Molecular evidence of sustained urban malaria transmission in Amazonian Brazil, 2014–2015

Abstract

The relative contribution of imported vs. locally acquired infections to urban malaria burden remains largely unexplored in Latin America, the most urbanised region in the developing world. Here we use a simple molecular epidemiology framework to examine the transmission dynamics of Plasmodium vivax in Mâncio Lima, the Amazonian municipality with the highest malaria incidence rate in Brazil. We prospectively genotyped 177 P. vivax infections diagnosed in urban residents between June 2014 and July 2015 and showed that local parasites are structured into several lineages of closely related microsatellite haplotypes, with the largest genetic cluster comprising 32% of all infections. These findings are very unlikely under the hypothesis of multiple independent imports of parasite strains from the rural surroundings. Instead, the presence of an endemic near-clonal parasite lineage circulating over 13 consecutive months is consistent with a local P. vivax transmission chain in the town, with major implications for malaria elimination efforts in this and similar urban environments across the Amazon.

Human mobility and urban malaria risk in the main transmission hotspot of Amazonian Brazil

“…Second, human mobility fuels malaria transmission in urban centers in the Amazon that are receptive-i.e., whose environmental conditions allow for malaria transmission from a human through a vector mosquito to another human [37]. Indeed, molecular analyses of parasite isolates provide evidence for sustained malaria transmission in the town of Mâncio Lima [20]. Vectors are increasingly abundant in this and other urbanized spaces in the Amazon and can sustain local malaria transmission.…”

“…Indeed, malaria rates tend to be lower in cities and towns, compared to surrounding rural settings, due to multiple factors such as improved housing and access to healthcare and limited availability of mosquito vector habitats [12]. Nevertheless, since the mid-1990s malaria cases have been increasingly reported within and near urban centers in the Amazon, consistent with sustained transmission in or around towns across the region [13][14][15][16][17][18][19][20].…”

“…Conversely, newly arrived urban families often maintain both urban and rural residences and rely on agricultural production for subsistence or additional income [26][27][28]. These factors leading to increased human mobility are key drivers of urban malaria risk, as parasites from rural villages are introduced and may spread in densely populated and receptive urban spaces, potentially leading to explosive epidemics or sustained endemic propagation of parasites [16,20,29].…”

Population genomics reveals the expansion of highly inbred Plasmodium vivax lineages in the main malaria hotspot of Brazil

“…Patterns of shared ancestry are consistent with gene flow between ML and the nearby city of CS, where massive malaria outbreaks have occurred in the mid-2000 [ 45 ] and local transmission remains high [ 16 ]. The extensive rural-urban mobility across the Amazon [ 46 ] continuously introduces parasites into densely populated and receptive urban spaces, leading to explosive epidemics [ 45 ] or endemic urban malaria transmission [ 47 ]. Although the directionality of gene flow cannot be determined by IBD analysis, the finding of shared ancestry between P .…”

Monthly biological larviciding associated with a tenfold decrease in larval density in fish farming ponds and reduced community-wide malaria incidence in northwestern Brazil

“…Malaria transmission in the Amazon is greatest in farming settlements, mining camps, and riverine villages, and typically low in cities and towns [ 2 , 3 ]. However, infections can also be acquired within and near urban centers across the region [ 4 – 9 ], where large populations of the primary local vector, Anopheles darlingi , thrive in natural and artificial water habitats. Human-made tanks or natural water bodies used for commercial aquaculture are increasingly common larval habitats in urban and peri-urban areas in the Amazon [ 7 , 10 – 13 ].…”