Submicroscopic infections and two malaria vectors are major contributors to residual malaria in an Amazonian village in Peru

In the Loreto region of Amazonian Peru, the primary malaria vector is Nyssorhynchus (or Anopheles) darlingi. The present year-long study sought to identify specific landscapes with the greatest risk of Plasmodium transmission, incorporating epidemiological data, landscape stratification models, satellite imagery, and vector biology. A monthly longitudinal cohort study and population screening of all residents of the focal village Santa Rita detected, among 353 inhabitants enrolled, a ratio of 17:1 submicroscopic/ microscopic malaria infections. Microscopy-detected human infections were seasonal, generally peaking with rising river levels and increasing rainfall, but submicroscopic infections, detected by qPCR, were perennial. Despite high mosquito net usage, inhabitants with outdoor occupations had significantly higher P. vivax infection rates compared with those with indoor occupations or those not working (35% vs. 21%, p = 0.012). A spatial grid subdivided the study area into anopheline mosquito sampling units where mosquitoes were collected monthly. Plasmodium-infected specimens of Ny. darlingi were detected in each of the 5 landscapes that were determined by a cluster analysis. A putative secondary vector, Anopheles near costai G1, was infected with Plasmodium vivax and Plasmodium malariae, reported herein for the first time in Peru.