Malaria is increasingly diagnosed in urban centers across the Amazon Basin. In this study, we combined repeated prevalence surveys over a 4-year period of a household-based random sample of 2,774 persons with parasite genotyping to investigate the epidemiology of malaria in Mâncio Lima, the main urban transmission hotspot in Amazonian Brazil. We found that most malarial infections were asymptomatic and undetected by point-of-care microscopy. Our findings indicate that as malaria transmission decreases, the detection threshold of microscopy rises, resulting in more missed infections despite similar parasite densities estimated by molecular methods. We identified genetically highly diverse populations of Plasmodium vivax and P. falciparum in the region; occasional shared lineages between urban and rural residents suggest cross-boundary propagation. The prevalence of low-density and asymptomatic infections poses a significant challenge for routine surveillance and the effectiveness of malaria control and elimination strategies in urbanized areas with readily accessible laboratory facilities.

亚马逊河流域城市中心越来越多地诊断出疟疾。在这项研究中，我们结合了 4 年期间对 2,774 名家庭随机样本进行寄生虫基因分型的重复流行率调查，以调查巴西亚马逊流域主要城市传播热点曼西奥利马的疟疾流行病学。我们发现大多数疟疾感染都是无症状的，并且无法通过护理点显微镜检测到。我们的研究结果表明，随着疟疾传播的减少，显微镜的检测阈值上升，导致更多的漏检感染，尽管通过分子方法估计的寄生虫密度相似。我们在该地区确定了间日疟原虫和恶性疟原虫遗传高度多样化的种群；城乡居民之间偶尔存在的共同血统表明了跨境传播。低密度和无症状感染的流行对实验室设施便利的城市化地区的常规监测以及疟疾控制和消除策略的有效性构成了重大挑战。