Household pit latrines as a potential source of the fly Musca sorbens--a one year longitudinal study from The Gambia.

OBJECTIVES: To assess whether the trachoma vector Musca sorbens was breeding in household latrines in a trachoma-endemic part of The Gambia.
METHODS: Longitudinal study of flies emerging from 16 sentinel household latrines selected at random from a list of all latrines present in four Gambian villages. Latrines were surveyed and fly traps were set over the drop hole for 24 h once per month for a year.
RESULTS: All the sentinel latrines were of the 'Gambian improved household latrine' design, which has a cement slab but is not ventilated or fly-proofed. The latrines were all in regular use by a family, mean number of users per latrine 14.8 (SD 8.0, range 2-29). Of 55 351 flies caught in 192 catches 54 130 (97.8%) were Chrysomya albiceps, 690 (1.2%) Musca domestica, 466 (0.8%) Chrysomya regalis and 65 (0.1%) M. sorbens. Of the M. sorbens caught 61 (93.8%) were female.
CONCLUSIONS: Gambian improved household pit latrines cannot be considered a source of the trachoma vector M. sorbens, and the promotion of pit latrines as a method to reduce M. sorbens is warranted. A large number of C. albiceps were caught emerging from the latrines, but this species is not considered to be of medical importance.