Onchocerca lupi Canine Infection
in Washington State

WA Veterinarian Magazine


Mar/Apr 2016

A veterinary ophthalmologist in western Washington recently diagnosed a confirmed case of Onchocerca lupi infection in an adult dog that presented with a scleral granuloma (Image 1). The dog had been imported to Washington from the southwestern United States approximately 1 year prior. The dog is currently being treated and appears healthy.

O. lupi is an emerging zoonotic parasite that infects dogs, cats, and humans, and is transmitted by black flies (Simulium sp.). Canine O. lupi infections can manifest as an acute or chronic form, with the acute form being more commonly reported (1). Typical clinical presentation involves ocular nodules usually on the eyelids, conjunctiva, and sclera, though many asymptomatic canines have been found with microfilariae present in their skin (1, 2). Feline ocular onchocerciasis caused by O. lupi appears rare, with only one published case report describing two felines that presented in the United States with episcleritis and orbital cellulitis (3).

O lupi
Image 1. Surgical removal of O. lupi nematodes from a scleral granuloma (canine). 2016 by Dr. AJ Marlar (image adapted with permission).

The epidemiology of canine O. lupi infections in the United States is not completely known, but current evidence suggests endemic disease transmission in the southwestern United States (1). At this time, it is unknown whether ongoing canine O. lupi transmission could occur in Washington State; black flies (Simulium tribulatum), a recently identified possible vector for O. lupi in southern California, are present in Washington State (4). Similar to heartworm disease and mosquitoes, the black fly vector is required to transmit infective stage microfilariae from an infected animal to another animal or human. All available evidence suggests the risk of this occurring is very low. At this point, the Washington State Department of Health has received only a single report of O. lupi infection described above which appears to be imported (i.e., the dog was likely exposed to the parasite in Arizona or New Mexico).

Veterinarians should consider O. lupi infection in any canine or feline patient that presents with ocular nodules, especially patients with previous history of travel from the southwestern United States. Suspect cases should be reported to Dr. Ron Wohrle at the Washington State Department of Health ([email protected] or (360)-236-3369). Consultation and/or referral of suspect cases to a board certified veterinary ophthalmologist for details on diagnostic and treatment protocols is recommended. 

For more information on O. lupi including details on recently described human cases, see:

Cantey PT, Weeks J, Edwards M, et al. The Emergence of Zoonotic Onchocerca lupi Infection in the United States — A Case–Series. Clin Infect Dis 2015; doi: 10.1093/cid/civ983


  1. Ontranto D, Giannelli A, Latrofa MS, et al. Canine Infections with Onchocerca lupi Nematodes, United States, 2011—2014. Emerg Infect Dis 2015 May [Feb 10, 2016]. http://dx.doi.org/10.3201/eid2105.141812
  2. Otranto D, Dantas-Torres F, Giannelli A, et al. Cutaneous distribution and circadian rhythm of Onchocerca lupi microfilariae in dogs. PLoS Negl Trop Dis 2013; 7:e2585
  3. Labelle AL, Daniels JB, Dix M, Labelle P. Onchocerca lupi causing ocular disease in two cats. Vet Ophthalmol 2011 Sep;14 Suppl 1:105-10. doi: 10.1111/j.1463-5224.2011.00911.x.
  4. Hassan HK, Bolcen S, Kubofcik J, et al. Isolation of Onchocerca lupi in Dogs and Black Flies, California, USA. Emerg Infect Dis 2015; 21:789-96.