Studies on the potential and public health importance of non-biting synanthropic flies in the mechanical transmission of human enterohelminths.

BACKGROUND: This study was aimed at examining the potential of non-biting synanthropic filth flies to acquire naturally eggs of human intestinal helminths from unsanitary sites, and its attendant public health importance.

METHODS: Body surface washings and gut contents of flies caught foraging while infected human faeces lay exposed at a garbage dump in Iperu, Ogun State, Nigeria and within 24 hours subsequently after removal of faeces from the dump were examined parasitologically by the formol-ether concentration technique. The viability of helminth eggs isolated from flies was determined by incubation under laboratory conditions.

RESULTS: A total of 303 flies were examined: Musca domestica (107; 35.3%), Chrysomya megacephala (125; 41.3%) and Musca sorbens (71; 23.4%). Eggs of Ascaris lumbricoides and Trichuris trichiura isolated from exposed human faeces were recovered from the body surfaces and or gut contents of flies caught before (141; 77.5%) and after removal of exposed faeces (44; 36.4%). Eggs of Taenia sp. were isolated only from the gut contents of three C. megacephala flies caught after removal of exposed faeces. Significantly more (p<0.05) eggs were recovered from fly gut contents than body surfaces and from flies caught before than after removal of exposed faeces. 93.1% (552; from exposed faeces) and 57.4% (408; from flies) of A. lumbricoides and T. trichiura eggs were viable.

CONCLUSIONS: Synanthropic flies may, because they carry viable eggs acquired naturally from unsanitary sites, be involved in the epidemiology of human intestinal helminthiases.