A multidimensional analysis of the risk of infection with Ehrlichia canis among urban dogs in Iquitos, Peru

Ehrlichia canis is a tick-borne bacterium that causes a potentially fatal disease in dogs called canine monocytic ehrlichiosis. In this cross-sectional study, we used a One Health framework to identify statistical associations between E. canis infection in dogs and multiple dog-related, human and environmental factors in Iquitos, Peru. Due to the lack of consensus regarding the positivity threshold for E. canis qPCR assays, we also evaluated if the factors associated with infection remained conserved regardless of the Ct value cut-off used: Ct < 35, a conservative but commonly accepted Ct cut-off for bacterial screening, or Ct ≤ 40, which has been used in several E. canis studies. Under the more conservative scenario, we found that the prevalence of E. canis among dogs was 19.6% (95% CI 15.8-23.9%). Additionally, we showed that risk factor analyses utilizing a qPCR Ct cut-off of 35 or 40 (with conventional PCR confirmation for samples with a Ct > 35) yield comparable results in statistical models, although some differences should be considered. Our findings suggest that in Iquitos, Peru, interventions to prevent E. canis infection should prioritize dogs living in houses with corrugated iron walls. Additionally, comprehensive strategies targeting dogs that have recently traveled and incorporating neutering/spaying and widespread acaricide programs may also prove beneficial. We also discuss the challenges encountered during molecular testing for E. canis detection, highlighting the broader difficulties of studying poorly understood intracellular pathogens in Global South countries.