New research suggests that house flies may be playing a significant role in fuelling Africa’s worst cholera outbreak in 25 years, by carrying the bacteria from contaminated environments directly onto human food.
Scientists say this mechanism could be accelerating the spread of the disease beyond the traditional routes of unsafe water and person-to-person transmission.
More than 300,000 cholera cases were reported across 25 African countries last year, and experts warn that the involvement of flies could make outbreaks spread faster and become harder to control.
Professor Romain Glele Kakaï from the University of the Witwatersrand’s School of Public Health said researchers examined how frequently flies pick up bacteria from contaminated water, how easily they transfer the bacteria to food, and how long they survive in the environment.
“The role of house flies is very determinant in the dynamics of cholera,” Kakaï said. “What the study showed is that when we incorporate house fly population dynamics into cholera transmission, the disease can spread more quickly than expected when flies are involved.”
He warned that cholera transmission could become highly explosive when environmental vectors such as flies are active.
“The model suggests that even a small initial contamination may lead to a large outbreak. Once contaminated, flies can mechanically transmit the bacteria to many individuals in a short time, producing outbreak dynamics that resemble sparks igniting dry grass,” Kakaï said.
Kakaï added that the fast movement of house flies makes cholera outbreaks more unpredictable.
“What we found is that if interventions are implemented at the very beginning of an epidemic, this helps to control the epidemic. When the epidemic is already established, control is very hard to do,” he said.
He said interventions aimed at reducing house fly populations should focus on waste areas where the insects are most likely to multiply, alongside broader hygiene and sanitation measures.
Health experts say the findings highlight the need for early, multi-pronged responses to cholera outbreaks, including improved waste management, food safety and water sanitation.