Survey for tick-borne pathogens in Amazonian ixodid ticks, Brazil.

The Amazon biome harbors an exceptional diversity of wildlife, yet remains understudied regarding tick-borne pathogens. This study investigated the species richness of ixodid ticks and the occurrence of associated microorganisms in three natural areas of the Brazilian Amazon. During 2023-2024, a total of 1084 ticks were collected from vegetation and vertebrate hosts and identified into 16 species, predominantly within the genus Amblyomma. A subset of 289 ticks was subjected to molecular screening for bacteria of the genera Rickettsia, Anaplasma, and Borrelia, as well as protozoa of the order Piroplasmida. No DNA of known pathogenic rickettsiae was detected. Instead, Rickettsia amblyommatis was identified in multiple Amblyomma species, while Rickettsia bellii and Rickettsia rhipicephali were detected at lower frequencies. Two isolates of R. amblyommatis were successfully established in Vero cell culture. Additionally, an Anaplasma sp. closely related to strains previously detected in South America, including in humans, and 'Candidatus Allocryptoplasma sp.' were identified in individual ticks. Borrelial DNA was detected in 11 ticks, with sequences clustering within the reptile-associated Borrelia group, including specimens collected from a red-footed tortoise, suggesting a potential reptile reservoir. No piroplasmid DNA was detected. These findings reveal a high richness of tick species and associated microorganisms in the Amazon, dominated by agents of unknown or uncertain pathogenicity. The apparent absence of confirmed pathogenic rickettsiae in preserved forest environments contrasts with other Brazilian regions and reinforces the need for continued epidemiological surveillance. Overall, this study provides baseline data and highlights the Amazon as a potential reservoir of neglected and emerging tick-borne agents.