C. L. Yadav

The epidemiology of fasciolosis in ruminants in different geo-climatic regions of north India

Epidemiological studies were conducted on Fasciola giagntica infection in different geo-climatic zones (hills, tarai and plains) in six states of north India during January 2001 to December 2004. Prevalence rates of 10.79, 13.90, 2.78 and 2.35 percent were recorded in cattle, buffaloes, sheep and goats, respectively. Animals in the tarai had the highest prevalence of fasciolosis followed by those in the hills and plains, respectively. The prevalence of infection in cattle and buffaloes was highest during the winters (11.84% cattle, 15.57% buffaloes) followed by summers and rains, respectively. However, the seasonal trends in sheep and goats were the reverse, with the peak prevalence during the rains (4.60% sheep, 2.71% goats). Abattoir studies revealed a higher prevalence in buffaloes (31.14%) than in sheep and goats. Screening of Lymnaea auricularia snails revealed that 5.48% of the snails harboured larval stages of F. gigantica. Also, the snails in the tarai had a higher prevalence (7.28%) of infection compared to those in the plains (1.57%). The results of the present study may help to devise an effective control strategy against fasciolosis in north India.

Genotyping of benzimidazole susceptible and resistant alleles in different populations of Haemonchus contortus from Himalayan and sub-Himalayan regions of North-West India

An allele-specific PCR was standardized to diagnose the mutation (Phe to Try) at residue 200 of the isotype 1 beta tubulin gene responsible for benzimidazole resistance in Haemonchus contortus adult and infective larvae. Adult and infective larvae of Haemonchus contortus were collected from sheep under different managemental practices (intensive and extensive) in temperate Himalayan regions (Mukteshwar and Kedarkhatta), sub-himalayan region (Pantnagar) of Uttarakhand state and subtropical region of Uttar Pradesh (Bareilly) in north-west India. Genotyping of adult H. contortus, collected from abomasi of slaughtered sheep reared under extensive management, by AS-PCR revealed that the frequency of resistant (r) alleles was significantly higher (P < 0.001) at Pantnagar (0.57) as compared to Bareilly (0.25) and Mukteshwar (0.08). Also, genotyping of infective larvae of the parasite from intensively managed sheep farms indicated that the frequency of resistant (r) alleles was significantly higher (P < 0.001) at Pantnagar (0.85) as compared to Kedarkattha (0.70) and Bareilly (0.62). The results revealed that managemental practices followed in the areas under study have a direct bearing on the spread of benzimidazole resistant alleles.

Immune responses against recombinant tick antigen, Bm95, for the control of Rhipicephalus (Boophilus) microplus ticks in cattle

Immune responses against Bm95 recombinant cattle tick antigen and its protective efficacy for control of Rhipicephalus (Boophilus) microplus ticks were determined in experimental crossbred cow calves. Anti-Bm95 antibody titers, as assessed by indirect ELISA, in immunized calves ranged from 196.1+/-13.7 on day 0 to 7979.9+/-312.5 on day 110 post-primary immunization. The rise in antibody titer was statistically significant (p<0.01) throughout the study period. Besides this, constantly higher lymphoproliferative response (LPR), as assessed by lymphocyte stimulation test, was observed from 10 days post-immunization, but a positive LPR of antigen stimulated cells in immunized animals was recorded only on day 50 and day 70 post-immunization. Following challenge of immunized calves with larvae of R. microplus, significant increase (p<0.01) in rejection percentage, mean number of damaged ticks, mean percentage of dead ticks, and decrease in engorgement weight were recorded in immunized animals. Also, there were significant differences (p<0.01) in preoviposition period, oviposition period, egg mass weight and percent hatchability between the immunized and control calves. The percent reduction in number of adult females in vaccinated calves, reduction in mean weight of egg masses, percent reduction in mean weight and reduction in fertility of engorged females collected from vaccinated calves were determined and the efficacy of Bm95 recombinant cattle tick antigen was 81.27%.

Detecting mutation in sodium channel gene in Rhipicephalus (Boophilus) microplus collected from northern India for genotyping deltamethrin-susceptible and deltamethrin-resistant alleles

Rhipicephalus (Boophilus) microplus is an economically significant pest of livestock in India. Allele-specific polymerase chain reaction (PCR) was employed to detect Phe→Ile substitution in the sodium channel gene in different populations of Rhipicephalus microplus collected from foothills (Kashipur, Pantnagar, Nagla and Dehradun) and high-altitude areas (Pithoragarh, Almora and New Tehri) of Uttarakhand state in northern India. The allele-specific PCR assay revealed 85% larvae to be homozygous susceptible, 3% to be homozygous resistant and 12% to be heterozygous. Homozygous resistant genotypes were recorded in two tick populations (Kashipur, 13% and Pantnagar, 4%); heterozygous genotypes in four tick populations (Kashipur, 45%; Pantnagar, 17%; Almora, 14%; and New Tehri, 3%) and 100% homozygous susceptible genotypic frequencies in three tick populations (Nagla, Dehradun and Pithoragarh). The highest rate of mutant allele (R) occurred in tick populations of Kashipur (35%) (p < 0.05), followed by Pantnagar (13%), Almora (7%) and New Tehri (1%). The results of the study suggested that frequent monitoring of the level of pyrethroid resistance was required to formulate any control strategy against ticks and hence extend the life of the existing acaricide(s).