Review of Newcastle disease virus with particular references to immunity and vaccination

BotCl, the First Chlorotoxin-like Peptide Inhibiting Newcastle Disease Virus: The Emergence of a New Scorpion Venom AMPs Family

Newcastle disease virus (NDV) is one of the most serious contagions affecting domestic poultry and other avian species. It causes high morbidity and mortality, resulting in huge economic losses to the poultry industry worldwide. Despite vaccination, NDV outbreaks increase the need for alternative prevention and control means. In this study, we have screened fractions of Buthus occitanus tunetanus (Bot) scorpion venom and isolated the first scorpion peptide inhibiting the NDV multiplication. It showed a dose dependent effect on NDV growth in vitro, with an IC₅₀ of 0.69 µM, and a low cytotoxicity on cultured Vero cells (CC50 > 55 µM). Furthermore, tests carried out in specific pathogen-free embryonated chicken eggs demonstrated that the isolated peptide has a protective effect on chicken embryos against NDV, and reduced by 73% the virus titer in allantoic fluid. The N-terminal sequence, as well as the number of cysteine residues of the isolated peptide, showed that it belongs to the scorpion venom Chlorotoxin-like peptides family, which led us to designate it "BotCl". Interestingly, at 10 µg/mL, BotCl showed an inhibiting effect three times higher than its analogue AaCtx, from Androctonus australis (Aa) scorpion venom, on NDV development. Altogether, our results highlight the chlorotoxin-like peptides as a new scorpion venom AMPs family.

Thermoresistant Newcastle disease vaccine effectively protects SPF, native, and commercial chickens in challenge with virulent virus

Background

Due to the more stability and a better homogenecity in immune response, the use of thermoresistant vaccines in different chicken types has been increased.

Objective

This study aimed to evaluate the efficacy of a newly developed Newcastle disease vaccine (ND.TR.IR) originating from I‐2 strain in specific pathogen‐free (SPF) and native and broiler chickens.

Methods

Following determination of pathogenicity indices on the candidate seed, three efficacy examinations were conducted. In the first experiment, 120 1‐day‐old SPF chickens were randomly allocated to six groups and either vaccinated with ND.TR.IR via eye drop at 1, 7, and 21 days of age (V₁, V₇, and V₂₁), or considered as non‐vaccinated control groups (C₁, C₇, and C₂₁). At 20th post‐vaccination day, sera hemagglutination inhibition (HI) antibody titres against ND virus (NDV) were measured and then the chickens were challenged by virulent NDV (vNDV). In the second and third experiments, the efficacy of ND.TR.IR vaccine was compared to routine vaccination program (B1 and LaSota) in native and broiler chickens that were vaccinated at 10 and 20 days of age, respectively. The HI antibody titres were measured on 10, 20, 30, and 40 days of age, and also challenge efficacy test with vNDV was conducted on 30 days of age.

Results

The studied virus, as a vaccinal seed, complied with the pathogenicity indices of avirulent NDV and molecular identity of I‐2 strain. In the efficacy evaluation trials, the vaccinated chickens had higher HI antibody titres against NDV compared with their corresponding control chickens (p < 0.05). Results of the challenge tests indicated 95% and 100% protection against vNDV in native, SPF, and broiler‐vaccinated chickens, respectively.

Conclusions

The present findings indicated that administration of ND.TR.IR induced appropriate HI antibody titres against NDV in SPF, native, and broiler chickens associated with good protection in efficacy test.

Comparison of Chicken Immune Responses to Immunization with Vaccine La Sota or ZG1999HDS Strain of Newcastle Disease Virus

Newcastle disease (ND) is a highly contagious avian disease. Global control of ND is mainly based on vaccination of poultry; however, reported outbreaks of ND in vaccinated flocks indicate a constant need to re-evaluate the existing vaccines and a development of the new ones. In this study, 4-week-old male chickens of the layer commercial hybrid were immunized oculonasally with a commercial NDV live La Sota vaccine (LS group), a suspension of lyophilized NDV strain ZG1999HDS (ZG group), or saline (Control (K) group). Antibody response was determined by haemagglutination inhibition (HI) assay. Cell-mediated immunity (CMI) was characterized by immunophenotyping of leukocyte's and T-lymphocyte's subpopulations (flow cytometry). Applied NDV strains did not cause any adverse reaction in treated chickens. Both strains induced the significantly higher HI antibody response in comparison to the control group, and overall antibody titer was higher in ZG group than in LS group. CMI, manifested as a higher proliferation of B- and T-helper cells, yielded better results in the ZG groups than in the LS group. Based on the obtained results, we conclude that the strain ZG1999HDS is immunogenic and is a suitable candidate for further research and development of poultry vaccines.

Efficacy of the Newcastle Disease Virus Genotype VII.1.1-Matched Vaccines in Commercial Broilers

Class II genotype VII Newcastle disease viruses (NDV) are predominant in the Middle East and Asia despite intensive vaccination programs using conventional live and inactivated NDV vaccines. In this study, the protective efficacies of three commercial vaccine regimes involving genotype II NDV, recombinant genotype VII NDV-matched, and an autogenous velogenic NDV genotype VII vaccine were evaluated against challenge with velogenic NDV genotype VII (accession number MG029120). Three vaccination regimes were applied as follows: group-1 received inactivated genotype II, group-2 received inactivated recombinant genotype VII NDV-matched, and group-3 received velogenic inactivated autogenous NDV genotype VII vaccines given on day 7; for the live vaccine doses, each group received the same live genotype II vaccine. The birds in all of the groups were challenged with NDV genotype VII, which was applied on day 28. Protection by the three regimes was evaluated after infection based on mortality rate, clinical signs, gross lesions, virus shedding, seroconversion, and microscopic changes. The results showed that these three vaccination regimes partially protected commercial broilers (73%, 86%, 97%, respectively, vs. 8.6% in non-vaccinated challenged and 0% in non-vaccinated non-challenged birds) against mortality at 10 days post-challenge (dpc). Using inactivated vaccines significantly reduced the virus shedding at the level of the number of shedders and the amount of virus that was shed in all vaccinated groups (G1-3) compared to in the non-vaccinated group (G-4). In conclusion, using closely genotype-matched vaccines (NDV-GVII) provided higher protection than using vaccines that were not closely genotype-matched and non-genotype-matched. The vaccine seeds that were closely related to genotype VII.1.1 provided higher protection against challenge against this genotype since it circulates in the Middle East region. Updating vaccine seeds with recent and closely related isolates provides higher protection.

Disinfection to control African swine fever virus: a UK perspective

A review of African swine fever (ASF) was conducted, including manifestations of disease, its transmission and environmental persistence of ASF virus. Findings on infectious doses of contemporary highly-pathogenic strains isolated from outbreaks in Eastern Europe were included. Published data on disinfectant susceptibility of ASF virus were then compared with similar findings for selected other infectious agents, principally those used in the UK disinfectant approvals tests relating to relevant Disease Orders for the control of notifiable and zoonotic diseases of livestock. These are: swine vesicular disease virus, foot and mouth disease virus, Newcastle disease virus and Salmonella enterica serovar Enteritidis. The comparative data thus obtained, presented in a series of charts, facilitated estimates of efficacy against ASF virus for some UK approved disinfectants when applied at their respective General Orders concentrations. Substantial data gaps were encountered for several disinfectant agents or classes, including peracetic acid, quaternary ammonium compounds and products based on phenols and cresols.

Immunogenicity of Newcastle disease virus strain ZG1999HDS applied oculonasally or by means of nebulization to day-old chicks

Newcastle disease (ND) is one of the classic viral infections of poultry which resists all the efforts of eradication. Newcastle disease virus (NDV) strain ZG1999HDS was isolated during the outbreak in 1,999 at a broiler farm in Croatia. Previous trials in chickens confirmed it to be a lentogenic pathotype and immunogenic by stimulating humoral and cell mediated immunity. Further characterization by deduced amino acid sequence at the cleavage site of fusion protein confirmed its lentogenic nature, and in vitro tests its oncolytic capacity. Owing to its immunogenicity, strain ZG1999HDS is considered for vaccine development. In this study, 1-day-old chicks were vaccinated using strain ZG1999HDS oculonasally or by nebulization. Strain ZG1999HDS induced humoral immune response in both immunized groups The cell-mediated immune response occurred earlier in the group immunized by nebulization, as shown by a higher frequency rate of T and B lymphocytes, and significantly higher expression of IFN-α in respiratory organs and IFN-γ expression in the spleen. Viral genomic RNA was not detected in investigated organs. Thus, NDV strain ZG1999HDS is immunogenic when administered by means of nebulization or oculonasally without any adverse effects and is therefore suitable for further research and vaccine development. Further research is needed regarding its tropism.

Protection conferred by commercial NDV live attenuated and double recombinant HVT vaccines against virulent California 2018 Newcastle disease virus (NDV) in chickens

Vaccines against virulent Newcastle disease virus (NDV) are widely available and can be protective, but improved vaccination protocols are needed to prevent clinical disease and reduce virus circulation. The present study evaluated the efficacy of two commercial vaccines alone or in combination: a live attenuated NDV vaccine (LV) and a recombinant herpesvirus of turkeys vector expressing the fusion protein of NDV and the virus protein 2 of infectious bursal disease virus (rHVT-ND-IBD). Chickens were vaccinated with one of four vaccination protocols: live vaccine (LV) at 1 and 11 days of age (DOA), rHVT ND-IBD and LV at 1 DOA, rHVT ND-IBD at 1 DOA boosted with an LV at 11 DOA, and rHVT ND-IBD at 1 DOA. The vaccinated birds were challenged at different time points (3 or 4 weeks of age) with the California 2018 virus. The mortality, clinical signs, mean death time (MDT), humoral response before and after vaccination, and virus shedding after challenge were evaluated. All vaccination protocols were able to prevent mortality, reduce virus shedding, and induce antibody levels before the challenge at 3 and 4 weeks-old. Overall, the antibody levels before the challenge at 4 weeks were significantly higher in all groups vaccinated with the rHVT ND-IBD when compared to levels in 3 week old birds. The combination of recombinant rHVT ND-IBD with a live vaccine at one-day-old seems to be a better combination, due to the absence of clinical signs, higher antibody levels pre and post-challenge, and reduced virus shedding at any time point after the challenge at 3 or 4 weeks of age with the California 2018 virus.

Protective efficacy of the Newcastle disease virus genotype VII-matched vaccine in commercial layers

Newcastle disease virus (NDV) is a major threat to the poultry industry worldwide, with a diversity of genotypes associated with severe economic losses in all poultry sectors. Class II genotype VII NDV are predominant in the Middle East and Asia, despite intensive vaccination programs using conventional live and inactivated NDV vaccines. In Egypt, the disease is continuously spreading, causing severe economical losses in the poultry industry. In this study; the protective efficacy of a commercial, inactivated recombinant genotype VII NDV–matched vaccine (KBNP-C4152R2L strain) against challenge with the velogenic NDV strain (Chicken/USC/Egypt/2015) was evaluated in commercial layers. Two vaccination regimes were used; live NDV genotype II (LaSota) vaccine on days 10, 18, and 120, with either the inactivated NDV genotype II regime or inactivated NDV genotype VII–matched vaccine regime on days 14, 42, and 120. The 2 regimes were challenged at the peak of egg production on week 26. Protection by the 2 regimes was evaluated after experimental infection, based on mortality rate, clinical signs, gross lesions, virus shedding, seroconversion, and egg production schedule. The results show that these 2 vaccination regimes protected commercial layer chickens against mortality, but some birds showed mild clinical signs and reduced egg production temporarily. However, the combination of live NDV genotype II and recombinant inactivated genotype VII vaccines provided better protection against virus shedding (20% and 0% vs. 60% and 40%) as assessed in tracheal swabs and (20% and 0% vs. 20% and 20%) in cloacal swabs collected at 3 and 5 D post challenge (dpc), respectively. In addition, egg production levels in birds receiving the inactivated NDV genotype VII–matched vaccine regime and in those given inactivated genotype II vaccines were 76.6, 79, 82, and 87.4% and 77.7, 72.5, 69, and 82.5% at 7, 14, 21, and 28 dpc, respectively. The results of this study indicate that recombinant genotype-matched inactivated vaccine along with a live attenuated vaccine can reduce virus shedding and improve egg production in commercial layers challenged with a velogenic genotype VII virus under field conditions. This regime may ensure a proper control strategy in layers.

Comparative protective immunity provided by live vaccines of Newcastle disease virus or avian metapneumovirus when co-administered alongside classical and variant strains of infectious bronchitis virus in day-old broiler chicks

This study reports on the simultaneous administration of live NDV or aMPV subtype B vaccines alongside two live IBV (Massachusetts-H120 and 793B-CR88) vaccines in day-old maternal-antibody positive commercial broiler chicks. In the first experiment, chicks were divided into four groups; one unvaccinated and three groups vaccinated with live NDV VG/GA-Avinew, live H120 + CR88, or VG/GA-Avinew + H120 + CR88. In the second experiment, live aMPV subtype B vaccine was used in place of NDV. Clinical signs were monitored daily and oropharyngeal swabs were taken at regular intervals for vaccine virus detection. Blood was collected at 21 dpv for serology. 10 chicks from each group were challenged with virulent strains of M41 or QX or aMPV subtype B. For IBV, after 5 days post challenge (dpc), tracheal ciliary protection was assessed. For aMPV, clinical scores were recorded up to 10 dpc. For NDV, haemagglutination inhibition (HI) antibody titres were assayed as an indicator of protective immunity. In both experiments, ciliary protection for IBV vaccinated groups was maintained above 90%. The protection against virulent aMPV challenge was not compromised when aMPV, H120 and CR88 were co-administered. NDV HI mean titres in single and combined NDV-vaccinated groups remained above the protective titre (>3 log2). Both experiments demonstrated that simultaneous administration of live NDV VG/GA-Avinew or aMPV subtype B alongside H120 and CR88 vaccines does not interfere with protection conferred against NDV, IBV or aMPV.

Evaluation of humoral immune responses to enterotropic lentogenic VG/GA vaccine of Newcastle disease in commercial turkey poults (Meleagris gallopavo)

Background

Villegas-Glisson/University of Georgia (VG/GA) strain of Newcastle disease virus (NDV) is recommended for the initial vaccination of commercially reared turkey poults. However, the vaccine-induced antibody responses have not been studied in this species. The level of systemic humoral immune responses against the NDV was investigated in commercial turkey poults vaccinated with the VG/GA vaccine. One hundred eighty-two hybrid strain of turkey poults (Meleagris gallopavo) were divided randomly into vaccinated and unvaccinated groups. The vaccinated group was given the VG/GA vaccine at 10 and 20 days of age. To investigate the vaccine immunity, the level of specific IgY and IgA in serum samples were determined using ELISA and haemagglutination inhibition assays (HI). The biological half-life of maternal antibodies was also determined before the immunization.

Results

VG/GA-specific antibodies were detected in the vaccinated turkey poults and were significantly higher in the vaccinated group compared to the unvaccinated group. IgY and IgA antibodies showed a significant increase in titers 14 days after the second vaccination and reached a peak on day 35 of age. The correlation coefficient and intra-rater reliability showed a significant correlation between the HI titers and IgY/IgA ELISA values. Maternal IgY and IgA levels were found to decline in the serum with half-lifes of 7.68 ± 2.35 and 2.18 ± 0.82 days, respectively.

Conclusions

Enterotropic lentogenic VG/GA vaccine induced a marked humoral immune response against the NDV in turkey poults. The positive correlation between IgY and IgA highlights the role of these two antibody classes in controlling the Newcastle disease in turkey poults.

Establishment of xMAP for the simultaneous detection of antibodies to Newcastle disease virus and avian influenza virus

Using Luminex xMAP (x = analyte, MAP = multi-analyte profiling) technology, a serological method for the simultaneous detection of antibodies to Newcastle disease virus (NDV) and avian influenza virus (AIV) was established. Nano-magnetic beads coated with purified NDV protein and AIV nucleoprotein were incubated with serum samples. Using biotinylated rabbit anti-chicken IgY and streptavidin-R-phycoerythrin, the optical signals measured by a Luminex 200 detection system indicated the quantification of NDV or AIV antibodies in the serum. Specific pathogen-free (SPF) chicken serum was used as a negative control. The Luminex xMAP assay developed in this study demonstrated high specificity as there was no cross-reaction with antibodies to infectious laryngotracheitis virus, infectious bronchitis virus, infectious bursal disease virus, avian leukosis virus, and Marek's disease virus. The results from reproducibility experiments showed that intra-coefficients of variation were 3.36 and 9.23% and inter-coefficients of variation were 6.50 and 7.66% for NDV and AIV, respectively. The results also indicated that the Luminex xMAP assay was 16 times more sensitive for NDV antibody detection and 1,024 times more sensitive for AIV antibody detection compared to the enzyme-linked immunosorbent assay (ELISA). A total of 300 chicken serum samples were subjected to both Luminex xMAP assay and ELISA, showing the coincidence rates of 98.67 and 98% for NDV and AIV antibody detection, respectively. This study provides a new method for the simultaneous detection NDV and AIV antibodies in the serum with high specificity and sensitivity.

Turkey humoral and cell-mediated immune responses to a Newcastle viscerotropic vaccine and its association with major histocompatibility complex

Immune responses to vaccines are mainly influenced by the nature of vaccines and host variation in response to vaccination. In this study we aimed to investigate turkey humoral and cell-mediated immune responses to a Newcastle viscerotropic vaccine and its association with major histocompatibility complex (MHC). Turkeys were vaccinated with Villegas–Glisson/University of Georgia (VG/GA) attenuated vaccine against Newcastle disease. The stimulation index of lymphocyte proliferation and antigen-specific local secretory IgA responses in bile, duodenum, ileum, as well as serum IgY and IgA responses were analysed by enzyme-linked immunosorbent assay. The turkey MHC class II B locus was selected as candidate gene for detection of associations with cellular and humoral immune responses. Significant differences were observed between both cellular and humoral responses of vaccinated and unvaccinated groups. A significant positive correlation was also found between ND specific IgY and ND specific IgA titres in serum, intestine (duodenum and ileum) and trachea. Moreover, the correlation between specific IgA titres in ileum and specific bile, duodenum and trachea was positively significant. High resolution melting analysis (HRM) was used to genotype MHC class II B exon 2. Eight melting profiles (A-G) were identified, among which, profile G showed a significant association with cellular response. The profile B revealed significant association with total IgA titres in serum and ileum. These findings help our understanding of the association of turkey MHC types with immune responses. Further correlation analysis between serum and mucosal antibody titres demonstrated that the levels of IgY and IgA in serum can give an impression about the levels of secretory IgA and situation of mucosal immunity. Based on the significant effects, ND specific IgY in serum appears to be a promising indirect marker for specific IgA in serum and trachea.

Effect of Newcastle disease virus level of infection on embryonic length, embryonic death, and protein profile changes

Background and Aim

Newcastle disease virus (NDV) is an obligate intracellular parasite. Virus can only live on living cells. The embryonated chicken eggs (ECEs) are one of the growth media of virus that is a cheap, easy to do, and accurate for showing patterns of virus change in the host. Higher virus titers indicate the higher number of viruses and more virulent to infect host. This research aimed to investigate the effect of different level of NDV titer infection in ECEs on protein profile, embryonic length, mortality, and pathological change.

Materials and Methods

The study used a completely randomized design of six treatments and seven replications. The treatments were different level of NDV titer infection in allantoic fluid (AF) of 9-11 days ECEs, i.e., P1=2⁰, P2=2⁶, P3=2⁷, P4=2⁸, P5=2⁹, and P6=2¹⁰ hemagglutination unit (HAU). All samples were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Data were analyzed using one-way ANOVA with p=0.05 for length of the embryo and descriptive analysis for embryo mortality, pathology change, and protein band.

Results

The result showed that protein profile of NDV-infected ECEs of all different levels is more complex than protein profile of no NDV-infected ECEs. NDV infected of all different levels showed longer size embryo, higher mortality embryo at the first 2 days, and higher occurrence of hemorrhagic in all part of bodies of embryo than those of no NDV infected.

Conclusion

It was concluded that NDV infection of all different level decreased health conditions of chicken embryo of ECEs of 9-11 days old. Different level of NDV infection of ECEs of 9-11 days old showed no significantly different embryo profiles. However, all of the NDV-infected embryos were shorter, death on the 2nd day, and suffered more hemorrhage on all body surfaces than uninfected NDV embryos.

The role of vaccination in risk mitigation and control of Newcastle disease in poultry

Newcastle disease is regarded as one of the most important avian diseases throughout the world and continues to be a threat and economic burden to the poultry industry. With no effective treatment, poultry producers rely primarily on stringent biosecurity and vaccination regimens to control the spread of this devastating disease. This concise review provides an historical perspective of Newcastle disease vaccination and how fundamental research has paved the way for the development of instrumental techniques which are still in use today. Although vaccination programmes have reduced the impact of clinical disease, they have historically been ineffective in controlling the spread of virulent viruses and therefore do not always offer an adequate solution to the world's food security problems. However, the continued development of novel vaccine technology and improved biosecurity measures through education may offer a solution to help reduce the global threat of Newcastle disease on the poultry industry.

Estimating serological immune response against Newcastle disease vaccine in Aseel, Kadaknath and White Leghorn chicken by haemagglutination inhibition test

The present study aimed to estimate serological immune response against Newcastle disease vaccine investigating70 Aseel, 75 Kadaknath and 85 White Leghorn chicks. The day-old chicks were vaccinated with a dose of 106.5EID50 of RDF1 strain through occulo-nasal route followed by a booster dose on 28th day. The sera collected on 7,14, 21, 28, 35 and 42 days post-immunization (dpi) were used to measure antibody titres through haemagglutinationinhibition test. The data were analyzed by analysis of variance using SPSS 16.0 statistical software. The corresponding mean antibody titre (log2) estimates were 8.10±0.22, 7.89±0.18, 7.92±0.16, 8.29±0.14, 8.40±0.16 and 8.94±0.19 in Aseel, 7.32±0.16, 7.74±0.13, 7.56±0.13, 7.86±0.17, 8.43±0.17 and 9.14±0.16 in Kadaknath, and 8.48±0.28,8.02±0.31, 8.29±0.33, 8.14±0.30, 7.68±0.29 and 7.73±0.29 in White Leghorn chicken. The estimates significantlyvaried among different dpi in Aseel and Kadaknath chicken except White Leghorn. Aseel and Kadaknath chickendemonstrated gradual increasing trend and higher means of antibody titres for longer periods of dpi and achievedthe highest at 42 dpi, whereas White Leghorn chicken showed an irregular trend, the highest titre being observed at7 dpi. Again the 3 chicken genotypes significantly varied in antibody titres at 7, 35 and 42 dpi; White Leghornchicken demonstrated the highest antibody titre at 7 dpi, while Kadaknath chicken showed the highest titre at 35and 42 dpi. The higher and longer immune responsive Aseel and Kadaknath chicken might be utilized for selectiveintrogression of their candidate genes in high productive chicken germplasm with less NDV response.

Kinetics of serum antibody response to Newcastle disease vaccine in Aseel, Kadaknath and White Leghorn chicken using ELISA

The study aimed to evaluate kinetics of serum antibody response to Newcastle disease (ND) vaccine investigating 120 chicks from Aseel, Kadaknath and White Leghorn (WLH) maintained at this institute. The day-old chicks were vaccinated with a dose of 106.5 EID50 of live attenuated ND vaccine F1 strain through occulo-nasal route followed by a booster dose on 28th day. The antibody titre means were estimated and varied significantly among different dpi in Aseel, Kadaknath and WLH. The immune sera in Aseel and Kadaknath had gradual inclining antibody titre levels for longer dpi with the highest titre means at 42 dpi, whereas the sera in WLH had an irregular trend in antibody levels with the highest titre mean at 7 dpi. Aseel, Kadaknath and WLH also varied in mean antibody titres at 7, 14 and 42 dpi. The highest titre means at each 7 and 14 dpi were in WLH followed by Aseel and Kadaknath, respectively, whereas at 42 dpi was in Aseel followed by WLH and Kadaknath. The results indicated importance of the vaccination of day-old chicks against ND to enhance maternal derived antibody response and also speak about much better antibody response to NDV in Aseel and Kadaknath native fowl.

Vitamin A dietary supplementation reduces the mortality of velogenic Newcastle disease significantly in cockerels

This project was undertaken to find ways of reducing mortalities and economic losses due to velogenic Newcastle disease (VND) in areas where the disease is enzootic. Four groups of cockerels of 44 birds each were used for this experiment. The birds in groups 1 and 2 received no dietary vitamin A supplementation, whereas groups 3 and 4 received 300 iu and 600 iu of vitamin A per kilogram of commercial feed, respectively, from 1 week of age till the end of the experiment. At 6 weeks of age, the birds in groups 2, 3 and 4 were inoculated intraocularly with a VND virus (duck/Nigeria/Plateau/Kuru/113/1991). The birds in Group 1 were given phosphate-buffered saline intraocularly. Clinical signs appeared in Group 2 birds on day 3 PI and in groups 3 and 4 on day 5 PI. The clinical signs included a drop in feed and water consumption, depression, diarrhoea, torticollis and paralysis in all the infected groups. The average body weights of all groups were significantly different from one another on day 14 PI with Group 2 birds having the lowest body weight. Mortalities were highest in Group 2 birds (0%, 93.18%, 72.73% and 56.82% in groups 1, 2, 3 and 4 respectively). The antibody response in all the groups was significantly different from one another on days 14 and 21 PI. Group 2 birds had the lowest titres on those 2 days and showed more severe atrophy of the bursa, spleen, thymus and fibrin deposition in the spleen and thymus than the birds in groups 3 and 4. The above observations show that vitamin A dietary supplementation delayed the onset of clinical signs and significantly reduced body weight loss, atrophy of the bursa, spleen and thymus, and mortalities by 36%. It also significantly potentiated haemagglutination inhibition antibody response.

Effects of Newcastle disease virus vaccine antibodies on the shedding and transmission of challenge viruses

Different genotypes of avian paramyxovirus serotype-1 virus (APMV-1) circulate in many parts of the world. Traditionally, Newcastle disease virus (NDV) is recognized as having two major divisions represented by classes I and II, with class II being further divided into sixteen genotypes. Although all NDV are members of APMV-1 and are of one serotype, antigenic and genetic diversity is observed between the different genotypes. Reports of vaccine failure from many countries and reports by our lab on the reduced ability of classical vaccines to significantly decrease viral replication and shedding have created renewed interest in developing vaccines formulated with genotypes homologous to the virulent NDV (vNDV) circulating in the field. We assessed how the amount and specificity of humoral antibodies induced by inactivated vaccines affected viral replication, clinical protection and evaluated how non-homologous (heterologous) antibody levels induced by live NDV vaccines relate to transmission of vNDV. In an experimental setting, all inactivated NDV vaccines protected birds from morbidity and mortality, but higher and more specific levels of antibodies were required to significantly decrease viral replication. It was possible to significantly decrease viral replication and shedding with high levels of antibodies and those levels could be more easily reached with vaccines formulated with NDV of the same genotype as the challenge viruses. However, when the levels of heterologous antibodies were sufficiently high, it was possible to prevent transmission. As the level of humoral antibodies increase in vaccinated birds, the number of infected birds and the amount of vNDV shed decreased. Thus, in an experimental setting the effective levels of humoral antibodies could be increased by (1) increasing the homology of the vaccine to the challenge virus, or (2) allowing optimal time for the development of the immune response.

Immune responses of poultry to Newcastle disease virus

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

Abundance of IFN-α and IFN-γ gene transcripts and absence of IL-2 transcripts in the blood of chickens vaccinated with live or inactivated NDV

As immune responses to live and inactivated vaccines might differ, temporal responses of broiler chickens to vaccination were examined on the basis of the abundance in the circulating blood of gene transcripts of IFN-α, IFN-γ and IL-2, critical cytokines for immune responses. Blood samples were collected 6, 12 and 24 hours, and 7 and 14 days following vaccination with either live or inactivated Newcastle disease virus, La Sota strain, at 14 days of age, and the abundance of transcripts for each cytokine was assayed by real-time RT-PCR. Physiological saline and vaccine emulsion without viral antigen were administered to control groups for live and inactivated vaccine groups, respectively. The abundance of IFN-γ transcripts was elevated during the early times following vaccination and had reached baseline by the seventh day but the abundance of IFN-α transcripts remained elevated. Transcripts for neither IFN gene were detected in the control birds. The abundance of transcripts for each IFN was not different between the two vaccinated groups at any time. Transcripts for IL-2 were detected only in spleens from chicken embryos that had been inoculated with the live virus. The results show that cells stimulated to produce IFN-α and IFN-γ enter the circulating blood but those stimulated to produce IL-2 do not, or in very low number, and the IFN responses to both vaccines are the same.

Assessment of the cell-mediated immune response in chickens by detection of chicken interferon-γ in response to mitogen and recall Newcastle disease viral antigen stimulation

The potential of a capture enzyme-linked immunosorbent assay (ELISA) specific for chicken interferon-gamma (ChIFN-gamma) has been evaluated as a tool to assess cell-mediated immunity (CMI) in the chicken. In a first step, ChIFN-gamma production and cell proliferation of mitogen-activated chicken splenocytes have been compared. In general, for each of the stimulation conditions where significant proliferation was observed, production of ChIFN-gamma could be measured by ELISA. In our hands, the combination of ionomycin and phorbol-12-myristate 13-acetate or the use of recombinant chicken interleukin-2 gave the most satisfactory results. Then, the CMI response induced by live or killed Newcastle disease virus (NDV) vaccines has been evaluated sequentially by ex vivo antigen-specific ChIFN-gamma production and cell proliferation of splenocytes from immune chickens. The ex vivo data showed that both types of NDV vaccines are capable of stimulating CMI responses to NDV in chickens as measured by the ChIFN-gamma ELISA. However, most of the chickens vaccinated with the live vaccine produced ChIFN-gamma after antigen recall stimulation, from 2 to 4 weeks after vaccination, when only some chickens vaccinated with the inactivated vaccine showed a specific response 4 weeks after vaccination. No significant proliferative responses to either NDV vaccine were detectable during the 4 weeks of the study. From our results, it appears that antigen-specific ChIFN-gamma production can be used as a good indicator of actively acquired immunity to NDV and that the sensitivity range of the capture ELISA test is well adequate to measure ex vivo release of ChIFN-gamma.