Molecular identification of Ehrlichia sp. strain San Luis and infection intensity of Candidatus Rickettsia andeanae in Amblyomma parvum ticks from northwestern Argentina

FERNANDEZ CAMILO; MONJE LUCAS

Buenos Aires

Congreso; II Congreso Internacional de Zoonosis y IX Congreso Argentino de Zoonosis; 2018

Asociación Argentina de Zoonosis

The existing records of Ehrlichia spp. infection in Argentina correspond to the findings of Ehrlichia canis in dog blood and in Rhipicephalus sanguineus sensu lato ticks, Ehrlichia cf. E. chaffeensis infecting Amblyomma parvum ticks and two novel Ehrlichia strains detected in Amblyomma tigrinum ticks denominated Ehrlichia sp. strain San Luis and Ehrlichia sp. strain Cordoba. Albeit E. chaffeensis was reported infecting A. parvum ticks, this assumption was based on the sequence of a portion of the 16S rRNA gene which has not enough polymorphism. Candidatus Rickettsia andeanae is a recently recognized species that belongs to the spotted fever group of rickettsiae. This Rickettsia was reported infecting A. parvum, A. tigrinum and Amblyomma pseudoconcolor ticks in Argentina, however there are no previous reports inquiring about co infection with other rickettsiales or the infection levels of Ca. R. andeanae in naturally infected ticks.Due to the sanitary importance of A. parvum and the necessity to confirm the identity of the ehrlichial agent infecting these ticks, this species was chosen in this study for Ehrlichia/Rickettsia detection and molecular characterization.Material and MethodsQuesting adult ticks were collected in Santiago del Estero, Argentina during December 2016 and species were determined by using standard taxonomic keys and then processed for DNA extraction.Samples were screened for Anaplasmataceae by a realtime PCR designed to amplify a 177bp fragment of the 16S rRNA gene of Ehrlichia and Anaplasma genera. Amplification of dsb gene was done in Ehrlichia spp. positive samples. Rickettsia spp. were tested by realtime PCR amplification of ompA gene.ResultsA total of 58 adult ticks were collected (49 A. parvum, 5 Amblyomma argentinae, 4 A. tigrinum). Two A. parvum ticks were positive to 16S rRNA PCR (sequences 100% identical to several Ehrlichia species) and dsb sequence obtained from these ticks was 100% identical to Ehrlichia sp. strain San Luis and 97% to E. chaffeensis.44 A. parvum ticks were positive for ompA, including ticks positive for Ehrlichia, with concentrations ranging from 2.3 × 103 to 2.1 × 106 copies per tick. The 212bp ompA fragment was 100% identical to Ca. R. andeanae. All ticks were negative for Anaplasma.DiscussionTicks in our study were collected close to the site where the presence of E. chaffeensis was previously reported by using 16S rRNA as molecular marker. Due to the small distance and to the absence of geographical barriers between the two sites, we assumed that the same Ehrlichia strain associated to A. parvum was detected in both studies. Hence we infer that the ehrlichial agent present in northwestern Argentina is in fact Ehrlichia sp. strain San Luis. Our results show that this ehrlichial agent is not limited to a single tick species and it is widely distributed in Argentina.Although very pertinent for our understanding of the ecoepidemiology of rickettsial pathogens, studies on the distribution of the levels of infection in ticks are scarce. Interestingly, the infection intensity of Ca. R. andeanae observed in A. parvum ticks was lower than the ones reported for R. parkeri and R. massiliae.