Rickettsia parkeri and Candidatus Midichloria sp. in Amblyomma triste ticks from protected areas of Buenos Aires Province (La Plata River Hydrographic Basin, Argentina)

Ticks are important vectors of bacteria belonging to the order Rickettsiales, several of which are causes zoonotic diseases. Amblyomma triste is the main vector of Rickettsia parkeri , the etiological agent responsible for most cases of human spotted fever rickettsiosis in Argentina. However, information on the circulation of rickettsial agents in protected areas of the La Plata River Hydrographic Basin, a region that includes highly urbanized environments and frequent contact between wildlife, domestic animals and humans, remains limited. The aim of this study was to investigate the presence of rickettsial bacteria in A. triste collected in protected areas of Buenos Aires Province, (La Plata River Hydrographic Basin, Argentina). Between September and December 2021, ticks were collected by vegetation flagging in four protected areas and analyzed individually. Polymerase chain reactions (PCR) for detecting the genus Rickettsia was initially performed using a simple PCR to amplify a variablesized fragment of the 23S-5S rRNA intergenic spacer. An initial PCR was performed with primers for a 16S rRNA fragment for the Anaplasmataceae family. A total of 247 adult ticks were examined. Twelve specimens (4.9%) tested positive for Rickettsia , and sequence analysis confirmed their identity as R. parkeri . Positive ticks were detected in Ciervo de los Pantanos National Park and Campos del Tuyú National Park. In addition, two specimens yielded sequences corresponding to Candidatus Midichloria sp. These findings confirm the presence of R. parkeri in A. triste populations from protected areas of the La Plata River Hydrographic Basin and provide the first evidence of Ca. Midichloria sp. in this tick species in Argentina. The results highlight the need for continued surveillance of tick-borne microorganisms in protected areas located near densely populated regions, where human exposure to infected ticks may occur.