Detection of Rickettsia spp. in questing ticks (Acari: Ixodidae) from forest fragments adjacent to agricultural and livestock farms in Casanare, Colombia

This study aimed to describe the diversity of ixodid tick species in rural forest areas of Yopal and Aguazul, Department of Casanare, Colombia, and to evaluate the presence of tick-borne Rickettsia sp., potentially impacting animal and human health. A cross-sectional study was conducted on questing ticks collected from forested farm areas that keep livestock and/or conduct agricultural activities. All ticks were subjected to DNA extraction and tested by PCR amplifying fragments of three rickettsial genes: gltA, htrA, and ompA. A total of 852 individual ticks (larvae, nymphs, and adults) and 15 additional larvae clusters were collected and identified as Amblyomma mixtum, Amblyomma cf. parvum, Amblyomma dissimile, Amblyomma spp., and Dermacentor spp. Rickettsia organisms were detected by PCR in 7.0% (16/230) of the individual larvae, 0.2% (1/488) of the nymphs, and 1.5% (2/134) of the adults. "Candidatus Rickettsia colombianensi" and Rickettsia amblyommatis were detected in 1.52% (13/852) and 0.47% (4/852) of the ticks, respectively. In addition, a novel genotype, Rickettsia sp. genotype Yopal, phylogenetically closest to Rickettsia canadensis, was identified in two A. mixtum males. Several tick and Rickettsia species were found in the study areas, suggesting the need for an in-depth study of nonspecific acute tropical febrile illness in the Department of Casanare and across Colombia. Priority areas for future studies include investigating the molecular, clinical, and epidemiological features of the presentation of tick species and the possible participation of "Ca. R. colombianensi," R. amblyommatis, and "Rickettsia sp. Yopal genotype of A. mixtum" to understand their role in human rickettsiosis in the study region.