Responses of the putative trachoma vector,Musca sorbens, to volatile semiochemicals from human faeces

Abstract

BackgroundThe putative vector of trachoma, Musca sorbens, prefers to lay its eggs on human faeces on the ground. This study sought to determine whether M. sorbens females were attracted to volatile odours from human faeces in preference to odours from the faeces of other animals, and to determine whether specific volatile semiochemicals mediate selection of the faeces.Methodology/Principal findingsTraps baited with the faeces of humans and local domestic animals were used to catch flies at two trachoma-endemic locations in The Gambia and one in Ethiopia. At all locations, traps baited with faeces caught more female M. sorbens than control traps baited with soil, and human faeces was the most successful bait compared with soil (mean rate ratios 44.40, 61.40, 10.50 [P<0.001]; 8.17 for child faeces [P=0.004]). Odours from human faeces and some domestic animals were sampled by air entrainment. Extracts of the volatiles from human faeces were tested by coupled gas chromatography-electroantennography with laboratory-reared female M. sorbens. Twelve compounds were electrophysiologically active and tentatively identified by coupled mass spectrometry-gas chromatography, these included cresol, indole, 2-methylpropanoic acid, butanoic acid, pentanoic acid and hexanoic acid.Conclusions/SignificanceIt is possible that some of these volatiles govern the strong attraction of M. sorbens flies to human faeces. If so, a synthetic blend of these chemicals, at the correct ratios, may prove to be a highly attractive lure. This could be used in odour-baited traps for monitoring or control of this species in trachoma-endemic regions.Author summaryMusca sorbens, also known as the Bazaar Fly, visits people’s faces to feed on ocular and nasal discharge. While feeding, M. sorbens can transmit Chlamydia trachomatis, the bacterium that causes the infectious eye disease trachoma. Around 1.9 million people worldwide are visually impaired or blind from this disease. Although it is believed that M. sorbens transmits trachoma, very few studies have looked at ways to control this fly. A large-scale trial has shown that control of fly populations with insecticide reduces active trachoma disease prevalence. Odour-baited traps for the suppression of disease vector populations are an attractive option as there is no widespread spraying of insecticide, however, highly attractive baits are critical to their success. Here we demonstrate that the preference of these flies for breeding in human faeces is probably mediated by odour cues, and we isolate chemicals in the odour of human faeces that cause a response in the antennae of M. sorbens. These compounds may play a role in the specific attractiveness of human faeces to these flies, perhaps by being present in greater amounts or at favourable ratios. These may be developed into a chemical lure for odour-baited trapping to suppress M. sorbens populations.

Towards an odour-baited trap to control Musca sorbens, the putative vector of trachoma

“…A small number of studies report M. sorbens trapping. Human faeces as an attractant in the Bristow trap caught totals of 250, 1138 and 152 M. sorbens over three studies, giving 16.7/11, 71.1/66 and 6.3/6 (mean/median) per 24 h 17 . In two studies that tested blue and yellow sticky traps, as well as sticky pots (equivalent to Bristow traps), blue sticky traps caught a mean of 4.87 and then 4.92 M. sorbens per trap night (24-h period) 12 .…”

“…Determining the optimal trap density becomes less important if the trap is cheap, easy to use and people are willing to have it placed outside their house and maintain it. Future studies could explore replacing The Buzz lure with M. sorbens-specific semiochemicals 17 , although developing such a lure to a field-ready state will require significant research investment, with the financial and timescale implications. Finally, few tools exist for the control of M. sorbens.…”

Analysis of volatiles from feces of released Przewalski’s horse (Equus przewalskii) in Gasterophilus pecorum (Diptera: Gasterophilidae) spawning habitat

“…Robinson et al . 27 found that butanoic acid from human feces induced EAG response of bazaar fly ( Musca sorbens Wiedemann), while that in steers’ rumens volatiles could attract stable fly 28 . Butanoic acid found in pig manures is one of the most active compounds that induce EAG response of female house fly, but acetic acid does not induce the same response 29 .…”

Eliminating Trachoma by 2020: Assessing Progress in Nigeria

“…The end goal of this campaign is to provide access to sanitation, including lavatories with soap, to all Nigerians, especially in rural areas. Studies have shown that access to basic pit latrines lead to a significant reduction in the numbers of eye-seeking flies, correlating with an overall reduction in trachoma [ 29 , 30 ].…”