Identification of Culicoides spp. and molecular screening for Onchocerca sp. DNA in a horse farm with insect bite hypersensitivity
The aim of this study was to clinically characterize insect bite hypersensitivity (IBH) lesions in horses, identify the Culicoides species involved, and assess the possible role of Onchocerca cervicalis in equine dermatitis. Since O. cervicalis is transmitted by dipterans of the genus Culicoides, a study was designed to explore whether local populations of these insects might be participating in the transmission of microfilariae.  A clinical diagnosis of IBH was made in horses from an equestrian school in Málaga, Spain, that did not respond to conventional treatment with repellents and insecticides. During the summer of 2022, Culicoides specimens were captured using a mini CDC UV-light trap. The collected Culicoides spp. were identified using morphological keys for species from the Iberian Peninsula and confirmed by molecular sequencing of the COX I gene. In addition, sequencing of the 16S gene was performed to determine the hosts on which engorged females had fed. PCR was also performed, and the resulting amplicons were sequenced for a pan-filarid COX I gene, which has previously been used for vector incrimination of various Onchocerca species in domestic and wild animals.  Skin lesions were located on the face, ears, ventral abdomen, mane, croup, costal region, tail base, and midline of the ventral abdomen. These highly pruritic lesions included alopecia, scaling, crusts, and lichenification. Two clinical forms of urticaria were also recognized. The morphology of wing patterns indicated the presence of C. imicola, C. newsteadi, and an unidentified species. Molecular analysis of the COX I gene confirmed that the latter corresponded to C. cataneii. Engorged females had fed mainly on horses, zebras, humans, and dogs. No filarial DNA was detected, suggesting the absence of O. cervicalis DNA or any of its developmental stages.