Spotlight on Ehrlichia ewingii (Sponsored by IDEXX)
Mar 27, 2012
CUSTOM VETERINARY MEDIA
In many parts of the United States, infection of dogs with the pathogen Ehrlichia ewingii is far more common than infection with the better-known Ehrlichia canis. Although these two ehrlichial pathogens share a phylogenetic similarity, there are many important differences, including tick vectors, host-cell tropisms, disease manifestations, geographic restrictions, and zoonotic potential. In fact, E. ewingii produces morulae in granulocytes rather than monocytes, is transmitted by a highly prevalent environmental tick (Amblyomma americanum, the lone star tick) as compared with the localized kennel tick (Rhipicephalus sanguineus, the brown dog tick), and often causes acute lameness or polyarthritis as a primary component of the dog's clinical presentation. It is important for veterinarians practicing in E. ewingii-endemic regions of the south central and southeastern United States to be familiar with tick transmission, disease consequences, diagnosis, treatment, and the zoonotic implications that are particular to E. ewingii.
Transmission and geographic distribution
The only proven competent vector for the trans mission of canine granulocytic ehrlichiosis is Amblyomma americanum, the lone star tick. Although E. ewingii infection has also been documented in dogs from both South America and Africa, the tick species responsible for natural transmission in those regions remains to be determined.1,2 Transstadial transmission in the lone star tick assures that ticks can be infected during all three stages of the life cycle (larva, nymph, and adult) and remain competent to transmit E. ewingii at their next blood meal.3,4