Eyeworm (Thelazia californiensis) in Dogs

One or more of the following symptoms are usually noticed during an infection of dog eyeworms: 

• Excessive tearing of the eyes
• Inflamed conjunctiva (conjunctivitis)
• Opaque corneas of the dog’s eyes
• Slow healing sores or ulcers on the corneas of the eye
• Blindness (rare)
• Itching of the dog’s eyes
• Excess of blood vessels on the whites of the eyes
• Small, white to cream colored, active worms on the dog’s eyes, looking similar to nylon fishing line
• Light sensitivity to the eyes
• Swollen eyes 
• Pus in the eyes

Types

Thelazia californiensis is a species of parasitic roundworm that affects dogs, cats, and sometimes humans. It was first discovered in California during the 1930s and was recognized as a new species of eyeworm at that time. There are approximately a dozen species of eyeworms, but Thelazia californiensis is the most prevalent type that occurs in domestic animals such as dogs. Three to four year old, large dogs are more likely to become infected than younger, smaller dogs.

The method of treatment to eliminate the Thelazia californiensis eyeworm must be determined by your veterinarian. Correct use of these medications is necessary to achieve complete elimination of the eyeworm infection. The following are a few methods that may be recommended or administered.

Local anesthetic may be administered to the dog’s eyes by your veterinarian. Then forceps will be used to carefully remove the worms from the eyes.

Anti-parasitic topical eye solutions and ointments such as selamectin, moxidectin and levamisole solutions, or levamisole and morantel ointments may be prescribed. Sometimes administering eye treatments to your dog can be difficult. It requires your dog to be still for a brief time, which may require some assistance, especially if your dog is experiencing a lot of pain and discomfort from the infection.

Injected anti-parasitic medication such as moxidectin is sometimes administered by the veterinarian. This will be injected into the muscle of the dog.

Anti-parasitic oral medication such as ivermectin tablets, moxidectin tablets, or milbemycin oxime tablets are often times prescribed. This is an easy way to treat the disease.