If your horse has grainy skin and swollen mucous membranes around the eyes, it could be periocular habronemiasis, a form of conjunctivitis caused by parasites. | Photo: Courtesy Dr. Nicole Verhaar

If your horse has grainy skin and swollen mucous membranes around the eyes, it could be periocular habronemiasis—a unique form of “pink eye” caused by parasites.

More common in tropical and subtropical climates, periocular habronemiasis appears as granulous lesions around the eye as a result of parasite infestations. But the invasive little nematodes aren’t limited to these warmer, more humid climates. A new study by researchers in the Netherlands has revealed that they can affect horses as far north as northwestern Europe.

“When an apparently simple conjunctivitis does not resolve after treatment, and there is increased conjunctival swelling or maybe even granuloma formation, keep this diagnosis in mind,” said Nicole Verhaar, DVM, an equine surgery resident at the University of Veterinary Medicine Hannover Equine Clinic, in Germany. She completed the study when she was a researcher at the Utrecht University Faculty of Veterinary Medicine, in the Netherlands