Effect of fly control on trachoma and diarrhoea

Background Domestic flies are accepted vectors of diarrhoea, but their role in trachoma transmission has never been quantified and no study has shown that fly control decreases the prevalence of trachoma. We assessed the effe ct of fly control on public health in a pilot study in Gambian villages. Methods We studied two pairs of villages-one pair in the 1997 wet season, a nd one pair in the 1998 dry season. For each pair, deltamethrin was sprayed for 3 months to control flies in one village whilst the other was used as a control. Fly populations were monitored with traps. We surveyed trachoma at baseline and at 3 months, and collected daily data on diarrhoea in child ren aged between 3 months and 5 years. Findings Fly control decreased numbers of muscid flies by around 75% in the intervention villages compared with controls. Trachoma prevalence was simi lar at baseline (wet season, prevalence in intervention village 8.8% vs con trol 12.2%; dry season, 18.0% vs 16.0%), but after 3 months of fly control there were 75% fewer new cases of trachoma in the intervention villages (we t season 3.7% vs 13.7%; dry season 10.0% vs 18.9%; rate ratio and relative risk of pooled data 0.25 [adjusted 95% CI 0.09-0.64], p=0.003). There was 2 2% less childhood diarrhoea in the wet season (14% vs 19%, period prevalenc e ratio 0.78 [0.64-0.95], p=0.01), and 26% less diarrhoea in the dry season (6% vs 8%; 0.74 [0.34-1.59], p=0.60) compared with controls. Interpretation Muscid flies are important vectors of trachoma and childhood diarrhoea in The Gambia. Deltamethrin spray is effective for fly control a nd may be useful for reducing trachoma and diarrhoea in some situations, bu t further research on sustainable fly-control methods is needed.