Short Communication

Immune Responses to Intermediate Strain IBD Vaccine atDi¡erent Levels of Maternal Antibody in Broiler Chickens

K. Kumar, K.C.P. Singh* and C.B. PrasadDepartment of Veterinary Microbiology, Bihar Veterinary College, Patna 800014, India*Correspondence

Kumar, K., Singh, K.C.P. and Prasad, C.B., 2000. Immune responses to intermediate strain IBD vaccine atdi¡erent levels of maternal antibody in broiler chickens.Tropical Animal Health and Production, 32(6), 357^360

Keywords: age, chickens, infectious bursal disease, maternal antibody, serology, vaccine

Abbreviations: AGPT, agar gel precipitation test; dpv, days post vaccination; IBD, infectious bursaldisease; io, intraocular; QAGPT, quantitative agar gel precipitation test; SE, standard error

INTRODUCTION

Infectious bursal disease (IBD) is widely prevalent in the region around Patna.Vaccination is the most important method of controlling the disease. Since thehatcheries from which chicks are procured vaccinate their parental stock with IBDvaccine, the chicks contain relatively high levels of antibody at the time of hatching.Wide variations in the level of maternal antibody have been reported in newly hatchedchicks and the rate of decline of maternal antibody has also been found to vary (Wyethand Chettle, 1990; Goddard et al., 1994). Therefore, it is imperative to study theimmune response at varying levels of maternal antibody to the intermediate strain IBDvaccine that is now most commonly used to control the disease.

MATERIALS AND METHODS

Antigen: The Poona strain of IBD virus in the form of a 50% bursal homogenate wasused as the reference antigen throughout this study.

Antiserum: Hyperimmune serum raised in our laboratory against a vaccine strain ofthe virus (Georgia strain, Indovax Pvt Ltd, Hissar, India) was used throughout as thereference antiserum. The serum was inactivated at 568C for 30 min and stored at 08C.

Vaccine: Cell culture-adapted, live, intermediate IBD virus vaccine (Georgia strain)

Tropical AnimalHealth and Production, 32 (2000) 357^360# 2000 Kluwer Academic Publishers. Printed in the Netherlands

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available in freeze-dried form (Indovax) was used. The vaccine was reconstituted indiluent supplied with the vial and used within a few hours after reconstitution.

Quantitative agar gel precipitation test (QAGPT): The level of precipitating antibodywas determined by the method of Cullen and Wyeth (1975) with some modi¢cations.

Experimental design: Eighty day-old broiler chicks were obtained from Golden RoseHatchery, Patna. The chicks were divided into four groups, each containing 20 birds.Each group was further subdivided into two subgroups, each comprising 10 birds. The¢rst subgroups in each group received IBD vaccine at a dose rate of 0.2 mlintraocularly at 0, 7, 14 or 21 days of age, respectively, while the second subgroupfrom each group received the same volume of phosphate-bu¡ered saline by the sameroute to serve as the unvaccinated control for the corresponding vaccinated subgroup.The maternal antibody level of all the chicks in the di¡erent subgroups was determinedby QAGPT just before vaccination/inoculation and the mean antibody level wascalculated separately for each subgroup. The vaccinated and the correspondingunvaccinated control subgroups were maintained separately under the same nutri-tional and managerial conditions. Serum samples were collected from 5^8 birds ineach subgroup at 7, 14, 21 and 28 days after inoculation and the level of antibodies wasdetermined by QAGPT.

Statistical analysis: Analysis of variance was performed as described by Snedecor andCochran (1967).

RESULTS

The mean antibody titres are shown in Table I. The level of maternal antibody inprevaccinated sera was highest at day-old and had disappeared by 21 days of age.These titres did not di¡er signi¢cantly from the pre-inoculated QAGPT titres ofcontrol birds for the corresponding age interval (Table I). The greatest immuneresponse was obtained when the intermediate vaccine was given at 21 days of age,when there was no maternal antibody present. The poorest immune response wasobserved in day-old vaccinated chicks, which had the highest level of maternalantibody at the time of vaccination.

DISCUSSION

Day-old chicks with the highest level of maternal antibody at the time of vaccinationshowed a very poor immune response to IBD vaccine. This agrees with the observa-tions of earlier workers that a high level of maternal antibody adversely a¡ects theimmune response to IBD vaccine (Mazariegos et al., 1990; Wyeth and Chettle, 1990;Goddard et al., 1994). It suggests that even the intermediate vaccine is not e¡ective inthe face of high levels of maternal antibody. The e¤cacy of the immune response is

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dependent on immunological maturity as well as on antigenic stimulation ofimmunocompetent cells during the early post-hatching period. Maturity of theimmune system occurs by about 5 months of age (Gordon and Jordan, 1982) butmuch antigenic stimulation, which leads to antigen-driven multiplication of immuno-compenent cells, takes place in the ¢rst few weeks of life when the chick experiences ahost of microorganisms after coming out of the sterile environment inside the egg(Tizard, 1996). The delayed seroconversion observed in 0^7-day-old chicks in thepresent study may be explained on these grounds.The ¢ndings suggest a steady improvement in the immune response to IBD vaccine

with age and as thematernal antibody level at the time of vaccination declines.This maybe attributed in part to a relatively larger proportion of vaccine virus escapingneutralization by maternal antibody at the time of vaccination (Skeeles et al., 1979;Coletti et al., 1994; Goddard et al., 1994). Beside the age factor, the low level ofmaternalantibody present in 14-day-old chicks may have played a role in the better immuneresponses at this age. Kumar (1999) observed better immune responses to IBD vaccinein 14-day-old chicks carrying maternal antibody than in the chicks of same age groupwithout maternal antibody. At low levels of maternal antibody, as in 14-day-old chicks,there may be formation of immune complex with vaccine virus, which could e¡ect abetter immune response. A number of workers have reported the stimulatory e¡ect ofimmune complex on the immune response of birds (Jeurissen et al., 1998).

TABLE IImmune response to IBD vaccine (intermediate strain) in broiler chickens

Mean+SE of titre of serum samplesAge at positive with the QAGPT at days after vaccination

vaccination öööööööööööööööööööööööööGroup (in days) 7 14 21 28

1 Day-old 1.63+0.829a 3.00+0.327c 1.00+0.267a ^ve(8) (8) (8) (8)

2 7 1.71+0.286a 2.00+0.309a 2.14+0.261a 2.14+0.143a

(7) (7) (7) (7)

3 14 1.00+0.218a 1.71+0.184a 3.57+0.369c 3.71+0.359c

(7) (7) (7) (7)

4 21 2.00+0.239a 3.00+0.286c 4.63+0.324c 4.75+0.250c

(8) (8) (8) (8)

Figures in parentheses indicate number of observations

``^ve'' indicates all serum samples negative in AGPTa,cMeans with di¡erent superscripts di¡er signi¢cantly (p50.05)

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Several other workers have reported a better immune response to IBD vaccines inthe absence of maternal antibody, similar to that observed in the chicks vaccinated at21 days of age. This may be due to the availability of all the vaccine virus to elicite animmune response in the vaccinated birds (Naqi et al., 1982; Coletti et al., 1994). Theresults of the present study suggest that the ideal age for vaccination of chickensagainst IBD is 21 days, when the maternal antibody is not detectable and so does notinterfere with the vaccine virus. However, care needs to be taken to ensure thatvaccination at this age does not leave a window of susceptibility before a su¤cientlevel of protective antibody is attained.

ACKNOWLEDGEMENTS

The authors thank the Associate Dean-cum-Principal, Bihar Veterinary College,Patna, for providing the necessary facilities and the Rajendra Agricultural University,Pusa, Bihar, for ¢nancial assistance in the form of a postgraduate fellowship to the ¢rstauthor to carry out this work.

REFERENCES

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Cullen, G.A. and Wyeth, P.J., 1975. Quantitation of antibodies to infectious bursal disease. VeterinaryRecord, 97, 315

Goddard, R.D., Wyeth, P.J. and Varney, W.C., 1994. Vaccination of commercial layer chicks againstinfectious bursal disease with maternally derived antibodies.Veterinary Record, 135, 273^274

Gordon, R.F. and Jordan, F.T.W., 1982. The avian immune system. In: Poultry Diseases, 2nd edn, (EnglishLanguage Book Society and Baillie© re Tindall, London), 328^341

Jeurissen, S.H.M., Janse, E.M., Lehrabach, P.R., Haddad, E.E., Avakian, A. and Whit¢ll, C.E., 1998. Theworking mechanism of an immune complex vaccine that protects chickens against infectious bursaldisease. Immunology, 95, 494^500

Kumar, S., 1999. Immune response of invasive intermediate strain infectious bursal disease virus vaccine inbroiler chickens, (MVSc thesis submitted to Rajendra Agricultural University, Bihar, Pusa, Samastipur,India)

Mazariegos, L.A., Lukert, P.D. and Brown, J., 1990. Pathogenicity and immunosuppressive properties ofinfectious bursal disease `intermediate' strains. Avian Disease, 34, 203^208

Naqi, S.A., Marquez, B. and Sahin, N., 1982. Maternal antibody and its e¡ect on infectious bursal diseaseimmunization. Avian Disease, 27, 623^631

Skeeles, J.K., Lukert, P.D., Fletcher, O.J. and Leonard, J.D., 1979. Immunisation studies with a cell cultureadapted infectious bursal disease virus. Avian Disease, 23, 456^465

Snedecor, G.W. and Cochran,W.G., 1967. Statistical Methods, 6th edn, (Oxford University Press and IBN,Calcutta)

Tizard, I.R., 1996.Veterinary Immunology, 5th edn, (W.B. Saunders, London)Wyeth, P.J. and Chettle, N.J., 1990. Use of infectious bursal disease vaccines in chicks with maternally

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(Accepted: 20 October 1999)

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