What is Eyeworm (Thelazia californiensis)?
The Thelazia californiensis species of dog eyeworms are whitish worms found in the eyes of domestic dogs and cats. Humans have been known to become infected, but it is very rare. The eyeworms visibly move across the dog’s eyes in a rapid, serpentine motion. As many as a 100 worms may be present in the tear ducts, on the conjunctiva (the mucous membrane that covers the front of the eyes) and under the eyelids. This species of eyeworm is most commonly found in western North America and is more prevalent during fly season (late spring through early fall).
Eyeworms are parasites of the orbits of the eye, found on the conjunctiva and under the lids and nictitating membrane. This disease is commonly known as thelaziasis.
Symptoms of 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.
Causes of Eyeworm (Thelazia californiensis) in Dogs
Transmission of face fly, housefly, or filth fly larvae is the cause of infection of the Thelazia californiensis species of dog eyeworm. The adult female eyeworm lays eggs in the tears of the eyes. Once in the tears, the eggs develop into larvae, which a face fly will then ingest. Inside the fly, the larvae develop for approximately 30 days at which time they will move to the mouth of the fly. When the adult flies are feeding near a dog’s eyes, the larvae move out of the fly’s mouth and move to the eyes of the dog. It takes about 3-9 weeks for the larvae to develop into adults and repeat the cycle.
Diagnosis of Eyeworm (Thelazia californiensis) in Dogs
Your veterinarian will examine and evaluate the dog’s eyes and tissues near the eyes. The eyes may be flushed (rinsed) to clean the infection and help to prevent secondary bacterial infection. The matter collected during the rinsing of the eyes may also be examined for presence of the worm. The dog eyeworms are usually very active and easy to see, making the diagnosis obvious. Your veterinarian may choose to remove the eyeworms. Most likely your dog will just be treated with medication. The medication will be sent home with instructions for continued treatment.
Treatment of Eyeworm (Thelazia californiensis) in 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.
Recovery of Eyeworm (Thelazia californiensis) in Dogs
In order to prevent eyeworms of the dogs, the fly population needs to be controlled. Controlling or eliminating the fly population and the opportunity for the face flies to feed on the dog’s eyes will significantly reduce the spread of the eyeworms. Waste management is necessary by removing accumulations of garbage, scraps, manure, and other matter and filth where flies like to live will help dramatically. While taking your dog for a walk in an area with a large fly population, using a fly repellent may be advisable.
Eyeworm (Thelazia californiensis) Questions and Advice from Veterinary Professionals
Medication Used
Hi, my dog is having swollen eyes for roughly one month. He can barely open his eyes. No tears form, the eyes are puffy, the conjuctiva is red and yellowish mucus can be seen if i try to open his eyelid. I think i see something black in his eyes, long in form but it is definitely not his iris. I saw that only on his right eye. Prior to this he had diarrhoea. Now he is well aside from swollen eyes and squinting his eyes whenever there is light. I am wondering what happen to his eyes. I hope to hear from you soon.
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Hi.My shih tzu dog aged 11. He has already been affected by this which lead to blindness. Now he is affected by this worms. Although we've met the vetenarian,his condition hasn't change but getting worst. Dr, could you suggest any kind of medication or home remedy to cure him. Tq
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I have a senior dog with a small white line in his pupil. It doesn’t seem to move so I am not convinced that it is a worm. No weeping or anything. He has early stage glaucoma.
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Does my dog of eye worms, parasite? I do not know. I need help urgently and fast because I fear of this leading to blindness. This may be a cause of not cleaning her eye tears daily. Please if you can answer me in short time. This is Urgent.
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There are many different causes of the symptoms which you are describing and with the severity described you would need to visit your Veterinarian for a diagnosis and for treatment (over the counter medicines probably will not solve this one). Possible causes are infection, parasites, keratoconjunctivitis sicca among other causes; without a hands on examination I couldn’t tell you the cause. To ensure that Lulu keeps her sight, visit your Veterinarian immediately. Regards Dr Callum Turner DVM
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Hello my 13 year old female yellow lab's left eye has been bothering her for about a month. The symptoms appeared over a 5 day period. I have been keeping her eyes clean by using warm water and a damp cloth when any eye boogers appear. Tonight however I noticed clear worm like looking objects in her eye; however not every time that I look in her eye do I see them. I live in the San Bernardino Mountains in California which I saw online is a geographical location that may have eyeworms. Though she mostly stays in and around the house with access only to hose water and not streams etc. Does this seem like worms or just mucus that looks like eyeworms as it moves around her eye? Thanks for your time.
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I live in Pittsburgh, Pa. My 13 yr old Lab has a dark sack on his right eyelid, is this a parasite and is there anything safe that I can put on it prior to a vets visit. Thank you, Vince
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I have a 3 day old puppy who today we noticed one eye is open and covered in worms. Trying to figure out what to do? They were born outside and we didn't find them til this morning. The mother is a stray that is skittish of humans that we been feeding about 4 months she is taken care of all 4 of them still but wondering what we can do to make sure all 4 survive.
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