Infectious bursal disease virus variant from commercial Leghorn pullets

An infectious bursal disease virus (IBDV) was isolated from 39-to-43-day-old commercial leghorn pullets suspected of having infectious bursal disease (IBD). These chickens had been vaccinated with a commercial live IBDV vaccine at 28 and 35 days of age. An isolate designated IN was recovered using specific-pathogen-free (SPF) chickens and the BGM-70 established cell line. Experimental studies using SPF chickens vaccinated with either inactivated vaccines made from the vaccine strain used in the problem flock or a standard-type vaccine indicated no protection against the IN isolate. However, two variants and another standard-type vaccine induced protection against the IN isolate. Cross-neutralization tests indicated that the IN isolate differed antigenically from commercial vaccine strains and was related to the variant IBDV strains recently isolated from broilers. To our knowledge, this is the first report of a variant IBDV recovered from commercial layer chickens in the United States.     

Bilateral effects of vaccination against infectious bursal disease and Newcastle disease in specific-pathogen-free layers and commercial broiler chickens

Different infectious bursal disease virus (IBDV) live vaccines (intermediate, intermediate plus) were compared for their immunosuppressive abilities in specific-pathogen-free (SPF) layer-type chickens or commercial broilers. The Newcastle disease virus (NDV) vaccination model was applied to determine not only IBDV-induced immunosuppression but also bilateral effects between IBDV and NDV. None of the IBDV vaccines abrogated NDV vaccine-induced protection. All NDV-vaccinated SPF layers and broilers were protected against NDV challenge independent of circulating NDV antibody levels. Sustained suppression of NDV antibody development was observed in SPF layers, which had received the intermediate plus IBDV vaccine. We observed a temporary suppression of NDV antibody development in broilers vaccinated with one of the intermediate, as well as the intermediate plus, IBDV vaccines. Different genetic backgrounds, ages, and residual maternal antibodies might have influenced the pathogenesis of IBDV in the different types of chickens. Temporary suppression of NDV antibody response in broilers was only seen if the NDV vaccine was administered before and not, as it was speculated previously, at the time the peak of IBDV-induced bursa lesions was detected. For the first time, we have demonstrated that the NDV vaccine had an interfering effect with the pathogenesis of the intermediate as well as the intermediate plus IBDV vaccine. NDV vaccination enhanced the incidence of IBDV bursa lesions and IBDV antibody development. This observation indicates that this bilateral effect of an IBDV and NDV vaccination should be considered in the field and could have consequences for the performance of broiler flocks.     

Proventriculitis in broiler chickens: effects of immunosuppression

Proventriculitis in broilers causes carcass condemnation when swollen proventriculi tear during evisceration. The cause of this proventriculitis is unknown, but several infectious agents have been associated with it. One such agent, infectious bursal disease virus (IBDV), has been implicated as a cause of proventriculitis, but a direct effect of this virus on the proventriculus has not been proven. The role of IBDV in proventriculitis may be indirect as a result of its ability to cause immunosuppression. The objective of this study was to understand how immunosuppression affects the incidence of proventriculitis in broiler chickens. Immunosuppression was induced in commercial and specific-pathogen-free broiler chickens using chemicals (cyclophosphamide and cyclosporin) or virus (IBDV). All groups were then exposed to a proventricular homogenate produced from diseased birds. At 7 and 14 days postinoculation, the incidence of proventriculitis in these groups was compared to that produced by homogenate exposure in immunocompetent broilers. All birds exposed to the proventricular homogenate from diseased birds developed proventriculitis. Cyclophosphamide and IBDV, both B cell suppressors, did not significantly affect the incidence or characteristics of the proventriculitis observed, although they did have an effect on the size of the proventriculus at 7 days postinoculation. Chickens immunosuppressed with cyclosporin, a T cell suppressor, developed more severe lesions and had a higher incidence of proventriculitis. These findings indicate that both B and T cells are involved in the immune response against proventriculitis, but cell-mediated immunity appears to have a more important role in controlling the disease. IBDV affects both humoral and cellular immunity in the chicken, so although under experimental conditions it didn't have a major effect on proventriculitis, it may explain why control of IBDV in the field seems to reduce the incidence of proventriculitis.     

Serological monitoring on layer farms with specific pathogen-free chickens

To monitor the existence of avian pathogens in laying chicken flocks, specific pathogen-free (SPF) chickens were introduced into two layer farms and reared with laying hens for 12 months. SPF chickens were bled several times after their introduction and examined for their sero-conversion to avian pathogens. As a result, antibodies to eight or ten kinds of pathogens were detected in SPF chickens on each farm. Antibodies to infectious bronchitis virus (IBV), avian nephritis virus, Mycoplasma gallisepticum and M. synoviae were detected early within the first month. Antibody titer to IBV suggested that the laying chickens were infected with IBV repeatedly during the experiment on both farms. However, antibodies to infectious bursal disease virus and 6 pathogens were not detected.     

Retrospective and prospective studies of transmissible viral proventriculitis in broiler chickens in Brazil

We investigated the occurrence and pathologic findings of transmissible viral proventriculitis (TVP) associated with the chicken proventricular necrosis virus (CPNV) in commercial broiler chickens in southeastern Brazil. Seventy-three broilers, 25–36 d old, with a history of reduced growth, were referred to our veterinary pathology services from 2013 to 2017. Broilers were clinically examined, weighed, and euthanized for postmortem examination. Broilers of different ages with proventricular histologic lesions were positive for CPNV by RT-PCR; however, the intensity of histologic lesions was higher among 33-d-old animals, and viral RNA detection was more frequent among those that were 28 d old. In the proventriculi of 35 of 73 (48%) broilers, lesions were characterized by glandular epithelial necrosis, lymphoplasmacytic and histiocytic infiltrates, and metaplasia of glandular epithelium to ductal epithelium. In 24 of 73 (36%) broilers with histologic TVP-compatible lesions, CPNV was detected by RT-PCR for the viral protein 1 (VP1) gene. Broilers with histologic lesions were lighter than expected compared to the Cobb 500 standard weight. TVP has not been reported previously in broiler chickens in Brazil, to our knowledge.     

Field trial in commercial broilers with a multivalent in ovo vaccine comprising a mixture of live viral vaccines against Marek's disease,infectious bursal disease,Newcastle disease,and fowl pox

A multivalent in ovo vaccine (MIV) was tested for safety and efficacy in a commercial broiler complex. The MIV comprised five replicating live viruses including serotypes 1, 2, and 3 of Marek's disease virus (MDV), an intermediate infectious bursal disease virus (IBDV) and a recombinant fowl poxvirus (FPV) vector vaccine containing HN and F genes of Newcastle disease virus (NDV). The performance of MIV-vaccinated broilers was compared with that of hatchmates that received turkey herpesvirus (HVT) alone (routinely used in ovo vaccine in the broiler complex). The chickens that hatched from the MIV-injected and HVT-injected eggs were raised under commercial conditions in six barns. Barn 1 housed 17,853 MIV-vaccinated chickens and each of the barns 2-6 housed 18,472-22,798 HVT-vaccinated chickens. The HVT-vaccinated chickens were given infectious bronchitis virus (IBV) and NDV vaccines at hatch and at 2 wk of age. The MIV-vaccinated chickens received IBV vaccine at hatch and IBV + NDV at 2 wk of age. The relative values of hatchability of eggs, livability and weight gain of chickens, and condemnation rates at processing were comparable between the MIV and the HVT groups (P > 0.05). Chickens from the MIV- and the HVT-vaccinated groups were challenged with virulent viruses under laboratory conditions. The resistance of vaccinated chickens against Marek's disease could not be assessed because of high natural resistance of unvaccinated commercial broilers to virulent MDV. The relative resistances of the MIV- and the HVT-vaccinated groups, respectively, against other virulent viruses were as follows: IBDV, 100% for both groups; NDV, 81% vs. 19%; FPV, 86% vs. 0%. The successful use of MIV under field conditions expands the usefulness of the in ovo technology for poultry.     

Reduced serologic response to Newcastle disease virus in broiler chickens exposed to a Chinese field strain of subgroup J avian leukosis virus

In this study, a Chinese field strain of subgroup J avian leukosis virus (ALV-J), NX0101, was studied for its immunosuppressive effects in both commercial broilers and SPF white Leghorn chickens infected at 1 day of age. Our data demonstrated that NX0101 induced much more significant body and immune organ weight loss in the infected commercial broiler chickens in an earlier age than that in the SPF white Leghorn chickens. At the same time antibody responses to vaccinations of Newcastle disease virus (NDV) and infectious bursa disease virus (IBDV) in the NX0101-infected chickens were also evaluated and compared between the commercial broiler chickens and the SPF white Leghorn chickens. Compared with the control group of chickens, the hemagglutination inhibition (HI) antibody response to NDV vaccines was significantly reduced in the NX0101-infected commercial broiler chickens from as early as 20 days after vaccination. However, no significant difference in HI antibody response was seen when HI titers reached their peaks in the NX0101-inoculated and control SPF white Leghorn chickens, except it declined significantly faster in infected birds. Neither of these two types of chickens showed significant decrease of antibody response to IBDV vaccination. Herein, we conclude that this NX0101 strain of ALV-J could selectively suppress humoral immune reactions to NDV, especially in broilers. But challenge experiments were not conducted and, therefore, it cannot be known if decreased antibody levels correlated with decreased protection against NDV in this case.     

Safety and efficacy of in ovo administration of infectious bursal disease viral vaccines

In ovo vaccination against Marek's disease virus and infectious bursal disease virus (IBDV) in commercial broilers in the United States is common. Little information exists as to the safety and efficacy of intermediate IBDV vaccines given in ovo. Experiments were initiated to determine the safety and efficacy of three commercially available live intermediate IBDV vaccines by in ovo route. Commonly used vaccines were given at 18 days of embryonation to specific-pathogen-free (SPF) broiler embryos (first and second study) or to commercial broiler embryos (third study) that had maternal antibody against IBDV. When any of the antigenic standard vaccines was given at full dose to SPF embryos, embryonic and 3-wk posthatch mortality increased. Vaccines also caused significant microscopic lesions in the bursa of Fabricius at 1 and 3 wk posthatch. In contrast, there was no adverse effect on embryonic or posthatch mortality when vaccines were given at half dose to SPF or commercial broiler embryos. However, significant microscopic lesions were evident at 1 and 3 wk posthatch in the bursae of SPF embryos given the vaccines at half dose. When vaccines were given at half dose to commercial broiler embryos, lesions were evident at 1 but not 3 wk of age. In the third study, in ovo vaccinated chickens were challenged with either a virulent standard (APHIS) or antigenic variant (variant E) IBDV virus at 3 wk of age. All vaccines produced at least 87% protection against the standard and 60% protection against the variant challenge IBDV, as measured by bursal weight to body weight ratios. This study was the first to examine the safety and efficacy of the three commonly used intermediate IBDV vaccines given in ovo in protection against standard and antigenic variant IBDV challenge viruses.     

Comparison of egg-yolk and serum antibody titers to four avian viruses by enzyme-linked immunosorbent assay using paired field samples

Eggs and blood were collected from 11 hens in each of nine broiler-breeder flocks in Quebec. Serum and egg-yolk extracts were assayed for antibody titers to infectious bursal disease virus (IBDV), infectious bronchitis virus (IBV), Newcastle disease virus (NDV), and reovirus (RV) by a commercial enzyme-linked immunosorbent assay (ELISA) kit. Comparison was made between egg-yolk and serum antibody titers by a regression analysis. A high correlation was observed between serum and yolk antibody titers to all the viruses tested (r = 0.9 for IBDV, 0.84 for IBV, 0.84 for NDV, and 0.91 for RV). Antibody monitoring of commercial breeder flocks using egg yolk instead of serum with commercial ELISA plates is thus feasible and is recommended.     

The exacerbating effect of infectious bronchitis virus infection on the infectious bursal disease virus-induced suppression of opsonization by Escherichia coil antibody in chickens

Chickens infected with infectious bronchitis virus (IBV) and infectious bursal disease virus (IBDV) commonly develop secondary infection of the respiratory tract with Escherichia coli, resulting in significant economic losses. To understand the host factors that may contribute to the E. coli infection, we investigated macrophage-mediated E. coli phagocytosis, intracellular bacterial killing, and development of opsonizing antibody in previously uninfected chickens and in those infected with IBV, IBDV, and IBDV plus IBV. Macrophages from the peripheral blood and the respiratory tracts of chickens infected with IBV or IBDV plus IBV efficiently performed in vitro phagocytosis of E. coli in the presence of positive-control serum (i.e., E. coli antiserum produced in normal chickens). Those macrophages also had adequate bactericidal activity, indicating that IBV and IBDV infections had not affected their phagocytic activity or bactericidal function. The phagocytic activity of macrophages remained unaffected (P < 0.05) when the positive-control serum was replaced with E. coli antiserum produced in chickens infected with IBV alone. However, when E. coli antisera raised in IBDV-infected and, especially, that produced in IBDV plus IBV-infected chickens were supplemented, the percentage of phagocytosis and number of bacteria ingested per phagocyte were significantly (P < 0.05) less. These results indicate that although IBDV alone has the potential to markedly reduce opsonizing ability of antibody, this effect is significantly (P < 0.05) exacerbated by IBV infection.     

Efficacy of VP2 protein expressed in E. coli for protection against highly virulent infectious bursal disease virus

The ability of a heat-inactivated whole virus from a highly virulent infectious bursal disease virus (hvIBDV) and VP2 protein from hvIBDV expressed in E. coli provided protection against a hvIBDV challenge in specific-pathogen-free (SPF) chickens. Six out of seven chickens that were injected three times with crude VP2 protein developed significant antibody titer against IBDV. However, only four out of the seven chickens survived the hvIBDV challenge. Despite showing low antibody titer profiles, all chickens immunized with the heat-inactivated whole virus also survived the challenged with hvIBDV. However, all of these chickens had bursal atrophy and mild to moderate depletion of lymphocytes. Thus, antibodies raised against IBDV VP2 protein expressed in E. coli and denatured IBDV proteins induced some degree of protection against mortality but not against bursal damage following challenge with hvIBDV.     

Pathological and immunological study of an in ovo complex vaccine against infectious bursal disease

The appearance of very virulent strains of infectious bursal disease (IBD) virus at the end of the 1980s made it necessary to develop more effective immunization procedures. To facilitate this, the immunogenicity and the immunosuppressive effect of a mild (G-87), an intermediate (LIBD) and an intermediate-plus (IBDV 2512) IBDV strain were tested after the in ovo inoculation of 18-day-old SPF and broiler chicken embryos. It was established that no noteworthy difference existed between the immunized and the control embryos in hatching rate and hatching weight. The higher the virulence of the vaccine virus strain, the more severe damage it caused to the lymphocytes of the bursa of Fabricius. In SPF chickens, the haemagglutination inhibition (HI) titres induced by a Newcastle disease (ND) vaccine administered at day old decreased in inverse ratio to the virulence of the IBD vaccine strain, while in broiler chickens this was not observed. Despite the decrease of the HI titre, the level of protection did not decline, or did so only after the use of the 'hot' strain. SPF chickens immunized in ovo with a complex vaccine prepared from strain IBDV 2512 and IBD antibody showed the same protection against Newcastle disease as the broilers. In broiler chicken embryos immunized in ovo, only strain IBDV 2512 induced antibody production, and such chickens were protected against IBD at 3 weeks of age. The complex vaccine administered in ovo has been used successfully at farm hatcheries as well.     

CAV与REV共感染SPF鸡对疫苗免疫反应的抑制作用

用1日龄SPF鸡人工感染鸡贫血病毒(CAV)和禽网状内皮增生病病毒(REV),探讨病毒感染对鸡体疫苗免疫反应的影响。结果表明,在用禽流感病毒(AIV,H5和H9)疫苗免疫后,CAV与REV单独感染均显著抑制了鸡体对H5和H9亚型禽流感病毒灭活疫苗的HI抗体反应,在CAV与REV共感染后,这种抑制作用更为明显。CAV单独感染后鸡体对新城疫病毒(NDV)和传染性法氏囊病病毒(IBDV)疫苗的免疫反应受到抑制,但与对照组在统计学上的差异不显著,然而,CAV可以显著加重REV感染对鸡体在NDV和IBDV疫苗免疫后抗体反应的抑制作用。从而证实CAV与REV共感染在疫苗免疫抑制上有协同作用。     

Protective efficacy of intermediate and intermediate plus infectious bursal disease virus (IBDV) vaccines against very virulent IBDV in commercial broilers

The evolution of very virulent (vv) infectious bursal disease virus (IBDV) has led to significant economic losses in many poultry-producing areas. Despite vigorous vaccination strategies, IBDV has been difficult to control. The protective efficacy of IBDV vaccines is traditionally evaluated in specific pathogen-free (SPF) chickens. But under field conditions, residual maternal antibody (mAb) levels may interfere with vaccine efficacy. In this study, commercial broilers with various levels of maternally derived antibodies were vaccinated with IBDV vaccines of different virulence (vaccines 1-3, intermediate; vaccine 4, intermediate plus). At an average maternal virus-neutralizing antibody (mAb) level of log2 10.8 (range 7.6-11.6) at day of vaccination, only the intermediate plus vaccine induced IBDV antibodies after 18 days, while the other intermediate vaccines did not. At average mAb levels of log2 6.7 (range 5.6-8.6) at day of vaccination, all vaccines induced circulating antibodies, although the onset of antibody production differed significantly between strains (P < 0.05). While the intermediate plus vaccine induced enzyme-linked immunosorbent assay antibody levels already at 14 days postvaccination (PV), the intermediate vaccines induced significant antibody levels 28 (vaccines 1, 2) and 35 (vaccine 3) days PV. The time of IBDV antibody induction correlated with the onset of bursa lesions. The severity of lesions was comparable between vaccines 1, 3, and 4 (lesion score 4), while vaccine 2 induce only mild lesions of score 1 in 23% of the tested birds. Despite the induction of antibodies, none of the tested vaccines fully protected against challenge with vvIBDV. All challenged birds had either significantly higher bursal lesion scores or a higher IBDV antigen load in the bursa or sometimes both in comparison with nonchallenged birds (P < 0.05). Our study demonstrates that the evaluation of IBDV-vaccine efficacy is difficult in commercial broilers. For the first time, it was shown that the onset of bursa lesions and recovery of IBDV-vaccinated broilers is delayed in the presence of mAb in comparison with SPF chickens but not suppressed as previously assumed. At the time of challenge, vaccinated birds may still have significant bursa lesions and may lack target cells for IBDV-challenge virus. To be able to evaluate vaccine efficacy in commercial broilers, parameters such as intrabursal IBDV-antigen load should also be considered in conjunction with bursa lesion scores.     

Pathogenicity of embryo-adapted serotype 2 OH strain of infectious bursal disease virus in chickens and turkeys

The pathogenicity of serotype 2 OH strain of infectious bursal disease virus (IBDV) to specific-pathogen-free (SPF) chicken embryos and 2-wk-old SPF chickens and turkey poults was investigated. The virus was pathogenic for chicken embryos after five passages as evidenced by pathologic changes in inoculated embryos. The embryo-adapted virus was not pathogenic for 2-wk-old SPF chickens and turkey poults as indicated by lack of clinical signs, gross or microscopic lesions in the bursa of Fabricius of inoculated birds. Bursa-to-body-weight ratios of the inoculated chickens and turkey poults were not significantly different from those of uninoculated controls. Virus-neutralizing antibodies to serotype 2 IBDV were detected in inoculated chickens and turkeys. Results of this study indicated that the embryo-adapted serotype 2 OH IBDV isolate that is pathogenic for chicken embryos is infectious but not pathogenic in chickens and turkeys.     

Susceptibility of Local Nigerian and Exotic Chickens to Infectious Bursal Disease by Contact Exposure

One hundred 6-week-old susceptible cockerels were inoculated with a pathogenic strain of infectious bursal disease virus (IBDV) and kept in the same pen as 100 each of 6-week-old pullets, local chickens and broilers. The cockerels developed depression and diarrhoea on day 3 post inoculation (PI) and most of the pullets and some of the local chickens and broilers showed similar signs on day 4 PI. Loss in weight was severe and similar in the pullets and local chickens, being significantly greater than that in the broilers from days 3–11 PI. The total mortality was 85%, 66.7%, 30% and 20% for the pullets, cockerels, local chickens and broilers, respectively. The lesions were more severe in the pullets and local chickens than in the broilers. IBDV antigen and antibody were detected, respectively, in all the bursal and serum samples from the infected chickens tested. The contact exposure method used in this study simulates better what happens in nature than inoculation with IBDV. The reduced mortality observed among the local chickens, compared with that (61.5%) seen in earlier studies using intraocular inoculation of IBDV, may have been due to behavioural differences that tend to result in their ingesting a relatively low dose of the virus.