Based on the possibility that “Anecdotal evidence suggests that smoke may play an important role by providing protection from biting insects and that efforts to reduce smoke may increase exposure, particularly to mosquitoes and malaria,” Biran et al., recently conducted a review of previous research. Various domestic sources of smoke were found including that from cooking fires and local herbs that were burnt to repel mosquitoes. Although they did not find much research that addressed the question directly, they were able to suggest the following:
- Smoke from domestic fuel use probably does not have much effect on mosquito feeding
- Mosquito feeding is affected by smoke from certain plant products traditionally used as repellents
- Soot from domestic fires, although not toxic to mosquitoes, does not impair the effectiveness of ITNs
- Soot may, however, increase the frequency with which nets are washed and thus accelerate the loss of insecticide from ITNs
The authors concluded that, “There appears to be a good health argument for continuing efforts to reduce indoor air pollution, even in areas where malaria is endemic. It is likely that such efforts will have substantial health benefits in reducing respiratory disease and unlikely that the reduction of smoke per se will have any significant health costs in terms of increased malaria.”
Smoke as a mosquito control intervention is not common – in fact it was as far back as 1923 that the Transactions of the Royal Society of Tropical Medicine and Hygiene contained an article explaining how smoke from burning straw was used to drive mosquitoes from hiding places where they could be manually killed.
While the identification of local repellent herbs was important, another common source of smoke that was not addressed in the recent article was the mosquito coil. These are cheap and ubiquitous in endemic communities, although some community members do complain about the fumes causing breathing problems. According to Pauluhn and Mohr, “Overnight exposure to the smoke from burning mosquito coils (manufactured in Indonesia) is unlikely to be associated with any unreasonable health risk.” Of course people in endemic communities use coils over many nights (see comment).
The question is whether coils work. Lawrance and Croft reviewed literature and concluded that, “There is no evidence that burning insecticide-containing mosquito coils prevents malaria acquisition. A randomized field trial should be conducted, with malaria incidence as a primary outcome. There is consistent evidence that burning coils inhibits nuisance biting by various mosquito species. The potential harmful effects of coil smoke on human users should be investigated.”
In the end we don’t need smoke and mirrors to control malaria, but reliable and adequate supplies of interventions of known value such as long-lasting insecticide treated nets.