ArticlesEffect of fly control on trachoma and diar rhoea
Introduction
Flies act as mechanical vectors of many pathogens, but they are commonly overlooked in public health interventions. Childhood diarrhoea causes 3·3 million deaths worldwide per year, with an estimated 1 billion cases of diarrhoea annually in children under 5 years.1 Flies are known vectors of diarrhoea-causing pathogens, particularly those requiring a minute inoculum such as shigella.2, 3, 4, 5 Chlamydia trachomatis causes trachoma, and has been found on flies fed on heavily infected laboratory culture media.6 There is an association between flies and trachoma,7, 8, 9 but as yet there are no field-based or epidemiological studies that show that flies are direct vectors of trachoma.
Trachoma is the main cause of preventable blindness worldwide.10 Such blindness is more common in women than men11 and results from repeated ocular C trachomatis infections over many years. In les-developed countries, young children are the reservoir of infection, and transmission is clustered within villages,10, 11, 12 but the mechanisms by which infection is spread are poorly understood. An intervention that lowers the frequency of transmission is likely to lower the prevalence of trachoma-related blindness in the future.
The WHO initiative for the global elimination of trachoma by the year 2020 (GET 2020) aims to control trachoma by eyelid surgery, antibiotic treatment, facial cleanliness, and environmental improvement (the SAFE strategy). However, the implementation and sustainability of antibiotic therapy is beset by poor compliance with topical application of ophthalmic tetracycline eye ointment13 and by the prohibitive cost of oral azithromycin. Trachoma is associated with poverty, and largely disappears under improved environmental conditions and access to better sanitation.14 Nonetheless, the prospect of rapid global improvement remains bleak. The SAFE strategy would be strengthened by the inclusion of realistic and sustainable methods to reduce trachoma transmission.
We undertook a pilot study to investigate the role of domestic flies in the transmission of trachoma and diarrhoea.
Section snippets
Study population
Our study took place in four villages over 3 months in the Sanjal area of The Gambia.15 One pair of villages was studied from September, 1997, to December, 1997 (the wet season), the other pair was studied from January, 1998, to April, 1998 (the dry season). The two pairs of villages were selected from 23 available small villages with populations of less than 400 in the Sanjal district on the basis of trachoma prevalence, lack of immediate access to primary health-care, homogeneous ethnic
Entomology
Muscid flies (Musca sorbens-bazaar fly: M domestica- housefly) were more abundant in the wet–season control village than in the dry–season control village the median (range) of the adjusted geometric mean numbers of flies per trap per day was 9·80 (2·29–37·3) versus 5·98 (2·41–38·3), respectively, for M sorbens; and 10·2 (2·5–102·9) versus 4·24 (1·14–12·05) respectively, for M domestica. Spraying resulted in 76% fewer M sorbens (2·15 [0·19–5·62], p=0·02) and 57% fewer M domestica (4·44
Diarrhoea
All resident children aged between 3 months and 60 months were recruited for diarrhoea surveillance, 263 children in total. Data were obtained for over 90% of possible child-days of observation, with no significant differences between villages or age groups. The distribution of numbers of children under 60 months per family was not significantly different in the four villages (table).
Children in the dry season had 58% less diarrhoea than those studied in the wet season (period prevalence
Discussion
In our pilot study the control of muscid flies lowered the transmission of trachoma and the period prevalence of diarrhoea in children. However, our study was done in only four small settlements and may have been affected by bias—for example, realisation that there were fewer flies at certain times might have made the mothers report less diarrhoea and led the nurse to make differential observations of trachoma. We cannot exclude this possibility, but it does not seem likely to have affected our
References (19)
- et al.
Reduction of transmission of shigellosis by control of houseflies (Musca domestica)
Lancet
(1991) - et al.
The housefly (Musca domestica) as a carrier of pathogenic micro organisms in a hospital environment
J Hosp Infect
(1992) - et al.
Impact of face-washing on trachoma in Kongwa, Tanzania
Lancet
(1995) - et al.
The magnitude of the global health problem of diarrhoeal disease: a ten year update
Bull World Health Organ
(1992) - et al.
A comparison of the role of Musca domestica (Linnaeus) and Chrysomya megacephala (Fabricius) as mechanical vectors of helminthic parasites in a typical slum area of metropolitan Manila
S E Asian J Trop Public Health
(1991) The isolation of Campylobacter jejuni from flies
J Hyg1
(1983)- et al.
Transmission of chlamydiae by the housefly
Br J Ophthalmol
(1981) The epidemiology of trachoma in Egypt
Br J Ophthalmol
(1931)- et al.
Studies in the epidemiology and control of seasonal conjunctivitis and trachoma in Southern Morocco
Bull World Health Organ
(1968)
Cited by (163)
Development of QuEChERS method for simultaneous detection of cyromazine and melamine residues in eggs
2024, Journal of Food Composition and AnalysisEvaluation of the efficacy of insecticide-treated scarves to protect children from the trachoma vector Musca sorbens (Diptera: Muscidae): A phase II randomised controlled trial in Oromia, Ethiopia
2022, eClinicalMedicineCitation Excerpt :In the field trial intervention arm, across all timepoints we found a 35% decrease in fly-eye contact relative to the control arm. Insecticide space spraying was associated with a 96% and 88% reduction in fly-eye contact in two studies conducted in The Gambia,5,6 although fly-eye contact was not measured in precisely the same way. At our study site, fly density and clustering around the eyes was extreme; catching all flies to count them, as was undertaken in previous trials in the Gambia,5,6 was not possible here without disturbing the flies and altering the count.
Frequency of Mass Azithromycin Distribution for Ocular Chlamydia in a Trachoma Endemic Region of Ethiopia: A Cluster Randomized Trial
2020, American Journal of OphthalmologyThe public health benefits of urban sanitation in low and middle income countries
2018, Utilities PolicyUrban Onsite Sanitation Upgrades and Synanthropic Flies in Maputo, Mozambique: Effects on Enteric Pathogen Infection Risks
2023, Environmental Science and Technology