programs have been implemented in many countries. All NDV isolates characterized to date are of one serotype and classified into classes I and II, with class II being further divided into twenty-one genotypes. Antigenic and genetic diversity is observed among the different genotypes. Current commercially available vaccines belonging to genotypes I and II are genetically divergent from strains that caused ND outbreaks worldwide in the last two decades. Reports of vaccination failures on their insufficient ability to inhibit infection or virus shedding have created renewed interest in developing vaccines homologous to virulent NDV circulating in the field. In this study, after vaccination with the most widely used LaSota vaccine (genotype II), chickens with different hemagglutination inhibition (HI) antibody levels were challenged with heterologous virulent NDV strains of genotypes VII and IX to evaluate how antibody levels relate to clinical protection and infection or virus shedding. Under the experimental condition, LaSota vaccine could fully protect birds from morbidity and mortality, but higher antibody levels were required to inhibit virus shedding. The number of birds shedding virus generally tended to decrease as the HI antibody titers increase in vaccinated birds. When the HI antibody titers reached ≥ 13 log₂ and ≥ 10 log₂, the virus shedding from JSC0804 strain (genotype VII) and F48E8 strain (genotype IX) could be completely inhibited, respectively, but it may be difficult to ensure that all individuals reach and maintain those levels in chicken flocks vaccinated according to routine procedure. Furthermore, the virus shedding in vaccinated birds was correlated with the amino acid similarity between the vaccine and challenge strains; more similarity, less virus shedding. The results obtained highlight that stringent biosecurity measures combined with vaccination are crucial for chicken farms to maintain a virulent NDV-free status.

Hemagglutinin-neuraminidase gene of genotype VII Newcastle disease virus strains isolated in Japan

Recently, genotype VII of Newcastle disease virus (NDV) has become the most prevalent NDV genotype in Asia. Here the hemagglutinin-neuraminidase (HN) gene of genotype VII NDV strains isolated in Japan was analyzed. Notably, point amino acid substitutions in the HN protein at position 347, which is located on the major linear epitope of the HN protein, were found in two strains. However, by a hemagglutination inhibition assay, major antigenic differences did not exist between the studied strains. Additionally, chickens vaccinated with the B1 strain did not exhibit clinical effects after challenge with variants possessing the substitution at position 347 (E to K), whereas all unvaccinated chickens subjected to this challenge died within 5 days.

Genomic and biological characteristics of Avian Orthoavulavirus-1 strains isolated from multiple wild birds and backyard chickens in Pakistan

Circulation of the dominant sub-genotype VII.2 of Avian Orthoavulavirus-1 (AOAV-1) is affecting multiple poultry and non-poultry avian species and causing significant economic losses to the poultry industry worldwide. In countries where ND is endemic, continuous monitoring and characterization of field strains are necessary. In this study, genetic characteristics of eleven AOAV-1 strains were analyzed isolated from wild birds including parakeets (n = 3), lovebird parrot (n = 1), pheasant (n = 1), peacock (n = 1), and backyard chickens (n = 5) during 2015-2016. Genetic characterization (genome size [15,192 nucleotides], the presence of typical cleavage site [^112-RRQKRF^-117]) and biological assessment (HA log 2⁷ to 2⁹ and intracerebral pathogenicity index [ICPI] value ranging from 1.50 to 1.86) showed virulent AOAV-1. Phylogenetic analysis showed that the studied isolates belonged to sub-genotype VII.2 and genetically very closely related (> 98.9%) to viruses repeatedly isolated (2011-2018) from commercial poultry. These findings provide evidence for the existence of epidemiological links between poultry and wild bird species in the region where the disease is prevalent. The deduced amino acid analysis revealed several substitutions in critical domains of fusion and hemagglutinin-neuraminidase genes. The pathogenesis and transmission potential of wild bird-origin AOAV-1 strain (AW-Pht/2015) was evaluated in 21-day-old chickens that showed the strain was highly virulent causing clinical signs and killed all chickens. High viral loads were detected in different organs of the infected chickens correlating with the severity of lesions developed. The continuous monitoring of AOAV-1 isolates in different species of birds will improve our knowledge of the evolution of these viruses, thereby preventing possible panzootic.

Protection of chicks from Newcastle disease by combined vaccination with a plasmid DNA and the pre-fusion protein of the virulent genotype VII of Newcastle disease virus

In this study, four codon optimized plasmids (designated as pCAG-optiF-1, 2, -3, and -4) containing modified F genes from the epidemic and virulent NDV genotype VII strain isolated in China that is expected to express the pre-fusion conformation of the F protein were constructed. The expression of these F variants in chicken-derived cells was detected by an indirect immunofluorescence assay and western blot analysis. Two soluble F variants (roptiF-1 and 2) potentially with the pre-fusion conformation were expressed and purified from suspended cells. Vaccination with each of the plasmids as a DNA vaccine conferred partial clinical protection to chicks against NDV. Comparatively, the plasmid pCAG-optiF-2 encoded a soluble protein with a mutant cleavage site and the potential pre-fusion conformation provided better protection than the other plasmids. Further investigation of the combined vaccinations with the plasmid DNA pCAG-optiF-2 prime + protein roptiF-2 boost vaccination strategy elicited more robust immunity, as confirmed by the detection of antibodies against NDV using enzyme-linked immunosorbent assay and virus neutralization assay, as compared to those vaccinated with only the plasmid pCAG-optiF-2 or protein roptiF-2. More importantly, the DNA prime + protein boost vaccination provided more efficacious protection against virulent NDV challenge, as evidenced by the complete clinical protection, reduced viral shedding, and limited virus replication in tissues of the challenge chicks. These results indicated that the pre-fusion conformation of the F protein could be considered as the target immunogen for the development of novel NDV vaccines.

Glycoprotein-C-gene-deleted recombinant infectious laryngotracheitis virus expressing a genotype VII Newcastle disease virus fusion protein protects against virulent infectious laryngotracheitis virus and Newcastle disease virus

To develop an alternative vectored vaccine against both Newcastle disease virus (NDV) and infectious laryngotracheitis virus (ILTV), the glycoprotein C (gC) gene was first deleted from an avirulent ILTV. Based on this gC-deleted ILTV mutant, a recombinant ILTV expressing the fusion protein (F) of a genotype VII NDV (designated ILTV-ΔgC-F) was then constructed. Expression of the NDV F protein in ILTV-ΔgC-F-infected LMH cells was examined with an immunofluorescence assay and western blotting. The F gene was stably maintained in the genome of ILTV-ΔgC-F and the F protein was stably expressed. Compared with the parental virus, ILTV-ΔgC-F demonstrated an increased penetration capacity in vitro, and an increased replication rate in vitro and in vivo. Both the parental virus and ILTV-ΔgC-F were avirulent in chickens. Vaccination of specific-pathogen-free chickens with ILTV-ΔgC-F induced ILTV-specific antibodies, detected with an enzyme-linked immunosorbent assay (ELISA), and provided complete clinical protection against virulent ILTV, although viral shedding and replication were detected in the respiratory tract in the early stage of infection in a very small number of birds. Vaccination with ILTV-ΔgC-F also provided significant protection against challenge with a virulent genotype VII NDV, although the level of NDV-specific antibodies detected with an ELISA was low. Notably, the numbers of birds that were positive for the virulent genotype VII NDV and the replication of the challenge virus NDV in selected target tissues were significantly lower in the ILTV-ΔgC-F-vaccinated chickens than in the control birds. Our results indicate that ILTV-ΔgC-F has potential utility as a bivalent candidate vaccine against both infectious laryngotracheitis and Newcastle disease.

Development of an Effective and Stable Genotype-Matched Live Attenuated Newcastle Disease Virus Vaccine Based on a Novel Naturally Recombinant Malaysian Isolate Using Reverse Genetics

Genotype VII Newcastle disease viruses are associated with huge economic losses in the global poultry industry. Despite the intensive applications of vaccines, disease outbreaks caused by those viruses continue to occur frequently even among the vaccinated poultry farms. An important factor in the suboptimal protective efficacy of the current vaccines is the genetic mismatch between the prevalent strains and the vaccine strains. Therefore, in the present study, an effective and stable genotype-matched live attenuated Newcastle disease virus (NDV) vaccine was developed using reverse genetics, based on a recently isolated virulent naturally recombinant NDV IBS025/13 Malaysian strain. First of all, the sequence encoding the fusion protein (F) cleavage site of the virus was modified in silico from virulent polybasic (RRQKRF) to avirulent monobasic (GRQGRL) motif. The entire modified sequence was then chemically synthesized and inserted into pOLTV5 transcription vector for virus rescue. A recombinant virus termed mIBS025 was successfully recovered and shown to be highly attenuated based on OIE recommended pathogenicity assessment indices. Furthermore, the virus was shown to remain stably attenuated and retain the avirulent monobasic F cleavage site after 15 consecutive passages in specific-pathogen-free embryonated eggs and 12 passages in one-day-old chicks. More so, the recombinant virus induced a significantly higher hemagglutination inhibition antibody titre than LaSota although both vaccines fully protected chicken against genotype VII NDV induced mortality and morbidity. Finally, mIBS025 was shown to significantly reduce both the duration and quantity of cloacal and oropharyngeal shedding of the challenged genotype VII virus compared to the LaSota vaccine. These findings collectively indicate that mIBS025 provides a better protective efficacy than LaSota and therefore can be used as a promising vaccine candidate against genotype VII NDV strains.

Molecular and biological characterization of the immunological potency of Newcastle disease virus oil emulsion-inactivated vaccines prepared from field isolate obtained from vaccinated chickens outbreak

This study was conducted to characterize the immunological parameters of chickens vaccinated with two formulated inactivated vaccines, water in oil (WO) and water in oil in water (WOW), prepared from velogenic Newcastle disease virus (vNDV) genotype VIIj isolated from outbreak among vaccinated chickens. Six groups (G1-G6) of commercial broiler chickens were established (n = 20). The G1-G3 were received homologous (WO and WOW) and heterologous (LaSota) inactivated vaccines, respectively. The G4 was vaccinated with live heterologous (LaSota) vaccine, while G5 and G6 were kept as control positive and control negative non-vaccinated groups. The antibody titers were measured against vNDV and LaSota antigens using hemagglutination inhibition (HI) test, the cytokine gene expressions of IFNγ, IL1β, IL4, IL6, IL8, and IL18 were quantified using real-time RT-PCR, and the virus shedding was titrated on chicken embryo fibroblast cells after challenging by vNDV. The classical clinical signs and 100% mortality were observed only in G5 after vNDV challenging. The highest HI titers were detected in G1, G2, and G3 using NDV/168 antigen with no significant differences among them. These groups showed higher HI titer than G4 (2-4log2). Cytokine gene expression of IFNγ, IL1, IL6, IL8, and IL18 were significantly downregulated in vaccinated chickens with upregulation of IL4 than non-vaccinated challenge group. Viral shedding titers were significantly (0.0001, p ≤ 0.001) reduced in all samples form vaccinated chickens. In conclusion, the prepared vaccines produced highly efficient immunological responses and could be used for controlling the NDV infection.

Recombinant infectious laryngotracheitis virus expressing Newcastle disease virus F protein protects chickens against infectious laryngotracheitis virus and Newcastle disease virus challenge

In this study, we isolated and identified an infectious laryngotracheitis virus (ILTV) that was naturally avirulent in specific pathogen-free (SPF) chickens, with the aim of developing a more efficacious vaccine against ILTV and Newcastle disease virus (NDV). We constructed a US9-deleted ILTV mutant based on this avirulent ILTV, and then constructed a recombinant ILTV (designated ILTV-ΔUS9-F) expressing the fusion protein (F) of the genotype VII NDV based on the US9-deleted ILTV mutant. Expression of the F protein in ILTV-ΔUS9-F-infected cells was confirmed by indirect immunofluorescence assay and western blotting. The inserted F gene was stably expressed in ILTV-ΔUS9-F. The growth kinetics of ILTV-ΔUS9-F were comparable to those of the wild-type ILTV strain. Vaccination of SPF chickens with ILTV-ΔUS9-F produced no clinical signs but did induce low levels of NDV-specific enzyme-linked immunosorbent assay and neutralizing antibodies. A single vaccination with 10⁴ plaque-forming units (PFU) of ILTV-ΔUS9-F provided good protection against both genotype VII and IX NDVs based on clinical signs, similar to the protection provided by the commercial live La Sota vaccine. Notably, ILTV-ΔUS9-F limited the replication and shedding of genotype VII NDV from oropharyngeal swabs more efficiently than the La Sota vaccine. In addition, vaccination with lower doses (10³ and 10² PFU) of ILTV-ΔUS9-F also provided sufficient clinical protection. These results indicated that ILTV-ΔUS9-F may be a bivalent vaccine candidate against both ILTV and NDV.

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.

Can genotype mismatch really affect the level of protection conferred by Newcastle disease vaccines against heterologous virulent strains?

Newcastle disease (ND), caused by virulent class II avian paramyxovirus 1 (Newcastle disease virus, NDV), occurs sporadically in poultry despite their having been immunized with commercial vaccines. These vaccines were all derived from NDV strains isolated around 70 years ago. Since then, class II NDV strains have evolved into 18 genotypes. Whether the vaccination failure results from genotype mismatches between the currently used vaccine strains and field-circulating velogenic strains or from an impaired immune response in the vaccination remains unclear. To test the first hypothesis, we performed a heterologous genotype II vaccine/genotype XI challenge in one-day old specific pathogen free (SPF) chicks and reproduced viral shedding. We then produced two attenuated strains of genotype II and XI by reverse genetics and used them to immunize two-week old SPF chickens that were subsequently challenged with velogenic strains of genotypes II, VII and XI. We found that both vaccines could induce antibodies with hemagglutination inhibition titers higher than 6.5 log₂. Vaccination also completely prevented disease, viral shedding in swabs, and blocked viral replication in tissues from different genotypes in contrast to unvaccinated chickens that died shortly after challenge. Taken together, our results support the hypothesis that, in immunocompetent poultry, genotype mismatch is not the main reason for vaccination failure.

Molecular characterization of a Class I Newcastle disease virus strain isolated from a pigeon in China

Constant monitoring is performed to elucidate the role of natural hosts in the ecology of Newcastle disease virus (NDV). In this study, an NDV strain isolated from an asymptomatic pigeon was sequenced and analysed. Results showed that the full-length genomes of this isolate were 15,198 nucleotides with the gene order of 3'-NP-P-M-F-HN-L-5'. This NDV isolate was lentogenic, with an intracerebral pathogenicity index of 0.00 and a mean time of death more than 148 h. The isolate possessed a motif of -(112)E-R-Q-E-R-L(117)- at the F protein cleavage site. In addition, 7 and 13 amino acid substitutions were identified in the functional domains of fusion protein (F) and haemagglutinin-neuraminidase protein (HN) proteins, respectively. Analysis of the amino acids of neutralizing epitopes of F and HN proteins showed 3 and 10 amino acid substitutions, respectively, in the isolate. Phylogenetic analysis classified the isolate into genotype Ib in Class I. This isolate shared high homologies with the NDV strains isolated from wild birds and waterfowl in southern and eastern parts of China from 2005 to 2013. To our knowledge, this study is the first to report a NDV strain isolated from pigeon that belongs to genotype Ib in Class I, rather than to the traditional genotype VI or other sub-genotypes in Class II. This study provides information to elucidate the distribution and evolution of Class I viruses for further NDV prevention.

Experimental infection with Brazilian Newcastle disease virus strain in pigeons and chickens

This study was designed with the goal of adding as much information as possible about the role of pigeons (Columba livia) and chickens (Gallus gallus) in Newcastle disease virus epidemiology. These species were submitted to direct experimental infection with Newcastle disease virus to evaluate interspecies transmission and virus-host relationships. The results obtained in four experimental models were analyzed by hemagglutination inhibition and reverse transcriptase polymerase chain reaction for detection of virus shedding. These techniques revealed that both avian species, when previously immunized with a low pathogenic Newcastle disease virus strain (LaSota), developed high antibody titers that significantly reduced virus shedding after infection with a highly pathogenic Newcastle disease virus strain (São Joao do Meriti) and that, in chickens, prevent clinical signs. Infected pigeons shed the pathogenic strain, which was not detected in sentinel chickens or control birds. When the presence of Newcastle disease virus was analyzed in tissue samples by RT-PCR, in both species, the virus was most frequently found in the spleen. The vaccination regimen can prevent clinical disease in chickens and reduce viral shedding by chickens or pigeons. Biosecurity measures associated with vaccination programs are crucial to maintain a virulent Newcastle disease virus-free status in industrial poultry in Brazil.

Development of a highly immunogenic Newcastle disease virus chicken vaccine strain of duck origin

Newcastle disease virus (NDV) strain NDRL0901 was developed as a live vaccine candidate for control of Newcastle disease. NDV isolate KR/duck/13/07 (DK1307) of duck origin was used as the selected vaccine strain. DK1307 was passaged 6 times in chickens. Then a single clone from the chicken-adapted virus (DK1307C) was finally selected, and the vaccine strain was named NDRL0901. DK1307C and the clone NDRL0901 viruses showed enhanced immunogenicity compared to the DK1307 virus. Principal component analysis based on fusion and hemagglutinin-neuraminidase genes revealed the codon usage pattern in the dataset is distinct separating duck viral sequences and avian sequences, and passage of the duck origin virus into the chicken host causes deviation in the codon usage pattern. The NDRL0901 virus was avirulent and did not acquire viral virulence even after 7 back passages in chickens. When day-old chicks were vaccinated with the NDRL0901 virus via spray, eye drops, and drinking water, the vaccinated birds showed no clinical signs and had significant protection efficacy (>80%) against very virulent NDV (Kr005 strain) infection regardless of the administration route employed. The results indicate that the NDRL0901 strain is safe in chickens and can offer protective immunity.

Characterization of complete genome sequence of genotype VI and VII velogenic Newcastle disease virus from Japan

The complete genome sequences of three strains of Newcastle disease virus (NDV) isolated from vaccinated commercial layer flocks in Japan in the span of three decades were characterized. All strains had genome lengths of 15,192 nucleotides consisting of six genes in the order of 3'-NP-P/V/W-M-F-HN-L-5'. The general genomic characteristics of the Japanese field strains were consistent with previously characterized class II NDV, except for those belonging to early genotypes (genotype I-IV), which lack the six nucleotide insertion at nucleotide positions 1,648-1,653 of the nucleoprotein (NP) gene. Phylogenetic analysis showed that the Japanese strains could be classified into genotypes VIc and VIIe using the complete genome sequence and the complete coding sequence of the fusion (F) gene according to the unified NDV classification system. Characterization of functional domains and neutralizing epitopes of the F and hemagglutinin-neuraminidase (HN) proteins of Japanese field strains revealed a total of 31 amino acid substitutions, as compared to vaccine strains Ishii and B1, which were widely used in Japan. Although virus neutralization (VN) test showed that poor flock immunity due to vaccination failure or partial and non-uniform immunization maybe the major factors involved in the mechanism of breakthrough infection of the Japanese field strains, approximately two to threefold decrease in the VN titers of the field NDV strains possessing a point mutation (E347K or E347G) at the linear epitope of the HN protein was observed, as compared to vaccine strain B1 and field strain 2440/69, which lack the point mutation. This study may be a useful reference in characterizing future ND outbreaks in vaccinated chickens and as a genetic map for future investigations regarding vaccine designs, reverse genetics systems, and development of molecular diagnostic tools to prevent future ND outbreaks in vaccinated poultry flocks.