Main

Sir,

We present a rare case of recurrent subconjunctival infection with the dog heart-worm Dirofilaria. This parasite is transmitted via mosquito bites1,2 and is well known to the veterinary profession as a parasite of cats and dogs.1,3 Humans are an accidental host. This zoonotic infection is increasing in incidence in Italy and France.4

Case report

A 25-year-old lady from West Africa came into the eye casualty complaining of an intermittent feeling of ‘something moving under her eyelid’. She had a past ocular history of a parasitic conjunctival infection with the dog heart-worm Dirofilaria. She had travelled to West Africa and France in the past year.

On examination a mobile mass was visible under the conjunctiva. She was immediately taken to theatre and given topical and subconjunctival anaesthesia. An incision was made into the inferior conjunctiva where a live worm was visible in the subconjunctival space (Figure 1). On making the incision, the worm started to move further towards the inferior fornix, but was prevented from doing so by grasping it gently with a pair of toothed forceps. As it was being held in the forceps, the worm made several twisting movements in an attempt to free itself, but was successfully extracted using firm, steady traction (Figure 2) and sent for histology. It was identified as a female Dirofilaria, possibly Dirofilaria repens.

Figure 1
figure 1

Worm visible in the subconjunctival space

Full size image
Figure 2
figure 2

The worm is removed with gentle traction

Full size image

She was given chloramphenicol ointment to apply four times a day for a week and asked to return for review in a fortnight. On her return visit, the eye was quiet with no signs of recurrence.

Comment

Dirofilaria has been termed the ‘cosmopolitan parasite’ as it has its highest incidence in the Mediterranean basin.1 Italy has the highest prevalence of D. repens with the number of cases increasing in the past 10 years.4,5 This is possibly because of a climate alteration that favours the mosquito population.4 Southern France and Sri Lanka have reported several cases of human infestation. A handful of human cases have also emerged in Australia, Thailand, Malaysia, Africa, Spain, Greece, the Netherlands, Israel, and ex-USSR countries. Dirofilaria immitis, D. tenuis, and D. ursi have been observed in humans in North America.1

Dirofilaria is a nematode that predominantly inhabits dogs and cats. The adult filaria lives in cutaneous connective tissue and emits blood microfilaria. These are transmitted by mosquitoes of the genus Aedes, Anopheles, or Culex.1,3 Dogs and cats are the final hosts. Humans are rarely infected and are accidental hosts. After an infected mosquito transmits the disease, the microfilaria becomes encysted into a subcutaneous nodule where it matures. The parasite is able to survive for several years in humans. Female worms outnumber male infestations by 5:1.4 Extracted worms are often immature.

The nematode is able to migrate and shows a preference for the upper body, especially the head and upper limbs. An Italian review4 of 60 cases found that 49 were subcutaneous, two in the omentum, two in breast tissue, two in lung, two in the epididymus, two in the spermatic cord, and one in the conjunctiva. Around the eye, sites most commonly affected are the subcutaneous tissue of the eyelids and the periorbital region.2 If ocular, it tends to appear in the eyelid or under the conjunctiva. An Australian report described an anterior chamber worm and an intravitreal worm was found in Malaysia.6

Patients with ocular Dirofilaria can present with pain and itching or awareness of an intermittent or continuous mass. On examination, the eye may be quiet or an area of hyperaemia and raised conjunctiva may be seen. Enlargement of satellite lymph nodes is occasionally seen.

Treatment is by surgical removal. No antiparasitical treatment is necessary.1,6