Susceptibility and protection of naive and vaccinated racing pigeons (Columbia livia) against exotic Newcastle disease virus from the California 2002-2003 outbreak

The susceptibility, immune response, and protection to challenge after vaccination in racing pigeons (Columbia livia) was assessed with the 2002-2003 exotic Newcastle disease (END) virus responsible for the most recent major outbreak in Southern California. Immunologically na?ve pigeons appeared resistant to disease, regardless of dose, after a natural route of exposure. Twenty percent morbidity was observed in each group of birds receiving between 10(2.1) and 10(8.1) 50% embryo infectious dose (EID50) per bird, with one bird succumbing to challenge in the 10(8.1) EID50/bird group at day 12 postinoculation. Although resistant to disease, birds in all groups continued to shed virus from either oral or cloacal route at the end of the 14-day sampling period, and seroconversion was only observed in birds receiving > or =10(6.1) EID50. Single or double vaccination of juvenile and adult birds with pigeon paramyxovirus virus type 1 (PPMV-1) vaccine followed by END challenge with 10(6.1) EID50/bird decreased the duration, incidence, and viral load. A positive correlation was observed between the presence of hemagglutination-inhibiting antibody titers at challenge and decreased viral shedding. Overt clinical signs of disease were not observed in any PPMV-1-vaccinated birds after challenge.     

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.     

Survival of exotic Newcastle disease virus in commercial poultry environment following removal of infected chickens

During the first weeks of 2003, after exotic Newcastle disease (END) was confirmed in commercial layer flocks in Southern California, it became apparent that the virus survival information in the literature varied widely and was difficult to extrapolate to current local conditions. The END Task Force used the information available in the literature and the recommendations of research scientists to establish protocols for safely handling manure from infected and depopulated premises. In an attempt to gain more applicable knowledge in the management of contaminated poultry manure in the course of the END outbreak, this virus survival study was designed and implemented. Environmental drag swabs were tested for END virus from two of the early-infected commercial ranches that consisted of several houses following immediate removal of the infected flocks. A total of 293 samples, composed of 168 manure drag swab pools, 72 dropping board swab pools, and 38 compost swab pools from 3 houses (ranch 1), and 180 manure belt scraper swab pools from ranch 2 were analyzed for ND virus isolation and characterization for 21 consecutive days postdepopulation. Thirteen manure drag swab pools (from houses 1 and 3) and two manure dropping board swab pools (from house 3) collected from ranch 1 were positive for END virus at 0, 1, 2, 3, 4, 7, 10, 12, and 16 days postdepopulation. No END virus was isolated after the 16th day following depopulation from any of the samples. All samples from ranch 2 were negative during the entire observation period.     

Pathogenesis of chicken-passaged Newcastle disease viruses isolated from chickens and wild and exotic birds

The pathogenesis of six Newcastle disease virus (NDV) isolates recovered from chickens (Ckn-LBM and Ckn-Australia) and wild (Anhinga) and exotic (YN parrot, pheasant, and dove) birds was examined after the isolates had been passaged four times in domestic chickens. Groups of 10 4-wk-old specific-pathogen-free white leghorn chickens were inoculated intraconjunctivally with each one of the isolates. The infected birds were observed for clinical disease and were euthanatized and sampled at selected times from 12 hr to 14 days postinoculation or at death. Tissues were examined by histopathology, by immunohistochemistry (IHC) to detect viral nucleoprotein (IHC/NP), and by in situ hybridization to detect viral mRNA and were double labeled for apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling ([TUNEL] or IHC/caspase-3) and viral nucleoprorein (IHC/NP). Birds infected with the three low virulence viruses (Ckn-LBM, YN parrot, and Ckn-Australia) did not develop clinical disease. Microscopic lesions were observed only at the inoculation site and in organs of the respiratory system. The detection of viral nucleoprotein (N) was restricted to the inoculation site. The pheasant and dove isolates were highly virulent for chickens with marked tropism for lymphoid tissues, confirmed by the presence of large numbers of cells positive for viral N protein and viral mRNA. Viral N protein was detected early in the cytoplasm of cells in the center of the splenic ellipsoids. The apoptosis assays (TUNEL and IHC/caspase-3) showed increased apoptosis in the splenic ellipsoids as well. Apparently, apoptosis is an important mechanism in lymphoid depletion during NDV infection.     

Protection of chickens from Newcastle and Marek's diseases with a recombinant herpesvirus of turkeys vaccine expressing the Newcastle disease virus fusion protein.

Recombinant strains of herpesvirus of turkeys (HVT) were constructed that contain either the fusion protein gene or the hemagglutinin-neuraminidase gene of Newcastle disease virus (NDV) inserted into a nonessential gene of HVT. Expression of the NDV antigens was regulated from a strong promoter element derived from the Rous sarcoma virus long terminal repeat. Recombinant HVT strains were stable and fully infectious in cell culture and in chickens. Chickens receiving a single intra-abdominal inoculation at 1 day of age with recombinant HVT expressing the NDV fusion protein had an immunological response and were protected (> 90%) against lethal intramuscular challenge at 28 days of age with the neurotropic velogenic NDV strain Texas GB. Recombinant HVT expressing the NDV hemagglutinin-neuraminidase provided partial protection (47%) against the same challenge. Chickens vaccinated with recombinant HVT vaccines had low levels of protection against NDV replication in the trachea when challenged ocularly. Recombinant HVT vaccines and the parent HVT strain provided similar levels of protection to chickens challenged with the very virulent RB1B strain of Marek's disease virus, indicating that insertion of foreign sequences into the HVT genome did not compromise the ability of HVT to protect against Marek's disease.     

Efficacy of avridine as an adjuvant for Newcastle disease virus antigen in chickens

Avridine, a lipoidal amine with interferon-inducing and adjuvant properties, was an effective adjuvant for Newcastle disease antigen (NDA) in chickens. Eleven vaccine lots were evaluated: 2 commercial water-in-oil vaccines, 4 experimental oil emulsion vaccines, 4 avridine-containing vaccines, and a control lot of nonadjuvanted antigen. Avridine significantly enhanced the immunologic responses of chickens against NDA. Chickens vaccinated with the avridine-containing vaccines had significantly higher antibody titers (hemagglutination inhibition) than did chickens vaccinated with the commercial vaccines. Experimental oil emulsion vaccines prepared from the same antigens as avridine-adjuvanted vaccines induced higher hemagglutination inhibition antibody titers after primary but not after booster vaccination. Use of avridine as an adjuvant for NDA in vaccines for chickens induced immunologic protection rates similar to those induced by oil emulsion vaccines, without causing the reactogenic and tissue residue problems associated with the use of oil vaccines in chickens.     

Newcastle disease virus pathogenesis in the respiratory tract of local or systemic immunized chickens.

Establishment of selective immunity, local or systemic, made it possible to evaluate the pathogenesis of Newcastle disease virus (NDV) in the respiratory tract of chickens that were previously immunized with beta-propiolactone-inactivated antigen. NDV was inoculated intranasally or intramuscularly to chickens in different states of immunity (local or systemic). Humoral antibodies protected chickens against intranasal as well as intramuscular infection. Local antibodies, on the other hand, conferred immunity only against intranasal challenge. The respiratory tract supported multiplication of the virus, producing a self-limited subclinical infection. Replication of the virus in this system was negligible, playing only a minor role in the pathogenesis of the disease.     

Efficacy of viable and inactivated Newcastle disease virus vaccines in turkeys

Market turkeys spray-vaccinated at 20 days of age with viable Newcastle disease virus (NDV) vaccine and challenged 7 weeks postvaccination failed to yield NDV by tracheal swabbing 4 days postchallenge but demonstrated serologic evidence of infection. Birds vaccinated subcutaneously with inactivated oil-emulsion (OE) NDV vaccine had virologic and serologic evidence of infection. Breeder hens vaccinated by spray with commercial La Sota vaccine at 19 weeks of age and revaccinated subcutaneously with OE vaccine at 32 weeks of age had an adequate level of resistance against a drop in egg production but demonstrated serologic evidence of infection when challenged with velogenic NDV at 38 weeks of age.     

Experimental infection of turkeys with avian pneumovirus and either Newcastle disease virus or Escherichia coli

Avian pneumoviruses (APVs) are RNA viruses responsible for upper respiratory disease in poultry. Experimental infections are typically less severe than those observed in field cases. Previous studies with APV and Escherichia coli suggest this discrepancy is due to secondary agents. Field observations indicate APV infections are more severe with concurrent infection by Newcastle disease virus (NDV). In the current study, we examined the role of lentogenic NDV in the APV disease process. Two-week-old commercial turkey poults were infected with the Colorado strain of APV. Three days later, these poults received an additional inoculation of either NDV or E. coli. Dual infection of APV with either NDV or E. coli resulted in increased morbidity rates, with poults receiving APV/NDV having the highest morbidity rates and displaying lesions of swollen infraorbital sinuses. These lesions were not present in the single APV, NDV, or E coli groups. These results demonstrate that coinfection with APV and NDV can result in clinical signs and lesions similar to those in field outbreaks of APV.     

鸽源新城疫病毒的鉴定及HN基因遗传演化分析

根据发病鸽群的临床症状、病理剖检、组织病理学变化,并结合RT-PCR方法对武汉地区某鸽场疑似鸽新城疫进行了确诊,同时对分离的2株鸽源新城疫病毒(NDV)进行了HN基因结构特征及其与已知毒株的遗传相关性分析。结果表明:两株鸽源NDV分离株HN基因片段均含有6个保守的糖基化位点。2株NDV分离株HN基因序列与参考株同源性在80.0%~97.2%,与湖北株(AY225110.HB92)、印度株(KM056357.ndv61/B1)、江苏株(GQ245832.YC-24-07-CH)、陕西株(JF795531.HX01)在同一分支上,为基因II型。研究为武汉地区鸽新城疫的防控提供了理论依据。