Causal mechanism and component causes in Mesoamerican-Sri Lankan nephropathy: the moderator's view.

Inspired by Conan Doyle's novels, the pro contender of this Polar View undertakes an elegant exercise in territory common to epidemiology and police investigation and concludes that cyclic episodes of dehydration in individuals exposed to heavy work in very hot climates is the cause of Mesoamerican and Sri Lankan nephropathy. The contender in the opposite camp accepts the idea that dehydration may play a key role in this condition but highlights a different explanation, that it is contaminated water used for rehydration that is the eventual cause of the disease.Causal mechanisms result from the combination of many components, i.e. conditions or events that are needed for the occurrence of the disease. If we adopt a global, extended approach to the problem, it is unlikely that cyclic dehydration is a key component in all cases. While credible in most cases in Central America, the cyclic dehydration hypothesis fails to explain most cases in Sri Lanka, where agrochemicals have been implicated as the most likely cause of this disease. The experience with Balkan nephropathy is an enduring lesson that full clarification of the causal mechanisms behind endemic nephropathies can be a decades-long process. Therefore, action to control Mesoamerican and Sri Lankan nephropathy should not be deferred. Deployable interventions include the provision of uncontaminated water sources, prevention of dehydration at work sites and the application of safety procedures for agrochemicals. The joint application of these interventions will most likely benefit the populations plagued by this endemic disease.