ANN ARBOR—Cut down tropical forests to prevent the spread of disease? Such drastic measures actually have been proposed in light of an apparent connection between forest cover and certain insect-borne, infectious diseases.

But a new analysis by researchers at the University of Michigan suggests that socioeconomic factors, rather than landscape, best explain patterns of at least one disease, American cutaneous Leishmaniasis (ACL), and that deforestation may make socially marginalized human populations more, not less, vulnerable to infection.

Their results will be published in Feb. 6 in the journal PLoS Neglected Tropical Diseases.

“The classical idea has been that people working or living close to the forest were at risk for the disease, but that view failed to consider such factors as quality of life and general level of health,” said the paper’s first author Luis Fernando Chaves, a graduate student in the U-M Department of Ecology and Evolutionary Biology.

The researchers examined county-level ACL case data from 1996 through 2000 for Costa Rica, a country in which approximately 20,000 acres of land are deforested annually to make way for cattle ranching and banana, mango and citrus fruit plantations. In addition to looking at such factors as percent forest cover, monthly rainfall, elevation and percent of the population living less than five kilometers (about three miles) from the forest edge, the U-M team also used scores on an index of social marginalization. This index, which takes into account income, literacy, level of education, average distance to health centers, health insurance coverage and other indicators of life at the margins of mainstream society, provides a single measure of quality of life.

“When we looked just at factors such as climate and the physical environment, we found no specific patterns with respect to the disease,” Chaves said. “But when we looked at the social data, we found clear patterns according to marginality.”

Putting everything together, the researchers discovered that in fact there is a relationship between ACL and deforestation, but it’s not the simple, “less forest, less disease” relationship that previously was believed to exist. Instead, there’s a complex connection with El Ni