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Subject: Veterinary Parasitology × Author: SAI SUMANTH, P × End date: 2022 × Start date: 2022 × Thesis Type: M.V.Sc. ×
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    ThesisItemOpen Access
    OCCURENCE OF OVINE INTRACELLULAR HAEMOPROTOZOAN PARASITES IN ANDHRA PRADESH AND THEIR ASSOCIATION WITH DRB1 GENE POLYMORPHISM
    (SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA, 2022-03) SAI SUMANTH, P; SREEDEVI, C (MAJOR); JYOTHI SREE, CH; SUDHAKAR, K
    The present study was carried out to detect Babesia spp. and Theileria spp. in sheep from Andhra Pradesh and to determine the relationship between ovine MHC-DRB1 gene polymorphism and genetic resistance/susceptibility to babesiosis and theileriosis. A total of 249 blood samples including healthy (n=224) and those showing clinical signs (n=25) suggestive of haemoprotozoan infection were collected from sheep from different zones in Andhra Pradesh. The blood samples were initially processed to detect Babesia and Theileria spp. by microscopic examination. Microscopic examination of Giemsa-stained thin blood smears revealed 12.9 (32/249) per cent prevalence of Theileia spp. DNA was isolated from each sample by modified high salt method and amplified by polymerase chain reaction for simultaneous detection of 18S rRNA gene of Babesia and Theileria spp. The Babesia/Theileria genus specific PCR amplified only 430 bp 18S rRNA specific to Theileria spp. in 34.9 (87/249) per cent of sheep samples. None of the samples yielded amplification specific for Babesia spp. or mixed infections. Samples positive for Theileria spp. were further subjected to semi-nested PCR for species specific differentiation. Out of 87 theileriosis sheep, 76 (87.6%) were found to be positive for T. luwenshuni infection and eleven sheep (12.4%) were positive for mixed infection with T. luwenshuni and T.ovis. Overall, the prevalence of T. luwenshuni and T. ovis in sheep was 34.9 (87/249) and 4.4 (11/249) per cent, respectively. Age was found to be significantly (P=0.05) associated with positivity for Theileria infection in sheep being high in adult animals. The prevalence of theileriosis in sheep was not significant with respect to gender, breed and region. The Ovar-DRB1 exon 2 of 249 sheep were amplified by nested PCR from DNA samples. The 296 bp PCR products were digested by REnase BstNI, which generated three genotypes ‘aa’ (86 bp, 87 bp and 123 bp), ‘ab’ (86 bp, 87 bp, 123 bp, and 210 bp) and ‘bb’ (86 bp and 210 bp) with frequencies of 72.0, 22.0 and 6.0 per cent, respectively and two alleles ‘a’ and ‘b’ with frequencies of 0.82 and 0.18, respectively. The χ2 test of independence revealed a significant association (P<0.05) between genotypes and infection status in sheep. Though the frequency of ‘aa’ genotype was more in both the healthy (66.7) and infected (81.6) group, a significantly high frequency of ‘bb’ (6.8) and ‘ab’ (26.5) genotypes was observed compared to the infected group. A proportion of 39.7 per cent of ‘aa’, 23.2 per cent of ‘ab’ and 21.4 per cent of ‘bb’ genotypes were positive for theileriosis among the respective genotype sheep. The frequencies of ‘bb’ genotypes were significantly (P<0.05) higher in the healthy group compared with the theileriosis sheep, which implied that there was an association between these genotypes and theileriosis resistance or susceptibility. Among theileriosis positive sheep the genotype frequencies of ‘aa’, ‘ab’ and ‘bb’ pattern were 81.6 (71), 14.9 (13) and 3.4 (3) per cent, respectively. The frequency of ‘a’ and ‘b’ allele among infected sheep was 0.89 and 0.11 and is not consistent with Hardy-Weinberg equilibrium (P<0.01). The corresponding allele frequencies in the healthy sheep were 0.80 and 0.20.