Ehrlichia spp. and Ehrlichioses in the Americas: Diversity, Distribution, Zoonotic Potential, and Challenges for Surveillance from a One Health Perspective

Tick-borne diseases represent a challenge to both human and animal health; however, the strength of the available evidence varies among Ehrlichia species. This critical narrative review analyzes the diversity, geographic distribution, vectors, hosts, zoonotic potential, diagnosis, and surveillance of ehrlichiosis. Information was obtained through structured searches of PubMed/MEDLINE and SciELO, complemented by searches in the CAPES Journal Portal, Google Scholar, Scopus, and Web of Science, as well as targeted searches of institutional sources, and backward and forward citation tracking. The synthesis distinguished between seroreactivity, molecular detection, isolation, clinical association, vector competence, and reservoir competence. Ehrlichia chaffeensis, E. ewingii, and E. muris subsp. eauclairensis are established human pathogens. Ehrlichia canis causes a widely distributed veterinary disease and has been molecularly confirmed in human infections; however, its frequency and population-level relevance are uncertain. For E. minasensis, E. japonica, and provisional taxa, detection in animals or ticks alone is insufficient to demonstrate zoonotic transmissions. In Latin America, particularly in Brazil, the limited evidence of human infection may reflect low clinical suspicion, limited access to PCR, the absence of specific surveillance, and the classification of cases as other febrile syndromes. Integrated surveillance is therefore recommended based on the early collection of human samples, investigation of animals and ticks linked to exposure, molecular characterization, and joint spatial and environmental analysis.