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20211
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Subject: Veterinary Parasitology × Author: PRATHYUSHA, S × End date: 2024 × Start date: 2020 × Type: Thesis × Thesis Type: M.V.Sc. ×
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    ThesisItemOpen Access
    STATUS OF RESISTANCE TO CYPERMETHRIN AND IVERMECTIN IN THE BROWN DOG TICK (Rhipicephalus sanguineus sensu lato) IN ANDHRA PRADESH
    (SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA, 2021-03) PRATHYUSHA, S; SREEDEVI, C (MAJOR); JYOTHISREE, Ch; SUDHAKAR, K
    The brown dog tick, Rhipicephalus sanguineus sensu lato, is an important disease vector of veterinary and public health importance that is distributed worldwide. The intensive use of acaricides for tick control exerts a strong selective pressure for brown dog ticks to become resistant to them. Information on acaricide resistance in R. sanguineus s.l. populations from India is meager and no such data from Andhra Pradesh though veterinarians frequently report treatment failures. The present study was aimed to characterize the level of resistance in R. sanguineus s.l. against most commonly used drugs, alpha cypermethrin and ivermectin in Andhra Pradesh and identify the mutation in sodium channel gene that corresponds with resistance of R. sanguineus s.l. to alpha cypermethrin. Fourteen tick populations were collected from naturally infested dogs at veterinary clinics, residence and stray dog in nine state municipal corporations/municipalities. Interviews were conducted with dog owners to gather information on the history of dog treatment with acaricides. The larval packet test (LPT) and larval immersion test (LIT) was used on the progeny of adult female ticks infesting dogs to test for resistance to cypermethrin and ivermectin respectively. Mortality data was analyzed by probit analysis to determine the median lethal concentrations (LC50) for each tick population and resistance was characterised based on relative susceptibility of the different tick populations against each acaricide. Compared with the most susceptible population, thirteen (92.6%) and six (42.9%) tick populations were classified as resistant to cypermethrin and ivermectin respectively. An inter-population variation in the phenotypic level of cypermethrin and ivermectin resistance was evident (resistance ratio at LC50% ranged from 1.55 to 13.29 and from 1.16 to 4.79, respectively). Tick populations classified as resistant were collected from dogs known to have been treated with cypermethrin and ivermectin. A molecular assay targeting a point mutation in the sodium channel was optimized to identify ticks expressing cypermethrin resistance. Then, all field collected phenotypically cypermethrin-resistant populations were evaluated employing this molecular assay to determine genotypes. As confirmed by DNA sequencing, a single nucleotide polymorphism of thymine to cytosine on domain III segment VI of the sodium channel was present at a high rate in phenotypically resistant tick populations that was not present in the susceptible population. The results of this study further emphasize the necessity to maintain acaricide efficacy through rotation of active ingredients used to control ticks.