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Kerala Veterinary and Animal Sciences University, Wayanad

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20171
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Subject: Veterinary Microbiology × Author: MANJU SOMAN × Thesis Type: Ph.D ×
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    ThesisItemOpen Access
    DEVELOPMENT OF A MODIFIED INACTIVATED VACCINE AND ITS COMBINATION WITH A RECOMBINANT PROTEIN AGAINST LEPTOSPIROSIS
    (COLLEGE OF VETERINARY AND ANIMAL SCIENCES MANNUTHY, THRISSUR, 2017-12-30) MANJU SOMAN; M.Mini
    The study was taken up with an aim to develop a foolproof technique for prevention of leptospirosis. It involved the development and immunity evaluation of a modified whole cell inactivated vaccine incorporating the predominant leptospiral serovars, Australis, Autumnalis and Pomona in hamsters. The study also ascertained the genus specific immunoreactivity of a truncated recombinant leptospiral LigA protein and its combination with the modified inactivated vaccine, in hamsters. The immunomodulatory effect of incomplete Freund’s adjuvant (IFA) and the aluminium hydroxide gel adjuvant in hamsters was also assessed. Primers were designed for a highly immunodominant region of the ligA gene, spanning nucleotides from 1873 to 3363. The PCR amplified 1491 bp fragment of ligA DNA was cloned into pET -32a vector and expressed in E.coli BL21(DE3). The conditions optimum for expression of this recombinant protein were analysed. Maximum expression was obtained following induction with 2 mM IPTG, at an incubation temperature of 28o C following six hours of incubation at 200 rpm shaking speed. The Ni-NTA purified rLigA protein was used for immunization of hamsters. The optimum concentration of the rLigA protein and modified inactivated vaccine required for immunisation of hamsters, was determined by immunising four sets of hamsters with four different concentrations of the antigens, 14 days apart. It was revealed that the concentration of 80µg/ 40 µg of Lig A protein and 108 leptospires per millilitre gave the maximum IgG ELISA and MAT titres.Six vaccine groups were set up for six different vaccine combinations which included the modified inactivated vaccine, rLigA protein and a combination of the modified inactivated vaccine and rLigA protein. Adjuvants IFA and aluminium hydroxide were used in the study. The serum antibody titres on days 0, 7,14 and 27 were determined by MAT and recombinant IgG ELISA The virulence of laboratory strains of Leptospira interrogans serovars Pomona (homologous) and Icterohaemorrhagiae (heterologous) was enhanced by serial passage in hamsters and these were used as challenge organisms in the study. The LD50, of the serovars Pomona and Icterohaemorrhagiae, in hamsters was determined as 106.893 organisms and 107.38 organisms, respectively and the challenge was carried out with 100 LD50 (≈109 ) organisms, on 28th day post first immunization. Challenge studies revealed maximum protection levels of 80 to 100 per cent in groups immunised by modified inactivated vaccine alone and combination of rLigA and inactivated vaccine. Groups immunised with rLigA protein alone showed 60-70 per cent protection to both serovars. The highest MAT titres to homologous and heterologous serovars were presented by the groups immunized with a combination of rLigA protein and modified inactivated vaccine. These groups elicited higher MAT titres to heterologous serovar Icterohaemorrhagiae compared to whole cell vaccine alone, which indicated the genus specificity contributed by the partial rLigA protein. It also showed that the inactivated vaccine and recombinant protein compliment each other in increasing the respective immunogenicity. The study revealed that IFA adjuvanted rLigA protein could elicit the maximum ELISA titres in hamsters, followed by the group immunised by IFA adjuvanted rLigA protein combined with modified inactivated vaccine. The IFA adjuvanted vaccine groups showed higher ELISA titres compared to those adjuvanted with aluminium hydroxide but the aluminium hydroxide adjuvanted vaccine groups showed consistent increase in antibody titres.