Velogenic Viscerotropic Newcastle Disease Virus Research Articles

Ultrastructure Microscopic Characterization of Apoptosis in Myelomoncytic Leukemia Cell Line Treated with Velogenic Viscerotropic Newcastle Disease Virus Strain AF 2240.

Leukemia is a group of hematologic malignancies in the bonemarrow that arise from the dysfunctional proliferation of developing leukocytes. It is classified as either acute or chronic based on the rapidity of proliferation and as myelocytic or lymphocytic based on the cell of origin. Newcastle Disease Virus (NDV) is an avian paramyxovirus, which has been demonstrated to possess significant oncolytic activity against mammalian cancers because its ability to kill tumor cells with limited toxicity to normal cells. In this study, the morphophical changes and apoptosis induction of WEHI 3B leukemia cell line treated with NDV strain AF2240 were studied by scanning electron microscopes and transmission electron microscopes techniques. Electron microscopy indicated that NDV strain AF 2240 significantly altered cell morphology and reduced cell viability. Furthermore, early apoptosis was observed 6 h post-inoculation by fluorescence microscope. Our results suggest that NDV has ability to induce significant apoptoic structural changes in WEHI 3B leukemia cell line. These findings provide new insights into the mechanism of action of NDV virotherapy and could lead to the development of more effective treatments for leukemia.

Experimental Velogenic Viscerotropic Newcastle Disease Virus Infection in Chickens Immunologically Impaired by Treatment with Cyclophosphamide

This study investigated whether lymphocytic depletion following chemical bursectomy influenced the severity of infection and development of lesions in chickens challenged with velogenic viscerotropic Newcastle disease virus (vvNDV). Cockerel chickens treated with cyclophosphamide on days 2, 3 and 4 post-hatch showed loss of weight, atrophy and lymphocytic depletion in the bursa of Fabricius and spleen. At 6 weeks of age, the chickens were assigned to four groups- Bursectomized intramuscularly vvNDV inoculated (BI), bursectomized uninfected (BU), non-bursectomized infected (NBI) and non-bursectomized uninfected (NBU) chickens. The BI and NBI chickens showed significant (P < .05) loss of weight than their uninfected controls. Depression, anorexia, greenish diarrhea, listlessness, tremor, and oculo-nasal discharges were observed in both infected groups, but were more severe and frequent in the NBI than in the BI chickens. Total mortalities were 100% and 95.5% for the NBI and BI chickens, respectively (P > .05). Lesions in both infected groups included atrophy of the bursa, spleen and thymus. Hemorrhages in the proventricular mucosa, intestines and cecal tonsils, as well as congestion and enlargement of the kidneys were significantly (P < .05) more severe and frequent in NBI than BI chickens. Histopathology showed necrosis and depletion of lymphocytes in the three lymphoid organs in both infected groups with more severity in the NBI than BI chickens. These results show that depletion of lymphocytes by treatment with cyclophosphamide may influence the severity of infection and development of lesions in vvNDV infection in cockerel chickens.

Microscopic Characterization and Annexin V Flowcytometry Analysis of Apoptosis in Myelomoncytic Leukemia Cell Line treated with Velogenic Viscerotropic Newcastle Disease Virus Strain Af 2240

Leukemia is a type of cancer caused by the unregulated proliferation of immature blood cells derived from mutated hematopoietic stem cells. The malignant cells arise from the standstill of normal blood cell maturation. Newcastle disease virus (NDV) and variants of this virus which cause severe disease in birds, have oncolytic properties and are potential anticancer agents because they can kill tumor cells with limited toxicity to normal cells. In this study, the morphophic changes and apoptosis induction of the NDV strain AF2240 treated WEHI 3B leukemia cell line were examined using phase contrast, fluorescence, scanning and annexin V flow cytometry techniques. Light microscopy and electron microscopy showed that NDV strain AF 2240 significantly altered cell morphology and reduced cell viability. In addition, early apoptosis was observed 6 h after inoculation by fluorescence microscopy and annexin V flow cytometry methods. Our results suggest that NDV is able to induce the apoptotic pathway in the WEHI 3B leukemia cell line and may have potential therapeutic utility in the treatment of leukemia.

Triple La Sota re-vaccinations can protect laying chickens for 3 months against drop in egg production caused by velogenic viscerotropic Newcastle disease virus infection.

One hundred and ten Isa Brown layers were vaccinated with La Sota, once at point of lay at 18 weeks and three times at peak of lay which occurred at 27–29 weeks of age. Thereafter, they were weekly monitored for haemagglutination inhibition (HI) antibody decline. The first batch A of the layers were challenged with velogenic viscerotropic Newcastle disease (vvND) virus (vvNDV) on day 24 post‐vaccination (PV), when the geometric mean titre (GMT) was 84.4, batch B were challenged on day 48 PV at GMT of 42.2, while batch C were challenged on day 97 PV at GMT of 21.1. The individual chicken HI antibody titres of the 10 layers in batch C at the day of challenge were: 7 layers had HI titres of 16, 2 layers had HI titres of 32 and 1 layer had HI titres of 64. Each challenge in the three batches produced no clinical signs including drop in egg production. But there was initial swelling of the spleen followed by atrophy with high antibody responses. The virus was recovered in all the cloacal swabs on days 3–9 post‐challenge (PC) at low titres. On days 145 PV and 48, post‐Batch C challenge the remaining hyperimmunized unchallenged layers demonstrated a drop in total % egg production (p < .05) and changes in egg quality. The HI GMT was 256. The virus was recovered in all the cloacal swabs on days 3–9 following appearance of clinical signs. There was no mortality in the experiment. Based on the above observations, it is concluded that triple La Sota re‐vaccination can protect layers against a drop in egg production in areas where vvNDV infection is enzootic.

Impact of single and mixed infections with Escherichia coli and Mycoplasma gallisepticum on Newcastle disease virus vaccine performance in broiler chickens: an in vivo perspective.

This study was designed to investigate, in an in vivo setting, the effects of single and combined infections with either Mycoplasma gallisepticum (MG) and/or Escherichia coli on the chicken immune response induced by Newcastle disease virus (NDV) vaccine. Humoral immunity was measured through detection of NDV antibody and anti-NDV IgG titres using haemagglutination-inhibition test and enzyme-linked immunosorbent assay, respectively. In addition, the expression levels of pro-inflammatory cytokines' genes (interleukin (IL) 6, IL4 and interferon (IFN) γ) were analysed using quantitative reverse transcription PCR. Significant (P<0·05) results in all immunological parameters were detected in the vaccinated noninfected chicken group in comparison with those in groups exposed to bacterial infections. Bacterial infection along with vaccination hampered the NDV antibodies production and reduced the vaccine upregulated cytokine genes. The vaccinated mixed infection group reported lower antibody titres and cytokines expression levels compared to those in the single infection groups. All the previously enhanced immunological parameters reflected the maximum protection post challenge with velogenic viscerotropic NDV in the vaccinated noninfected chicken group. These findings provide novel insights into the immunosuppression activities of MG and E. coli infection in chickens vaccinated against NDV. This study hopes to provide a better insight to the immunosuppressive action of bacterial pathogens in chickens. This will help to improve biosecurity strategies during NDV vaccination in the future.

Lesions of velogenic viscerotropic Newcastle disease virus infection were more severe in broilers than pullets

ABSTRACT This study compared the pathologic effects of velogenic Newcastle disease (ND) virus in broilers and pullets using the normal pathogenic dose of the virus following an earlier report that challenge of the two types of chickens with a low dose of the virus caused mortalities in broilers but none in pullets. One hundred and twenty chickens (10 weeks old) were randomly assigned into four groups (n = 30 each): inoculated intramuscularly with velogenic viscerotropic ND virus (vvNDV) pullets – IP, uninfected pullets – UP, infected broilers – IB and uninfected broilers – UB. Anorexia, depression, ruffled feathers, green diarrhoea, tucking of the head under their wings, droopy wings and prostration were observed on days 2 and 3 post inoculation (PI) in groups IP and IB respectively. Mortality in IP and IB was 100%. Weight loss was significant (P < 0.05) by day 4 PI in both IP and IB when compared with their controls. Percentage weight loss in IP and IB were 20.26% and 38.66%, respectively. Proventricular, intestinal and caecal tonsil haemorrhages were significantly (p < 0.05) more severe in group IB than IP. Histopathology showed more severe necrosis and depletion of the lymphocytes in the bursa of Fabricius, thymus and spleen of group IB than IP. The above observations show that the lesions of vvNDV infection may be more severe in IB than IP.

Variations of immunoglobulin A in serum, tracheal, and intestinal tissues in chickens following inoculation of two strains of Newcastle disease vaccines

To elucidate secretory immunoglobulin A (IgA) response as a part of mucosal immunity, it is decided to compare the effectiveness of intraocular administration of Hitchner B1 and thermostable I-2 vaccines in broiler chickens challenged with viscerotropic velogenic Newcastle disease virus (vvNDV) (Herts33). For this purpose, 301-day-old chicks were randomly divided in to the four groups. Groups 1 and 2 were inoculated with I-2 and HB1 vaccines twice via intraocular route with 1-week intervals, and groups 3 and 4 were considered positive and negative controls and birds were challenged 2 weeks after the second inoculation. Protection rate in I-2 and HB1 vaccine groups was 100% and 97% respectively with no significant differences (P > 0.05). All vaccinated groups showed elevation in ND HI antibody titer after vaccination. There were no significant differences (P > 0.05) in ND HI antibody between two vaccinated groups. First levels of detectable total IgA in a serum sample were observed 3 dpv1. No significant differences (P > 0.05) were observed between two vaccinated groups in IgA antibody titer in sera. The vaccinated groups were evaluated by IHC for detection IgA in the trachea and intestine. There were some differences between the vaccinated groups but these differences were not significant. Experimental studies have shown that both vaccines induce antibody production in mucosal surface and circulatory system and thermostable I-2 vaccine could be successfully used in the broiler chicken as effective as HB1 vaccine, so I-2 vaccine could be a suitable heat resistance candidate to reduce mortality in the poultry industry faced to vvND.

Pathology and Distribution of Velogenic Viscerotropic Newcastle Disease Virus in the Reproductive System of Vaccinated and Unvaccinated Laying Hens (Gallus gallus domesticus) by Immunohistochemical Labelling

This study investigated the pathological changes in the reproductive system of laying hens that lead to the poor egg production and quality in Newcastle disease (ND) and the distribution of the virus in the system. Two hundred and forty Isa-Brown pullets were divided randomly into vaccinated and unvaccinated groups (n=120 each). The vaccinated group was given Hitchner B1 vaccine at 1 day of age, La Sota vaccine at 4 weeks of age and Komarov vaccine at 9 and 16 weeks of age. At the peak of egg production, the laying hens (32 weeks old) were assigned randomly into four groups (n=60): VC, vaccinated with ND vaccines and inoculated intramuscularly with velogenic viscerotropic ND virus (vvNDV); VU, vaccinated unchallenged; UC, unvaccinated challenged; and UU, unvaccinated unchallenged. UC hens showed depression, diarrhoea and later torticollis. Mortality in UC hens was 90%. VC hens showed mild anorexia. The body weights of the UC hens were significantly (P <0.05) lower than those of UU hens. VC and UC hens showed a significant (P <0.05) drop in egg production. Only UC hens produced abnormal eggs and initially had swollen, oedematous, hyperaemic oviducts followed by atrophy and shortening of the reproductive tract with atresia of the ovarian follicles. The histopathological changes were of necrosis of the epithelium and secretory glands. VC hens showed mild inflammatory changes in the oviduct. Immunohistochemical labelling showed extensive presence of the virus in the ovary, infundibulum, magnum, isthmus, uterus and vagina of UC hens and in the ovary of VC hens. These changes will be the cause of serious egg production problems, especially in vaccinated layers in countries where vvNDV is enzootic.

Low dose velogenic viscerotropic Newcastle disease virus infection caused 30% mortalities in Anak broilers but none in Lohmann Brown layer chickens

ABSTRACTThe aim of this project was to find out the comparative susceptibilities of broilers and layer chickens to a low dose of velogenic viscerotropic Newcastle disease virus (vvNDV) infection using mortalities as the main indicator. Five weeks old Anak broilers and Lohmann Brown layer chicks were inoculated with vvNDV. The birds were monitored daily for clinical signs and disease evolution was evaluated. Clinical signs consisting of depression and diarrhea appeared at 3 days post-inoculation (DPI) in broilers and at 2 DPI in layer chickens resulting in total mortalities of 30% and 0% in broilers and layer chickens, respectively. Weight loss was statistically, significant in infected broilers on 3 to15 DPI (p < 0.05), while no such difference was observed in the weight of infected layer chicks (p > 0.05). Macroscopic lesions were similar but more severe in broilers compared to layer chickens and included proventricular haemorrhages, intestinal and caecal ulcers. But atrophy of the bursa, spleen and thymus and necrosis and depletion of lymphocytes in the three organs were severe in the infected broilers and pullets Antibody response was significantly (p < 0.05) higher in the layer chickens but virus isolation was more frequent in the broilers.

Susceptibility of primary chicken intestinal epithelial cells for low pathogenic avian influenza virus and velogenic viscerotropic Newcastle disease virus

Avian influenza virus (AIV) and Newcastle disease virus (NDV) share a high tropism for the avian respiratory epithelium and may cause severe clinical disease associated with high mortality. Both viruses have different pathotypes, which may lead to differences in the severity of the disease. Respiratory epithelial cells were shown to be the primary target cells for infection and replication. Nevertheless, intestinal epithelial cells (IECs) were also suggested as target cells for both viruses in avian species. Most studies on AIV and NDV focused on the respiratory tract, while information regarding the virus-host interaction at the intestinal epithelial cell interface is lacking. We established a primary chicken IEC culture model. Primary chicken embryo fibroblast cultures (CEFs) were used for comparison. IECs and CEFs were infected with a low infectious dose (LID; multiplicity of infection, MOI, of 0.01) or high infectious dose (HID, MOI of 1), of low pathogenic AIV (LPAIV) H9N2 or velogenic viscerotropic NDV (vvNDV) Herts 33/56. Virus replication, mRNA expression pattern of the type I and type III interferon (IFN) and related genes IFIT5 (interferon-induced protein with tetratricopeptide repeats 5) and ISG12 (interferon stimulated gene 12) were investigated at four, 16, and 24h post infection (hpi). The results suggest high susceptibility of primary chicken IECs for these AIV and NDV strains. Replication rates and expression pattern of IFNs as well as related genes differed between the infecting viruses as well as cell culture systems. Both viruses induced an IFN λ-increase of more than 30-fold in IECs, while IFN-α and IFN-β mRNA expression was either downregulated or only slightly increased with up to 10fold changes for the latter at 24h post LPAIV-infection. These results suggest a possible role of IFN λ in the control of viruses at the gut epithelial surface. LPAIV induced upregulation of IFIT5 as well as ISG12 expression in a dose and time dependent manner, while vvNDV infection only led to slight upregulation of IFIT5 and downregulation of ISG12, indicating differences in the down-stream regulation of the antiviral immune response between investigated viruses. Overall, our data demonstrate that IECs are a suitable model to investigate selected parameters of virus-host interaction for AIV and NDV and may be used to study other strains as well as other host species.

Effect of phylogenetic diversity of velogenic Newcastle disease virus challenge on virus shedding post homologous and heterologous DNA vaccination in chickens

ABSTRACTNewcastle disease (ND) is a highly devastating disease for the poultry industry as it causes high economic losses. In this present study, a DNA vaccine containing the F and HN surface antigens of a highly virulent Newcastle disease virus (NDV), NDV/1/Chicken/2005 (FJ939313), was successfully generated. Cell transfection test indicated that the vaccine expressed the F and HN genes in Hep-2 cells. The main objective of this study was to compare the extent of protection induced by DNA vaccination after homologous and heterologous NDV-challenge as determined by the amount of NDV shedding after challenge. NDV-antibody-negative chickens were vaccinated either once, twice or thrice intramuscularly at 7, 14 and 21 days old and were challenged 14 days post vaccination with either homologous virus (vaccine-matched velogenic viscerotropic Newcastle disease virus (vvNDV) strain, FJ939313), phylogenetically related to group VII, or a phylogenetically divergent heterologous virus (unmatched vvNDV strain, AY968809), which belongs to genogroup VI and shows 84.1% nucleotide similarity to the NDV-sequences of the DNA vaccine. Our data indicate that birds, which received a single dose of the DNA vaccine were poorly protected, and only 30–40% of these birds survived after challenge with high virus shedding titre. Multiple administration of the DNA vaccine induced high protection rates of 70–90% with reduced virus shedding compared to the non-vaccinated and challenged birds. Generally, homologous challenge led to reduced tracheal and cloacal shedding compared to the heterologous vvNDV strain. This study provides a promising approach for the control of ND in chickens using DNA vaccines, which are phylogenetically closely related to the circulating field strains.

Pathogenesis of New Strains of Newcastle Disease Virus From Israel and Pakistan.

In the past few years, Newcastle disease virus (NDV) strains with epizootic characteristics belonging to subgenotypes VIIi and XIIIb emerged in the Middle East and Asia. In this study, 2 NDV strains-1 representative of subgenotype VIIi isolated in Israel (Kvuzat/13) and 1 representative of subgenotype XIIIb isolated in Pakistan (Karachi/07)-were characterized by intracerebral pathogenicity index and detailed clinicopathologic assessment. The intracerebral pathogenicity index values for Kvuzat/13 and Karachi/07 were 1.89 and 1.85, respectively, classifying these strains as virulent by international standards. In 4-week-old White Leghorn chickens, both strains caused 100% mortality within 4 (Kvuzat/13) and 5 (Karachi/07) days postinfection. Histopathology and immunohistochemistry for NDV nucleoprotein showed that both strains had wide systemic distribution, especially targeting lymphoid organs and mucosa-associated lymphoid tissues in the respiratory and intestinal tracts. Results of the animal experiment confirm that both Kvuzat/13 and Karachi/07 are highly virulent and behaved as velogenic viscerotropic NDV strains.

Viscerotropic velogenic Newcastle disease virus replication in feathers of infected chickens.

Newcastle disease viruses (NDVs) cause systemic diseases in chickens with high mortality. However, little is known about persistence of NDVs in contaminated tissues from infected birds. In this study, we examined viral replication in the feather pulp of chickens inoculated with viscerotropic velogenic NDV (vvNDV) genotype VII. Reverse transcription real-time PCR and immunohistochemistry were used to investigate viral persistence in the samples. vvNDV was detected in the oropharynx and cloaca and viral antigens were detected in the feathers, suggesting that feathers act as sources of viral transmission.

Infectious bursal disease vaccine ameliorates velogenic Newcastle disease virus infection in immunopotentiated chickens

In the present study, the potential immunoprotective role of infectious bursal disease (IBD) vaccine on immunopotentiated chickens challenged with velogenic viscerotropic Newcastle disease virus (vvNDV) genotype VIId was investigated. The chickens were divided into five groups vaccinated with NDV vaccine, but group (G1) was kept as control unvaccinated birds. The G2 and G4 were immunopotentiated using mannan oligosaccharides (MOS) while G3 and G5 received MOS and IBD vaccine. The G1, G2, and G3 were infected with vvNDV while G4 and G5 served as uninfected birds. The humoral response to NDV vaccine was measured by hemagglutination inhibition test while cellular response was estimated by chicken interleukin-2 ELISA, total and differential leucocytic count, bursa body weight index, and histopathological examination of the bursae. The results revealed that the immunopotentiated groups possessed a good cellular and humoral response to vvNDV although the severity of histopathological lesions was variable. The G3 had the best cellular and humoral response, and IBD vaccine enhanced the immune response against the infection with vvNDV. Histopathologically, the typical bursal lesions of NDV were observed in G1 such as lymphocytic depletion, acute inflammatory reaction, and degenerative changes of the bursal follicles. In contrast, such histopathological changes in the immunopotentiated groups were less evident both in severity and prevalence, while the immune reactive lymphoid hyperplasia was a prominent finding in G4 and G5. In conclusion, the immunopotentiation of the chickens as well as NDV and IBD vaccination improved the bird immunity and diminished the immunosuppressive effect of the vvNDV.

Experimental intraocular infection of exotic cockerels with field strain of velogenic Newcastle disease virus in Nigeria

Experimental intraocular (conjunctival) infection of exotic cockerels with a new field strain of viscerotropic velogenic Newcastle Disease Virus (NDV) was conducted to explore the concurrence of some pathological changes with humoral immune responses. After the NDV infection of 4-week-old cockerels, pathologic changes and antibody responses were observed. The clinical signs observed after the artificial inoculation included inappetence, depression, diarrhea, dyspnea, wing and leg paralysis, torticollis and weight loss. Morbidity due to the NDV was 100%, but mortality was 80% by day 18-21 post-infection. Early hyperthermia followed by terminal hypothermia, decreased packed cell volume (PCV), and 231.4 folds peak-antibody response were observed. Necrotic and/or inflammatory lesions were present in the proventriculus, intestine, liver, spleen, kidney and brain. Neurologic and digestive tract perturbations occurred in 10% and 85% of cases, respectively. The disease consistently caused stunted growth, decreased PCV, and necro-inflammatroy lesions concurrent with antibody response, suggesting probable involvement of immune-mediated mechanisms and cell membrane desialylation by viral neuraminidase in the pathogenesis.

Separate Evolution of Virulent Newcastle Disease Viruses from Mexico and Central America

An outbreak of Newcastle disease (ND) in poultry was reported in Belize in 2008. The characteristics of three virulent Newcastle disease virus (NDV) isolates from this outbreak (NDV-Belize-3/08, NDV-Belize-4/08, and NDV-Belize-12/08) were assessed by genomic analysis and by clinicopathological characterization in specific-pathogen-free (SPF) chickens. The results showed that all three strains belong to NDV genotype V and are virulent, as assessed by the intracerebral pathogenicity index and the polybasic amino acid sequence at the fusion protein cleavage site. In 4-week-old SPF chickens, NDV-Belize-3/08 behaved as a typical velogenic viscerotropic NDV strain, causing severe necrohemorrhagic lesions in the lymphoid organs, with systemic virus distribution. Phylogenetic analysis of multiple NDV genotype V representatives revealed that genotype V can be divided into three subgenotypes, namely, Va, Vb, and Vc, and that all tested Belizean isolates belong to subgenotype Vb. Furthermore, these isolates are nearly identical to a 2007 isolate from Honduras and appear to have evolved separately from other contemporary viruses circulating in Mexico, clustering into a new clade within NDV subgenotype Vb.

Pathologic Characterization of Genotypes XIV and XVII Newcastle Disease Viruses and Efficacy of Classical Vaccination on Specific Pathogen-Free Birds

To characterize the clinicopathologic features of recently described genotypes of Newcastle disease virus (NDV), 1 representative strain of genotype XIV and 2 of genotype XVII, all isolated from West Africa, were used to infect groups of ten 4-week-old specific pathogen-free chickens. The pathobiology of these 3 strains was compared to a South African NDV strain classified within genotype VII. All chickens infected with the 4 viruses died or were euthanized by day 4 postinfection due to the severity of clinical signs. Gross and histologic lesions in all infected chickens included extensive necrosis of lymphoid tissues (thymus, spleen, bursa of Fabricius, cecal tonsils, gut-associated lymphoid tissue), gastrointestinal necrosis and hemorrhages, and severe hemorrhagic conjunctivitis. Immunohistochemical staining revealed systemic viral distribution, and the most intense staining was in the lymphoid organs. Results demonstrate that the 3 West African strains from the previously uncharacterized genotypes XIV and XVII are typical velogenic viscerotropic NDV strains with lesions similar to the South African strain. Under experimental conditions, QV4 and LaSota NDV vaccine strains successfully protected chickens from morbidity and mortality against the genotype VII and one genotype XVII NDV strain, with no significant differences in the amount of virus shed when 2 vaccine schemes were compared.

Immunization with a Thermostable Newcastle Disease Virus K148/08 Strain Originated from Wild Mallard Duck Confers Protection against Lethal Viscerotropic Velogenic Newcastle Disease Virus Infection in Chickens

Newcastle disease (ND) is one of the most devastating poultry infections because of its worldwide distribution and accompanying economical threat. In the present study, we characterized the ND virus (NDV) K148/08 strain from wild mallard duck, with regard to safety, thermostability, immunogenicity, and protective efficacy against velogenic ND viral infection. The NDV K148/08 strain offered enhanced immunogenicity and safety relative to commercially available vaccine strains. The NDV K148/08 strain was safe in 1-day-old SPF chicks after vaccination using a coarse or cabinet-type fine sprayer. We demonstrated that the NDV K148/08 strain elicited high levels of antibody responses and provided protective efficacy against lethal NDV challenge. In addition, the thermostability of the NDV K148/08 strain was as high as that of the thermostable V4 strain. Therefore, the NDV K148/08 strain may be useful to ensure NDV vaccine performance and effectiveness in developing countries, especially in remote areas without cold chains.

The combination of attenuated Newcastle disease (ND) vaccine with rHVT-ND vaccine at 1 day old is more protective against ND virus challenge than when combined with inactivated ND vaccine

The recurrent outbreaks of fatal Newcastle disease (ND) in commercial poultry flocks throughout the world indicate that routine vaccinations are failing to sufficiently induce the high levels of immunity necessary to control ND. There is a need for vaccination programmes that could be initiated at 1-day-old for mass application and which would induce a long-lasting immunity, with no need for a booster vaccination at a later age. In this context, the duration of immunity delivered by a vaccination programme including a recombinant herpesvirus of turkeys expressing the F gene of ND virus (rHVT-ND) and live ND vaccine at 1-day-old was compared with a classical programme that included a conventional live and an inactivated ND vaccine at the same age in commercial layer chickens. The humoral, cell-mediated and local immunity were followed weekly and birds were challenged with a viscerotropic velogenic ND virus strain at 6 and 10 weeks of age. We determined that immunity induced by the vaccination programme involving the rHVT-ND vaccine was more protective than that provided by the conventional vaccine-based regime. This might be related to a T-helper type 1 (Th1) cellular-driven immunological response, in contrast to the T-helper type 2 (Th2) humoral-oriented immune response provided by the current conventional vaccine-based vaccination programmes.

Characterization and comparison of the pathogenicity of viscerotropic velogenic Newcastle disease virus isolates in Korea

Characterization and comparison of the pathogenicity of viscerotropic velogenic Newcastle disease virus isolates in Korea