Want More Malaria? Keep Chopping Down Tropical Rainforests
There are countless reasons to stop the deforestation of tropical rainforests and preserve biodiversity. And now it looks like we may be able to add disease control to that already long list.
According to a study recently published in the journal PLOS Neglected Tropical Diseases, preserving the biodiversity of tropical forests could help reduce the spread of malaria. This belief flies in the face of the more accepted view that clearing the Amazon rainforest for agricultural purposes curbs malaria transmission.
The idea for the study came about after its lead researcher, Gabriel Laporta, an epidemiologist at Brazil’s University of Sao Paulo, came across material about the history of malaria epidemics in Brazil’s southeastern Atlantic Forest during the 1940s and ’50s.
“The Brazilian Government was desperate as the incidence of malaria reached five percent of the population,” Laporta tells TakePart. “The malaria burden was mitigated by deforesting a ‘sanitary cordon’ around cities. As a result of this deliberate loss of biodiversity, Raulino Reitz [a Brazilian botanist and historian] pioneered an incredible catalogue of the Brazilian Atlantic Forest flora. After reading about this, I talked with my colleagues—Paulo Inácio Prado, Roberto Kraenkel, Renato Coutinho, and Anice Sallum—and we decided to work on the connection between the conservation of biodiversity and the spread of malaria.”
Laporta and his team used a mathematical model to examine two factors that can affect malaria transmission in forested areas. The numbers of warm-blooded animals—birds such as toucans and quails, and mammals such as howler monkeys and squirrels—and the numbers of mosquitoes that don’t carry malaria.
“The mathematical model is a representation of the dynamics of malaria transmission,” says Laporta. “Briefly, this dynamic includes an infected human with malaria parasites that is bitten by a susceptible mosquito vector. This mosquito vector becomes infected and can transmit the parasite to another human.”
“But when we included ecological interactions into this dynamic—warm-blooded animals that act as non-competent hosts, and non-vector mosquitoes that compete with mosquito vectors for blood-meals—our model showed that these aspects of biodiversity can hinder malaria transmission and are thus an important part of the forest ecosystem.”
The researchers conclude in their author summary in PLOS that, “Forest conservation and malaria control are not incompatible and thus biodiversity issues should be included in all malaria eradication programs in order to achieve the desirable goals of biological conservation and maintenance of low malaria transmission.”
While some have suggested that Laporta’s study used an equation that might have artificially increased the rates of malaria transmission, he responds that, “with regard to this criticism, it is important to note that we presented an explicit derivation of malaria’s basic reproduction number of our mathematical model based on consolidated techniques from the specialized literature.”
In any case, with deforestation continuing at a rapid pace, this certainly seems like an idea worth considering while we still can.
Do you think these researchers have established a strong connection between conservation and the spread of malaria?