Diversity and eco-epidemiology of ectoparasites and Rickettsia spp. associated with the opossums Didelphis albiventris Lund in livestock farms from Argentinian Pampas region.

Many ectoparasite species serve as vectors for bacteria that are significant to both public and animal health, with wild, domestic and synanthropic mammals acting as reservoirs. However, limited information exists on the circulation and incidence of these vectors in Argentina. We examined the diversity, prevalence and abundance of ectoparasites, along with the presence of Rickettsia spp., of Didelphis albiventris Lund (Didelphimorphia, Didelphidae) within a rural landscape of the Pampas region, Argentina. We also analysed variations in ectoparasite populations concerning seasonality, livestock farm type and farmers' management practices. Seven species of hematophagous ectoparasites were collected, including mites (Mesostigmata, Laelapidae: Laelaps echidninus Berlese); ticks (Ixodida, Ixodidae: Ixodes loricatus Neumann); fleas (Siphonaptera, Rhopalopsyllidae: Polygenis platensis Jordan and Rothschild and Polygenis rimatus Jordan); Stephanocircidae: Craneopsylla minerva wolffhuegeli (Rothschild, Pulicidae: Ctenocephalides felis Bouché); and lice (Phthiraptera, Polyplacidae: Polyplax spinulosa Burmeister). Additionally, two bacteria were detected: Rickettsia felis Bouyer et al. (Rickettsiales, Rickettsiaceae) and Rickettsia sp. (Rickettsiales, Rickettsiaceae) were closely related to Rickettsia bellii Philip et al. (Rickettsiales, Rickettsiaceae). Fleas were the most prevalent and abundant group, with C. felis showing the highest values of mean abundance and prevalence. Parasitological comparisons between dairy farms and feedlots revealed similar results, with comparable densities of D. albiventris in both farm types. Ectoparasite abundance varied seasonally, peaking during the colder season. Regression analysis indicated higher ectoparasite infestation levels on farms with more dogs. The detection of pathogenic bacteria, coupled with the high prevalence and abundance of vectors, such as C. felis, suggests a significant epidemiological risk in the region. The commensal behaviour of D. albiventris facilitates it to thrive in areas modified by anthropogenic activity, positioning this species as a potential nexus between wild and domestic epidemiological cycles of parasites and emerging pathogens. Therefore, our findings suggest that D. albiventris plays a key role in the transmission and maintenance of ectoparasites and ectoparasite-borne bacteria within these ecosystems.