Correlation of haemagglutinin-neuraminidase and fusion protein content with protective antibody response after immunisation with inactivated Newcastle disease vaccines

Overcoming scientific barriers in the transition from in vivo to non-animal batch testing of human and veterinary vaccines

INTRODUCTION

Before release, vaccine batches are assessed for quality to evaluate whether they meet the product specifications. Vaccine batch tests, in particular of inactivated and toxoid vaccines, still largely rely on in vivo methods. Improved vaccine production processes, ethical concerns, and suboptimal performance of some in vivo tests have led to the development of in vitro alternatives.

AREAS COVERED

This review describes the scientific constraints that need to be overcome for replacement of in vivo batch tests, as well as potential solutions. Topics include the critical quality attributes of vaccines that require testing, the use of cell-based assays to mimic aspects of in vivo vaccine-induced immune responses, how difficulties with testing adjuvanted vaccines in vitro can be overcome, the use of altered batches to validate new in vitro test methods, and how cooperation between different stakeholders is key to moving the transition forward.

EXPERT OPINION

For safety testing, many in vitro alternatives are already available or at an advanced level of development. For potency testing, in vitro alternatives largely comprise immunochemical methods that assess several, but not all critical vaccine properties. One-to-one replacement by in vitro alternatives is not always possible and a combination of methods may be required.

Relationship Between the Serotypes and Hemagglutinin Gene Sequences of Avibacterium paragallinarum

Avibacterium paragallinarum has been subtyped into three serogroups (A, B, and C) and nine serovars (A-1, A-2, A-3, A-4, B-1, C-1, C-2, C-3, and C-4) according to the Page and Kume schemes. Both schemes use the hemagglutination inhibition test for serotyping. However, the relationship between the hemagglutinin gene (HMTp210) sequences and serotypes of A. paragallinarum is still unclear. This problem is partly due to the lack of information on the complete HMTp210 sequence from the formal reference strain of Page serogroup B (strain 0222 or Spross). In this study, we determined the complete HMTp210 sequence of strain Spross. The sequence of Spross and those of other HMTp210 sequences retrieved from GenBank were used to conduct phylogenetic analyses to investigate the relationship between the serotypes and HMTp210 sequences of A. paragallinarum. Four phylogenetic clusters, designated clusters A-1, A-2, B, and C, were identified. Clustering based on complete HMTp210 sequences correlates with serotyping based on hemagglutination inhibition tests. Serovar A-2 was found to contain a chimeric HMTp210 gene that might have resulted from recombination between serovar A-1 and serovar C-1. In addition, phylogenetic analysis based on partial sequences (approximately nucleotides 1-1200) of HMTp210 was sufficient to discriminate between serogroups A, B, and C. These findings could be valuable for developing a molecular method for serotyping of A. paragallinarum.

Immunogenicity of Newcastle Disease Vaccine in Southern Ground-hornbill (Bucorvus leadbeateri)

The southern ground-hornbill (Bucorvus leadbeateri; hereafter SGH) is endangered in South Africa, Namibia, and Swaziland. Through a conservation program established in South Africa by the Mabula Ground Hornbill Project, wild populations are being re-established by the reintroduction of captive-reared birds. The SGH is susceptible to infection with avian avulavirus 1, which causes Newcastle disease (ND). Four different vaccines to protect against ND were administered through various vaccination schedules and evaluated by serologic monitoring to assess the efficiency and safety of various combinations of vaccines (live versus inactivated/killed), vaccine strains (Ulster strain, live; Avivac Cellimune, live; VG/GA strain, live; and Avivac Struvac, killed), and administration routes (intraocular versus subcutaneous versus intramuscular injection versus oral). We vaccinated 75 individuals and evaluated antibody titers in 53 individuals (24 juveniles, 13 subadults, and 16 adult SGH; 26 males and 27 females) over a period of 9 years. Antibody titers to avian avulavirus 1 in sera were monitored by a hemagglutination inhibition test. Protective titers were generated with 3/6 vaccine regimes tested in the SGH. The highest vaccine titers were established in birds vaccinated with the Ulster strain in the conjunctiva and followed with an intramuscular Struvac injection (mean log₂ titer 8.6 ± 2.6) booster. Our aim was 1) to assess whether optimal vaccination protocols could be developed and 2) to then be able, by oral administration, to remove the need to recapture free-roaming, reintroduced birds to administer the initial vaccine or booster, thus remove the threat or mortality associated with ND to this endangered avian species in both captive birds and birds released back into the wild.

Comparison of chemical extraction methods for determination of 146S content in foot-and-mouth disease oil-adjuvanted vaccine

AIMS

To compare antigen extraction efficiency of chemical methods such as benzyl alcohol, chloroform, sodium citrate, extraction buffer with Tween-20 (EBT) and isopropyl myristate for determination of 146S content in the fresh and stored FMD oil-adjuvanted vaccines.

METHODS AND RESULTS

Standard vaccine with antigen payload of 10, 5 and 5 µg per cattle dose (2 ml) for serotypes O, A and Asia1, respectively, was used to compare the antigen extraction efficiency of five chemical methods: benzyl alcohol, chloroform, sodium citrate, EBT buffer and isopropyl myristate. The purity of the extracted 146S antigen was quantified by caesium chloride (CsCl) ultracentrifugation. Serotype-specific sandwich ELISA (sELISA) was developed to identify the serotype and to compare the 146S in aqueous phase and ultrafractions. The antigen recovery was also tested in stored trivalent vaccine. Coefficient of regression was calculated to assess the predictive power of the benzyl alcohol extraction method. Of the five methods, benzyl alcohol showed consistent antigen recovery of >90% in monovalent as well as trivalent vaccines. Ultrafraction showed a 1·4 ratio at A259/239 nm in UV spectrophotometry indicating the presence of 146S. sELISA revealed that the antigen recovery was significantly less in ultrafractions than that of aqueous phase. Further, there was no significant difference in antigen recovery from stored trivalent vaccine for 12 months, indicating the usefulness of the benzyl alcohol method. Linear regression model revealed R²  = 0·99 with a narrow band of predictive interval.

CONCLUSIONS

The benzyl alcohol method was efficient in extracting 146S from the monovalent and trivalent fresh and stored FMD vaccines. CsCl density gradient precisely quantified the 146S, while sELISA identified the serotype of the vaccine.

SIGNIFICANCE AND IMPACT OF THE STUDY

When the benzyl alcohol method is coupled with CsCl density gradient and sELISA, it has the potential to determine the 146S content of FMD vaccine.

Comparative efficacy of commercial inactivated Newcastle disease virus vaccines against Newcastle disease virus genotype VII in broiler chickens

Newcastle disease is still causing huge economic losses and devastating outbreaks in poultry flocks despite implementation of extensive vaccination programs. Five commercial broiler chicken groups were established as G1 (non-vaccinated, non-challenged group) and G2 (non-vaccinated, challenged group), and 3 vaccinated challenged groups as G3 (vaccinated with heterologous inactivated Newcastle disease virus (NDV) genotype II (NDV II) vaccine), G4 (vaccinated with homologous inactivated NDV genotype VII (NDV VII) vaccine), and G5 (vaccinated with bivalent (heterologous inactivated NDV II plus H5) vaccine) were used. Challenge test was done using a velogenic NDV genotype VII (vNDV VII) at 28-d olds. Respiratory signs, greenish diarrhea, and obvious post-mortem lesions of vNDV VII appeared in all the challenged birds whether vaccinated or not. In addition, the mortality rate decreased from 93.3% in G2 to 46.7%, 53.3%, and 66.7% in G4, G5, and G3, respectively. Overall, 2 wk postchallenge; body weight loss (%) had increased mainly in G2, with some improvement in chickens in G4 followed by G5 and chickens of G3 showed the least improvement. At 28 d (day of challenge), the highest hemagglutination inhibition values were 4.3 and 5.4 log2 in chickens in G4 and G5, respectively, which increased in all groups after the challenge. Cytokine (IL-6 and IFN-γ) levels were significantly higher (P < 0.05) in the vaccinated groups than that in the non-vaccinated group, especially in G5. Viral shedding in the trachea was higher than that in the cloacal swabs in all vaccinated and non-vaccinated challenged groups with peak shedding on the 6th day post challenge for both swabs, and the lowest viral shedding titers were observed in chickens in G5. Therefore, the use of homologous genotype NDV with inactivated vaccine conferred a higher clinical protection in terms of body weight loss and mortality against vNDV VII challenge in broiler chickens; however, the heterologous vaccine used in G5 induced the highest cell-mediated immune response and hemagglutination inhibition titers with the lowest viral shedding titer.

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.

Vaccination with Astragalus and Ginseng Polysaccharides Improves Immune Response of Chickens against H5N1 Avian Influenza Virus

To determine the effect of astragalus and ginseng polysaccharides (APS, GPS) on immune response and improvement of H5N1 vaccine, 360-day-old broilers were randomly divided into 8 groups of 45 chicks, comprising APS groups (1-3); GPS groups (4-6); vaccine group (7); and blank control (8) (without polysaccharide and vaccine). From day 12 after hatch groups 1-3 were given APS and groups 4-6 with GPS both at 100, 200, and 400 (mg/kg), respectively. At day 15 after hatch, groups 1-7 were vaccinated with 0.3 mL H5N1 vaccine subcutaneously; daily weight gain (DWG) and serum Ig antibody (by HI-test) were measured on 3, 7, 14, and 28 days after vaccination. Serum antibody titers and expression of cytokines (IL-2, IL-10, I FN-γ, and TNF) were determined by ELISA and RT-PCR. Results revealed that all the polysaccharide groups were numerically increased in antibody levels and the expression of cytokines was significant (P < 0.05) in the APS and GPS groups compared to corresponding vaccine group and blank control. DWG was higher (P < 0.05) in 400 mg/kg APS groups than control groups. Thus oral supplements of GPS and APS have shown their potential in the improvement of immune response and could be used as adjuvant in a formulation of H5N1 vaccine.

Construction of recombinant baculovirus vaccines for Newcastle disease virus and an assessment of their immunogenicity

Newcastle disease (ND) is a lethal avian infectious disease caused by Newcastle disease virus (NDV) which poses a substantial threat to China's poultry industry. Conventional live vaccines against NDV are available, but they can revert to virulent strains and do not protect against mutant strains of the virus. Therefore, there is a critical unmet need for a novel vaccine that is safe, efficacious, and cost effective. Here, we designed novel recombinant baculovirus vaccines expressing the NDV F or HN genes. To optimize antigen expression, we tested the incorporation of multiple regulatory elements including: (1) truncated vesicular stomatitis virus G protein (VSV-GED), (2) woodchuck hepatitis virus post-transcriptional regulatory element (WPRE), (3) inverted terminal repeats (ITRs) of adeno-associated virus (AAV Serotype II), and (4) the cytomegalovirus (CMV) promoter. To test the in vivo efficacy of the viruses, we vaccinated chickens with each construct and characterized the cellular and humoral immune response to challenge with virulent NDV (F48E9). All of the vaccine constructs provided some level of protection (62.5-100% protection). The F-series of vaccines provided a greater degree of protection (87.5-100%) than the HN-series (62.5-87.5%). While all of the vaccines elicited a robust cellular and humoral response subtle differences in efficacy were observed. The combination of the WPRE and VSV-GED regulatory elements enhanced the immune response and increased antigen expression. The ITRs effectively increased the length of time IFN-γ, IL-2, and IL-4 were expressed in the plasma. The F-series elicited higher titers of neutralizing antibody and NDV-specific IgG. The baculovirus system is a promising platform for NDV vaccine development that combines the immunostimulatory benefits of a recombinant virus vector with the non-replicating benefits of a DNA vaccine.

Multiplex immunoassay for in vitro characterization of acellular pertussis antigens in combination vaccines

Vaccines characterization is required to ensure physical, chemical, and biological integrity of antigens and adjuvants. Current analytical methods mostly require complete antigen desorption from aluminum-based adjuvants and are not always suitable to distinguish individual antigens in multivalent formulations. Here, Luminex technology is proposed to improve the analytics of vaccine characterization. As proof of concept, TdaP (tetanus, diphtheria and acellular pertussis) combination, adjuvanted with aluminum hydroxide, was chosen as model formulation to quantify and determine the level of adsorption of acellular pertussis (aP) antigens onto adjuvant surface at the same time. The assay used specific antibodies bound to magnetic microspheres presenting unique digital signatures for each pertussis antigen, allowing the simultaneous recognition of respective antigens in the whole vaccine, avoiding laborious procedures for adjuvant separation. Accurate and reproducible quantification of aP antigens in TdaP vaccine has been achieved in the range 0.78-50 ng/mL, providing simultaneously information on antigen identity, quantity, and degree of adsorption to aluminum hydroxide. The current study could further be considered as a model to set up in vitro potency assays thus supporting the replacement of animal tests accordingly to the 3Rs concept.

Stabilizing effects of excipients on dissociation of intact (146S) foot-and-mouth disease virions into 12S particles during storage as oil-emulsion vaccine

Most conventional foot-and-mouth disease virus (FMDV) vaccines contain oil-adjuvant. Their potency decreases upon prolonged storage. Intact (146S) FMDV particles can dissociate into 12S degradation products with a concomitant decrease in immunogenicity. We therefore measured virion stability in vaccines using two previously developed ELISAs to separately quantify 12S and 146S particles. Virions completely dissociated into 12S particles within 3 months after oil-emulsification. Dissociation occurred at a much lower rate in a comparable aqueous solution that was not oil-emulsified. Thus, oil-emulsification stimulates virion dissociation, presumably due to the protein denaturing effect of the oil-water interface. In real-time stability studies the stability of oil-adjuvanted virions of four different FMDV strains was significantly increased by addition of sucrose and BSA in a synergistic manner. Contrary to BSA addition, the effect of sucrose addition was concentration dependent. This study illustrates the importance of analysing antigen integrity after oil-emulsification and provides methods for FMDV vaccine stabilization.

Overcoming the susceptibility gap between maternal antibody disappearance and auto-antibody production

In the first 10-14 days of a chick's life, protection is conferred by maternal antibodies. Further broiler protection is achieved by active vaccination. However, the high level of maternal antibodies interferes with the induction of an effective immune response by vaccination at a young age. As a result, there is a gap between the reduction in protective maternal antibodies and elevation of self-produced antibodies following active vaccination. The major aim of this study was to test an approach consisting of passive and active vaccination to overcome this gap and to provide continuous resistance to infectious viral diseases during the broiler's growth period. Newcastle disease virus (NDV), which is one of the world's most prevalent infectious diseases of poultry, was tested as a model. Following subcutaneous injection of 18 hemagglutination-inhibiting (HI) units of anti-NDV immunoglobulin Y per 1-day-old chick, protective log2 antibody titers above 4 could be detected to at least 17 days of age. The combination of passive immunization on day 1 of age with attenuated live vaccination on day 10 led to high protective titers throughout the entire growth period, up to 41 days of age. Moreover, the HI titers in the group of birds immunized with the combined vaccination were significantly more homogeneous than those in the group vaccinated only with live virus. Thus, full protection against NDV of all broilers in flock during their entire growth period was achieved by a vaccination regime that combines passive immunization and live vaccination.

Astragalus polysaccharide enhances immunity and inhibits H9N2 avian influenza virus in vitro and in vivo

This study investigated the humoral immunization of Astragalus polysaccharide (APS) against H9N2 avian influenza virus (H9N2 AIV) infection in chickens.The effects of APS treatment on H9N2 infection was evaluated by an MTT [3(4, 5-dimethylthiazol-2-yl)-2, 3-diphenyl tetrazolium bromide] assay and analysis of MHC and cytokine mRNA expression. The effect on lymphocyte and serum antibody titers in vivo was also investigated. IL-4, IL-6, IL-10, LITAF, IL-12 and antibody titers to H9N2 AIV were enhanced in the first week after APS treatment. The results indicated that APS treatment reduces H9N2 AIV replication and promotes early humoral immune responses in young chickens.

Generation of a genotype VII Newcastle disease virus vaccine candidate with high yield in embryonated chicken eggs

To generate a genotype VII Newcastle disease virus (NDV) vaccine with high yield in embryonated chicken eggs, we selected genotype VII NDV strain JS5/05, which possesses a high virus titer in embryos as the parental virus. Using reverse genetics, we generated a genetically tagged derivative (NDV/AI4) of JS5/05 by changing the amino acid sequence of the cleavage site of the F0 protein. Pathogenicity tests showed that NDV/AI4 was completely avirulent. NDV/AI4 was genetically stable and replicated efficiently during 10 consecutive passages in embryos. More importantly, serologic assays showed that oil-emulsion NDV/AI4 induced higher hemagglutination inhibition (HI) titers against the prevalent virus than oil-emulsion LaSota vaccine in chickens and geese. Moreover, NDV/AI4-induced HI titers rose faster than those elicited by LaSota in chickens. Both NDV/AI4 and LaSota provided protection against clinical disease and mortality after the challenge with the genotype VII NDV strain JS3/05. However, NDV/AI4 significantly reduced virus shedding from the vaccinated birds compared to LaSota. Taken together, these results suggest that NDV/AI4 can provide better protection than LaSota and is a promising vaccine candidate against genotype VII NDV.

DNA-chitosan nanoparticles improve DNA vaccine-elicited immunity against Newcastle disease virus through shuttling chicken interleukin-2 gene

In this study, pCAGG-ChIL2 plasmid DNA containing the chicken interleukin-2 (ChIL-2) gene was used to prepare DNA-chitosan nanoparticles (CNPs). The CNPs prepared were spherical, with mean diameters between 100 and 200 nm, have a positive surface charge, and could protect DNA against DNase I degradation. The CNPs prepared were successfully used to transfect the Df-1 cell line with almost no cytotoxicity. CNPs prepared at an amino group to phosphate group ratio (N/P ratio) of 16 provided the highest transfection efficiency (1.1%) in medium with a pH of 6.5. When pCAGG-ChIL2 CNPs were administered to chickens simultaneously with a DNA vaccine against Newcastle disease virus (NDV), haemagglutination inhibition antibody titers and serum interferon-γ (IFN-γ) levels were significantly higher than in chickens immunised with the NDV DNA vaccine alone (p < 0.05). The results demonstrate that pCAGG-ChIL2 CNPs improve DNA vaccine-elicited immunity against NDV challenge.

Immunogenicity and protective efficacy of virosome based vaccines against Newcastle disease

Virosome based vaccines against Newcastle disease (ND) were prepared and evaluated for their immunogenicity and protective efficacy in chickens. Envelop of Newcastle disease virus (NDV) was solubilised with Triton X-100 to yield virosomes which were later on encapsulated in poly-lactide-co-glycolide (PLG) microspheres. The birds were immunized intranasally with virosomes or PLG microspheres encapsulated virosomes, and efficacy of these preparations was compared with commercial LaSota vaccine. The preparations protected the chickens against virulent virus challenge infection, however the microencapsulated virosome vaccine gave slightly lesser degree of protection than non encapsulated counterpart. The humoral and cell mediated immune response generated as well as the protection afforded by virosome preparations were found to be comparable with LaSota vaccine. The results substantiate the potential of virosome based vaccines to provide high level of immunity and protection against Newcastle disease.

The influence of the inactivating agent on the antigen content of inactivated Newcastle disease vaccines assessed by the in vitro potency test

An in vitro potency test has recently been included in the European Pharmacopoeia (EP) monograph (01/2007:0870) to assess the potency of inactivated Newcastle disease (ND) vaccines. This enzyme linked immunosorbent assay (ELISA) is an attractive alternative for the existing in vivo potency tests especially with regard to the objective of the European Authorities to Replace, Reduce and Refine the use of laboratory animals for production and quality control of immunobiologicals. In the present study the influence of the inactivant on the antigen content established by ELISA was evaluated. Therefore, oil based vaccines containing similar concentrations of beta-propiolactone (BPL) or formaldehyde inactivated Newcastle disease virus (NDV) were examined by ELISA and in the in vivo potency tests outlined in the EP. The results obtained demonstrate that the use of formaldehyde as inactivant lowered the in vitro potency compared to BPL as inactivant. In contrast, the in vivo potency was not affected. Therefore, the ELISA should not be used to compare the potency of commercial ND vaccines containing formaldehyde inactivated NDV with those containing BPL inactivated NDV. However, the ELISA is considered an attractive alternative for the existing in vivo potency tests since it can be used by vaccine manufacturers for the release of inactivated ND vaccines.

Determination of minimum hemagglutinin units in an inactivated Newcastle disease virus vaccine for clinical protection of chickens from exotic Newcastle disease virus challenge

The potency of inactivated Newcastle disease virus (NDV) vaccines in the United States is currently determined using vaccination and challenge of experimental animals against a velogenic strain of NDV. Because velogenic strains of NDV are now classified as select agents in the United States, all vaccine potency testing must be performed in live animals under biosafety level 3 agriculture conditions. If the minimum amount of inactivated viral antigen required for clinical protection can be determined using other methods, vaccines meeting these criteria might be considered of adequate potency. The linearity of correlation between the hemagglutination (HA) assay measurement and the 50% embryo infectious dose titer ofNDV Hitchner B1 vaccine virus was determined. Correlation between hemagglutinin units (HAU) per vaccine dose, clinical protection, and antibody response was then determined using a vaccinate-and-challenge model similar to Chapter 9 of the U.S. code of federal regulations approved method for vaccine potency testing. The dose providing 50% protection of an in-house water-in-oil emulsion vaccine formulated with inactivated NDV B1 was determined to be between 400 and 600 HAU from two separate trials. A positive correlation (R2 = 0.97) was observed between antibody response and HAU per vaccine dose. Serum antibody responses from vaccinated birds indicate HA inhibition titers >2(5) log2 would provide 100% protection from morbidity and mortality and require a minimum protective dose of 1000 HAU per bird. These are the first studies to examine establishing both a minimum protective HAU content for inactivated ND vaccines and a minimum serologic response necessary to ensure potency.

Effects of phytate and phytase on the performance and immune function of broilers fed nutritionally marginal diets

The effects of phytate and phytase on broiler performance and cellular and humoral immunity was assessed by using 504 Cobb 500 female broilers fed nutritionally marginal diets. At 1 d of age, the chicks were randomly allocated to 6 treatments in a 2 x 3 factorial arrangement including 2 levels of phytate P (0.22 or 0.44%) and 3 dose rates of an Escherichia coli-derived phytase [0, 500, or 1,000 phytase units (FTU)/kg of feed]. Both low- and high-phytate diets were corn and soy based with the same nutritional specifications (AME 2,900 kcal/kg, CP 21.00%, Ca 0.78%, and nonphytate P0.28%), differing only in the concentration of phytate P. The immune status of birds was measured at 14, 21, and 28 d of age. The results revealed that phytase improved feed intake, BW, and feed conversion ratio (P < 0.05), whereas high dietary phytate depressed bird performance (P < 0.05). There was no interaction between phytate and phytase on bird performance. Feeding phytase increased the percentages of erythrocyte rosette-forming cells and erythrocyte-antibody complement cells by 3.03 and 1.83% at d 21, and by 2.76 and 2.20% at d 28, respectively (P < 0.05). The percentages of CD4(+)CD8(+) T lymphocyte subsets were also increased by phytase (P < 0.05), without affecting the ratio of CD4(+) and CD8(+). The levels of intestinal secretory IgA were improved with phytase at d 14, 21, and 28 (P < 0.05). Antibodies against Newcastle disease virus vaccine were enhanced at d 21 and 28 in the high-phytate diets with phytase addition (P < 0.05). Increasing the phytase dose to 1,000 FTU/kg did not improve immune function further than 500 FTU/kg. The results suggest that application of phytase in nutritionally marginal diets could enhance lymphocyte numbers and the seral and mucosal antibodies of 1- to 28-d-old broilers, suggesting that both phytate and phytase may have a role in gastrointestinal health and immune competence.

Variation of a newcastle disease virus hemagglutinin-neuraminidase linear epitope

Fifty-six Newcastle disease virus strains collected from 2000 to 2006 could be grouped into subgenotype VIId. However, they displayed cumulative mutations in and around the linear epitope of hemagglutinin-neuraminidase (residues 345 to 353) with time. The antigenicities of the variants that became predominant in Korea differ from each other and from the wild type.

Rapid quality control of a live attenuated Peste des petits ruminants (PPR) vaccine by monoclonal antibody based sandwich ELISA

Peste des petits ruminants (PPR) is a highly contagious and economically important viral disease of goats and sheep. A homologous Vero cell-based attenuated PPR vaccine developed in our laboratory and used extensively throughout the country, is available for control of PPR. The presently used quality control test, titration in Vero cells for PPR virus titre in vaccine batches, takes at least 6-8days to determine the quality and dose of vaccine. In this study, 74 freeze-dried PPR vaccine batches were tested simultaneously by both virus titration and PPR sandwich ELISA (S-ELISA) to correlate the titre of the vaccine virus with reactivity in S-ELISA. It was found that the vaccine batches with titre more than 10(3)TCID(50)/ml gave positive results in S-ELISA and correlated well with the virus titre of the freeze-dried vaccines. The correlation coefficient between the virus titration and S-ELISA reactivity was estimated as 0.96, indicating a high correlation between the two parameters based on 74 batches of freeze-dried PPR vaccine. The vaccine batches with titres of 3.0, 4.3, 4.5, 5.0, 6.5 and 7.0 had shown a positive reaction when tested in two-fold dilutions in S-ELISA at 1, 5, 6, 7, 8 and 9log2 titres, respectively. The test vaccine batches were found to be negative in S-ELISA when the titre of the vaccine was less than 10(3)TCID50/ml, suggesting that the vaccine could not be passed for field use. It is concluded that S-ELISA could be a preliminary tool useful for the quality control of PPR vaccine as it is rapid and easy to perform when compared to virus titration.

Analyses of the results of different test systems in the 2005 global proficiency testing schemes for infectious bursal disease virus and Newcastle disease virus antibody detection in chicken serum

The results of global proficiency testing schemes (PTS) for serological tests to detect antibodies against infectious bursal disease virus (IBDV) and Newcastle disease virus (NDV) in chicken serum, in which 125 and 120 laboratories, respectively, participated from Africa, Asia, Europe, Central and South America, were used to analyse the performances of different antibody test systems such as virus neutralization tests, haemagglutination inhibition tests, enzyme-linked immunosorbent assays and agar gel precipitation tests. All laboratories were asked to carry out their routine diagnostic tests for the detection of IBDV and NDV antibodies as usual. This global ring trial provided a large amount of data on variation within and between laboratories and test systems used worldwide. The data showed that the variation between the quantitative test results of different laboratories (R(between)) using the IBDV virus neutralization tests and the NDV haemagglutination inhibition test was higher (about double) compared with the variation within commercial enzyme-linked immunosorbent assay systems. Although both tests are often referred to and used as the "gold standard" in experimental and scientific studies, official procedures and for the validation of tests, this study shows that there is an urgent need for a global implementation of recommended test procedures and/or the inclusion of international reference sera in these studies.

Chinese herbal ingredients are effective immune stimulators for chickens infected with the Newcastle disease virus

This study was conducted to determine the efficacy of 4 Chinese herbal ingredients (CHI) as immune stimulators for an active vaccine in chickens using both in vitro and in vivo assays. The CHI used were Astragalus polysaccharide (APS), Isatis root polysaccharide (IRPS), Propolis polysaccharide, and Epimedium flavone at various concentrations. Two hundred 14-d-old male White Roman chickens were randomly divided into 10 groups. Chickens in groups 1 to 9 were inoculated with the New-castle disease virus (NDV) strain IV vaccine by intranasal and intraocular administration. Chickens in groups 1 to 8 were also administered subcutaneously on the dorsal region of the neck with 0.5 mL of the corresponding CHI at 2 doses: 29 and 58 mg/kg of BW for APS and IRPS and 7.25 and 14.5 mg/kg of BW for the others, once daily for 3 successive days. In group 9 (CHI-free control) and group 10 (both vaccine- and CHI-free control), chickens were injected with 0.5 mL of physiological saline. New-castle disease virus-specific serum hemagglutination inhibition antibody (Ab) production in immunized chickens was quantified using established methods. The results indicate that a majority of the CHI used at appropriate concentrations were effective in enhancing in vitro proliferation of chick embryo fibroblasts in response to the NDV infection. In vivo administration of CHI to vaccinated chickens (7.25 to 58 mg/kg of BW, depending on type) increased serum anti-NDV hemagglutination inhibition Ab titer concentrations, compared with the administration the NDV alone. For all CHI, a beneficial effect on the Ab production was observed on d 21 after the initiation of the vaccination. On the basis of the in vivo doses used, Propolis polysaccharide and Epimedium flavone were more potent than APS and IRPS in promoting the humoral immune response in the young birds (P < 0.05). Collectively, these findings suggest that appropriate doses of CHI can be used as novel, effective immune stimulators for chickens.

Expression of the Newcastle disease virus fusion protein in transgenic maize and immunological studies

Transgenic plants have been employed successfully as a low-cost system for the production of therapeutically valuable proteins, including antibodies, antigens and hormones. Here, we report the expression of the fusion (F) gene of the Newcastle disease virus (NDV) in transgenic maize plants. The expression of the transgene, driven by the maize ubiquitin promoter, caused accumulation of the F protein in maize kernels. The presence of the transgene was verified by Southern and western blots. Feeding chickens with kernels containing the F protein induced the production of antibodies, which conferred protection against a viral challenge. This protection was comparable to that conferred by a commercial vaccine. Possible uses of this plant-based F protein as a potential mucosal vaccine are discussed.

Quantification of the effect of vaccination on transmission of avian influenza (H7N7) in chickens

Recent outbreaks of highly pathogenic avian influenza (HPAI) viruses in poultry and their threatening zoonotic consequences emphasize the need for effective control measures. Although vaccination of poultry against avian influenza provides a potentially attractive control measure, little is known about the effect of vaccination on epidemiologically relevant parameters, such as transmissibility and the infectious period. We used transmission experiments to study the effect of vaccination on the transmission characteristics of HPAI A/Chicken/Netherlands/03 H7N7 in chickens. In the experiments, a number of infected and uninfected chickens is housed together and the infection chain is monitored by virus isolation and serology. Analysis is based on a stochastic susceptible, latently infected, infectious, recovered (SEIR) epidemic model. We found that vaccination is able to reduce the transmission level to such an extent that a major outbreak is prevented, important variables being the type of vaccine (H7N1 or H7N3) and the moment of challenge after vaccination. Two weeks after vaccination, both vaccines completely block transmission. One week after vaccination, the H7N1 vaccine is better than the H7N3 vaccine at reducing the spread of the H7N7 virus. We discuss the implications of these findings for the use of vaccination programs in poultry and the value of transmission experiments in the process of choosing vaccine.

Improved protection from velogenic Newcastle disease virus challenge following multiple immunizations with plasmid DNA encoding for F and HN genes

Specific-pathogen free (SPF) chickens were inoculated with the plasmid constructs encoding the fusion (F) and haemagglutinin-neuraminidase (HN) glycoproteins of Newcastle disease virus (NDV), either individually or in combination and challenged with velogenic NDV. The antibody level against NDV was measured using commercial enzyme linked immunosorbent assay (ELISA). In the first immunization regimen, SPF chickens inoculated twice with NDV-F or NDV-HN constructs elicited antibody responses 1 week after the second injection. However, the levels of the antibody were low and did not confer significant protection from the lethal challenge. In addition, administration of the plasmid constructs with Freund's adjuvant did not improve the level of protection. In the second immunization regimen, chickens inoculated twice with the plasmid constructs emulsified with Freund's adjuvant induced significant antibody titers after the third injection. Three out of nine (33.3%) chickens vaccinated with pEGFP-HN, five of ten (50.0%) chickens vaccinated with pEGFP-F and nine of ten (90.0%) chickens vaccinated with combined pEGFP-F and pEGFP-HN were protected from the challenge. No significant differences in the levels of protection were observed when the chickens were vaccinated with linearized pEGFP-F. The results suggested that more than two injections with both F and HN encoding plasmid DNA were required to induce higher level of antibodies for protection against velogenic NDV in chickens.

Virosome and ISCOM vaccines against Newcastle disease: preparation, characterization and immunogenicity

The purpose of this study was to prepare and characterize virosomes and ISCOMs containing envelope proteins of Newcastle disease virus (NDV) and to evaluate their immunogenicity in target animals (chickens). Virosomes were prepared by solubilization of virus with either Triton X-100 or octyl glucoside (OG) followed by detergent removal. Biochemical analysis revealed that these virosomes contained both the haemagglutinin-neuraminidase protein (HN) and the fusion protein (F), with preserved biological activity. Acidic environment triggered the fusion between virosomes and chicken erythrocyte ghosts. Formation of ISCOMs was achieved by solubilizing phospholipids, cholesterol, envelope protein antigen and Quil A in Triton X-100. The ISCOM particles were formed by removal of the detergent. In each formulation the relative HN content correlated with the capability to agglutinate red blood cells. The immunogenicity of these lipid-based subunit vaccines was determined in chickens after subcutaneous immunization. The relative HN content of the subunit vaccines correlated with the haemagglutination-inhibition (HI) antibody titres. Virosomes prepared with Triton X-100 and ISCOMs offered high clinical protection (> 80%) upon challenge with virulent NDV. Virosomes prepared with OG yielded lower clinical protection despite high HI antibody titres. Virosomes with reduced antigen density showed poor immunogenicity and protection. In conclusion, ND virosomes and ISCOMs were found to be immunogenic and provided good protection.