Stuti Vatsya

Evaluation of acaricide resistance mechanisms in field populations of Rhipicephalus (Boophilus) microplus collected from India

ABSTRACT A study was conducted to monitor the status of deltamethrin resistance in field populations of Rhipicephalus (Boophilus) microplus from different geographical locations of Uttarakhand state in northern India and mechanisms involved therein. The highest 50% lethal concentration (LC50) was recorded for the Kashipur population of ticks [0.0175%; resistance factor (RF) = 34.26] followed by Nagla (0.00273%; RF 5.35), Dehradun (0.00266%; RF 5.21), Pantnagar (0.002402%; RF 4.71), Almora (0.00164%; RF 3.21), and the lowest was recorded for the ticks from New Tehri (0.00104%; RF 2.04) when compared with the reference susceptible Pithoragarh strain (LC50 0.00051%; RF 1.0). The in vitro laboratory evaluation revealed three tick populations to have deltamethrin-resistant phenotypes (RF > 5); two populations to be tolerant (RF 3–5) and one population to have susceptible phenotypes (RF < 3). Synergism studies revealed the likely involvement of monoxygenases (minor role) and esterases in the resistant phenotypes of Nagla ticks; the involvement of esterases in imparting resistance in Dehradun ticks; and no role for the metabolic detoxification mechanism in Kashipur ticks. This is the first report from India describing the development of deltamethrin resistance in R. microplus. The results suggest that integrated management of ticks including strategic and judicious use of acaricides, is required before deltamethrin resistance becomes established in this part of the country and spreads to other areas.

Detection of benzimidazole resistance in gastrointestinal nematodes of sheep and goats of sub-Himalyan region of northern India using different tests.

The present investigation was planned with the objective of studying the status of benzimidazole (BZ) resistance in gastrointestinal nematodes (GIN) of sheep and goats of different agro-climatic zones of sub-Himalyan region of northern India using in vivo faecal egg count reduction test (FECRT) and in vitro tests namely egg hatch assay (EHA) and larval development assay (LDA). Out of fourteen flocks, FECRT detected resistance in eight flocks (two sheep flocks and six goat flocks) with FECR% ranging from 54.95 to 90.86. Pre treatment coproculture contained predominantly Haemonchus contortus, followed by Trichostrongylus spp., Oesophagostomum and Strongyloides, while post treatment coproculture results showed that only H. contortus survived fenbendazole (FBZ) (in FECRT) or thiabendazole (TBZ) (in LDA) treatment except in three flocks of Tarai region {one sheep flock (Us1), and two goat flocks (Ug1 and Ug5)} where BZ resistant Trichostrongylus were also detected. The GIN of those eight farms which were found resistant by FECRT were also detected resistant by EHA. Arithmetic mean and range of ED50 value of susceptible group was found to be 0.059 μg/ml and 0.037-0.096 μg/ml, respectively, and the same for the resistant group were found to be 0.119 μg/ml and 0.101-0.147 μg/ml, respectively. With LDA, the arithmetic mean and range of LC50 value of susceptible group was found 0.0030 μg/ml and 0.001-0.005 μg/ml, respectively, and those of resistant group was found 0.0105 μg/ml and 0.009-0.012 μg/ml, respectively. The values of Spearman rank correlation coefficient indicated that negative correlation was found between FECR% and ED50 and between FECR% and LC50 while positive correlation existed between ED50 and LC50 value and the p-values indicated that these correlations were statistically highly significant. In the present study, FECRT and EHA gave comparable results with regard to detection of BZ resistance in GIN in sheep and goats. Although with LDA, the threshold LC50 value could not be established as for EHA but LDA indicated the presence of low level of resistance in GIN of both sheep and goats. For effective worm control, regular monitoring for anthelmintic resistance is important to know the status of anthelmintic efficacy in a particular agro-climatic zone. The baseline information thus generated will enable timely management of benzimidazoles resistance in GIN.

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.

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).