Forests provide many life supporting services to individuals living in tropical countries, but public health is not often considered one of them. In fact, for many years the best way to fight malaria was thought to be the destruction of the tropical forests and swamps that sheltered disease-carrying mosquitoes. However, new research published last week in PLOS Neglected Tropical Diseases suggests not only that this approach may have been ineffective, but also that malaria control should now be counted among the many services provided by healthy forest ecosystems.
Using data from several villages on the edges of forest ecosystems in Brazil’s Atlantic rainforest and a model predicting the spread of malaria based on biodiversity metrics the authors found that an increase in biodiversity around human settlement decreased the incidence of malaria. The authors offer two primary explanations for this result. First, increasing biodiversity increases the number of potential hosts (mammals) for the mosquitoes, thus increasing the number of “dead-end” hosts, or hosts who are infected but do not pass the disease onto another mosquitoes. Second, increasing biodiversity supports additional species of non-vector mosquitoes which compete with the vector mosquitoes for the scarce resource of available blood and thus reduce the number of vector mosquitoes.
While counter-intuitive — increasing mosquitoes and their food source reduces the spread of malaria? — these results provide another example of how greater system complexity can buttress the over-all functionality of the human-environmental system. As the authors suggest:
The absence of malaria cases can be explained by the diffuse mosquito vector competition and dead-end transmission of parasites provided by high abundances of mosquitoes and vertebrates. Greater abundance of mosquitoes and vertebrates can be correlated with higher levels of biodiversity, which increases ecosystems functional redundancy, thus decreasing the chances of malaria occurrence, which is in keeping with the insurance hypothesis . . . an insurance effect is the ability of an ecosystem to buffer perturbations . . . as well as the ability of the species in the community to respond differentially to perturbations . . . these mechanisms that hinder malaria parasite transmissions are services provided by the forest ecosystems.
Nor is this an isolated result, the study cites several other examples of work that have shown decreasing levels of biodiversity increase the risk of contracting schistosomiasis, West Nile, hantavirus, and Lyme disease.
While the public health benefits of preserving forests and biodiversity have, until now, been overlooked these benefits have substantial economic implications. Malaria alone is estimated to reduce per capita income by nearly $4,000 in some countries. If protecting intact and highly biodiverse forest ecosystems is an effective means of fighting this disease, it adds a powerful and appealing argument to the already substantial case for forest and biodiversity protection.