Flies and public health – A brief review
By Dr Cathy Smallridge
It has long been known that flies are insects of public health importance [1]. It is estimated that flies may be responsible for transmitting up to 65 different disease organisms [2]. Some fly species also lay eggs on live animals and humans, and the emerging larvae cause a wound in which they feed, creating pain, illness and distress [3].
Flies visit places such as dumps, sewers and garbage heaps. They feed on faecal matter, pus from sores, sputum and all sorts of decomposing matter such as decaying fish, eggs and meat. Flies regurgitate and excrete their waste wherever they come to land, and in this way they can mechanically transmit disease organisms. Flies can carry disease organisms on their mouth parts, through their vomitus, on their body and leg hairs, on the sticky pads of their feet and through the intestinal tract via their faeces. They are known to transmit typhoid, bacillary dysentery, amoebic dysentery, giardiasis [1] and worms [4].
Diarrhoeal infections due to Vibrio cholerae are normally spread through faecal-oral routes, but research suggests flies may also play a role in the transmission of cholera [5]. Similarly, the spread of gastrointestinal infections due to Campylobacter spp. may be explained by the seasonal activity of flies [6]. Flies are also implicated in the transmission of E. coli, Salmonella, and Shigella [7]. Whether flies are capable of transmitting COVID-19 has not been demonstrated as yet, but they have been demonstrated to transmit Turkey coronaviruses[8] and it is known that the virus can be detected in sewerage water [9]
The house fly has been demonstrated to transmit Chlamydia [10], as has the Australian bushfly [11]. Trachoma, the disease caused by Chlamydia, can cause death among children. Established infections are difficult to treat and can cause blindness.
Fly management requires an integration of many approaches including limiting flies access to resources, physical exclusion, chemical control and trapping (for example, see https://www2.health.vic.gov.au/-/media/health/files/collections/policies-and-guidelines/p/technical-note-number-23—flies.pdf)
References
1. Scott, H.G. and K.S. Littig, Flies of Public Health Importance and their Control, U.D.o.H.E.a. Welfare, Editor. 1962: Atlanta, Georgia.
2. Jacobs, S.B., House Flies, in https://ento.psu.edu/extension/factsheets/house-flies, P.S. University, Editor. 2013: Pensylvania.
3. Francesconi, F. and O. Lupi, Myiasis. Clinical Microbiology Reviews, 2012. 25(1): p. 79.
4. El-Sherbini, G.T. and E.T. WEl-Sherbini, The role of cockroaches and flies in mechanical transmission of medical important parasites. Journal of Entomology and Nematology, 2011. 3(7): p. 98-104.
5. Fotedar, R., Vector potential of houseflies (Musca domestica) in the transmission of Vibrio cholerae in India. Acta Tropica, 2001. 78(1): p. 31-34.
6. Ekdahl, K., B. Normann, and Y. Andersson, Could flies explain the elusive epidemiology of campylobacteriosis? BMC Infectious Diseases, 2005. 5(1): p. 11.
7. Forster, M., et al., Pilot study on synanthropic flies (eg Musca, Sarcophaga, Calliphora, Fannia, Lucilia , Stomoxys) as vectors of pathogenic microorganisms. Parasitology Research, 2007. 101: p. 243-246.
8. Calibeo-Hayes, D., et al., Mechanical transmission of turkey coronavirus by domestic houseflies (Musca domestica Linnaeaus). Avian diseases, 2003. 47(1): p. 149-153.
9. Ahmed, W., et al., First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community. The Science of the total environment, 2020. 728: p. 138764-138764.
10. Forsey, T. and S. Darougar, Transmission of chlamydiae of the housefly. . Br. J. Ophthalmol., 1981. 65: p. 147–50.
11. Da Cruz, L., et al., Seasonal variation in trachoma and bush flies in north-western Australian Aboriginal communities. Clinical & experimental ophthalmology, 2002. 30(2): p. 80.
