Ehrlichiosis in Dogs: A Comprehensive Review about the Pathogen and Its Vectors with Emphasis on South and East Asian Countries

SIMPLE SUMMARY: In dogs, ehrlichiosis is caused by three Ehrlichial species, namely Ehrlichia canis, E. ewingii, and E. chaffeensis; however, E. canis is the pathogen that most affects platelets, monocytes, and granulocytes. Globally, Rhipicephalus sanguineus is mainly responsible for vectoring the Ehrlichia species; however, Haemaphysalis longicornis is also involved in vectoring this species in east Asian countries. This disease causes acute, sub-clinical, and chronic clinical complications. There is no preferable age or sex for ehrlichiosis. The disease can be diagnosed by various methods including microscopy, indirect immunofluorescence test (IFAT), and polymerase chain reaction (PCR). The treatment of choice for ehrlichiosis includes doxycycline, rifampicin, and minocycline. Overall, this review describes the infection rate of Ehrlichia in dogs, the associated reported prevalence in east and south Asian countries, currently used therapy, and associated vectors responsible for the disease transmission as well as future perspectives. ABSTRACT: Ehrlichiosis in dogs is an emerging vector borne rickettsial zoonotic disease of worldwide distribution. In general, three Ehrlichial species (Ehrlichia canis, E. ewingii, and E. chaffeensis) are involved in infecting dogs. Among them, E. canis is the well-known etiological pathogen affecting platelets, monocytes, and granulocytes. Dogs act as a reservoir, while the main vector responsible for disease transmission is Rhipicephalus sanguineus. However, in east Asian countries, Haemaphysalis longicornis is considered the principal vector for disease transmission. This disease affects multiple organs and systems and has three clinical manifestations, including acute, subclinical, and chronic. Definitive diagnosis involves visualization of morulae on cytology, detection of antibodies through an indirect immunofluorescence test (IFAT), and DNA amplification by polymerase chain reaction (PCR). In canine ehrlichiosis, no predilection of age or sex is observed; however, Siberian Huskies and German Shepherds are more likely to develop severe clinical manifestations. Doxycycline, rifampicin, and minocycline are proven to be effective drugs against canine ehrlichiosis. This review is intended to describe a brief overview of Ehrlichia infection in dogs, its reported prevalence in east and south Asian countries, and the latest knowledge regarding chemotherapy and associated vectors responsible for the disease transmission. This manuscript also identifies the prevailing knowledge gaps which merit further attention by the scientific community.