A study of cutaneous myiasis in Sri Lanka

Cutaneous myiasis (CM) due to Diptera fly larvae shows different patterns in different regions. Many modalities of treatment have been described. The objectives of our study were to identify the species causing CM in Sri Lanka, the common sites of infestation, and the contributory factors, and to assess some treatment modalities, in particular mineral turpentine and certain herbal preparations.

All patients with CM admitted or referred to the Dermatology Unit at the General Hospital, Kalutara, over 18 months starting from July 1997, and all patients with CM from the orthopedic and surgical wards of the National Hospital of Sri Lanka in Colombo over 6 months from July 1997, were studied. Details of the history and examination were recorded on specially designed forms. Maggots extracted were identified at the Department of Parasitology, Faculty of Medicine, University of Colombo. The modalities of treatment employed in the patients were recorded. In the Department of Parasitology, a colony of Chrysomya megacephala was maintained. Homogenized leaf extracts of Azadirachta indica (neem) and Pongamia pinnata (Indian beech) and mineral turpentine (active ingredient--low aromatic white spirits) were tested for efficacy in killing C. megacephala larvae in vitro. Leaf extracts were not used directly on patients.

There were 16 patients (10 males and five females; the sex of one patient was not recorded). The mean age was 58.5 years (range, 11-94 years). Identification of larvae revealed C. bezziana in 14 (87.5%) and C. megacephala in two (12.5%) patients. The foot was affected in 15 (93. 7%) and the scalp in one patient. The immediate predisposing factor for CM in dermatology patients was infected dermatitis. The other relevant associated factors were: diabetes mellitus, psychiatric illness, leprosy, and mental subnormality. Turpentine was a useful adjunct in the removal of maggots manually. There were no side-effects to turpentine. In the in vitro testing, turpentine was 100% effective in killing maggots. Some patients required surgical removal under anesthesia. Indian beech and neem leaf extracts were not effective against Chrysomya larvae in vitro.

All cases of CM were due to larvae of Chrysomya species. The commonest was C. bezziana. C. megacephala larvae causing CM have been reported for the first time in Sri Lanka. The foot was the site of predilection. Dermatitis, psychiatric illness, leprosy, diabetes, and mental subnormality were some contributory factors. Topically instilled mineral turpentine, followed by manual removal of maggots, was effective in most cases. The plant extracts tested in vitro were ineffective. As C. bezziana is an obligatory parasite capable of penetrating deeply, the importance of preventive measures is emphasized.