Live Infectious Bronchitis Virus Vaccines Research Articles

Infectious Bronchitis Coronavirus: Genome Evolution in Vaccinated and Non-Vaccinated SPF Chickens.

Infectious Bronchitis virus (IBV) continues to cause significant economic losses for the chicken industry despite the use of many live IBV vaccines around the world. Several authors have suggested that vaccine-induced partial protection may contribute to the emergence of new IBV strains. In order to study this hypothesis, three passages of a challenge IBV were made in SPF chickens sham inoculated or vaccinated at day of age using a live vaccine heterologous to the challenge virus. All birds that were challenged with vaccine heterologous virus were positive for viral RNA. NGS analysis of viral RNA in the unvaccinated group showed a rapid selection of seven genetic variants, finally modifying the consensus genome of the viral population. Among them, five were non-synonymous, modifying one position in NSP 8, one in NSP 13, and three in the Spike protein. In the vaccinated group, one genetic variant was selected over the three passages. This synonymous modification was absent from the unvaccinated group. Under these conditions, the genome population of an IBV challenge virus evolved rapidly in both heterologous vaccinated and non-vaccinated birds, while the genetic changes that were selected and the locations of these were very different between the two groups.

Genomic Stability for PCR Detection of Infectious Laryngotracheitis Virus and Infectious Bronchitis Virus in Poultry Dust Samples Stored Under Different Conditions.

Dust collected from the poultry house has been increasingly used as a population-level sample to monitor the presence of pathogens or to evaluate the administration of live vaccines. However, there are no guidelines for the storage of this sample type. This study investigated the stability of infectious laryngotracheitis virus (ILTV), a DNA virus, and infectious bronchitis virus (IBV), an RNA virus, in poultry dust kept under temperature and moisture conditions that mimic on-farm and laboratory storage. Dust samples were collected from chicks spray vaccinated with a live IBV vaccine and inoculated with a field ILTV strain via eye drop. Samples were stored under different moisture conditions (dry = 2% moisture, moist = 22%-71% moisture) and temperatures (-20, 4, 25, and 37 C) for different durations (0, 7, and 14 days, and 1, 2, 3, and 4 mo) in a factorial arrangement, followed by quantitative PCR for detection of virus genome copies (GC). The length of storage, moisture level, and storage temperature affected the viral genome load for ILTV and IBV but did not affect the number of positive samples for each virus. All treatment combinations were ILTV positive for at least 4 mo. In dry dust samples, all storage temperatures or durations had quantifiable ILTV or IBV GC. Moisture addition had a detrimental effect on viral genome load, causing an overall reduction of 0.3 log 10 for ILTV GC (7.29 and 6.97 log 10, P = 0.0001), and 1.3 log 10 for IBV GC (5.95 and 4.66 log 10, P = 0.0001), which are unlikely to have biologic significance. In conclusion, dry dust can be stored at any temperature up to 37 C for at least 4 mo without loss in qPCR detection of ILTV or IBV GC. Collection or storage of moist dust should be avoided, or air drying prior to storage is recommended if only moist dust is available.

Comparative Protective Efficacies of Novel Avian Paramyxovirus-Vectored Vaccines against Virulent Infectious Bronchitis Virus in Chickens.

Viral vectored vaccines are desirable alternatives for conventional infectious bronchitis virus (IBV) vaccines. We have recently shown that a recombinant Newcastle disease virus (rNDV) strain LaSota expressing the spike (S) protein of IBV strain Mass-41 (rLaSota/IBV-S) was a promising vaccine candidate for IBV. Here we evaluated a novel chimeric rNDV/avian paramyxovirus serotype 2 (rNDV/APMV-2) as a vaccine vector against IBV. The rNDV/APMV-2 vector was chosen because it is much safer than the rNDV strain LaSota vector, particularly for young chicks and chicken embryos. In order to determine the effectiveness of this vector, a recombinant rNDV/APMV-2 expressing the S protein of IBV strain Mass-41 (rNDV/APMV-2/IBV-S) was constructed. The protective efficacy of this vector vaccine was compared to that of the rNDV vector vaccine. In one study, groups of one-day-old specific-pathogenic-free (SPF) chickens were immunized with rLaSota/IBV-S and rNDV/APMV-2/IBV-S and challenged four weeks later with the homologous highly virulent IBV strain Mass-41. In another study, groups of broiler chickens were single (at day one or three weeks of age) or prime-boost (prime at day one and boost at three weeks of age) immunized with rLaSota/IBV-S and/or rNDV-APMV-2/IBV-S. At weeks six of age, chickens were challenged with a highly virulent IBV strain Mass-41. Our challenge study showed that novel rNDV/APMV-2/IBV-S provided similar protection as rLaSota/IBV-S in SPF chickens. However, compared to prime-boost immunization of chickens with chimeric rNDV/APMV-2, rLaSota/IBV-S and/or a live IBV vaccine, single immunization of chickens with rLaSota/IBV-S, or live IBV vaccine provided better protection against IBV. In conclusion, we have developed the novel rNDV/APMV-2 vector expressing S protein of IBV that can be a safer vaccine against IB in chickens. Our results also suggest a single immunization with a LaSota vectored IBV vaccine candidate provides better protection than prime-boost immunization regimens.

Combination of TLR2 and TLR3 agonists derepress infectious bursal disease virus vaccine-induced immunosuppression in the chicken

Live intermediate plus infectious bursal disease virus (IBDV) vaccines (hot vaccines) are used for protection against the virulent IBDV strains in young chickens. We evaluated the potential of Toll-like receptor (TLR) agonists to alleviate hot vaccine-induced immunosuppression. The combination of Pam3CSK4 and poly I:C synergistically upregulated IFN-β, IFN-γ, IL-12, IL-4, and IL-13 transcripts and cross-inhibited IL-1β, IL-10, and iNOS transcripts in the chicken peripheral blood mononuclear cells (PBMCs) as analyzed by quantitative real-time PCR. Further, four-week old specific pathogen free White Leghorn chickens (n = 60) were randomly divided into six groups and either immunized with hot IBDV vaccine with or without Pam3CSK4 and/or poly I:C or not vaccinated to serve as controls. The results indicated that poly I:C alone and in combination with Pam3CSK4 alleviated vaccine-induced immunosuppression, as evidenced by greater weight gain, increased overall antibody responses to both sheep erythrocytes and live infectious bronchitis virus vaccine, upregulated IFN-γ transcripts and nitric oxide production by PBMCs (P < 0.05), and lower bursal lesion score in the experimental birds. In conclusion, poly I:C alone and its combination with Pam3CSK4 reduced the destruction of B cells as well as bursal damage with restoration of function of T cells and macrophages when used with a hot IBDV vaccine.

Resiquimod enhances mucosal and systemic immunity against avian infectious bronchitis virus vaccine in the chicken

Adjuvant enhancing mucosal immune response is preferred in controlling many pathogens at the portal of entry. Earlier, we reported that a toll-like-receptor 7 (TLR7) agonist, resiquimod (R-848), stimulated the systemic immunity when adjuvanted with the inactivated Newcastle disease virus vaccine in the chicken. Here, we report the effect of R-848 when adjuvanted with live or inactivated avian infectious bronchitis virus (IBV) vaccines with special emphasis on mucosal immunity. Specific pathogen free (SPF) chicks (n = 60) were equally divided into six groups at two weeks of age and immunized with either inactivated or live IBV vaccine adjuvanted with or without R-848. Groups that received either PBS or R-848 served as control. A booster was given on 14 days post-immunization (dpi). R-848 enhanced the antigen specific humoral and cellular immune responses when co-administered with the vaccines as evidenced by an increase in the antibody titre in ELISA and stimulation index in lymphocyte transformation test (LTT) till 35 dpi and increased proportion of CD4+ and CD8+ T cells on 21 dpi in the flow cytometry. Interestingly, it potentiated the IgA responses in the tear and intestinal secretions when used with both live and inactivated IBV vaccines. The combination of IBV vaccine with R-848 significantly up-regulated the transforming growth factor beta 4 (TGFβ4) transcripts in the peripheral blood mononuclear cells (PBMCs) than that of the respective vaccine per se. An enhanced secretory IgA response is likely due to the up-regulation of TGFβ4, which is responsible for class switching to IgA. In conclusion, co-administration of R-848 with inactivated or live IBV vaccine enhanced the systemic as well as mucosal immune responses in the chicken.

Investigation of Cross Neutralization of Egyptian Variant 2 among both Classic and Variant Vaccinal Infectious Bronchitis Viruses

Infectious Bronchitis Virus (IBV) is considered an important virus which may cause major losses in the poultry industry. One of the most important and effective tool that control the infection spread is the vaccination strategy. The present study was undertaken to determine the antigenic relationship between the currently used IBVs, classic and variant vaccinal strains, and the dominating Egyptian variant-2, IBV which could be relatively reflecting the quality of such vaccine. The recommended doses of the monovalent live IBV vaccines of Ma5, H120, 4/91 & CR88, and bivalent vaccine of H120-D274 were administrated via the eye-drop route in groups of 2-week-old SPF-chickens. Three weeks after vaccination, immunized and control chickens were bled, and serum samples were collected. Sera were tested individually for measuring the IBV-Haemagglutination Inhibiting (HI) antibodies against each of IBV-haemagglutinating antigen prepared from the reference classic M41 strain and the Egyptian variant.2 strain (Egy/12/2b spike protein), and IBV- neutralizing antibodies against the Egyptian variant-2 strain. The chicken groups vaccinated with the commercial live vaccines of strains Ma5, H120, 4/91, CR88 and H120-D274 of IBV respectively developed mean serum HI-antibody titers of 6.8, 6.5, 4.9, 5.0 and 5.5 log 2 with the reference classic strain M41-HA antigen, and 3.0, 3.0, 4.4, 4.0, and 4.6 log 2 with the Egyptian variant.2 strain-HA antigen. However, the obtained results revealed utility of VN test more than HI test for assessment of the antigenic relatedness between the vaccinal and challenge strains of IBV as well as testing quality of different commercial live IBV vaccines using the sera of vaccinated chickens against the field strain(s) matched with the homologous strain(s); the antigenic relatedness (r 1 ) between the dominating Egyptian variant-2 strain, and the vaccinal strains, CR88, D274-H120 and H120 of IBV were 33%, 55% and 17% respectively.

Improved vaccine strategies of infectious bronchitis disease to reduce shedding of virulent virus from infected birds

Infectious bronchitis (IB) threatens the economies of entire nations, by adversely affecting the backyard farmers, poultry producers and poultry industry throughout the world. Infectious bronchitis virus (IBV), a member of the Coronaviridae family, is probably one of the most avian pathogens prevalent in the poultry industry worldwide. In the field which presents difference structures, especially in the S1 spike protein. Complicated immune response against IBV due to few similarities between serotypes. High mutation rate of the virus, in addition to the management and environmental factors, compromise the efficacy of the available vaccines and difficult the control of disease. Prepared effective IB vaccines from any IBV strain stimulates the immunity widely against morbidity and mortality after challenge with virulent IBV strains. On the other hand, vaccinates with live IBV vaccines do not reduce infection or viral shedding after challenge. In order to compare the prepared IBV vaccines taken four different IBV genotypes to determine stimulating immunity and the amount of viral shedding after challenge, two hundred fifty one day broiler chicks divided into five groups and vaccinated with oil-adjuvant vaccines prepared of Iraqi isolates (II, I-II, I- III and I-IV). different inactivated IB viruses including strains QX, CH Baghdad M 2014, CH Baghdad F1 2013, CH Babylon F2 2013, and an allantoic fluid control. Using a hemagglutination inhibition test for serum analysis after challenge with virulent IBV (Variant2) to knowledge antibody content against each of the vaccine antigens, Monitored the vaccinated birds daily for of morbidity and mortality were recorded, and used PCR to determine the amount of viral copy of examined clinical samples in selected periods of viral shedding. All vaccines used in the study gave good protection against morbidity and mortality, except the control group. Homologous vaccines gave good protection and lowest viral shedding in the trachea, kidney and feces compared to the heterogeneous vaccines.Key word: infectious bronchitis disease, inactivated vaccines, hemagglutination inhibition, viral load, challenge.

Different evolutionary trajectories of vaccine-controlled and non-controlled avian infectious bronchitis viruses in commercial poultry.

To determine the genetic and epidemiological relationship of infectious bronchitis virus (IBV) isolates from commercial poultry to attenuated live IBV vaccines we conducted a phylogenetic network analysis on the full-length S1 sequence for Arkansas (Ark), Massachusetts (Mass) and Delmarva/1639 (DMV/1639) type viruses isolated in 2015 from clinical cases by 3 different diagnostic laboratories. Phylogenetic network analysis of Ark isolates showed two predominant groups linked by 2 mutations, consistent with subpopulations found in commercial vaccines for this IBV type. In addition, a number of satellite groups surrounding the two predominant populations were observed for the Ark type virus, which is likely due to mutations associated with the nature of this vaccine to persist in flocks. The phylogenetic network analysis of Mass-type viruses shows two groupings corresponding to different manufacturers vaccine sequences. No satellite groups were observed for Mass-type viruses, which is consistent with no persistence of this vaccine type in the field. At the time of collection, no vaccine was being used for the DMV/1639 type viruses and phylogenetic network analysis showed a dispersed network suggesting no clear change in genetic distribution. Selection pressure analysis showed that the DMV/1639 and Mass-type strains were evolving under negative selection, whereas the Ark type viruses had evolved under positive selection. This data supports the hypothesis that live attenuated vaccine usage does play a role in the genetic profile of similar IB viruses in the field and phylogenetic network analysis can be used to identify vaccine and vaccine origin isolates, which is important for our understanding of the role live vaccines play in the evolutionary trajectory of those viruses.

Infectious bronchitis vaccine virus detection and part-S1 genetic variation following single or dual inoculation in broiler chicks

ABSTRACTAn investigation was undertaken of the extent of genetic variation occurring within infectious bronchitis virus (IBV) vaccine strains following vaccination of day-old broiler chicks. Chicks were divided into seven groups, with two groups receiving single Massachusetts (Mass) vaccinations while the other four were inoculated with combinations of different IBV serotypes; Mass, 793B, D274 and Arkansas (Ark). The remaining group was maintained as an unvaccinated control. Following vaccination, swabs and tissues collected at intervals were pooled and RNA was extracted for detection of IBV by reverse transcription polymerase chain reaction. Positive amplicons were sequenced for the part-S1 gene and compared to the original vaccine strain sequences. Single nucleotide polymorphisms, amino acid variations and hydrophobicity changes were identified and recorded for each sampling point. A total of 106 single nucleotide polymorphisms were detected within 28 isolates. The average single nucleotide polymorphism counts of swab isolates were greater than those found in tissue samples. This translated into 64 amino acid changes; however only six resulted in a change to the hydrophobicity properties. All hydrophobic alterations occurred within swab isolates and the majority were recovered at 3 days post vaccination suggesting such changes to be detrimental to early virus survival. Nucleotide deletions were seen only in the group given the combination of Mass and Ark. Of the 16 sequenced samples in this group, 13 contained the same AAT deletion at position 1033 1035 in the Ark strains. Findings presented in this study demonstrate alteration in the S1 nucleotide sequence following co-administration of live IBV vaccines.

Genetic mutations in live infectious bronchitis vaccine viruses following single or dual in vitro infection of tracheal organ cultures.

Despite regular co-vaccination of two different strains of live infectious bronchitis vaccine viruses, little is known about possible mutations in these viruses following vaccination. As an alternative to chicks, this study used an in vitro infection model to identify single-nucleotide polymorphisms (SNPs) within the part-S1 gene of two live infectious bronchitis virus vaccine strains (793B and Massachusetts) following single or dual inoculation onto tracheal organ cultures. Results indicate that viral titres reduced over the duration of the study; conversely, the amount of detected infectious bronchitis virus genome increased. Results demonstrate a greater number of non-synonymous SNPs in both vaccine strains when they are co-inoculated, compared with the single inoculations. The influence of the increased SNP and hydrophobic properties of the translated proteins on the vaccine viruses' virulence is unknown.

Heterologous live infectious bronchitis virus vaccination in day-old commercial broiler chicks: clinical signs, ciliary health, immune responses and protection against variant infectious bronchitis viruses

ABSTRACTGroups of one-day-old broiler chicks were vaccinated via the oculo-nasal route with different live infectious bronchitis virus (IBV) vaccines: Massachusetts (Mass), 793B, D274 or Arkansas (Ark). Clinical signs and gross lesions were evaluated. Five chicks from each group were humanely killed at intervals and their tracheas collected for ciliary activity assessment and for the detection of CD4+, CD8+ and IgA-bearing B cells by immunohistochemistry (IHC). Blood samples were collected at intervals for the detection of anti-IBV antibodies. At 21 days post-vaccination (dpv), protection conferred by different vaccination regimes against virulent M41, QX and 793B was assessed. All vaccination programmes were able to induce high levels of CD4+, CD8+ and IgA-bearing B cells in the trachea. Significantly higher levels of CD4+ and CD8+ expression were observed in the Mass2 + 793B2-vaccinated group compared to the other groups (subscripts indicate different manufacturers). Protection studies showed that the group of chicks vaccinated with Mass2 + 793B2 produced 92% ciliary protection against QX challenge; compared to 53%, 68% and 73% ciliary protection against the same challenge virus by Mass1 + D274, Mass1 + 793B1 and Mass3 + Ark, respectively. All vaccination programmes produced more than 85% ciliary protection against M41 and 793B challenges. It appears that the variable levels of protection provided by different heterologous live IBV vaccinations are dependent on the levels of local tracheal immunity induced by the respective vaccine combination. The Mass2 + 793B2 group showed the worst clinical signs, higher mortality and severe lesions following vaccination, but had the highest tracheal immune responses and demonstrated the best protection against all three challenge viruses.

Genetic Analysis of the S1 Gene of 4/91 Type Infectious Bronchitis Virus Isolated in Japan

S1 gene sequences for infectious bronchitis virus (IBV) strains of the 4/91 genotype (commonly called 793B) isolated from field outbreaks in Japan were analyzed to ascertain the relationship to 4/91 vaccine strain. Three field isolates (JP/Wakayama/2003, JP/Iwate/2005 and JP/Saitama/2006) from flocks not immunized with a 4/91 type live IBV vaccine and one isolate (JP/Wakayama-2/2004) from a flock immunized with a 4/91 type live vaccine were examined. The amino acid identities among JP/Wakayama/2003, JP/Iwate/2005 and JP/Saitama/2006 were about 98%, whereas the identities to the 4/91 vaccine strain and JP/Wakayama-2/2004 were about 90%. Three of the field isolates, JP/Wakayama/2003, JP/Iwate/2005 and JP/Saitama/2006, were classified into a cluster closely related to French and Spanish isolates, but different from the cluster including the vaccine and JP/Wakayama-2/2004. These results indicate that JP/Wakayama/2003, JP/Iwate/2005 and JP/Saitama/2006 were derived from foreign field isolates, but not from the vaccine strain. On the other hand, the S1 gene of JP/Wakayama-2/2004 revealed high sequence similarity with that of the 4/91 vaccine strain and appeared to be a vaccine-like virus derived from a vaccine. The field isolates of 4/91 genotype IBV could be distinguished from other genotypes by using the BalI and Pst I enzymes in addition to the polymerase chain reaction (PCR) -restriction fragment length polymorphism (RFLP) methods of Mase et al. [16] using Hae II and EcoR I enzymes. Furthermore, the 4/91 vaccine strain and vaccine-like isolate (JP/Wakayama-2/2004) could be differentiated from the other field isolates by Bgl II digestion. This method, therefore, would assist in identification of field isolates of the 4/91 genotype as outbreaks of IBV in vaccinated flocks.

Avian coronavirus infectious bronchitis attenuated live vaccines undergo selection of subpopulations and mutations following vaccination

In this study, we were interested in determining if high titered egg adapted modified live infectious bronchitis virus (IBV) vaccines contain spike gene related quasispecies that undergo selection in chickens, following vaccination. We sequenced the spike glycoprotein of 12 IBV vaccines (5 different serotypes from 3 different manufacturers) directly from the vaccine vial, then compared that sequence with reisolated viruses from vaccinated and contact-exposed birds over time. We found differences in the S1 sequence within the same vaccine serotype from different manufacturers, differences in S1 sequence between different vaccine serials from the same manufacturer, and intra-vaccine differences or quasispecies. Comparing the sequence data of the reisolated viruses with the original vaccine virus, we were able to identify in vivo selection of viral subpopulations as well as mutations. To our knowledge, this is the first report showing selection of a more fit virus subpopulation as well as mutations associated with replication of modified live IBV vaccine viruses in chickens. This information is important for our understanding of how attenuated virus vaccines, including potential vaccines against the SARS-CoV, can ensure long-term survival of the virus and can lead to changes in pathogenesis and emergence of new viral pathogens. This information is also valuable for the development of safer modified live coronavirus vaccines.

S1 gene characteristics and efficacy of vaccination against infectious bronchitis virus field isolates from the United States and Israel (1996 to 2000)

The S1 genes of isolates of avian coronavirus infectious bronchitis virus (IBV) from commercial chickens in the US and Israel (20 isolates from each country) were studied using reverse transcription-polymerase chain reaction restriction fragment length polymorphism and sequencing. Partial sequences spanning the amino terminus region of S1 from amino acid residues 48 to 219, based on the Beaudette strain, were used for analysis. Phylogenetic clustering and high-sequence identity values were used to identify isolates that appeared to be derived from live IBV vaccines used in the two countries. Novel variant strains, unrelated by S1 sequencing and restriction fragment length polymorphism analyses to reference and vaccine strains, were also identified. Based on S1 sequence identity to available vaccines, the potential to use vaccination to control IBV infections was evaluated. Vaccination with commercial live strains Massachusetts (Mass), Arkansas (Ark) or DE/072/92, generally produced immunity against vaccine-related field isolates displaying high S1 sequence similarities (≥90%) to the respective vaccine strains. Immunization with a bivalent vaccine containing the Mass and Ark strains provided good cross-protection, averaging 81% against challenge with five variant isolates from the US having amino acid identity values ranging from 62 to 69% to Mass and from 68 to 83% to Ark, respectively. In contrast, the H120 vaccine strain induced low levels of protection, ranging from 25 to 58% against variant field isolates from Israel with amino acid identity values from 65 to 67%.

Cross‐reactive cellular immune responses in chickens vaccinated with live infectious bronchitis virus vaccine

Summary Two‐week‐old chickens were vaccinated intra‐nasally with a live infectious bronchitis virus (IBV) vaccine (H120). On days 4, 7, 11 and 14 post‐vaccination (p.v.) spleen mononuclear cells (MNC) prepared from control and vaccinated chickens were stimulated in vitro with homologous (strain M41) and heterologous (strains 7 and 793/B) virus antigens. Antigen‐specific lymphoproliferation and interleukin‐2 (IL‐2) and interferon‐y (IFN) production were used to measure cross‐reactive cell mediated immune responses. In antigen‐specific lymphoproliferation assays, it was found that while 4/16 vaccinated birds responded to the homologous antigen, only one responded to an heterologous antigen (strain 7). However, IL‐2 production was seen in the supernatants of spleen MNC from vaccinated chickens stimulated with all three antigens. Production of IFN was also demonstrated in samples stimulated with the homologous and one heterologous (strain 7) antigen. Thus it appears that, following vaccination of chickens with live IBV vaccine, cross‐reactive cellular immune responses occur that vary in magnitude with the strain of IBV used for in vitro stimulation.

Attenuation of Lentogenic Newcastle Disease Virus Strain B-1 by Cold Adaptation

The Hitchner B-1 strain of Newcastle disease virus was plaque-cloned and then serially passaged 36 times in specific-pathogen-free (SPF) chicken embryos incubated at two different temperatures. Virus passaged at a reduced temperature (29 C) was identified as cold-adapted (Ca) and virus passaged at the normal temperature (37 C) was designated non-cold-adapted (non-Ca). The Ca and non-Ca B-1 viruses were compared with the parent B-1 and a commercial B-1 vaccine. In vitro Ca B-1 characteristics included adaptation for more rapid growth at 29 C and the aquisition of temperature sensitivity indicated by substantially reduced growth at 41 C, properties not seen with non-Ca B-1. Embryo mean death times for the Ca virus (140 hr) were longer than for non-Ca B-1 (107 hr) and parent B-1 (121 hr) viruses. The Ca virus retained a rapid (< 2 hr) hemagglutination (HA) elution rate but lost the property of binding the monoclonal antibody AVS-I typical of other B-1 strains. The pathogenicity of the Ca B-1 strain was compared to the non-Ca B-1, parent B-1 strain, and a commercial B-1 strain vaccine in 1-day-old broiler-type chickens. Pathogenicity was evaluated by assessing the severity of respiratory disease signs and the incidence of airsacculitis, perihepatitis, and pericarditis lesions in inoculated chicks. A respiratory disease index was calculated for each B-1 strain based on daily observation scores that determined the presence or absence of disease signs (coughing, rales, labored breathing, death) from 1 to 14 days following intratracheal inoculation with 10(6) 50% egg infective doses of virus per chick. The lower respiratory disease index obtained for the Ca B-1 strain (0.075) indicated it was less pathogenic than the commercial B-1 vaccine (0.296) and the non-Ca (0.478) and parent (0.521) B-1 strains. Ca B-1-infected chicks had only a 5% incidence of air sac lesions, compared to chicks given non-Ca (65%), Hitchner B-1 (65%), or a commercial B-1 vaccine (30%). Immunogenicity tests performed in 1-week-old SPF leghorn chickens demonstrated that Ca B-1 induced complete protection when administered intraocularly as a single entity. However, when Ca B-1 was given in combination with a modified live infectious bronchitis virus vaccine, chickens were only partially protected (60-75%) against Texas GB strain-induced neurotropic velogenic Newcastle disease.

Cell mediated and humoral immune response of chickens to live infectious bronchitis vaccines

A lymphocyte transformation microassay was used to study cell-mediated immune (CMI) responses in chickens following inoculation with live infectious bronchitis virus vaccines H 120 and H 52 and challenge with Massachusetts-41 (M-41). Humoral immunity was monitored for comparison, using haemagglutination inhibition (HI) microassay. Specific stimulation of infectious bronchitis virus sensitised lymphocytes was demonstrated by their lack of response to Mycoplasma synoviae and Newcastle disease virus antigens. Positive infectious bronchitis virus stimulation indices appeared before HI titres and ranged from 2.0 to 7.1 over a period of five to 33 days after primary vaccination with H 120. Revaccination with H 52 produced a strong secondary HI response and a relatively weak CMI response. Challenge of vaccinated and revaccinated birds also resulted in strong HI and weaker CMI secondary responses but the more pronounced CMI responses were in the revaccinated-challenged group. There was no correlation between CMI and HI antibody production but a negative correlation was demonstrated between peak CMI responses after vaccination and severity of clinical symptoms after subsequent challenge.

Response of chicken vaccinated with live infectious bronchitis virus vaccine to killed Newcastle disease vaccine.

Response of chicken vaccinated with live infectious bronchitis virus vaccine to killed Newcastle disease vaccine.