Echinococcus granulosus (Taeniidae) and autochthonous echinococcosis in a North American horse.

We report the first documented case of autochthonous echinococcosis in a horse of North American origin. Three fully mature and viable unilocular hydatid cysts of Echinococcus granulosus (Batsch, 1786) were an incidental finding at necropsy in the liver of a 14-yr-old gelding thoroughbred that had been foaled in Virginia and raised in Maryland. Protoscolices were armed with 2 rows of 28-37 rostellar hooks; small hooks measured 23-30 microns; large hooks measured 26-33 microns. Morphologically, these were compatible with rostellar armature considered typical for the equine strain of E. granulosus currently known primarily from the United Kingdom. This horse had a history of fox hunting, and huntsman at some premises in the region are known to feed uncooked viscera from horse carcasses to their dogs. These factors would support maintenance of infection by E. granulosus in equine hosts. The putative introduction and establishment of the equine strain of E. granulosus and recognition of endemic equine hydatid disease in the eastern U.S.A. warrants monitoring and additional investigation.