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Human and other faeces as breeding media of the trachoma vector Musca sorbens
P M Emerson1, R L Bailey, G E Walraven
1Medical Research Council Laboratories, Banjul, The Gambia. pemerson@mrc.gm
Abstract:
The fly Musca sorbens Wiedemann (Diptera: Muscidae) apparently transmits Chlamydia trachomatis, causing human trachoma. The literature indicates that M. sorbens breeds predominantly in isolated human faeces on the soil surface, but not in covered pit latrines. We sought to identify breeding media of M. sorbens in a rural Gambian village endemic for trachoma. Test breeding media were presented for oviposition on soil-filled buckets and monitored for adult emergence. Musca sorbens emerged from human (6/9 trials), calf (3/9), cow (3/9), dog (2/9) and goat (1/9) faeces, but not from horse faeces, composting kitchen scraps or a soil control (0/9 of each). After adjusting for mass of medium, the greatest number of flies emerged from human faeces (1426 flies/kg). Median time for emergence was 9 (inter quartile range = 8-9.75) days post-oviposition. Of all flies emerging from faeces 81% were M. sorbens. Male and female flies emerging from human faeces were significantly larger than those from other media, suggesting that they would be more fecund and live longer than smaller flies from other sources. Female flies caught from children's eyes were of a similar size to those from human faeces, but significantly larger than those from other media. We consider that human faeces are the best larval medium for M. sorbens, although some breeding also occurs in animal faeces. Removal of human faeces from the environment, through the provision of basic sanitation, is likely to greatly reduce fly density, eye contact and hence trachoma transmission, but if faeces of other animals are present M. sorbens will persist.
Insights
Musca sorbens flies, which transmit the bacteria causing trachoma, primarily breed in human feces. Controlling human waste is key to reducing fly populations and preventing disease transmission.
Area of Science:
- Medical Entomology
- Public Health
- Tropical Medicine
Background:
- Trachoma, a leading cause of preventable blindness, is transmitted by the fly Musca sorbens.
- Musca sorbens is believed to breed in exposed human feces, but definitive breeding sites in endemic areas require identification.
Purpose of the Study:
- To identify the preferred larval breeding media for Musca sorbens in a rural Gambian village.
- To understand the role of different fecal types in Musca sorbens proliferation and potential impact on trachoma transmission.
Main Methods:
- Experimental oviposition of Musca sorbens on various potential breeding media including human, calf, cow, dog, and goat feces, horse feces, and kitchen scraps.
- Monitoring of adult fly emergence from presented media over time.
- Measurement of fly size and comparison between flies emerged from different media and those caught from children's eyes.
Main Results:
- Musca sorbens successfully emerged from human, calf, cow, dog, and goat feces, with significantly higher emergence rates and numbers from human feces (1426 flies/kg).
- Flies emerging from human feces were larger, suggesting greater fecundity and longevity.
- Female flies caught from children's eyes were similar in size to those from human feces, indicating human feces as a primary source.
Conclusions:
- Human feces are the optimal larval breeding medium for Musca sorbens, though some breeding occurs in animal feces.
- Environmental management focusing on the removal of human feces through sanitation is crucial for reducing fly populations and trachoma transmission.
- Persistence of Musca sorbens is likely if animal feces remain in the environment, necessitating comprehensive waste management strategies.
