Abstract
BackgroundAs malaria endemic countries strive towards elimination, intensified spatial heterogeneities of local transmission could undermine the effectiveness of traditional intervention policy.MethodsThe dynamic nature of large-scale and long-term malaria heterogeneity across Brazilian Amazon basin were explored by (1) exploratory analysis of Brazil’s rich clinical malaria reporting database from 2004 to 2018, and (2) adapting Gini coefficient to study the distribution of malaria cases in the region.ResultsAs transmission declined, heterogeneity increased with cases clustering into smaller subpopulations across the territory. In 2004, the 1% of health units with the greatest number of cases accounted for 46% of all reported Plasmodium vivax cases, whereas in 2018 52% of P. vivax cases occurred in the top 1% of health units. Plasmodium falciparum had lower levels of transmission than P. vivax, and also had greater levels of heterogeneity with 75% of cases occurring in the top 1% of health units. Age and gender stratification of cases revealed peri-domestic and occupational exposure settings that remained relatively stable.ConclusionThe pathway to decreasing incidence is characterized by higher proportions of cases in males, in adults, due to importation, and caused by P. vivax. Characterization of spatio-temporal heterogeneity and risk groups can aid stratification for improved malaria control towards elimination with increased heterogeneity potentially allowing for more efficient and cost-effective targeting. Although distinct epidemiological phenomena were clearly observed as malaria transmission declines, the authors argue that there is no canonical path to malaria elimination and a more targeted and dynamic surveillance will be needed if Brazil decides to adopt the elimination target.
Highlights
As malaria endemic countries strive towards elimination, intensified spatial heterogeneities of local transmission could undermine the effectiveness of traditional intervention policy
Baseline epidemiology From 2004 to 2018, 5,496,673 malaria cases were notified in the Brazilian Amazon Basin: 4,443,459 (81%) were P. vivax; 990,280 (18%) were P. falciparum; 40,829 (0.7%) were P. vivax / P. falciparum mixed infections; and 22,105 (0.4%) were other malaria species
Borrowing from econometrics, the Gini coefficient was utilized to demonstrate that heterogeneity in the distribution of malaria cases is increasing over time (Fig. 4a). This is closely associated with decreasing incidence of malaria cases (Fig. 4b). These results suggest that the spatial distribution of malaria cases across populations was dependent on changing transmission intensity and the size of the population at risk
Summary
As malaria endemic countries strive towards elimination, intensified spatial heterogeneities of local transmission could undermine the effectiveness of traditional intervention policy. As countries accelerate towards malaria elimination, reduction in malaria transmission is highly variable leading to significant heterogeneities in residual transmission across their territories [1,2,3,4] In such circumstance, a ‘one size fits all’ approach to public policy and intervention. Brazil has seen long-term trends of nationwide reductions in notified Plasmodium vivax and Plasmodium falciparum cases since 2000, and a retreat of malaria into the Amazon Basin in the north of the country [5] These epidemiological trends have been dependent on socio-economic development, and sustained effective. In Brazil, treatment is provided publicly and free of charge in government-run Health Units, including hospitals and mobile healthcare workers in both urban and rural communities [6] From these Health Units, data on treated cases are digitally recorded in the Malaria Epidemiological Surveillance Information System (SIVEP) database. The collected data span a crucial period, as many regions of Brazil are nearing and some even achieving local malaria elimination, providing examples of what malaria elimination looks like from a health system perspective
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