Immunization of turkeys with a DNA vaccine expressing either the F or N gene of avian metapneumovirus

In this study we compared protection by DNA vaccination with the F (pCMV-F) or N (pCMV-N) gene from avian metapneumovirus (aMPV) in turkeys. One-week-old turkey poults received two intramuscular injections 2 wk apart. Birds were challenged with a turkey-embryo-adapted aMPV at 5 wk of age. Birds vaccinated with pCMV-F had decreased clinical signs of disease as well as significantly reduced virus load in tracheal swabs compared with birds vaccinated with pCMV-N or unvaccinated control birds. Serum neutralizing antibodies were significantly higher in birds receiving pCMV-F compared with all other groups. These results indicate that DNA vaccination with the F, but not N, gene of aMPV can induce significant protection against aMPV infection.     

Evaluation of the effectiveness of two infectious bronchitis virus vaccine programs for preventing disease caused by a California IBV field isolate

Infectious bronchitis virus CA99 serotype was isolated from several broiler flocks in Northern California. The virus caused late-onset respiratory disease and increased airsacculitis condemnation in affected flocks despite the use of an established infectious bronchitis virus vaccination program. An experimental study compared Holland/Arkansas and Massachusetts/Arkansas vaccination protocols to determine the efficacy of commercial infectious bronchitis virus vaccines in reducing respiratory disease and airsacculitis lesions found at processing that were associated with a CA99 field isolate. All vaccination groups were given Massachusetts/Connecticut strains of infectious bronchitis virus vaccines at age 1 day followed by vaccination with either Holland/ Arkansas or Massachusetts/Arkansas vaccine strains at 18 days of age. Birds were challenged at age 31 days with a CA99 field isolate. Gross pathology, histopathology, and virus isolation were evaluated. Chickens vaccinated with Holland/Arkansas had marginally better protection against CA99 challenge than chickens vaccinated with Massachusetts/Arkansas, although differences were not statistically significant.     

Maternal antibody to infectious bronchitis virus: its role in protection against infection and development of active immunity to vaccine

Chicks hatched with high levels of maternal antibody had excellent protection (>95%) against infectious bronchitis virus (IBV) challenge at 1 day of age, but not at 7 days (<30%). This protection significantly (P<0.05) correlated with levels of local respiratory antibody and not with serum antibody.A high percentage of both maternal antibody-positive (Mab+) and maternal antibody-negative (Mab-) chicks failed to produce IBV antibody when vaccinated at 1 day of age by the intraocular route. In addition, Mab+ chickens had a weaker virus-neutralizing antibody response to a second IBV vaccination compared to Mab- birds (P<0.05). Mab+ chicks experienced a more rapid decline (P<0.01) in maternal antibody after 1-day-of-age vaccination compared to their unvaccinated counterparts.A monoclonal antibody-based blocking ELISA that measured antibody levels specific to S1 glycoprotein of IBV correlated well with virus-neutralizing antibody titers.     

Immunosuppression and histopathological changes in the bursa of fabricius associated with infectious bursal disease vaccination in chicken

The effect of the infectious bursal disease (IBD) live virus vaccine on the immune response of chicken was evaluated by the assessment of antibody response following vaccination as well as resistance to challenge with virulent virus. Birds were vaccinated at various ages and later challenged with a heterologous vaccine (NDV) or wild-type IBD virus. The BF was examined for histological changes at regular intervals. Antibody levels to NDV were monitored.

Significantly higher mortality rates were observed in birds vaccinated with IBD vaccine than unvaccinated birds (P < 0.01) following challenge, BF from vaccinated birds showed marked lymphocyte depletion and cellular infiltration with mononuclear cells.

Intraocular NDV (NDV-i/o) vaccine given at day old largely prevented the immunodepressive effect of IBD vaccination on NDV vaccine. Groups that received IBD vaccine on day 14 but no NDV i/o suffered higher mortality (41.2%) and showed lower antibody response than those vaccinated on day 1 (0%) or controls which did not receive IBDV (11.8%).     

Immunization of day-old chicks having maternally derived antibodies against infectious bronchitis: degree of protection as monitored by ciliary activity after intratracheal challenge.

One-day-old chicks with maternally derived antibodies were vaccinated against infectious bronchitis (IB) with 3000 EID50 of the IB vaccine virus designated H120. The degree of protection induced by intranasal-eye drop (IE) vaccination was compared to that achieved by spray (S) vaccination. The protection afforded by vaccination was monitored by intratracheal challenge with IBV strain M-41 (clinical signs, ciliary activity in tracheal explants, virus isolation) and by serological tests (ovoneutralization, microneutralization in cell culture, haemagglutination inhibition (HI) test, ELISA). Intranasal-eye drop vaccination provided protection against intratracheal challenge. Immunity developed around 31 days of age. Spray vaccination failed to give protection against challenge by the same route. No difference was demonstrable in effectiveness between the two routes of vaccination by serological tests. No elevation of the antibody level occurred in either group. The level of maternally derived antibodies declined with age.     

Avian influenza mucosal vaccination in chickens with replication-defective recombinant adenovirus vaccine

We evaluated protection conferred by mucosal vaccination with replication-competent adenovirus-free recombinant adenovirus expressing a codon-optimized avian influenza (AI) H5 gene from A/turkey/WI/68 (AdTW68.H5ck). Commercial, layer-type chicken groups were either singly vaccinated ocularly at 5 days of age, singly vaccinated via spray at 5 days of age, or ocularly primed at 5 days and ocularly boosted at 15 days of age. Only chickens primed and boosted via the ocular route developed AI systemic antibodies with maximum hemagglutination inhibition mean titers of 3.9 log2 at 32 days of age. In contrast, single vaccination via the ocular or spray routes maintained an antibody status similar to unvaccinated controls. All chickens (16/16) subjected to ocular priming and boosting with AdTW68.H5ck survived challenge with highly pathogenic AI virus A/chicken/Queretaro/14588-19/95 (H5N2). Single ocular vaccination resulted in 63% (10/16) of birds surviving the challenge followed by a 44% (7/16) survival of single-sprayed vaccinated birds. Birds vaccinated twice via the ocular route also showed significantly lower (P < 0.05) AI virus RNA concentrations in oropharyngeal swabs compared to unvaccinated-challenged controls.     

A single vaccination of commercial broilers does not reduce transmission of H5N1 highly pathogenic avian influenza

ABSTRACT: Vaccination of chickens has become routine practice in Asian countries in which H5N1 highly pathogenic avian influenza (HPAI) is endemically present. This mainly applies to layer and breeder flocks, but broilers are usually left unvaccinated. Here we investigate whether vaccination is able to reduce HPAI H5N1 virus transmission among broiler chickens. Four sets of experiments were carried out, each consisting of 22 replicate trials containing a pair of birds. Experiments 1-3 were carried out with four-week-old birds that were unvaccinated, and vaccinated at day 1 or at day 10 of age. Experiment 4 was carried out with unvaccinated day-old broiler chicks. One chicken in each trial was inoculated with H5N1 HPAI virus. One chicken in each trial was inoculated with virus. The course of the infection chain was monitored by serological analysis, and by virus isolation performed on tracheal and cloacal swabs. The analyses were based on a stochastic SEIR model using a Bayesian inferential framework. When inoculation was carried out at the 28th day of life, transmission was efficient in unvaccinated birds, and in birds vaccinated at first or tenth day of life. In these experiments estimates of the latent period (~1.0 day), infectious period (~3.3 days), and transmission rate parameter (~1.4 per day) were similar, as were estimates of the reproduction number (~4) and generation interval (~1.4 day). Transmission was significantly less efficient in unvaccinated chickens when inoculation was carried out on the first day of life. These results show that vaccination of broiler chickens does not reduce transmission, and suggest that this may be due to the interference of maternal immunity.     

Humoral antibody response and assessment of protection following primary vaccination of chicks with maternally derived antibody against avian infectious bronchitis virus

Commercially bred chicks with maternally derived antibody to avian infectious bronchitis virus (IBV) were hatched in isolated conditions and a number vaccinated within the first three weeks of life with live IBV strain H120. Humoral antibody responses were assayed by haemagglutination inhibition (HI) or neutralisation (SN) tests, and the degree of protection against challenge with the virulent Massachusetts M41 strain assessed on the basis of tracheal ciliary activity four days after challenge. Maternal antibody in unvaccinated chicks declined linearly with a mean half-life of five to six days based on both HI and SN tests; these chicks were protected against challenge until four weeks old. There was complete correlation between ciliary activity and histopathological findings, but little between protection and antibody titre. It was concluded that the optimum age for primary vaccination was about two weeks.     

Avian infectious bronchitis: cross-protection studies using different Australian subtypes

The cross-immunity of vaccinated chickens after challenge with some Australian infectious bronchitis viruses was assessed by humoral antibody responses and by ciliary activity in tracheal rings of vaccinated chickens following challenge. Four viruses were used for vaccination: Vac 3, Vac 4, both current infectious bronchitis vaccine viruses, and Q1/76 and N2/62. IBV N1/62 (synonym T0 and infectious bronchitis virus N9/74 (synonym Appin) were used to challenge the vaccinated chickens. Results showed a lack of correlation between humoral antibody levels and protection. Cross-immunity was found after vaccination with each subtype, but was lower for Vac 3 and Vac 4 than for Q1/76 and N2/62.     

Immunization of broiler chickens with a commercial infectious laryngotracheitis vaccine in the drinking water.

Seventy-five thousand broiler chickens in four flocks were immunized at four weeks of age with a commercial infectious laryngotracheitis vaccine administered in the drinking water. Three of the flocks exhibited a vaccine reaction represented by mild respiratory illness between seven and 14 days after vaccination. Immunity challenge experiments demonstrated 97% protection in one trial and 67% in another trial in which the dose of challenge virus was increased fourfold. In the latter trial a parallel comparative vaccination by eye administration was 87% protective. None of the vaccinated birds died of the challenge exposure whereas all the unvaccinated control chickens became ill, several showed the acute severe form of the disease and 36% died. Similar favourable results were obtained in large-scale water immunization programs involving more than 200,000 birds. Serum antibody levels determined before immunity challenge were, within wide limits, inversely related to the severity of clinical disease which developed from the challenge inoculation.     

Duration of immunity engendered by a single dose of a cold-adapted strain of Avian pneumovirus

The duration of immunity after a single dose of a cold-adapted strain of Avian pneumovirus (APV) was studied. Turkeys were vaccinated at 1 wk of age and challenged with virulent virus 3, 7, 10, and 14 wk later. Nonvaccinated groups were also challenged at the same times. No clinical signs were observed in the vaccinated birds after vaccination or after any challenge. No viral RNA was shed by the vaccinated birds after any challenge. The nonvaccinated birds shed viral RNA after all challenges. Avian pneumovirus-specific humoral antibodies were detected in the vaccinated birds until 14 wk after vaccination. The results of this preliminary study indicate that inoculation with a single dose of a cold-adapted strain of APV at 1 wk of age provides protection until 15 wk of age.     

Comparison of duration of immunity in chickens infected with a live infectious bronchitis vaccine by three different routes.

Three groups of chicks were vaccinated by aerosol, intra-ocular and drinking water routes with a live infectious bronchitis (IB) vaccine. At one, two, six, 15 and 32 weeks after vaccination five birds from each group were sampled for testing for IB haemagglutination-inhibiting (HI) antibodies and challenged. Assessment of susceptibility to infection was measured by recovery of virus from individual tracheas and from kidney and gonad pools four days after challenge. Virus was isolated from all kidney and gonad pools of birds challenged one week after vaccination, the kidney and gonad pools of the drinking water vaccinates at two weeks, the kidney pool of the intra-ocular group at 15 weeks and all organ pools except the gonads of the intra-ocular group at 32 weeks. Tracheal resistance was found in most of the birds challenged one week after vaccination and in all the birds tested at two weeks but had begun to wane by six weeks after vaccination. No correlation was found between low HI antibody titres of individual birds and their susceptibility to challenge measured by reisolation of virus from the traches, but birds with titres over log2 6 were always resistant.     

The resistance of meat chickens vaccinated by aerosol with a live V4 Newcastle disease virus vaccine in the field to challenge with a velogenic Newcastle disease virus

Meat chickens housed on a commercial broiler farm in Australia were vaccinated once at 10 to 11 days-of-age by aerosol with live V4 Newcastle disease virus (NDV) vaccine. Groups of vaccinated and unvaccinated birds were flown to Malaysia, where they were challenged with a virulent strain of NDV. Survival rates in vaccinated chickens challenged 7, 14, 21 or 31 d after vaccination were 0.47, 0.77, 0.97 and 0.92, respectively. All unvaccinated chickens died due to Newcastle disease (ND) following challenge. Chickens in Australia and Malaysia were bled and the serums tested for haemagglutination-inhibiting (HI) antibody to NDV. Many vaccinated birds with no detectable antibody, and all birds with a log2 titre of 2 or greater, survived challenge. The results showed that this V4 vaccine induced protective immunity in a significant proportion of chickens within 7 d of mass aerosol vaccination. This early immunity occurred in the absence of detectable circulating HI antibody. Non-HI antibody mediated immunity continued to provide protection up to 31 d after vaccination. Almost all vaccinated birds were protected within 3 w of vaccination. It is concluded that the V4 vaccine is efficacious and could be useful during an outbreak of virulent ND in Australia.     

A standardized enzyme-linked immunosorbent assay for infectious bronchitis virus: comparison with hemagglutination-inhibition and virus-neutralization assays for measuring protective antibody levels in chickens

An enzyme-linked immunosorbent assay (ELISA) was developed to measure antibodies to infectious bronchitis virus (IBV) in chickens. The results are reported in IBV standard ELISA values calculated by comparing antibody levels in test sera with antibody levels in a series of standard reference sera. The IBV standard ELISA values were good indicators of responses to vaccination and the immune status of experimentally challenged birds. Although the assay was not serotype-specific, the sensitivity makes it ideally suited for determining the immune status of poultry flocks. The assay results compared favorably with other laboratory results, including virus-neutralization titers, hemagglutination-inhibition levels in sera, virus isolation from vaccinated/challenged birds, and the tracheal ring test results.     

Vaccination of ostriches (Struthio camelus, Linnaeus, 1758) against Newcastle disease: evidence for vaccine compatibility and seroconversion after vaccinations using the hemagglutination inhibition and virus neutralization tests

Newcastle disease (ND) remains to be the worldwide most important infectious disease of poultry. This epizootic is in Germany and many other countries a notifiable disease. Prophylactic vaccination is the major tool for the control of ND in poultry and other birds. Eighty-three ostriches (Struthio camelus) which were kept on farms in Germany were checked for the presence of NDV-specific antibodies. Some of these birds are said to be vaccinated against Newcastle disease. Only some of these ostriches contained antibodies which were measurable in haemagglutination inhibition and virus neutralisation tests. Twenty-three previously unvaccinated ostriches were vaccinated with commercially available vaccines. Both the LaSota live and inactivated oil emulsion vaccines were well tolerated following conjunctival or subcutaneous application, respectively. Neither local nor systemic side reactions were observed. After the vaccinations high antibody titres were detected in hemagglutination inhibition and virus neutralisation tests. A strong correlation between both established methods (r = 0.92; < 0.001) were noted.     

Reciprocal Antibody and Complement Responses of Two Chicken Breeds to Vaccine Strains of Newcastle Disease Virus, Infectious Bursal Disease Virus and Infectious Bronchitis Virus

Serum antibody responses and haemolytic complement activity were evaluated in White Leghorn (WLH) and Rhode Island Red (RIR) chickens that were vaccinated with live-attenuated vaccines of Newcastle disease virus, or infectious bronchitis virus, or infectious bursal disease virus by means of ocular challenge at 10 times the normal vaccination dose. Complement titres in non-vaccinated birds were significantly higher in WLH birds compared to RIR birds. The lentogenic viral infection resulted in an immediate stimulation of complement activity, followed by a decrease to initial complement levels within 2 weeks post vaccination, when the antibody response took over immune defence. As compared to WLH chickens, RIR birds mounted a faster and significantly higher antibody response to the vaccine viruses used. In WLH hens, significantly higher haemolytic complement activity post vaccination was found as compared to RIR hens. Possible consequences of the observed differences in immune responsiveness of the two breeds to viral vaccines are discussed.     

SOME IMMUNOLOGICAL ASPECTS OF A RECENT AUSTRALIAN ISOLATE OF INFECTIOUS BRONCHITIS VIRUS

An infectious bronchitis virus, designated G48, isolated from birds during an outbreak of nephritis in a previously vaccinated broiler flock, overcame the resistance induced in birds vaccinated with 2 commercially available vaccines. Birds vaccinated with the A isolate of infectious bronchitis resisted challenge with this new virus. Cross neutralisation studies revealed that the new virus was serologically distinct from the 4 viruses tested. Homologous antiserum to G48 did not neutralise the other viruses and only antiserum to the A virus completely neutralised the new virus.     

Effects of differences in virulence of different serovars of Haemophilus paragallinarum on perceived vaccine efficacy

The virulence of four South African field isolates of NAD-dependent Haemophilus paragallinarum and two field isolates of NAD-independent H. paragallinarum has previously been tested in unvaccinated chickens. In this study, the disease profiles caused by the NAD-dependent isolates of H. paragallinarum in vaccinated chickens were studied. It was shown that the clinical signs induced in the vaccinated chickens were substantially less severe than were those in unvaccinated chickens, as was expected. However, due to the high virulence of the serovar C-3 isolates, clinical signs in the vaccinated chickens challenged with this isolate were still detected. These were as severe as those occurring in unvaccinated chickens challenged with serovar B-1 isolates. Although the clinical signs induced in unvaccinated birds challenged with serovar A-1 were more severe than those occurring when vaccinated birds were challenged with serovar C-3, the overall disease profiles were similar. Substantial clinical signs were recorded in vaccinated birds challenged with serovar C-3. This could be interpreted as vaccination failure if the disease profile obtained in unvaccinated birds is not considered. It was found that a high level of protection was provided by this vaccine against challenge by serovar C-3. The high virulence of this serovar resulted in the development of clinical signs in vaccinated birds. These findings could possibly explain the large number of so-called vaccination failures that are reported in South Africa.     

Safety and efficacy of the cell-associated vaccine prepared by an attenuated infectious laryngotracheitis virus.

The safety and efficacy of the cell-associated (C-A) vaccine prepared by chicken embryo fibroblast (CEF) cells infected with the tissue-culture-modified strain of infectious laryngotracheitis (ILT) virus were studied in chickens. Over seventy percent of chickens inoculated with the C-A vaccine by the subcutaneous (S.C.) or intramuscular (I.M.) route at 1 day of age was protected against challenge with a virulent strain of ILT virus without any clinical signs. Chickens vaccinated with the C-A vaccine at 1 day of age acquired immunity within 6 days after vaccination, and the protection rate maintained more than 60% until 10 weeks post-vaccination. The C-A vaccine was invariably effective for chickens at various age. There was no evidence that the development of immunity was hindered by further vaccination with Newcastle disease and infectious bronchitis combined live vaccine. In addition, the C-A vaccine was safe when chickens were inoculated with 10 doses. In the field trials of the C-A vaccine, no adverse reaction was observed, and over 65% of vaccinated chickens was protected against the challenge of the virulent ILT virus at 8 weeks after vaccination.