Ecoepidemiology of Rickettsia parkeri in the Paraná Delta, Argentina

BELDOMENICO PM; COLOMBO VC; MONJE LD; ANTONIAZZI LR; NAVA S

Hyderabad

Congreso; 17th International Congress on Infectious Diseases; 2016

International Society of Infectious Diseases

Background: In South America, several cases of human rickettsiosiscaused by Rickettsia parkeri were documented in Uruguay,southern Brazil and the Paraná River delta of Argentina. There, themain tick vector is Amblyomma triste. Adults of A. triste seek bloodmeals from largemammals(including humans), whereas immaturestages feed on small rodents.Methods & Materials: With the aim of shedding light on theecology of this emerging disease,weconducted field studies at sitesof the Paraná River delta, which consisted of systematic collectionof ticks and blood samples from rodents (Fig. 2) and cattle, and alsoquesting ticks from the vegetation. Sampling sessions were carriedout monthly during 2011 and 2012 at 16 points that differed intheir exposure to cattle and vegetation type (natural or implantedforest).Results: Prevalence of infection in adult questing ticks washigh (20.4%). Interestingly, the distribution of R. parkeri infectionintensity observed in A. triste ticks was distinctly bimodal, withapproximately 60% of the infected ticks presenting high rickettsialloads (Fig. 3). Questing ticks were more frequently found in naturalgrasslands than in implanted forests, and prevalence of infectionwere greater in those from grasslands (26%) than in forestedareas (8.3%). The dominant rodent species were Akodon azarae andOxymycterus rufus. In both, the seroprevalence to R. parkeri wasgreater in those captured in grasslands than in implanted forests.The presence of cattle had a significant positive effect on the burdensof ticks on rodents and the abundance of questing ticks in thevegetation. Most cattle (90%) were seropositive, and the seasonality.Conclusion: The risk of human exposure to R. parkeri infectedticks in the Paraná River delta is high. Our results suggest thatthe silvopastoral activities that are on the rise in the region affectthe dynamics of infection of R. parkeri. Cattle appear to favour theoccurrence of the pathogen, whereas forestation seems to reduceit.