Molecular Evidence for Vector Implication of Onchocerca lupi in Los Angeles County, CA

Onchocerca is a genus of roundworm most commonly associated with the human infection onchocerciasis, or river blindness. While typically a zoonotic infection of ungulate populations, canine cases (Onchocerca lupi) have been identified in the United States and Greece. In 2012, Los Angeles County, Veterinary Public Health Program identified 3 cases of Onchocerca spp. infections in domestic canines. Samples from the ensuing blackfly collections were sent to the Global Health Infectious Disease Research Unnasch Laboratory for parasite isolation and vector species identification. Species-specific primers were designed and optimized for O. lupi using a non- specific cytochrome oxidase (COI) gene target (689bp) previously utilized in Onchocerca identification as a base. A secondary, nested PCR primer set (115bp) was additionally designed to aid in the screening process. Extracted DNA samples from the collected blackflies were screened for the presence of the parasite and positive samples were further tested against the larger fragment for confirmation. The primers designed for the study were determined to be specific to O. lupi and not cross-reactive with other Onchocerca species or Dirofilaria immitis. Of the 213 blackflies screened, 6 samples tested positive for parasite presence. The blackfly species was identified as Simulium spp. The presence of the O. lupi parasite in the black fly population implicates that this is the likely vector in the LA County cases. While the blackfly identification was unable to be determined to the species level, the identification of Simulium spp. confirms the typically suspected vector in Onchocerca infections. Concerns of cross-species transmission make O. lupi an important parasite for public health study