Chronic illness as a result of low-level exposure to synthetic pyrethroid insecticides: a review of the debate.

Synthetic pyrethroid insecticides are widely used in public health and agriculture throughout the world and generally considered to be the safest class of insecticides available. In contrast to this belief stands a recent debate in Germany, around possible chronic effects of exposure to low levels of pyrethroid residues, particularly in the household. The debate is reviewed with a view to its potential implications on the use of synthetic pyrethroids on insecticide-treated nets (ITNs) for malaria control. Media coverage, rather than conclusive evidence from carefully planned scientific investigations, seems the underlying factor in the debate. However, chronic effects can presently not be excluded with certainty, as relevant toxicological data do not exist in the open scientific literature. Properly designed neuro-behavioural studies on groups with long-term exposure to low doses of synthetic pyrethroids should be conducted. This will require establishment of a working definition of "case" and "exposure". Meanwhile pyrethroids should continue to be used for public health interventions that contribute substantially to morbidity and mortality reduction, such as ITNs for malaria control.