Efficacy of single dose recombinant herpesvirus of turkey infectious bursal disease virus (IBDV) vaccination against a variant IBDV strain.

The use of viral vectors for transgenic expression of immunogenic proteins is a current trend in the poultry industry. The objective of this work was to assess the protection against the variant E of infectious bursal disease virus (IBDV), conferred by day-one vaccination with a commercial recombinant herpesvirus of turkey (HVT) vaccine (VAXXITEK) expressing the immunogenic viral protein 2 from a classical IBDV. In separate trials, 1-day-old specific-pathogen-free (SPF) or broiler chickens were vaccinated by the subcutaneous route and challenged with the variant E strain at 18 or 28 days of age. Bursa/body weight ratio and bursal histopathology were assessed as protection criteria. Protection was demonstrated at both challenge points, bursal indexes in vaccinated SPF and broiler groups were significantly higher than in the challenged controls. The commercial vaccine protected against bursal damage as indicated by significantly lower bursal lesion scores in the vaccinated birds. These experimental results indicate that a single dose of the recombinant HVT-IBDV confers protection against variant E challenge even though the VP2 expressed by the recombinant herpes virus belongs to a standard strain.

Biological and phylogenetic characterization of virulent Newcastle disease virus circulating in Mexico.

In 2002-2003, velogenic Newcastle Disease Virus outbreaks, closely related to the Mexican isolates, were confirmed in the United States (U.S.) in southern California, Arizona, Nevada, and Texas. In this report, virulent NDVs isolated in Mexico between 1998 and 2006 were subjected to biologic characterization, using standard pathogenicity tests, and to phylogenetic analysis. Chicken embryo mean death time (MDT) test results ranged from 39.7 to 61.5 hours, and intracerebral pathogenicity index (ICPI) values were between 1.59 and 1.94, compared to a possible maximum value of 2.0. These isolates showed a dibasic amino acid motif at the fusion protein cleavage site sequence required for host systemic replication. Phylogenetic analysis indicated that the Mexican virulent NDVs belong to the class II, genotype V viruses and can be clearly divided in two groups as follows: isolates from 1998 to 2001 with close epidemiologic relationship with the latest U.S. NDV outbreaks, and phylogenetically distinct viruses, isolated from 2004 to 2006, which showed higher virulence. The assessment of the evolution of viruses from Mexico and other neighboring countries will aid in the U.S surveillance efforts for early detection of highly virulent NDV.

Avian adeno-associated virus-based expression of Newcastle disease virus hemagglutinin-neuraminidase protein for poultry vaccination.

The avian adeno-associated virus (AAAV) is a replication-defective nonpathogenic virus member of the family Parvoviridae that has been proved to be useful as a viral vector for gene delivery. The use of AAAV for transgenic expression of Newcastle disease virus (NDV) hemagglutinin-neuraminidase (HN) protein and its ability to induce immunity in chickens were assessed. Proposed advantages of this system include no interference with maternal antibodies, diminished immune response against the vector, and the ability to accommodate large fragments of genetic information. In this work the generation of recombinant AAAV virions expressing the HN protein (rAAAV-HN) was demonstrated by electron microscopy, immunocytochemistry, and western blot analysis. Serological evidence of HN protein expression after in ovo or intramuscular inoculation of the recombinant virus in specific-pathogen-free chickens was obtained. Serum from rAAAV-HN-vaccinated birds showed a systemic immune response evidenced by NDV-specific enzyme-linked immunosorbent assay and hemagglutination inhibition testing. Positive virus neutralization in embryonated chicken eggs and indirect immunofluorescence detection of NDV infected cells by serum from rAAAV-HN vaccinated birds is also reported. A vaccine-challenge experiment in commercial broiler chickens using a Venezuelan virulent viscerotropic strain of NDV was performed. All unvaccinated controls died within 5 days postchallenge. Protection up to 80% was observed in birds vaccinated in ovo and revaccinated at 7 days of age with the rAAAV-HN. The results demonstrate the feasibility of developing and using an AAAV-based gene delivery system for poultry vaccination.

Protection against infectious bursal disease virulent challenge conferred by a recombinant avian adeno-associated virus vaccine.

The development and use of recombinant vaccine vectors for the expression of poultry pathogens proteins is an active research field. The adeno-associated virus (AAV) is a replication-defective virus member of the family Parvoviridae that has been successfully used for gene delivery in humans and other species. In this experiment, an avian adeno-associated virus (AAAV) expressing the infectious bursal disease virus (IBDV) VP2 protein (rAAAV-VP2) was evaluated for protection against IBDV-virulent challenge. Specific pathogen free (SPF) birds were inoculated with rAAAV-VP2 or with a commercial intermediate IBDV vaccine and then challenged with the Edgar strain. IBDV-specific antibody levels were observed in all vaccinated groups; titers were higher for the commercial vaccine group. The live, commercial vaccine induced adequate protection against morbidity and mortality; nevertheless, initial lymphoid depletion and follicular atrophy related to active viral replication was observed as early as day 14 and persisted up to day 28, when birds were challenged. No bursal tissue damage due to rAAAV-VP2 vaccination was observed. Eight-out-of-ten rAAAV-VP2-vaccinated birds survived the challenge and showed no clinical signs. The bursa:body weight ratio and bursa lesion scores in the rAAAV-VP2 group indicated protection against challenge. Therefore, transgenic expression of the VP2 protein after rAAAV-VP2 vaccination induced protective immunity against IBDV challenge in 80% of the birds, without compromising the bursa of Fabricius. The use of rAAAV virions for gene delivery represents a novel approach to poultry vaccination.

Infectious bursal disease subunit vaccination.

Infectious bursal disease virus (IBDV) is the causative agent of infectious bursal disease, a nosologic entity with global economic importance in poultry. The viral protein 2 (VP2) is recognized as the virus' major antigenic protein. The goal of this study was to generate yeast (Pichia pastoris)-based protein expression from the VP2 gene of the Edgar strain of IBDV and from the hypervariable region of the VP2 gene (hvVP2) to test the protection afforded against virulent IBDV challenge when inoculated in chickens. The genetic material used for protein expression was obtained from paraffin-embedded tissue. Specific-pathogen-free chickens were vaccinated with the expressed products and challenged with the homologous strain (Edgar). After challenge, no morbidity or mortality was observed in the birds vaccinated with the whole VP2, compared with 30% morbidity and mortality in the hvVP2-vaccinated birds and with 90% morbidity and 60% mortality in the unvaccinated, challenged controls. Immunohistochemistry detection of the challenge virus and some extent of bursal damage were observed in all challenged birds, indicating active replication of the challenge virus despite vaccination. As determined by bursal index values, the protection against postchallenge bursal atrophy was significantly higher (P < 0.05) in the VP2 group than in the unvaccinated and hvVP2-vaccinated birds. Overall, the results indicated that paraffin-embedded tissue can be used as a source of genomic material for transgenic protein expression, that Pichia pastoris-expressed VP2 retains its immunogenicity, and that VP2 subunit vaccination conferred partial protection to challenge; it protected against clinical signs and death but not against IBDV infection.

Genetic characterization, pathogenicity, and protection studies with an avian adenovirus isolate associated with inclusion body hepatitis.

An avian adenovirus (AAV) was isolated from liver samples of two 2-wk-old broiler-breeder flocks obtained from grandparents vaccinated at 10 and 17 wks of age with an autogenous inactivated vaccine containing the European AAV 8 (8565 strain) and 11 (1047 strain) serotypes (AAV8/11 vaccine). Affected broiler-breeders exhibited clinical signs and macroscopic and microscopic lesions associated with inclusion body hepatitis (IBH). The isolated adenovirus, identified as Stanford, was molecularly characterized as European serotype 9. The pathogenicity of the Stanford strain was confirmed after inoculation of specific-pathogen-free (SPF) chickens at 1-7 days of age, causing 100% and 20% mortality, respectively. The level of protection against IBH was evaluated in two broiler-breeder progenies from AAV 8/11-vaccinated grandparent flocks and a commercial broiler flock by challenge at 1 or 7 days of age with the AAV 8 and 11 serotypes and/or the Stanford strain. The broiler-breeder progenies and the commercial broiler flock exhibited protection against IBH after challenge. No significant differences in mean body weights were observed at 3 wk of age in any of the evaluated groups. We conclude that broiler-breeder progenies from 30- to 50-wk-old grandparents vaccinated with the AAV 8/11 vaccine were adequately protected against challenge with the AAV 8 and 11 serotypes and the Stanford strain.

Valores hematológicos en pollos de engorde expuestos de forma contínua a bajas dosis de aflatoxina B1 en el estado Zulia Venezuela / Haematological values in broiler chicks during long time low level exposure to aflatoxin B1 in Zulia state Venezuela

Se realizó un estudio para determinar el efecto de bajas concentraciones (70 µg/kg de Aflatoxina B1 purificada (AFB1) sobre los valores hematológicos de pollos de engorde, la exposición a niveles subclínicos de AFB1 es causa de bajo rendimiento en la industria avícola a consecuencia de sintomatología que va desde anemia hasta un comprometimiento de la respuesta inmune. Se utilizaron 480 pollos de la línea Hubbard x Hubard de un día de edad y se dividieron en dos grupos de 240 animales: Control (T1) alimento comercial sin niveles detectables de AFB1 y Tratamiento (T2) alimento contaminado con 70 µg/kg de AFB1. El día 42 se tomaron muestras de sangre de 32 aves de cada grupo para determinar: Proteínas Totales (PT) Hematocrito (Hcto), Hemoglobina (Hem), Recuento de Glóbulos Rojos (GR), Recuento de Glóbulos Blancos (GB) y Hemograma (DIF). La base de datos fue analizada para un diseño completamente aleatorizado a través de un análisis de la variancia y comparaciones de medias utilizando la opción GLM del SAS. Los valores para el T1 fueron: (PT) 3,18 ± 0,42 g/dl; (Hcto) 28,9 ± 2,48 por ciento); (Hem) 9,05 ± 1,10 g/dl; (GR) 2,65 ± 0,41 millones/mL; (GB) 6951,56 ± 3435 glóbulos/mL, los cuales no difieren de los resultados del T2. Todas las aves del ensayo presentaron linfopenia, heterolilia y monocitosis, lo que es compatible con un hemograma de stress calorico. Se concluye que 70 µg/kg AFB1 durante seis semanas no es capaz de afectar significativamente la respuesta hematológica en pollos de engorde