Comparison of vaccines against infectious bursal disease

Protocatechuic acid, a new active substance against the challenge of avian infectious bursal disease virus

The present study aims to investigate the potential antiviral activity of protocatechuic acid (PCA) and its mechanism against infectious bursal disease virus (IBDV) infection. In the curative test, dosages of PCA of 40, 20, and 10 mg/kg, the survival rate was 90, 90, and 60%, respectively, and the BW gain was 36.63, 31.85, and 51.8%, respectively. The survival rate for the Astragalus polysaccharide (ASP) group was significantly lower than those of the birds treated with 20 mg/kg or 40 mg/kg of PCA. The bursa indeces of chickens in 40 mg/kg, 20 mg/kg, and ASP groups were significantly higher than that of the infection group, whereas a significant increase of the spleen index was found in birds with 20 mg/kg PCA in comparison with other challenged groups. The birds treated with 20 mg/kg or 40 mg/kg of 3,4-dihydroxybenzoic acid also showed slightly higher levels of IBDV clearance in the bursa of Fabricius. Furthermore, the chickens treated with 20 mg/kg of PCA induced a significant lymphocyte proliferation and a significant increase in the CD4+/CD8+ ratio in comparison with the ASP chickens. These results imply that chickens treated with 20 mg/kg of PCA for 5 d could effectively induce active nonspecific immune responses against the IBDV infection.

Biological properties of a naturally attenuated infectious bursal disease virus isolated from a backyard chicken flock

The biological properties of an infectious bursal disease (IBD) virus isolated from bursas collected during an outbreak in a village chicken flock in Macedonia are described. The mortality rate was 50%. Two viruses coexisted in the bursas of infected chickens (IBDVwt and IBDVtc). The virus termed IBDVtc grows on chicken embryo fibroblast (CEF) cells from the first passage. Specific pathogen free chickens inoculated with IBDVtc at passage level 4 did not develop any clinical signs of disease. Some discrete bleeding on the leg muscles was seen and the bursa of Fabricius revealed pathological lesions similar to those caused by classical strains. However, the bursa recovered quickly (bursa lesion score 2) by 14 days post infection (PI). We also found evidence of bursal repopulation by means of perinuclear antigen staining. Strong CD3 influx was evident at 4 days PI, and at 33 days PI the CD3+ cell finding was comparable to the control. The mean antibody titre was 9.2 log 2 at 14 days PI. The amino acid composition of VP2 in IBDVwt (222 Ala, 242 Ile, 253 Gln, 256 Ile, 279 Asp, 284 Ala, 294 Ile and 299 Ser) is described. The same sequence was found in IBDVtc, except for two point mutations, at Gln253→His and Ala284→Thr. Such amino acid substitution is responsible for partial attenuation and the ability of the strain to replicate in cell culture. None of the commercial vaccine viruses has a similar arrangement of amino acids in the variable domain of IBDV. This strongly suggests that IBDVtc originates from a very virulent strain. To the best of our knowledge, this is the first report of a concomitant infection of chickens with highly pathogenic IBDV and its mutant counterpart.

Evaluation of the immunogenicity, stability, pathogenicity, and immunodepressive potential of four commercial live infectious bursal disease vaccines

The study was divided into three experiments. In each, day-old specific pathogen free (SPF) White Leghorns were injected subcutaneously with one of the following commercial live infectious bursal disease (IBD) vaccines: Burcell, Bursine, Clone Vac D-78, and S-706. In the first experiment, the immunogenicity of each vaccine was determined by challenge with virulent IBDV at 25 days of age. All four vaccines were equally efficacious in preventing clinical IBDV infection. The second experiment determined the stability and pathogenicity of the four vaccines by successive back passage of each virus in SPF chicks for 4 consecutive weeks. Although all vaccines were capable of spreading to contact controls, only the two intermediate vaccines (D-78 and S-706) produced slightly atrophied bursae and moderate microscopic bursal lesions. However, both vaccines were stable, because neither reverted back to increase virulence nor resulted in morbidity or mortality associated with virulent IBDV after successive passage. In the third experiment, the immunodepressive potential of each vaccine virus was determined by examining the ability of IBD-vaccinated birds to respond to Newcastle disease (ND) virus vaccination. None of the four vaccines was found to be immunodepressive, as all IBD vaccinated birds responded to NDV vaccination.

Increased virulence of an infectious bursal disease live virus vaccine after passage in chicks

A live infectious bursal disease virus vaccine increased in virulence when passaged six times in susceptible birds, as judged by damage to the bursa of Fabricius. It is suggested that the increase in virulence of this vaccine was due to the selection of a virulent subpopulation which had been present in the vaccine since its original isolation from the field and which had not been eliminated during its attenuation by passage in cell culture. The vaccine was then plaque purified and a virus strain was selected which protected against challenge, did not damage the bursa and appeared not to passage in birds.

Simultaneous application of live turkey herpesvirus and infectious bursal disease vaccines against Marek's disease and infectious bursal disease

The efficacy of cell-associated (CA) and cell-free (CF) infectious bursal disease (IBD) vaccines in maternal antibody (MAb)-bearing broiler chickens was compared. Compatibility and potency of a mixed vaccine combining live CA turkey herpesvirus (HVT) and CA IBD vaccine viruses were also tested against gross lesions induced by Marek's disease (MD) or IBD in specific-pathogen-free chickens. Both CA and CF IBD vaccines provided significant protection against gross bursal lesions of IBD in the presence of MAb. Although chickens receiving the CA vaccine showed a slightly higher (60 to 86.7%) protective index (PX) than CF vaccine recipients (40 to 66.7%), there was no statistical difference in their PX between comparable CA and CF IBD vaccines. The HVT and IBD virus (IBDV) were compatible when they were combined as a live bivalent mixed HVT-IBDV vaccine. Based on the incidence of gross lesions induced by challenge exposure to MD or IBD, potency of the mixed vaccine was similar to that of the monovalent HVT or IBD vaccine. Antagonism did not occur between the two component vaccines when they were applied simultaneously.

Effect of infectious bursal disease on natural killer cell activity and mitogenic response of chicken lymphoid cells: role of adherent cells in cellular immune suppression

A pathogenic isolate of infectious bursal disease virus (IBDV) caused persistent and extensive lesions in the bursa but mild and transient lesions in the thymuses of chickens of lines 63 and P. The effect of IBDV on two cellular immune functions, namely, natural killer cell cytotoxicity and mitogenic response, was studied. The natural killer cell activity was not consistently influenced, but the virus, during the first 2 weeks of infection, caused transient depression of the blastogenic response of spleen cells to phytohemagglutinin. Studies on mitogenic hyporesponsiveness revealed that the functional impairment was mediated by a suppressor cell that shared several characteristics with macrophages; i.e., the suppressor cell was adherent to plastic, was phagocytic, and resisted treatment with antithymocyte and antibursa cell sera. Removal of suppressor cells from the spleens of virus-infected chickens resulted in restoration of the mitogenic response of cells. Further, in mixing experiments, the suppressor cell isolated from the spleens of virus-infected chickens also inhibited the mitogenic response of normal spleen cells. We concluded that reduced mitogenic response of lymphocytes in IBDV-infected chickens was not due to a lack of functional T-cells, as suggested previously by others, but was due to macrophage-like suppressor cells. The suppressor cells, although present in certain normal chickens, became activated during early stages of IBDV infection.

Studies on a vaccine against infections bursal disease

An infectious bursal disease vaccine, registered for use in breeder flocks, was studied for efficacy on the day-old offspring of vaccinated hens and for virulence in susceptible day-old and 6-week-old chickens. When given to susceptible day-old chicks and 6-week-old cockerels, the vaccine was found to induce atrophy and pathology of the bursa of Fabricius similar to that observed in field infections. Chicks vaccinated at day-old had markedly lowered titres in the haemagglutination inhibition test to Newcastle disease virus, when this was given 2 weeks later, but the response of the 6-week-old cockerel was similar to that of control birds. Maternal antibody induced by the vaccine protected chicks against infection at day-old.

Comparison of inactivated and live infectious bursal disease virus vaccines in White Leghorn breeder flock

Leghorn breeder chickens, which had received live infectious bursal disease (IBDV) virus vaccine at 12 weeks of age and had been injected subcutaneously at 20 weeks of age with an inactivated IBDV oil emulsion vaccine, produced very high antibody titers which persisted for at least 9 months and were more uniform than those obtained from breeders receiving only the live IBDV vaccine. Breeders vaccinated with the inactivated IBDV oil emulsion vaccine at 12 and 20 weeks of age had antibody titers higher than breeders which received only the live IBDV vaccine at 12 weeks of age; titers were lower than in the group which received both the live and inactivated oil emulsion IBDV vaccines. Maternal antibody levels in chickens derived from parent flocks vaccinated with the inactivated oil emulsion IBDV vaccine were higher and more uniform than in chickens derived from parent flocks vaccinated with the live IBDV vaccine. Maternal antibody persisted longer in chickens derived from parent flocks vaccinated at 20 weeks of age with the inactivated oil emulsion IBDV vaccine than in chickens vaccinated by the other procedures. The titers remained quite high up to 16 days of age.

Vaccination against infectious bronchitis and the immunosuppressive effects of infectious bursal disease

An immunosuppressive effect was demonstrated in chickens which were infected with infectious bursal disease virus (IBDV) early in life and prior to or shortly after vaccination with infectious bronchitis virus (IBV). This effect was evident by an increased susceptibility to respiratory tract infection with IBV and reduced virus-serum neutralizing antibody levels. Chickens which were hatched from dams susceptible to infectious bursal disease (IBD) were less responsive to IBV immunization attempts, if exposed to IBDV, than were those individuals hatched from IBD immune dams. However, in some cases, chickens from IBD immune dams were also more susceptible to IBV challenge when they had been exposed to IBDV and when compared to birds unexposed to IBDV but vaccinated against IB. An effect of cyclophosphamide on the bursa of Fabricius also had an immunosuppressive action on IBV immunity which was similar to the results from IBDV exposure. The data engendered from these trials may explain the unsatisfactory immunity sometimes observed under field conditions when broilers and replacement pullets are vaccinated at an early age.