Thelazia, the eyeworm, is a spiruroid nematode and numbers 16 different species.

The Asiatic eyeworm, Thel. callipaeda, has recently been found in many European countries. Its host is the dog, the cat, the fox and man.

Vectors are non-biting flies (Phortica variegata and scurivirgo) which ingest the larvae whilst feeding on the host's tears. The larvae mature in the fly then move out of its mouth into the eye of a new host. There larvae grow into adults which lay their eggs in the tear canal.

In the first study (Study 1) 10 veterinary practices in Southern Switzerland submitted all the eyeworms that they found in dogs' eyes between September 2005 and 2006 to the Institute of Parasitology, University of Zürich, Switzerland. In addition the Institute checked all foxes killed during the hunting season for Thelazia.

During July 2006 the first 100 dogs coming to my companion animal practice were checked for eyeworm (Study 2).

In Study 1, 71 cases of eyeworm were diagnosed in dogs, 35% had both eyes affected. Thelazia was also found in one or both eyes in 5.6 % of 126 foxes.

Clinical symptoms varied from mild conjunctivitis, follicular conjunctivitis to severe, fluorescin positive corneal ulceration.

In Study 2, 7 of 100 dogs were found to be infected with eyeworm. Three dogs didn't present any clinical signs of ocular disease, having been brought into the practice for a booster vaccination.

All worms were identified as Thelazia callipaeda.

Amongst the dogs there was no age or sex predilection, the German Shepherd Dog was overrepresented and there seems to be a predilection for large breeds.

To find the eyeworms it was important to use a good light source, apply local anaesthetic and to look behind the third eyelid for at least 10 seconds, as when the worms are very small only their movement can be detected.

Treatment consisted in removal of the worm with forceps and application of Moxidectin injectable 1-2 drops (Cydectin 1 %, Fort Dodge) locally into the eye and repeating the application after 2 weeks.

As preventative treatment the spot-on preparation Imidaclopridum and Moxidectin (Advocate, Bayer) was used successfully.

As more people take their animals abroad it is important to be aware of this parasite which could be imported into the UK by dogs returning from the continent.