Distribution and acaricide resistance status of the theileriosis vector, Rhipicephalus appendiculatus Neumann (Acarina:Ixodidae) in response to changing climate in Zimbabwe
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Date
2023
Authors
Nemaungwe, Tinotenda Mercy
Journal Title
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Publisher
University of the Free State
Abstract
Tick control is a key aspect of managing Tick-Borne Diseases (TBDs) with chemical control being the widely applied method. However, continued application of chemicals can lead to the development of resistance. A recent increase in theileriosis in Zimbabwe coupled with indications of shifts in outbreaks from seasonal to spontaneous, raised possibilities of acaricide resistance by the vector, Rhipicephalus appendiculatus. Factors behind changes in the spatio-temporal distribution of the tick and the disease it transmits are poorly understood. This study evaluated the distribution of the theileriosis vector, R. appendiculatus, its response to frequently applied acaricides and the implications of current management practices on acaricide resistance development in Zimbabwe. Initially, the thermal tolerance of larvae, nymphs and adult R. appendiculatus ticks were assessed followed by modeling the current and future distribution of suitable habitats using MaxEnt. Bioassays were then conducted to determine the tick’s resistance status to frequently applied acaricides namely amitraz and deltamethrin. Furthermore, a survey was undertaken to understand the relation between tick management strategies and acaricide resistance development in ticks of economic importance.Results indicated that suitable habitats for R. appendiculatus may expand into previously non-endemic areas between 2040 and 2060 if temperatures rise by 2 °C. This expansion may be aided by the ability of the species to tolerate higher temperatures during assays than those recorded in the environment. Results further showed that R. appendiculatus populations are still highly susceptible to amitraz and deltamethrin (Resistance ratios<4). In contrast, the indicator species R. decoloratus which was used for comparison had 50% of populations moderately resistant to amitraz and two dip tanks resistant to deltamethrin (4<RR<10). Farmers noted a high prevalence of TBDs which they attributed to a breakdown in the national tick management program. However, there were indications of practices by farmers which might lead to the development of resistance even in the three-host ticks in future. These include, indiscriminate use of acaricides and poor rotation of acaricide molecules. Overall, this study suggests that current theileriosis outbreaks may be driven by the spread of R. appendiculatus into non-endemic areas rather than acaricide resistance development. Therefore, there is a need for national programs to expand surveillance and control measures into areas previously non-endemic, but predicted to be suitable for the theileriosis vector.
Description
Dissertation (M.Sc.(Zoology))--University of the Free State, 2023