Malaria in Brazil: an overview

Abstract

Malaria is still a major public health problem in Brazil, with approximately 306,000 registered cases in 2009, but it is estimated that in the early 1940s, around six million cases of malaria occurred each year. As a result of the fight against the disease, the number of malaria cases decreased over the years and the smallest numbers of cases to-date were recorded in the 1960s. From the mid-1960s onwards, Brazil underwent a rapid and disorganized settlement process in the Amazon and this migratory movement led to a progressive increase in the number of reported cases. Although the main mosquito vector (Anopheles darlingi) is present in about 80% of the country, currently the incidence of malaria in Brazil is almost exclusively (99,8% of the cases) restricted to the region of the Amazon Basin, where a number of combined factors favors disease transmission and impair the use of standard control procedures. Plasmodium vivax accounts for 83,7% of registered cases, while Plasmodium falciparum is responsible for 16,3% and Plasmodium malariae is seldom observed. Although vivax malaria is thought to cause little mortality, compared to falciparum malaria, it accounts for much of the morbidity and for huge burdens on the prosperity of endemic communities. However, in the last few years a pattern of unusual clinical complications with fatal cases associated with P. vivax have been reported in Brazil and this is a matter of concern for Brazilian malariologists. In addition, the emergence of P. vivax strains resistant to chloroquine in some reports needs to be further investigated. In contrast, asymptomatic infection by P. falciparum and P. vivax has been detected in epidemiological studies in the states of Rondonia and Amazonas, indicating probably a pattern of clinical immunity in both autochthonous and migrant populations. Seropidemiological studies investigating the type of immune responses elicited in naturally-exposed populations to several malaria vaccine candidates in Brazilian populations have also been providing important information on whether immune responses specific to these antigens are generated in natural infections and their immunogenic potential as vaccine candidates. The present difficulties in reducing economic and social risk factors that determine the incidence of malaria in the Amazon Region render impracticable its elimination in the region. As a result, a malaria-integrated control effort--as a joint action on the part of the government and the population--directed towards the elimination or reduction of the risks of death or illness, is the direction adopted by the Brazilian government in the fight against the disease.

Figure 1

Number of malaria cases registered yearly from 1960 to 2009 in the Brazilian Amazon according to the Plasmodium species responsible. The great increase of malaria cases during late 70's and 80's was due to massive and uncontrolled migration to the Amazon region of people attracted by colonization programmes, sponsored by the government. The highest figures were recorded in 1999 (637 470 cases) when the government decided to implement the Plan for Intensification of Actions for Malaria Control (PIACM) in high-risk areas focusing on the early diagnosis and treatment of the cases. The circle with the intersection lines shows that the present number of malaria cases corresponds to the figures recorded in 1983. Notice also the progressively decreasing proportion of cases due to P. falciparum after 1988. In 1990 44.3% of cases were due to P. falciparum and the situation of the most prominent predominance of P. vivax transmission was reached in 1999 (only 18.6% of cases being due to P. falciparum).

Figure 2

Areas of malaria transmission in Brazil according to the Annual Parasitary Index (API) in the years of 2000 and 2008. The Amazonian Annual Parasite Index (API, number of cases/thousand inhabitants) indicates success and failures of the control measures in some counties. Low API: < 10 cases; medium API: 10 to 49.9 cases; high API: > 50 cases. The distribution of transmission is not regular since 57 (7.1%) out of the 807 municipalities in the Amazon states concentrate 80% of the total registered malaria cases and only three (0.4%) of them accounts for 18% of the Amazonian cases.

Figure 3

Evolution of the proportion of malaria cases due to Plasmodium falciparum in the Amazon from the year of 1999 to 2009. Since P. falciparum gametocytes only appear in the peripheral blood after 8 to 10 days of infection, prompt diagnosis and adequate treatment of the P. falciparum malaria cases can interrupt parasite transmission more efficiently than it can do in the case of P. vivax malaria, in which gametocytes are already present in the circulation in the first three days of blood infection [15]. * Beginning of the new therapy artemether/lumefantrine, the first line regimen for non-complicated falciparum malaria in Brazil. Source: Sivep - Malaria - Data updated on September 9th, 2008.

Figure 4

Malaria fatality rates and number of hospitalizations due to the disease in the Brazilian Amazon from 1999 to 2009. The number of hospitalizations due to malaria in the Brazilian Amazon dropped from 53,450 in 1994 to 18,037 in 2000 and 4,442 in 2009 as did the number of registered deaths attributed to the disease (from 897 in 1984 to 58 in 2009) as well as the fatality rate (from 0.038% in 2000 to 0.013% in 2009). The malaria cases seen in Brazil are being rapidly diagnosed and treated (59% of all malaria cases in 2008 registered in the Amazon were treated in the first 48 hours after appearance of symptoms, Malaria/SVS/MS, 2009), diminishing both the transmission and the occurrence of severe cases.

Figure 5

Number of cases of autochthonous malaria seen outside the Amazon region. The peak registered in 2002 is due to an outbreak of Plasmodium falciparum malaria observed in the State of Ceará, Northwestern Brazil. Cases seen outside the Amazon are mainly due to the transmission by Anopheles (Kertezia) occurring in the Atlantic forest possibly maintained by the involvement of infection of monkeys.

Figure 6

The Brazilian Biome Map and location of Research Centres. The Amazon region covers 40% of the surface of South America and 5% of the surface of the world, and 61% of its territory is in Brazil. It has the largest hydrographic network on earth, covering 20% of the worlds fresh water reserves and shelter the largest number of life forms on earth; the Atlantic forest (seasonal semideciduous forests) is the third largest Brazilian biome that stretches for about 4 000 km along the Atlantic coast between Rio Grande do Norte and Rio Grande do Sul; the "Caatinga" (semiarid steppe of Northeast Brazil) is located on the north-east coast is the largest dry forest region in South America and characterized by a semi-arid climate, low and unregular rainfall, fertile soils and an apparently dry vegetation; the Cerrado (Brazilian Savanna) is located on the large plateau that occupies the central highlands. Influenced by the four surrounding biomes, the fauna and flora of the Cerrado is extremely rich and the climate is hot and semi-humid; the Pantanal (Brazilian wetlands) is located in the watershed of the Upper Paraguay Rivers the largest area of fresh water marshes in the world, shared between Brazil (60%), Bolivia and Paraguay. The Pampas are the fertile South American lowlands in the southernmost end of Brazil, the climate is mild and contain unique wildlife because of the different terrains around it.