Malaria in Brazil: what happens outside the Amazonian endemic region

Abstract

Brazil, a country of continental proportions, presents three profiles of malaria transmission. The first and most important numerically, occurs inside the Amazon. The Amazon accounts for approximately 60% of the nation's territory and approximately 13% of the Brazilian population. This region hosts 99.5% of the nation's malaria cases, which are predominantly caused by Plasmodium vivax (i.e., 82% of cases in 2013). The second involves imported malaria, which corresponds to malaria cases acquired outside the region where the individuals live or the diagnosis was made. These cases are imported from endemic regions of Brazil (i.e., the Amazon) or from other countries in South and Central America, Africa and Asia. Imported malaria comprised 89% of the cases found outside the area of active transmission in Brazil in 2013. These cases highlight an important question with respect to both therapeutic and epidemiological issues because patients, especially those with falciparum malaria, arriving in a region where the health professionals may not have experience with the clinical manifestations of malaria and its diagnosis could suffer dramatic consequences associated with a potential delay in treatment. Additionally, because the Anopheles vectors exist in most of the country, even a single case of malaria, if not diagnosed and treated immediately, may result in introduced cases, causing outbreaks and even introducing or reintroducing the disease to a non-endemic, receptive region. Cases introduced outside the Amazon usually occur in areas in which malaria was formerly endemic and are transmitted by competent vectors belonging to the subgenus Nyssorhynchus (i.e., Anopheles darlingi, Anopheles aquasalis and species of the Albitarsis complex). The third type of transmission accounts for only 0.05% of all cases and is caused by autochthonous malaria in the Atlantic Forest, located primarily along the southeastern Atlantic Coast. They are caused by parasites that seem to be (or to be very close to) P. vivax and, in a less extent, by Plasmodium malariae and it is transmitted by the bromeliad mosquito Anopheles (Kerteszia) cruzii. This paper deals mainly with the two profiles of malaria found outside the Amazon: the imported and ensuing introduced cases and the autochthonous cases. We also provide an update regarding the situation in Brazil and the Brazilian endemic Amazon.

Fig. 1. : number of malaria cases registered yearly (1961-2013) in Brazil according to the Plasmodium species. After small variations, the low figures recorded in 1961 were slightly augmented in 1970 with most of cases being registered in the Amazon, region that started to concentrate the majority of cases registered in Brazil from 1967 on. The numbers increased steadily thereafter, as a result of the intense, rapid and disorganised colonisation of the Amazon, reaching more than 573 thousand cases in 1989. Two peaks of cases were registered in 1999 and 2005 (around 630 and 600 thousand cases respectively) in spite of a general tendency to decrease the numbers in the last two decades. The circle with the intersection lines shows that the present number of cases corresponds to the figures recorded around 1980, when the percentage of Brazilian cases registered in the Amazon exceeded the 90%. Notice also the progressively decreasing proportion of cases due to Plasmodium falciparum since 1988.

Fig. 2. : Brazilian territorial surface occupied by the Atlantic Forest: map comparing the extension of the area covered by vegetation in 1500 and in 2012. Originally, the Atlantic Forest extended along the Atlantic Coast of Brazil from the state of Rio Grande do Norte, in the Northeast Region, to the north to Rio Grande do Sul, in the South Region, reaching parts of southeastern Paraguay and northern Argentina. Before the European occupation, the Atlantic Forest covered a total area of 1,300,000 km2, representing 15% of the country’s territory. Presently, only 7-8% of the residue forest still exists (Fundação SOS Mata Atlântica/INPE 2008).

Fig. 3. : Anopheles (Kerteszia) cruzii, the mosquito vector of both the human and simian malarias in the Atlantic Forest of southern and southeast Brazil. Photo by Genilton Vieira.

Fig. 4. : the malaria vector Anopheles (Kerteszia) cruzii breeds in water accumulated in the axils of shaded and epiphyte bromeliads, such as Vriesea sp. Photo by Genilton Vieira.

Fig. 5. : in some conditions, Anopheles (Kerteszia) cruzii may bite both at the canopy of the trees and close to the ground, which may favour the transmission of simian plasmodia to human in the wild or in the close vicinity of the forest.