Seasonal population dynamics, species aggregation, and preferred attachment sites of ixodid ticks infesting cattle in northwest Ethiopia.

Abstract

This longitudinal study (February 2023 to January 2024) investigated species-specific ixodid tick dynamics on cattle in two contrasting agro-ecological zones of northwest Ethiopia: the semiarid lowland of Fendika (Tach-Armachiho district) and the humid mid-highland of Seguaj (Gondar-Zuria district). The study assessed seasonal dynamics, epidemiological indices, aggregation patterns, and attachment-site preferences in relation to environmental conditions. Sixty-one randomly selected cattle were examined monthly for one year. A total of 12,217 ixodid ticks were collected. The overall mean infestation prevalence was 83.7%, with similar rates in Fendika (84.3%) and Seguaj (83.1%); however, the mean tick burden was higher in Seguaj (23.2 ± 2.3 ticks/animal) than in Fendika (12.9 ± 0.7 ticks/animal). Nine ixodid species from the genera Amblyomma, Hyalomma, and Rhipicephalus were identified, showing marked variation in abundance and seasonality between agro-ecological zones. Rhipicephalus decoloratus dominated in Seguaj (56.78%), whereas Amblyomma variegatum was more abundant in Fendika (31.64%). Hyalomma rufipes, R. evertsi, and R. praetextatus were also more common in Fendika. Clear species-specific seasonal patterns were observed: R. decoloratus peaked in the post-rainy season, A. variegatum during the main rainy season, and H. rufipes during the hot short-rain season, while immature stages were concentrated mainly in the post-rainy period. Tick distribution was highly aggregated (D > 0.75), indicating that a small proportion of cattle harbored most ticks. Distinct attachment-site preferences were observed; A. variegatum and R. decoloratus favored the dewlap and ventral regions, whereas H. rufipes and R. evertsi primarily infested the anogenital area. In conclusion, ixodid tick dynamics in northwest Ethiopia are structured by species-specific responses to agroecology and climate. Effective control should target peak activity periods of key species, prioritise heavily infested animals, and account for species-specific attachment sites. Although farmers’ acaricide use varied during the study, the consistent seasonal and spatial patterns indicate that environmental drivers remained the primary determinants of tick dynamics.