Introduction
The increase in the growth of poultry production in recent times is attributed to increased demand for animal protein as a result of population growth [1,2]. One of the major constraints to the development of the poultry industry is outbreaks of diseases [3]. Among the diseases that cause significant losses in chickens in developing countries is infectious bursal disease (IBD), which causes high morbidity and mortality rates [4,5].
The IBD is an acute, highly contagious, immunosuppressive infection of young chickens caused by the IBD virus (IBDV) [6,7]. IBD virus belongs to the genus Avibirnavirus in the family Birnaviridae, and the genome consists of double-stranded RNA segments, designated A and B, enclosed within a nonenveloped icosahedral capsid [8,9]. The IBDV destroys lymphocytes and macrophages and, as a result, suppresses the immune system, leading to vaccination failure and concurrent infections [10–12]. Vaccination and strict biosecurity measures constitute effective methods of controlling IBD, although, in practice, control is largely dependent on active vaccination [7].
Most commercially available conventional live IBDV vaccines are based on classical virulent strains. Those classified as mild vaccines exhibit only poor efficacy in the presence of certain levels of maternally derived antibodies (MDAs) and against very virulent IBD virus (vvIBDV). Intermediate and intermediate plus or hot vaccines have a much better efficacy by breaking through higher levels of MDAs, but they can induce moderate to severe bursal lesions and may not fully protect chickens against infection by vvIBDV or antigenic variant strains [13].
MDAs also provide protection against mortality, lesions of the bursa of Fabricius (BF) and immunosuppression due to IBD. Thus, the response to vaccination can be adversely affected by MDAs, as some IBD vaccines may be neutralized by MDAs [14–16]. There is a paucity of data on the efficacies of commercial live IBD vaccines on antibody (Ab) decay and response to IBDV infection in chickens in Nigeria. Also, information on the response of chickens to Newcastle disease (ND) vaccine La Sota following vaccination with commercial live IBD vaccines in Nigeria is not available. Therefore, in this study, the efficacies of five commercial live IBD vaccines on Ab decay and response to a vvIBDV and ND vaccine La Sota were assessed in Institute de Selection Animale (ISA) brown chicks.
Materials and Methods
Study location
The experiment was carried out in the Poultry Research Pen of the Ahmadu Bello University Veterinary Teaching Hospital (ABUVTH), Nigeria.
Ethical clearance
The Ahmadu Bello University Committee on Animal Use and Care (ABUCAUC) granted the ethical clearance for this study.
Experimental chickens
Three hundred and fifty ISA Brown 1-day-old chicks were obtained from a commercial hatchery and to the Poultry Research Pen.
Housing and management
The poultry research pen was thoroughly cleaned, washed and disinfected before the arrival of the birds. Also, there was effective rodent and insect control. The chicks were brooded on deep litter and provided with a floor space of 0.10 m2 per bird. Wood shaving served as the litter material and feed, and water was provided ad libitum.
IBD vaccines
Available commercially live IBD vaccines (Bur-706, MB-Strain, B87-Strain, Bursa-B2K, and HIPRA) were purchased from Afrivet Services Konsults, Abuja, Nigeria.
ND vaccine La Sota
ND vaccine La Sota manufactured by the National Veterinary Research Institute (NVRI) Vom, Plateau State, Nigeria, was purchased from NVRI Reference Laboratory; care of Kano State Veterinary Hospital Kundila, Unguwa Uku, Tarauni Local Government Area, Kano State, Nigeria.
Infectious bursal disease virus
A characterized (vvIBDV suspension (109.76CID50/ml) [17] was obtained from the Department of Veterinary Medicine, Faculty of Veterinary Medicine, Ahmadu Bello University (A.B.U) Zaria, Nigeria.
Experimental design
The 350 1-day-old ISA brown chicks were randomly assigned into seven groups (A, B, C, D, E, F, and G) of 50 chicks each. Chicks in groups A, B, C, D, and E were vaccinated with Bur-706, MB-Strain, B87-Strain, Bursa-B2K, and HIPRA live IBD vaccines (at 0.5 ml/chick orally), respectively, at 14 and 28 days of age (doa), and challenged with the vvIBDV (at 0.1 ml/chick orally) at 35 doa. Groups F and G served as positive and negative controls, respectively. At 42 doa, all groups were vaccinated with ND vaccine La Sota. Blood was collected at 1, 7, 14, 21, 28, 35, 42, and 49 doa, and serum was harvested. The serum was analyzed for IBDV Ab titres using enzyme-linked immunosorbent assay (ELISA) and ND Ab titres using a haemagglutination inhibition (HI) test.
Serological tests
ELISA was carried out according to the method described by BIOCHEK SMART VETERINARY DIAGNOSTICS; Zul Nr: BGVV-B 308, Lot/Ch B: CH4383, SLD 88P Ascot, UK. The IBDVAb titre was calculated automatically using software [18]. Serum samples with the S/P ratio (S=serum sample and P=positive control) ≤ 45 log10 were considered negative. Ratios >45 log10 (titres higher than 65 og10) were considered protective, as indicated in the BIOCHEK SMART VETERINARY DIAGNOSTICS ELISA Kit manual.
ND Ab titre was determined using the HI test as described by OIE [19].
Data analyses
Data were expressed as mean ± SE of the mean (Mean ± SEM). These were subjected to repeated measure one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison post-hoc tests. Values of p ≤ 0.05 were considered significant. GraphPad Prism 5.0 for Windows (GraphPad Software, San Diego, CA) was used for the statistical analysis.
Results
IBD virus ELISA Ab titres
From 1 to 14 doa, the IBDV ELISA Ab titres decreased in all groups of chickens and showed no significant (p > 0.05) differences. At 21 doa (7 days postfirst vaccination), there was significantly (p < 0.05) increased ELISA Ab titres in groups A to E compared to F and G. Also, at 35 doa (7 days postsecond vaccination), the ELISA Ab titres were significantly (p < 0.05) increased in groups A to E compared to F and G. At 42 (7 days postchallenge dpc), there was a decrease in IBDV ELISA Ab titre in groups A to E, but an increase in group F compared to their respective levels at 35 doa. This was followed by a significant (p > 0.05) decrease in the IBDV ELISA Ab titres in groups A to F at 49 doa (14 dpc); but this titre was significantly (p < 0.05) higher in A to E than in F at 42 and 49 doa (Fig. 1).
ND HI Ab titres
The ND HI Ab titre decreased in all groups of chickens and showed no significant (p > 0.05) differences from 1 to 35 doa. At 42 doa, the HI Ab titre was significantly (p < 0.05) higher in groups A to E than in F. At 49 doa, the HI was significantly (p < 0.05) increased in all groups of chickens, with the highest in G followed by D and the least in F (Fig. 2).
Discussion
Chicks screened for antibodies to IBDV at 1-day-old showed that they had protective ELISA Ab titre, which persisted up to 7 doa and declined by 14 doa. These antibodies are indicative of MDA resulting from passive transfer from breeders to the chicks [20,21], as there was no history of vaccination of the chicks against IBD. The implication of MDA above the protective level at 1 and 7 doa in this study is that chicks may not succumb to IBDV infection/vaccination if they were to be challenged/vaccinated during these periods. This nonresponse might be associated with infection/vaccine virus neutralization by the MDA [16].
Figure 1.
Mean IBD ELISA Ab (log10) titre of commercial pullets vaccinated with Bur-706 (A), MB-Strain (B), B87-Strain (C), Bursa-B2K (D), and HIPRA (E) at 14 and 28 days of age and challenged with a vvIBDV at 35 days of age. Values with different alphabets on the same day differ significantly at p < 0.05.
Figure 2.
Mean ND HI Ab (log2) titre of commercial pullets vaccinated with Bur-706 (A), MB-Strain (B), B87-Strain (C), Bursa-B2K (D), and HIPRA (E) at 14 and 28 days of age and challenged with a vvIBDV at 35 days of age. Values with different alphabets on the same day differ significantly at p < 0.05.
The decrease in MDA below the protective level in chicks at 14 doa in this study is consistent with that reported in other studies [20,21]. In another study, there was a slight variation in IBD MDA decrease below protective level [6,22]. Differences in the breed of chicks, strains of vaccine virus used in the parent stocks, and time of Ab assay might be responsible for this variation in MDA decrease. The decrease in MDA to below protective levels in all groups of chicks at 14 doa in the present study suggests that the chicks might be susceptible to IBDV infection/vaccination if challenged/vaccinated as there might be no complete virus neutralization by the MDA.
At 21 and 35 doa, the significantly higher IBDV ELISA Ab titre in groups A to E indicates that there was a vaccine taken in this study. This, therefore, suggests that all the live vaccines assessed were immunogenic as they resulted in Ab production, that is, Ab due to vaccination. The significant decrease in IBDV ELISA Ab titre in groups A to E at 42 doa (7 dpc) might be due to possible virus neutralization by the protective IBDV Ab [16]. On the other hand, the slight increase in IBDV ELISA Ab titre in group F might be associated with Ab production following the IBDV challenge at 35 doa, that is, Ab due to infection [23]. These suggestions were made as the ELISA kit used in this study could not differentiate between IBDV Ab due to vaccination and those due to infection. At 49 doa (14 dpc), the decrease in IBDV Ab titre in all groups might be indicative of spontaneous Ab breakdown over time. However, the higher IBDV Ab titre in groups A to E compared to F, despite a decrease from their respective values at 42 doa, reiterates the immunogenicity of the live vaccines used in this study.
The HI Ab titre for ND at 1-day-old for all groups suggests a passive transfer of MDA from parent stocks as previously suggested for IBDV Ab. This could indicate the possible protection of all the chickens against ND [21,24]. The decrease in ND MDA up to 35 doa might be associated with catabolism of the MDA due to their nutritional role and/or spontaneous breakdown over time [16,25]. At 42 doa, the slight increase in HI Ab titre in groups A to F might be linked to the nonspecific immune response induced by the vvIBDV challenge. However, this speculation requires further investigation.
The increased ND HI Ab titre in all groups at 49 doa indicates that NDV La Sota was immunogenic, thus suggesting vaccine take. However, the higher HI Ab in groups A to E compared to F suggests that they were less immunosuppressed, probably as a result of protection against the IBDV challenge and/or had enhanced immune stimulation by the initial IBDV vaccinations at 14 and 28 doa.
The outcome of this study, therefore, suggests that the efficacy of each live IBDV vaccine and their possibility of interfering with MDA should be determined before their use for vaccination. In addition, the MDA of chicks should be determined before vaccination to avoid possible neutralization, which may lead to failed immunization. This is because a lack of this information about live vaccines would result in difficulty in controlling IBD especially due to vvIBDV.
Conclusion
The live vaccines (Bur-706, MB-Strain, B87-Strain, Bursa-B2K, and HIPRA) were immunogenic following vaccination. The vaccines decreased the decay of IBDV Ab and mitigated the decreased response to ND vaccine La Sota in the chicks following the vvIBDV challenge, with more effects induced by Bursa-B2K. The effects of these live vaccines on the bursa of Fabricius and other immune organs require further investigation.
Acknowledgments
The authors wish to acknowledge the committed efforts of Mr. Edima Abaja, Mr. David Leo, and Mal. Lawal Musa of the Veterinary Teaching Hospital, Department of Veterinary Medicine, Department of Veterinary Surgery and Radiology, respectively, of Ahmadu Bello University, Zaria.
