Ulisses Confalonieri, Professor of Public Health, Fundación Oswaldo Cruz, Rio de Janeiro
Malaria incidence in Brazil rose steadily in the 1970s and 1980s, from just 52,469 cases in 1970 to 577,520 in 1989 (1). By 1994, reported cases still exceeded half a million (2). In 1970, 72 percent of all malaria cases in the country were in the Amazon Basin (3); by 1985, this figure had risen to 99 percent (4). Today, virtually all endemic malaria occurs in the Amazon region (5).
While malaria has long been endemic in Brazil, the dramatic surge in malaria cases over the past two decades in the Amazon can be attributed to a complex set of interrelated factors: rapid population growth, migration and displacement of laborers and indigenous people, the growth of gold mining, environmental destruction, and misguided development. Two subpopulations’ gold miners and indigenous Indians have borne the greatest burden of increased malaria incidence.
The Brazilian Amazon is home to the world’s largest remaining tropical forests as well as significant mineral reserves. Since the 1960s, the government has instituted a series of ambitious plans to develop and colonize the Amazon Basin to relieve some of the pressures of urban poverty, crowding, and social unrest in other regions of Brazil. As a result of these efforts, which were heavily subsidized by the government, population growth in the region soared. Between 1970 and 1980, population growth rates in the Amazon region were above 5 percent per year, the highest in Brazil (6). The construction of the Belem-Brasilia highway and the Trans-Amazon highway further spurred the growth of logging, agribusiness, and mining in the region.
More recently, a “gold rush” in the Amazon has made the region a magnet for migrants, in particular from the poverty-stricken northeastern region. Gold prospectors and miners, called “garimpeiros,” have flocked to mining sites in the Brazilian Amazon, with the highest proportions moving to the states of Rondonia, Para, Mato Grosso, and Roraima in search of economic opportunities. 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. In 1988, for instance, 50 percent of all malaria transmission in Mato Grosso occurred at gold mining sites (7).
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. Even when infected miners do buy medicine (often paid for with gold), they usually stop taking it once the fever recedes, but before they are entirely cured. As a result, drug-resistant strains of malaria that are much more difficult and expensive to treat have emerged.
The high exposure of miners to the heavy metal mercury, which is commonly used to extract raw gold from mine tailings, is probably also an important factor in the high malaria incidence. From 3 to 5 kilograms (kg) of mercury are used to extract 1 kg of gold (8), and the lack of environmental controls at most mining sites means that exposures to mercury probably exceed limits set by the World Health Organization. Researchers are beginning to suspect that mercury exposure can suppress or damage the immune system, perhaps making the garimpeiros more susceptible to malaria infection (9).
Miners are not the only victims of the Amazon gold rush. In fact, the local Indian population has suffered far worse. The mineral wealth of many Indian reservations makes them a prime target for invasion by garimpeiros.To a great extent, the development of the Brazilian Amazon has been defined by the invasion of traditional Indian territories and the appropriation of their natural resources. Disease transmission and depopulation have been the devastating result.
The Roraima Gold Rush provides a vivid illustration. In 1987, garimpeiros invaded the homeland of 10,000 Yanomami Indians. By 1989, an estimated 40,000 miners were working within the land of the Yanomami, the last large, semi-isolated, and traditional Indian group in the Americas (10). The consequences were immediate: cultural conflicts, violence, epidemics, starvation, and high mortality imperiled the very existence of the Yanomami as a people. Nor was this the first time that development had threatened Indian communities in the region. In the early 1970s, epidemics of measles and influenza brought by workers constructing the Perimetral Norte highway wiped out three Yanomami communities in northern Amazonas State (11).
The Roraima Gold Rush and subsequent immigration by garimpeiros have dramatically increased malaria incidence and deaths among the Indians. A survey at the Indian Hospital in the city of Boa Vista showed that malaria was the main cause of admission of Yanomami Indians from 1987 to 1989. Of the 144 deaths reported during this period, malaria was responsible for over half (51.8 percent) (12). Estimates suggest that nearly 10 percent of the Yanomami population died of malaria between 1987 and 1990. Overall, about 20 percent of the Yanomami population contracted malaria, and in some of the villages the parasite infected more than 90 percent of the community.
Although the Roraima Gold Rush is waning, the legacy of malaria infection continues to pose a risk to Amazonian Indians. Between 1991 and 1995, malaria was responsible for 25 percent of all Yanomami deaths (13). Annual rates of malaria incidence in areas where contact with miners and other immigrants is frequent are as high as 1,350 per 1,000 population, meaning that some individuals have had more than one attack of malaria in just one year. This is in sharp contrast to rates in the villages not affected by the invasion of outsiders, which run around 20 cases per 1,000 population. It is also substantially higher than malaria incidence among the general Amazonian population, estimated to be around 40 per 1,000 (14)(15).
Starting in 1990, the Brazilian government intervened to remove the garimpeiros from the Yanomami territory, but with little apparent effect. Because the lure of gold remained, the garimpeiros simply moved to other mining areas in the state of Roraima. As a consequence, malaria spread to the four ethnic groups of eastern Roraima and became the leading cause of death there between 1991 and 1994 (16).
While the reasons behind the extremely high incidence of malaria among indigenous Indians are not completely understood, many factors, both socioeconomic and environmental, may be playing a role. First, malaria control activities such as housespraying and case detection and treatment that had been successful in the southeastern and northeastern regions of Brazil were unsuccessful in the heavily forested areas of the Amazon because of logistical and organizational difficulties and population mobility (17). In addition, most mosquito bites occur outdoors, making domestic indoor spraying for malaria control ineffective. Second, the physical isolation of many of the groups in the Amazon may increase their susceptibility to malaria. Third, because most of these communities are in remote areas, the people have only limited access to health services. Virtually all of the 350 Yanomami villages can be reached only by plane.
In addition, culturally determined behaviors may increase the risk of malaria transmission or make treatment difficult. For example, the custom of bathing in rivers early in the morning and late in the afternoon coincides with the peak hours of mosquito activity. Also, the mobility associated with subsistence fishing and hunting can be a problem, because some cases of malaria need an uninterrupted two-week course of drugs, which is difficult to administer in the face of frequent travel. On the other hand, the structure of Yanomami huts may offer some protection from malaria; the cone-shaped and closed huts are often filled with dense smoke from cookfires inside, which tends to repel mosquitoes.
The outlook for the future is guarded. As long as profits from mining appear to be lucrative, mining will probably continue to play a role in malaria transmission in the Amazon region. At the same time, continued high rates of deforestation could also increase the population of malaria-carrying mosquitoes and facilitate the spread of the disease (18).
References and Notes
1. Donald Rolfe Sawyer, “Malaria and the Environment,” Documento de Trabalho, No. 13 (Instituto Sociedade, Populacão e Natureza, Brasília, Brazil, March 1992), p. 2.
2. Pedro Luiz Tauil, “Comments on the Epidemiology and Control of Malaria in Brazil,” Mem. Inst. Oswaldo Cruz, Vol. 81, Supplement II (1986), p. 39.
3. Op. cit. 1.
4. Pedro L. Tauil, “Malária: Agrava-Se O Quadro Da Doença No Brasil,” Ciencia Hoje, Vol. 2, No. 12 (May-June 1984), pp. 58-59.
5. Op. cit. 1.
6. Agostinho Cruz Marques, “Migrations and the Dissemination of Malaria in Brazil,” Mem. Inst. Oswaldo Cruz, Vol. 81, Supplement II (1986), p. 17.
7. Ibid., p. 28.
8. Steven G. Gilbert and Kimberly S. Grant-Webster, “Neurobehavioral Effects of Developmental Methyl Mercury Exposure,” Environmental Health Perspectives, Vol. 103, Supplement 6 (1995), p. 136.
9. J. Bernier, “Immunotoxicity of Heavy Metals in Relation to Great Lakes,” Environmental Health Perspectives, Vol. 103, Supplement 9 (December 1995), pp. 23-24.
10. Margareth Marmori, “A Historia Do Conflito,” Ciencia Hoje, Vol. II, No.64, (July 1990), p. 75.
11. Alcida R. Ramos, “Yanomami Indians in North Brazil Threatened by Highway,” (November 1978), pp. 1-30.
12. Oneron A. Pithan et al., “A Situacao de Saude dos Indios Yanomami: Diagnostico a Partir da Casa do Indio de Boa Vista, Roraima, 1987-1989. PESQUISA. Cadernos de Saude Publica, RJ, 7(4): 563-580, out/dez, 1991.
13. Maria Stella de Castro Lobo, “O Caso Yanomami Do Brasil: Uma Proposta Estrategica De Vigilancia Epidemiologica,” Rio de Janeiro, 1996. Escola Nacional de Saude Publica, Mestrado em Saude Publica, Area de Concentracao: Epidemiologia Geral, p. 50.
14. Ibid.
15. Op. cit. 6.
16. Ulisses Confalonieri, “Amazon Health Report: Indigenous People’s of Brazil,” draft paper (The World Bank, Washington, D.C., 1994).
17. Op. cit. 1, p. 12.
18. J.F. Walsh et al., “Deforestation: Effects on Vector-borne Disease,” Parasitology, Vol. 106 (1993) (Cambridge University Press), p. S58.
