EVALUATION OF TRIVALENT INACTIVATED VACCINE FOR BLUETONGUE AT FARM LEVEL
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Date
2007-10
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
ABSTRACT:
The present study was taken up to evaluate the efficacy of trivalent (BTV-2, 9 and 15) BEI inactivated montanide adjuvanted bluetongue (BT) vaccine in farm sheep. Further attempts were also made to compare single dose and double dose regimens. Comparison was also made between monovalent and trivalent inactivated bluetongue vaccines. Three serotypes grown in vero cells were successfully inactivated by 0.1 M BEI + 0.04% Formalin. Each dose of trivalent vaccine consisted of 106.0 TCID50 of each of BTV 2, 9 and 15 serotypes with montanide as adjuvant. Vaccinated sheep were monitored for antibody by AGID, c-ELISA and SNT. AGID detected antibody to BTV in six vaccinated sheep earliest on day 7 post vaccination (PV) while a maximum of 17 out of 19 animals were positive on day 28 PV. AGID did not detect antibody in two of the vaccinated animals during the experimental period. c-ELISA detected immune response to BTV in all the vaccinated sheep on day 7 PV. Serotype specific SN50 (log2) titers in vaccinates ranged from 2 – 6.78. Higher titers were noticed against BTV-2 and lower titers against BTV 9 and BTV 15. Two animals found negative by AGID were also negative by SNT. No significant difference was found in the immune response between the single dose group and double dose group indicating that booster vaccination may not have any beneficial effect. Among sheep vaccinated with monovalent inactivated BT vaccine (BTV 2 or 9 or 15), AGID detected immune response earliest on day 7 PV in BTV 2 vaccinated sheep and on day 14 PV in BTV 15 vaccinated sheep. AGID detected antibody in all the 6 animals given BTV 2 on day 28 PV while only 5 out of 6 animals seroconverted against BTV 15 on day 57 PV. However none of the animals responded against BTV 9. c-ELISA detected antibody to BTV in the BTV 2 and BTV 15 vaccinated groups. No antibody was detected in group given BTV 9. There was no difference in the c-ELISA response between single and double dose groups. Higher PI values in c-ELISA were noticed in the animals given trivalent vaccine compared to the titers in monovalent groups. Challenge studies were conducted in 3 groups of sheep given trivalent inactivated BT vaccine, with the blood positive for BTV 2 or BTV 9 or BTV 15 after 150 days of vaccination. All the 3 controls showed pyrexia and BTV could be demonstrated by RT-PCR. In vaccinated groups one animal from each group showed pyrexia and was positive for BTV RNA by RT-PCR. It is concluded that trivalent BEI inactivated BT vaccine was effective in eliciting good humoral immune response.
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