Morphological description and multilocus genotyping of spp. in red deer () in Switzerland.

Onchocercosis is a parasitic disease caused by over 30 spp. (Nematoda: Filarioidea) and predominantly affecting ungulates. Four spp. have been described in the European red deer (). and form subcutaneous nodules in the back region. The other two species, and the lesser-known , are found freely in the subcutaneous tissue of carpal and tarsal joints, and the sternal region, respectively. The presence of spp. in eight red deer shot in the hunting season during September 2020 in the Grisons region, Switzerland, was investigated by analysing nodules and free worms in the subcutaneous tissue. The obtained worms were morphologically and genetically identified as , and . The latter two are first reports from Switzerland, and morphological redescriptions of these two species are presented. and are newly described from the sternal region of deer. One female of was found free in the subcutaneous tissue of the sternal region, an atypical presentation for this species. Phylogenetic analyses were based on four mitochondrial and one nuclear loci, revealing that belongs to a clade which so far only included non-cervid spp. Analysis of sequences from this study and GenBank entries revealed two distinct subpopulations of : one from European red deer and another from Japanese serow and sika deer. Morphological identification can be challenging, also because worm location in the host is less strictly determined than previously described. Genetic identification is straightforward for , and for which complete data of five loci are now available whereas genetic data of is still lacking.