The Thelazia callipaeda eye worm is carried by a common fruit fly and there have been numerous cases of dogs becoming infected in European countries such as France, Italy, Spain and Greece.
But in 2017, pet owners were warned that the parasitic worm that can cause blindness in dogs and cats could spread to the UK after news reports highlighted three dogs that brought the worm back to the UK from mainland Europe.
The 2016-17 cases were reported on at the time by Veterinary Record, which described the worm as a "significant threat to the UK canine population".
Reported cases after that were few and far between until Vet Chris Dixon discovered the worms in the eye of Labrador Retriever imported to the UK from Serbia in July 2021, showing that the threat of thelaziasis in the UK remains.
What is thelaziasis?
Thelaziasis is an infection caused by thelazia callipaeda – a parasitic eye worm.
It's carried and transmitted by a common species of fruit fly that feeds on eye secretion and deposits the worm's larvae into the eyes of carnivores, including cats, dogs and humans.
The larvae then settle and reproduce in the host's tear canals, the inner lining of the eyelids and layers of the lining of the eyeballs.
Because dogs spend more time digging around outside in areas where the fly can be found they seem to be more susceptible to the infection than cats.
The earliest record of thelaziasis is from 1910 when two scientists observed adult worms in a dog’s eyes in China. Thelazia callipaeda has a long historical prevalence in Russia and the Far East.
A 2017 Veterinary Record report published by the British Medical Journal (BMJ) warns of a growing number of dogs in Europe contracting the parasite.
The article also describes three cases of dogs affected in the UK. One was a puppy imported from Romania; one, a fox terrier, had recently returned from a trip to Italy and another, a highland terrier, from a trip to France.
The danger is that a fly could land on an infected dog and then pass the worm on to other cats, dogs and even humans, causing the infection to spread.
What are the symptoms of thelaziasis?
Common symptoms are mild or severe inflammation of the inner lining of the eyelids, characterised by swelling and oozing; ocular ulcers and permanent blindness.
Adult worms can be seen floating in the eyes of infected pets, but larvae and eggs can only be seen by using specialist magnifying equipment.
Not all infected pets will show symptoms. In one of the cases described by the Veterinary Record article, the worms were inadvertently spotted during a neutering procedure.
Worms can be removed under anaesthesia and the eyes treated with antibiotics. Further doses of antibiotics may be prescribed to target any remaining eggs and larvae.
All three dogs diagnosed with eye worms in the UK responded well to ointments for bacterial infections, antibiotics and eyewashes, and made full recoveries.
How to prevent thelaziasis
Fortunately, the risk of thelaziasis in the UK remains extremely rare and so far has been limited to a few isolated cases.
Try preventing flies from getting close to your pet's eyes and feeding on their tears.
Dogs are more susceptible to eye worms than cats because they spend more time in areas where fruit flies are likely to be, so be vigilant about flies circling around your dog when you're out for a walk.
Be aware that fruit flies can often be found in oak woodland areas. The flies tend to prefer these areas, especially in the hot months of the year.
You may want to consider avoiding taking pets abroad to countries where the parasite is widely found.
Veterinary Record says thelazia callipaeda is common in Italy, France, Switzerland, Germany, Spain, Portugal, Bosnia and Herzegovina, Croatia, Romania, Bulgaria, Hungary and Greece.
Some cases have also been reported in Belgium and Serbia.
If you are considering becoming a pet parent, bear in mind that dogs and cats can be imported from Europe – like in the case of the one-year-old collie suffering from eye worms who was imported from Romania. Make sure that you know what your pet’s original place of birth is and take preventative measures if needed.
It's also worth noting that there’s a large number of dogs being illegally imported from Europe to the UK, so be extra cautious when buying. If you suspect your dog might have been infected with the parasite, seek immediate veterinary help. Catching the infection as early as possible can prevent further complications and permanent eye damage.
Does ManyPets pet insurance cover thelaziasis?
ManyPets pet insurance policies will cover your pet for an eye worm infection if your pet isn’t already suffering from it when you take out the policy or has had it in the last two years.
If your pet has suffered from it in the past but at least three months have passed since any treatment or advice, our Pre-Existing conditions policy will cover thelaziasis.