Vector competence, vectorial capacity of Nyssorhynchus darlingi and the basic reproduction number of Plasmodium vivax in agricultural settlements in the Amazonian Region of Brazil
Abstract:Background
Brazilian malaria control programmes successfully reduced the incidence and mortality rates from 2005 to 2016. Since 2017, increased malaria has been reported across the Amazon. Few field studies focus on the primary malaria vector in high to moderate endemic areas,
Nyssorhynchus darlingi
, as the key entomological component of malaria risk, and on the metrics of
Plasmodium vivax
propagation in Amazonian rural communities.
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“…Brazil's government-sponsored settlement of the Amazon region and development of the trans-Amazonian highway has led to substantial deforestation (7,36) and a simultaneous resurgence in malaria (12), partially reversing the prior success of malaria control programs (8). Despite the recent focus on emerging mosquito-transmitted viruses like Zika and chikungunya, malaria is resurging in a number of regions of South America more broadly, particularly in regions undergoing rapid land conversion and political and economic turmoil (11,37,38). Our work provides clear large-scale evidence that deforestation increases malaria, by using econometric techniques that approximate the gold standard of randomized controlled trials with observational data where controlled experiments are impossible.…”
Section: Discussionmentioning
confidence: 99%
“…Following the late 1960s, malaria expanded rapidly in the Amazon basin, reaching over 600,000 cases a year at the turn of the 21st century-primarily Plasmodium vivax and Plasmodium falciparum transmitted by Anopheles (Nyssorhynchus) darlingiparalleling large-scale deforestation and land use intensification following government-sponsored settlement (7)(8)(9)(10)(11)(12). Prior to this, Brazilian malaria control efforts had dramatically reduced malaria incidence from 6 million cases annually in the 1940s to fewer than 50,000 cases in the early 1960s (8).…”
Deforestation and land use change are among the most pressing anthropogenic environmental impacts. In Brazil, a resurgence of malaria in recent decades paralleled rapid deforestation and settlement in the Amazon basin, yet evidence of a deforestation-driven increase in malaria remains equivocal. We hypothesize an underlying cause of this ambiguity is that deforestation and malaria influence each other in bidirectional causal relationships—deforestation increases malaria through ecological mechanisms and malaria reduces deforestation through socioeconomic mechanisms—and that the strength of these relationships depends on the stage of land use transformation. We test these hypotheses with a large geospatial dataset encompassing 795 municipalities across 13 y (2003 to 2015) and show deforestation has a strong positive effect on malaria incidence. Our results suggest a 10% increase in deforestation leads to a 3.3% increase in malaria incidence (∼9,980 additional cases associated with 1,567 additional km2 lost in 2008, the study midpoint, Amazon-wide). The effect is larger in the interior and absent in outer Amazonian states where little forest remains. However, this strong effect is only detectable after controlling for a feedback of malaria burden on forest loss, whereby increased malaria burden significantly reduces forest clearing, possibly mediated by human behavior or economic development. We estimate a 1% increase in malaria incidence results in a 1.4% decrease in forest area cleared (∼219 fewer km2 cleared associated with 3,024 additional cases in 2008). This bidirectional socioecological feedback between deforestation and malaria, which attenuates as land use intensifies, illustrates the intimate ties between environmental change and human health.
“…Brazil's government-sponsored settlement of the Amazon region and development of the trans-Amazonian highway has led to substantial deforestation (7,36) and a simultaneous resurgence in malaria (12), partially reversing the prior success of malaria control programs (8). Despite the recent focus on emerging mosquito-transmitted viruses like Zika and chikungunya, malaria is resurging in a number of regions of South America more broadly, particularly in regions undergoing rapid land conversion and political and economic turmoil (11,37,38). Our work provides clear large-scale evidence that deforestation increases malaria, by using econometric techniques that approximate the gold standard of randomized controlled trials with observational data where controlled experiments are impossible.…”
Section: Discussionmentioning
confidence: 99%
“…Following the late 1960s, malaria expanded rapidly in the Amazon basin, reaching over 600,000 cases a year at the turn of the 21st century-primarily Plasmodium vivax and Plasmodium falciparum transmitted by Anopheles (Nyssorhynchus) darlingiparalleling large-scale deforestation and land use intensification following government-sponsored settlement (7)(8)(9)(10)(11)(12). Prior to this, Brazilian malaria control efforts had dramatically reduced malaria incidence from 6 million cases annually in the 1940s to fewer than 50,000 cases in the early 1960s (8).…”
Deforestation and land use change are among the most pressing anthropogenic environmental impacts. In Brazil, a resurgence of malaria in recent decades paralleled rapid deforestation and settlement in the Amazon basin, yet evidence of a deforestation-driven increase in malaria remains equivocal. We hypothesize an underlying cause of this ambiguity is that deforestation and malaria influence each other in bidirectional causal relationships—deforestation increases malaria through ecological mechanisms and malaria reduces deforestation through socioeconomic mechanisms—and that the strength of these relationships depends on the stage of land use transformation. We test these hypotheses with a large geospatial dataset encompassing 795 municipalities across 13 y (2003 to 2015) and show deforestation has a strong positive effect on malaria incidence. Our results suggest a 10% increase in deforestation leads to a 3.3% increase in malaria incidence (∼9,980 additional cases associated with 1,567 additional km2 lost in 2008, the study midpoint, Amazon-wide). The effect is larger in the interior and absent in outer Amazonian states where little forest remains. However, this strong effect is only detectable after controlling for a feedback of malaria burden on forest loss, whereby increased malaria burden significantly reduces forest clearing, possibly mediated by human behavior or economic development. We estimate a 1% increase in malaria incidence results in a 1.4% decrease in forest area cleared (∼219 fewer km2 cleared associated with 3,024 additional cases in 2008). This bidirectional socioecological feedback between deforestation and malaria, which attenuates as land use intensifies, illustrates the intimate ties between environmental change and human health.
“…For instance, the landscapes shown in Fig. 7 started colonization in the 1970s [34] and currently have high levels of transmission, with an estimated malaria incidence of 45–100 cases per day and a P. vivax reproduction number of 3.3–16.8 [48]. Fig.…”
Background
Plasmodium falciparum
malaria is a threat to public health, but
Plasmodium vivax
malaria is most prevalent in Latin America, where the incidence rate has been increasing since 2016, particularly in Venezuela and Brazil. The Brazilian Amazon reported 193,000 cases in 2017, which were mostly confirmed as
P. vivax
(~ 90%). Herein, the relationships among malaria incidence rates and the proportion of accumulated deforestation were contrasted using data from the states of Acre and Rondônia in the south-western Brazilian Amazon. The main purpose is to test the hypothesis that the observed difference in incidence rates is associated with the proportion of accumulated deforestation.
Methods
An ecological study using spatial and temporal models for mapping and modelling malaria risk was performed. The municipalities of Acre and Rondônia were the spatial units of analysis, whereas month and year were the temporal units. The number of reported malaria cases from 2009 until 2015 were used to calculate the incidence rate per 1000 people at risk. Accumulated deforestation was calculated using publicly available satellite images. Geographically weighted regression was applied to provide a local model of the spatial heterogeneity of incidence rates. Time-series dynamic regression was applied to test the correlation of incidence rates and accumulated deforestation, adjusted by climate and socioeconomic factors.
Results
The malaria incidence rate declined in Rondônia but remained stable in Acre. There was a high and positive correlation between the decline in malaria and higher proportions of accumulated deforestation in Rondônia. Geographically weighted regression showed a complex relationship. As deforestation increased, malaria incidence also increased in Acre, while as deforestation increased, malaria incidence decreased in Rondônia. Time-series dynamic regression showed a positive association between malaria incidence and precipitation and accumulated deforestation, whereas the association was negative with the human development index in the westernmost areas of Acre.
Conclusion
Landscape modification caused by accumulated deforestation is an important driver of malaria incidence in the Brazilian Amazon. However, this relationship is not linearly correlated because it depends on the overall proportion of the land covered by forest. For regions that are partially degraded, forest cover becomes a less representative component in the landscape, causing the abovementioned non-linear relationship. In such a scenario, accumulated deforestation can lead to a decline in malaria incidence.
“…A recent study carried out in the Brazilian Amazon region reported R 0 of P. vivax transmitted by An. darlingi ranging from 3.3 to 58.7, suggesting malaria hyperendemicity at levels similar to those found for P. falciparum in sub-Saharan Africa [46]. Had we included in the R o estimate the vectorial capacity of the two main biting species in southeastern Venezuela, Ny.…”
Malaria cases in Latin America reached ~1 million in 2017 and 2018, with 53% and 51% reported from Venezuela, respectively. In this study, we characterized the spatiotemporal dynamics of malaria transmission between 2007-2017 in southern Venezuela, the main endemic area of the country. We found that disease transmission was focal and more prevalent in the southeast of southern Venezuela where two persistent hotspots of Plasmodium vivax (76%) and P. falciparum (18%) linked to deforestation for illegal gold mining accounted for ~60% of the country-wide number of cases. Incidence has increased nearly tenfold in the last decade, showing an explosive epidemic growth due to a significant lack of disease control. We suggest that a source-sink pattern of Plasmodium sp.dispersal account for the re-emergence and progression of malaria transmission in the last 4 years across the country due to the internal migration of infected people to and from the hotspots and other malaria-prone ecosystems. We observe a similar pattern explaining the spillover of cases across international borders affecting neighboring countries. This study provides baseline epidemiological data and guidance for malaria control to further assess the dynamics of cross-border malaria, the role of asymptomatic carriers, drug-resistant evolution, and innovative control efforts in the Latin America region.
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