Amazonian malaria: asymptomatic human reservoirs, diagnostic challenges, environmentally driven changes in mosquito vector populations, and the mandate for sustainable control strategies

Abstract

Across the Americas and the Caribbean, nearly 561,000 slide-confirmed malaria infections were reported officially in 2008. The nine Amazonian countries accounted for 89% of these infections; Brazil and Peru alone contributed 56% and 7% of them, respectively. Local populations of the relatively neglected parasite Plasmodium vivax, which currently accounts for 77% of the regional malaria burden, are extremely diverse genetically and geographically structured. At a time when malaria elimination is placed on the public health agenda of several endemic countries, it remains unclear why malaria proved so difficult to control in areas of relatively low levels of transmission such as the Amazon Basin. We hypothesize that asymptomatic parasite carriage and massive environmental changes that affect vector abundance and behavior are major contributors to malaria transmission in epidemiologically diverse areas across the Amazon Basin. Here we review available data supporting this hypothesis and discuss their implications for current and future malaria intervention policies in the region. Given that locally generated scientific evidence is urgently required to support malaria control interventions in Amazonia, we briefly describe the aims of our current field-oriented malaria research in rural villages and gold-mining enclaves in Peru and a recently opened agricultural settlement in Brazil.

Figure 1

Map of South America showing the malaria-endemic areas with different shadding pattern according to transmission levels in 2008. Source of data: Pan American Health Organization, 2009. Report on the Situation of Malaria in the Americas, 2008. Washington, DC. Available at: http://new.paho.org/hq/index.php?option=com_content&task=view&id=2459&Itemid=2049

Figure 2

Deforestation for slash-and-burn agriculture (left) and dwellings surrounded by rain forest (right) in the agricultural settlement of Remansinho, near Acrelândia, Acre, northwestern Brazil (Pictures by Marcelo U. Ferreira).

Figure 3

Map of Peru showing the areas with highest levels of malaria transmission, the Departments of Loreto (where one of our field sites is located) and Madre de Dios (where our second Peruvian field site is located). The different shadding patterns (as in Figure 1) reflect different transmission levels in 2008. Source of data: Ministry of Health of Peru, 2009.

Figure 4

Gold-mining enclave surrounding the rain forest in the Department of Madre de Dios, Peru (Picture by Marta Moreno).