44 - Ehrlichiosis

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•First Described: Ehrlichia canis was first described in 1935 (Algeria). Ehrlichia ewingii was described in 1992 (United States). Ehrlichia chaffeensis was described in 1991 (United States). The first report of naturally occurring ehrlichiosis in a cat occurred in France in 1986.Cause: The most important species causing disease in dogs are E. canis (canine monocytic ehrlichiosis) and E. ewingii (canine granulocytic ehrlichiosis).•Affected Hosts: Ehrlichia canis causes disease in dogs, humans, and cats. Ehrlichia ewingii causes disease in dogs, humans, and goats and has been detected in a clinically ill cat. Ehrlichia chaffeensis causes disease in humans, possibly dogs and goats, and has been detected in a clinically healthy cat. Ehrlichia muris eauclairensis causes disease in humans and possibly dogs. Panola Mountain Ehrlichia causes disease in dogs, goats, and humans in the United States.Geographic Distribution: Ehrlichia canis is distributed worldwide, but is more prevalent in tropical and subtropical regions. Ehrlichia ewingii is primarily found in the south-central and southeastern United States. Most reports of Ehrlichia chaffeensis infection are from the southern and south-central United States, but it has also been identified in Africa. Ehrlichia muris subsp. eauclairensis has been found in the Upper Midwest of the United States. Panola Mountain Ehrlichia has been found in the southeastern United States.•Mode of Transmission: Rhipicephalus sanguineus ticks (E. canis); Amblyomma americanum ticks (E. ewingii and E. chaffeensis), Ixodes scapularis ticks (E. muris subsp. eauclairensis), and A. americanum and Amblyomma maculatum ticks (Panola Mountain Ehrlichia).•Major Clinical Signs: Dogs—typical clinical signs of E. canis infection are fever, lethargy, inappetence, weight loss, cutaneous and mucosal petechial and/or ecchymotic hemorrhages, lymphadenomegaly, splenomegaly, and uveitis. Ehrlichia ewingii primarily causes fever, lethargy, inappetence, and signs of polyarthritis. Cats—typical clinical signs of E. canis infection are fever, lethargy, inappetence, weight loss, hyperesthesia, and joint pain. Ehrlichia ewingii was detected in a clinically ill cat with thrombocytopenia and anemia.•Differential Diagnoses: Other tick-borne diseases (e.g., granulocytic anaplasmosis, Lyme borreliosis, babesiosis, and cytauxzoonosis [cats]), bartonellosis, hemotropic mycoplasmosis, leptospirosis, and other systemic non-vector-borne diseases such as lymphoma, multiple myeloma, and systemic primary immune-mediated disease.•Public Health Aspects: All four Ehrlichia species can infect and cause disease in humans. The most virulent human pathogen is E. chaffeensis and results in the highest percentage of hospitalizations and death compared with the other North American Ehrlichia species.