First description of Onchocerca jakutensis (Nematoda: Filarioidea) in red deer (Cervus elaphus) in Switzerland

Twenty-seven species of the genus Onchocerca (Nematoda; Filarioidea) can cause a vector-borne parasitic disease called onchocercosis. Most Onchocerca species infect wild and domestic ungulates or the dog, and one species causes river blindness in humans mainly in tropical Africa. The European red deer (Cervus e. elaphus) is host to four species, which are transmitted by blackflies (simuliids) or biting midges (ceratopogonids). Two species, Onchocerca flexuosa and Onchocerca jakutensis, produce subcutaneous nodules, whereas Onchocerca skrjabini and Onchocerca garmsi live free in the hypodermal serous membranes. During the hunting season, September 2013, red deer (n = 25), roe deer (Capreolus c. capreolus, n = 6) and chamois (Rupicapra r. rupicapra, n = 7), all shot in the Grisons Region (Switzerland) were investigated for the presence of subcutaneous nodules which were enzymatically digested, and the contained Onchocerca worms were identified to species by light and scanning electron microscopy as well as by PCR/sequencing. In addition, microfilariae from skin samples were collected and genetically characterized. Neither nodules nor microfilariae were discovered in the roe deer and chamois. Adult worms were found in 24% of red deer, and all of them were identified as O. jakutensis. Two morphologically different microfilariae were obtained from five red deer, and genetic analysis of a skin sample of one red deer indicated the presence of another Onchocerca species. This is the first report of O. jakutensis in Switzerland with a prevalence in red deer similar to that in neighbouring Germany.