Seasonal dynamics of Amblyomma cajennense (Fabricius, 1787) sensu stricto in a degraded area of the Amazon biome, with notes on Rickettsia amblyommatis infection

Abstract

Abstract Background The tick Amblyomma cajennense sensu stricto (s.s.) frequently parasitizes animals and humans in the Amazon biome, in addition to being a vector of Rickettsia amblyommatis. In the present study, we evaluated the population dynamics of A. cajennense s.s. in a degraded area of the Amazon biome, and the presence of rickettsial organisms in this tick population. Methods The study was carried out in a rural area of the Santa Inês municipality (altitude: 24 m), Maranhão state. Ticks were collected from the environment during 24 consecutive months, from June 2021 to May 2023. The region is characterized by two warm seasons: a rainy season from November to May, and a dry season from June to October. We characterized the temporal activity of A. cajennense s.s. on the vegetation, by examining questing activity for each life stage (larvae, nymphs, adults [males and females]), in relation to the dry and rainy season. Ticks collected in this study were randomly selected and individually tested by a TaqMan real-time PCR assay that targeted a 147-bp fragment of the rickettsial gltA gene. Results Overall, 1,843 (62.4%) adults (52.6% females and 47.4% males), 1,110 (37.6%) nymphs and 398 larval clusters were collected. All adult females and nymphs were morphologically identified as A. cajennense s.s. Larval activity was observed from April to December, with a peak from June to September (dry season). Nymphs peaked from September to November (transition period between dry and rainy seasons). Adult ticks were abundant from October to May (spring/summer/early autumn). The infection rate by R. amblyommatis in A. cajennense s.s. ticks were at least 7% (7/99). Conclusion Our data suggest a 1-year generation pattern for A. cajennense s.s., with a well-defined seasonality of larvae, nymphs and adults in the Amazon biome. Larvae predominating during the dry season, nymphs in the dry-rainy season transition and adults in the dry season. The presence of R. amblyommatis in adults suggest that animals and humans in the study region are at risks of infection by this spotted fever group rickettsial agent.