Detection of a novel spotted fever group rickettsia in Amblyomma parvum ticks (Acari: Ixodidae) from Argentina

The present study evaluated the rickettsial infection in Amblyomma parvum ticks collected in Northwestern Cordoba Province, Argentina. Each tick was subjected to DNA extraction and tested by polymerase chain reaction (PCR) targeting fragments of the rickettsial genes gltA and ompB. Nine (69.2%) out of 13 adult ticks yielded expected PCR products for the two rickettsial genes. Products from the ompB PCR were sequenced, generating DNA sequences 100% identical for the nine PCR-positive ticks. Three of these ticks were tested in another battery of PCR targeting fragments of the rickettsial genes gltA, htrA, and ompA. Products from the gltA, htrA, and ompA PCRs were sequenced generating DNA sequences 100% identical for the three PCR-positive ticks. The rickettsia detected in the A. parvum ticks was designated as Rickettsia sp. strain Argentina. Phylogenetic analyses performed with partial sequences of the rickettsial genes gltA, htrA, ompB, and ompA showed that Rickettsia sp. strain Argentina belonged to the spotted fever group, being distinct from all known Rickettsia species and genotypes available in GenBank, representing possibly a new Rickettsia species. This was the first evidence of rickettsial infection in the tick A. parvum, and the third report of rickettsial infection among the Argentinean tick fauna. The role of Rickettsia sp. strain Argentina as a human pathogen is unknown. Further studies are needed to obtain tissue-cultured isolates of Rickettsia sp. strain Argentina, in order to better characterize it and to determine its taxonomic status as a new species.