Submitted to: Journal of the American Veterinary Medical Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2009
Publication Date: 7/15/2010
Citation: Reinstein, S.L., Lucio-Forster, A., Bowman, D.D., Eberhard, M.L., Hoberg, E.P., Pot, S., Miller, P.E. 2010. Surgical extraction of intraocular Parelaphostrongylus tenuis (Nematoda: Metastrongyloidea) in a horse. Journal of the American Veterinary Medical Association. 237:196-199. Interpretive Summary: Parelaphostrongylus tenuis, also referred to as the meningeal worm, is considered a common neurotropic parasite in white-tailed deer (Odocoileus virginianus) from eastern North America. Infections generally remain subclinical in white-tailed deer. In atypical hosts, however, the migration through the central nervous system results in a variety of neurologic abnormalities. Reports in atypical bovid and camelid hosts are not uncommon, and infections are often associated with severe disease and mortality. It is believed that these infections have been acquired by domestic or free-ranging ungulates sharing common range with snail intermediate hosts infected from larvae in the feces of white-tailed deer, or in the context of game farms or zoos. We report the first confirmed case of infection by P. tenuis in an equine host from Wisconsin. To our knowledge, this is the first confirmed report of parelaphostrongylosis in a horse due to P. tenuis. This also documents the first report of an eye which remained sighted after intraocular migration of P. tenuis and surgical intervention to remove the parasite. Although apparently rare in equine hosts, P. tenuis infection should be considered when an intraocular parasite is identified in the horse, with or without concurrent neurological disease.
Technical Abstract: Case Description – A 4-year-old Hanoverian horse from Wisconsin presented for evaluation of a worm-like structure in the anterior chamber of the right eye. Clinical Findings – Ophthalmic examination of the right eye revealed a white, thin, mobile parasite, presumably a nematode, present in the ventral anterior chamber. Fundic examination of the right eye revealed vitreous opacities. Ophthalmic examination of the left eye was normal. Treatment and Outcome – The horse was treated with neomycin-polymyxin B-dexamethasone ophthalmic solution in the right eye, potassium penicillin, flunixin meglumine, and general anesthesia for surgical removal of the parasite. The parasite was extracted through a corneal stab incision using an iris hook and forceps. The horse was discharged the day following surgery. Gross and microscopic examination identified the parasite as an adult metastrongyloid nematode, consistent with a fully developed male of Parelaphostrongylus tenuis. Clinical Relevance – To the authors' knowledge, this is the first case report of intraocular parelaphostrongylosis in a horse. This also documents the first report of an eye which remained sighted after intraocular migration of P. tenuis.