Eyeworm Infection in a Dog

The increased frequency of emerging parasites, especially those of zoonotic concern, in the United States can be attributed to increased global travel. Nonnative parasite species translocated to a new geographic area can infect new host species and cause severe disease.  

Thelazia callipaeda (ie, oriental eye worm) is a nematode that reportedly infects dogs, cats, rabbits, wild carnivores (eg, red foxes), and humans.^1,2 T callipaeda requires Phortica spp drosophilid flies as an intermediate host in order to transmit to a new host and complete its life cycle. The flies feed on lacrimal secretions of an infected host, taking up first-stage larvae during feeding and depositing infective third-stage larvae after nematodes have developed.

This case report documented T callipaeda infection in an otherwise healthy 7.5-year-old Labrador retriever with no known travel history outside Dutchess County, New York. The patient was presented with a 3-week history of unilateral epiphora and blepharospasm unresponsive to treatment with a neomycin, polymyxin-B, and dexamethasone ophthalmic preparation. 

Nasolacrimal duct flush using gentamicin sulfate 0.3% and dexamethasone 0.2% in saline, followed by ivermectin (100 µg/mL) in saline allowed recovery of adult worms morphologically and molecularly identified as T callipaeda. Systemic ivermectin treatment eliminated the infection; no further treatment was required.  

This case report highlights an autochthonous infection of T callipaeda in the United States. T callipaeda is endemic in many Asian countries and has been documented in Europe since 2001.¹ Its zoonotic potential and ability to infect and use native Phortica spp as intermediate hosts in the United States make it a parasite of concern.^1,3 

In dogs and cats in Europe, documented ocular clinical signs of T callipaeda infection include conjunctival edema and hyperemia, conjunctivitis, epiphora, mucopurulent discharge, uveitis, and corneal abrasions.⁴ Additional studies of thelaziasis in dogs have suggested that moxidectin or milbemycin can be effective treatments.⁵

Key pearls to put into practice:

Travel history is not always an indicator of potential infection with novel or emerging parasites in the United States. Competent hosts for a variety of parasites can be found worldwide. It is therefore important to consider possible infection with atypical parasites.

Zoonotic potential should always be assumed when handling parasites unless true species identity is known. Many, but not all, parasites require an intermediate host for infection. Proper collection of parasites and safe handling of samples are important to ensure accurate diagnosis and safety of pet owners and clinic staff.

Controlling intermediate hosts like drosophilid flies is difficult. Owners should be made aware of how T callipaeda is transmitted, as knowing what to look for can help limit transmission to humans and/or other pets in the household.