The results of the present study confirm that malaria is endemic to the Brazilian state of Pará, in particular in the poorer regions of the state. The disease thus constitutes a major public health problem for the Brazilian Amazon region, which was responsible for only 5.3% of the national GNP in 2010 , but accounts for 98% of the country’s cases of malaria. In 2011, 86% of the recorded cases were caused by P. vivax (Figure 2), a rate similar to that recorded in previous years .
In Pará, the variation in the number of reported cases between 2003 and 2011 indicates that the incidence of the disease continues to grow, with an increase of 3.43% in the API in 2011 in comparison with 2003 (Table 1). The environment does not only determine the distribution and incidence of the disease. The transmission of malaria appears to be favoured by conditions of poor sanitation conditions, which provide opportunities for host infection. Additionally individual characteristics, such as genetic predisposition, acquired immunity, age, family composition, occupation, education, religious beliefs, and culture are also important. The different species of parasite and vector found in the local environment should also be taken into consideration [7–9].
The potential effects of a number of geographic and environmental factors on the transmission rates of malaria are also well documented [10, 11]. These include natural features, such as high temperatures, rainfall, and humidity, as well as anthropogenic modifications of the environment, such as deforestation and ongoing colonization, based on the establishment of settlements with inadequate living conditions, and the generally adverse conditions of rural life. All this factors contribute to the proliferation of malaria in the Amazon region.
Important divergences in results have been found in studies that have analysed the potential relationships between the incidence of malaria and socio-economic indices such as personal income, education, and public services, which appear to be related to the different approaches used to measure the incidence of malaria and poverty levels . Given the practical difficulties of collecting reliable epidemiological and socio-economic data directly from the study areas, the approach adopted in the present study, based on the set of official statistics available for the 143 municipalities of the state of Pará, can be considered to be valid, due to the combination of ready access to reliable and standardized data and the low cost of the procedure. The results of the present study indicate that this approach is effective for the evaluation of the potential effects of socio-economic and environmental factors on the risk of infection with malaria.
Marked differences were found in this risk of infection in the different regions of the Brazilian state of Pará, considering the 143 municipalities included in the analysis. At least a third of these municipalities were characterized as moderate to high risk areas for the transmission of malaria, in particular the 15 (10.49%) that returned API scores of over 50 in 2011. The worst affected regions were the Marajó Archipelago and the Southwest, whereas the number of municipalities with high risk scores in the Southeast and Northeast declined considerably during the course of the study period.
In the specific case of the south-eastern mesoregion, the improvements in the infection rates observed during the study period may have been related to the evidence of economic growth in the region, which has resulted in improvements in the living conditions of the local population, with increasing investments in basic infrastructure, such as public water supplies and sanitation, the electric grid and paved streets. These advances have a positive effect on the prevention of the disease in the less economically privileged sectors of the society, and almost certainly contributed to the reduction in the numbers of reported cases and the incidence of malaria in the different municipalities .
However, the rural population is known to be more vulnerable to infection with malaria than urban residents. This is clearly shown in the results of the present study, given that the regions with the lowest indices of quality of life – Northeast, and Southwest – are characterized by lack of infrastructure, with much of the population living along rivers, creeks, and lakes, often in close proximity to swamps and marshes, and other areas prone to flooding, which represent ideal habitats for the proliferation of anopheline mosquitoes. This obviously leads to an increased incidence of malaria in these areas, and contributes to the considerably different transmission rates recorded in the different mesoregions of the state.
In addition, it is important to point out that malaria is endemic in the nine States of the Brazilian Amazon Region, where the number of cases has fluctuated over the years . The analysis of the reasons for malaria transmission points to the social and economic development linked to an inadequate management of the environment, whose effects of the forest disturbances from selective logging, forest fires and road construction have been contributing to the highest malaria risk in some States of the Brazilian Amazon .
Comparing the incidence of malaria (API) at the start (2003) and end (2011) of the study period, it is clear that infection rates were highest in the Southwest, and increased 8.82% over the study period, while the rates in the Northeast and the Marajó Archipelago increased by more than 90%. In the Southeast, by contrast, the infection rate declined considerably, by 78% (Table 1). As seen in other developing countries where the incidence of malaria is high [15–18], the economically less privileged sectors of the society are the most affected. Populations with reduced economic conditions also have less opportunity for treatment , and are thus more vulnerable to the effects of the disease, which can worsen to a fatal condition, in some cases.
The present study indicates a systematic association between the QLI, based on a range of socio-economic variables, and the risk of contracting malaria (based on the API) in the municipalities of the Brazilian state of Pará. In the specific case of per capita income – an index of economic development – there was a clear negative relationship with the API, which decreased progressively with increasing income, as seen in the Belém metropolitan area and the southeast of the state. In other regions, such as the Marajó Archipelago and the Southeast, by contrast, the decline in incomes was accompanied by a marked increase in infection rates.
The categorization of the data for the state of Pará based on the quality of life index (QLI) resulted in the classification of 69.23% of its municipalities as either regular or poor (Table 3). The greatest concentrations of municipalities in these categories were identified in the Northeast, Southeast, and Marajó mesoregions, coinciding with the distribution of the municipalities with the highest risk of malaria, based on the API. The results of this study thus indicate a clear inverse association between the API and the QLI, that is, the municipalities having the lowest quality of life tended to have the highest risk of malaria. Similar findings have been reported in a number of previous studies [12, 18, 20].
However, many studies of this kind have produced inconclusive findings. A review of the literature found mixed results , with some studies demonstrating a significant association between poverty and malaria, whereas others found no such relationship. This contradiction has been explained by the methods used to classify malaria, given that, whereas studies based on personal reports of the disease or fever found no association, those based on parasitological data, as in the case of the present study, found a negative association between socio-economic status and the incidence of the disease .
Overall, the results of the present study indicate that, in addition to the local geographic and environmental factors that favour the transmission of the disease in the Amazon region, a set of secondary factors are also closely associated with the potential risk of infection with malaria (based on the API), in particular poverty. This scenario is defined by low income, inadequate public sanitation, water supply, and refuse collection, as well as low education levels. Many communities, in particular isolated, underprivileged rural settlements, present all these characteristics, reinforced by reduced access to preventive measures and treatment, and thus reinforcing the vulnerability of the poorest sectors of the population [22, 23].