Seasonality of the Rickettsia vectors Amblyomma ovale and Amblyomma sculptum on dogs in Atlantic Forest and Cerrado biomes of Minas Gerais, Brazil: hypotheses for human rickettsiosis seasonality

• Dogs in the Atlantic Forest biome are exposed to infestation by adult Amblyomma ovale • A seasonal pattern of Amblyomma ovale infestation in dogs was observed • Hypothesis of relationship between vector seasonality and human rickettsiosis is explored • In the Cerrado biome dogs are highly exposed to the vector of Rickettsia rickettsii, Amblyomma sculptum . Free-ranging rural dogs in Brazil are parasitized by ticks from indigenous ixodofauna including Amblyomma sculptum and Amblyomma ovale , vectors of Rickettsia rickettsii and Rickettsia parkeri strain Atlantic Rainforest (ARF), respectively. Therefore, dogs are important sentinels and hosts for ticks and tick-borne diseases of public health relevance. This study evaluated abundance, and seasonal dynamics of these tick species infesting free-ranging rural dogs in two municipalities of Minas Gerais State, southeastern Brazil: Araguari (Cerrado biome remnants) and Guaxupé (Atlantic Forest remnants). Tick collections were conducted monthly between 2022 and 2024 through systematic examinations of dogs as well as environmental sampling in Guaxupé. In Araguari, canine infestations were dominated in spring by nymphs of A. sculptum an important vector of R. rickettsii while adults of this tick were rarely detected. This pattern reflects the limited suitability of dogs as hosts for adult A. sculptum and suggests that canine exposure is dependent on the presence of primary hosts, such as capybaras and equines. In contrast, Rhipicephalus linnaei was the most prevalent and abundant species on dogs in Guaxupé, particularly among animals more confined to household environments, reinforcing its synanthropic and endophilic behavior. Infestations by R. linnaei showed no clear seasonality, supporting a continuous life cycle without diapause. Amblyomma ovale exhibited high prevalence and abundance on dogs in Guaxupé, likely associated with humid Atlantic Forest fragments that favor its life cycle. Only adult A. ovale ticks were found on dogs, and they showed marked seasonal aggregation during spring, with peak abundance in November and persistence into summer. In conclusion, this study provides the first detailed characterization of the seasonal pattern of adult A. ovale infesting dogs. In addition, an exploratory hypothesis regarding a possible relationship between vector seasonality and human rickettsiosis is proposed, warranting further investigation.