As a result of these efforts, which were heavily subsidized by the government, population growth in the region soared. By 1991, between 400,000 and 600,000 garimpeiros had moved to the region. The gold mining boom has had several unintended consequences, including high levels of environmental degradation from mine tailings, deforestation, and deteriorating living conditions. In particular, malaria has swept mining towns across the region. Conditions in mining camps provide perfect conditions for malaria infection and transmission.
Temporary shelters provide little or no mosquito protection.
In addition, the garimpeiros themselves are highly susceptible to malaria because they are often migrants from areas free from malaria, and thus lack immunity to the disease. In their search for gold, miners also routinely destroy the banks of local streams. The widened river beds then become swamplike habitats perfect for mosquito breeding. The costs of treating malaria are beyond most miners' means, so many infected miners go untreated. As a result, drug-resistant strains of malaria that are much more difficult and expensive to treat have emerged.