Ticks are blood-sucking parasites which transmit the agents of diseases in both human and animals. The aim of this study was to determine the seasonal frequency of tick infestation of sheep, and to investigate the effect of climatic condition and geographical location on the tick infestation of sheep in Golestan Province, Iran. Ticks were collected from sheep monthly from October 2014 to December 2015 at 45 study sites, including hillside, plain and coastal areas of Golestan province. The collected ticks were identified morphologically using the relevant keys. Poisson regression was used to find the relationship between tick abundance and weather variables. The identified tick specimens belonged to 3 genera and 9 species including Hyalomma marginatum, Hy. anatulicum, Hy.asiaticum, Hy. excavatum, Rhipicephalus bursa, Rh. turanicus, Rh. sanguineus, Haemaphysalis parva and Ha. punctata. The number of tick species in the coastal area was fewer than those of the other two topographic regions. The dominant species in the coastal and plain regions was Hy. marginatum, while in the hillside area was Rh. turanicus. Monthly activity of ticks on sheep revealed two peaks of activities in June and July for Hy. marginatum in the coastal and plain regions, and 1 peaks of activities in August in the hillside area for Rh. turanicus. Poisson regression analysis showed a significant correlation between the average monthly temperature and the density of Hy. marginatum, Hy. anatulicum and Rh. turanicus in the coastal, plain and hillside areas respectively. Also, the average monthly relative humidity significantly correlated with the density of Hy. marginatum in the coastal, Hy. marginatum and Hy. anatulicum in plain, and Rh. turanicus in hillside areas (P < 0.05). Hy. marginatum was the most frequent species with a prevalence of 49% in this study, and had the highest density in coastal and plain area. This species is well known as a vector of CCHF. Rh. turanicus was the second abundant species in this study. Maximum and minimum occurrence of ticks was observed in June and January respectively. In this study Hy. marginatum, Hy. anatulicum, Rh. bursa, Rh.turanicus and Rh. sanguineus were identified as the most abundant ticks in the studied area, which are proven vectors for different pathogens of ruminants, therefore can cause infection in sheep when grazing. This should be noted in mapping the more safe pastures for livestock grazing, to prevent their infestation in tick, and tick-borne diseases.

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