Hyperendemic malaria transmission in areas of occupation-related travel in the Peruvian Amazon

Abstract

BackgroundPlasmodium vivax and Plasmodium falciparum cause a significant illness burden in Peru. Anopheline indices for populated communities in the peri-Iquitos region of Loreto have been reported to be remarkably low, with entomological inoculation rates (EIR) estimated at one to 30 infective bites per year based on a few studies in close proximity to the urban centre of Iquitos and surrounding deforested areas. Local reports suggest that a large number of the reported cases are contracted outside of populated communities in undeveloped riverine areas frequented by loggers and fishermen.MethodsTo better understand vectorial capacity in suspected high malaria transmission zones in a rural district near Iquitos, Peru, mosquito collections were conducted at different points in the seasonality of malaria transmission in 21 sites frequented by occupational labourers. Prevalence of Plasmodium spp in vectors was determined by circumsporozoite protein ELISA on individual mosquitoes. Slide surveillance was performed for humans encountered in the zone.ResultsIn total, of 8,365 adult female mosquitoes examined, 98.5% were identified as Anopheles darlingi and 117 (1.4%) tested positive for sporozoites (P. falciparum, P. vivax VK210 or P. vivax VK247). Measured human biting rates at these sites ranged from 0.102 to 41.13 bites per person per hour, with EIR values as high as 5.3 infective bites per person per night. Six percent of the 284 blood films were positive for P. vivax or P. falciparum; however, 88% of the individuals found to be positive were asymptomatic at the time of sampling.ConclusionsThe results of this study provide key missing indices of prominent spatial and temporal heterogeneity of vectorial capacity in the Amazon Basin of Peru. The identification of a target human subpopulation as a principal reservoir and dispersion source of Plasmodium species has important implications for vaccine development and the delivery of effective targeted malaria control strategies.

Epidemiology of Plasmodium vivax Malaria in Peru

“…Despite the fact that Loreto has been considered to be hypoendemic for malaria transmission,16 routine surveillance data and epidemiological studies suggest that malaria transmission in the region is highly heterogeneous, with some areas in relatively remote Amazonia having entomological inoculation rates (EIRs) rivaling those found in holoendemic regions of Africa 19. More than 80% of the total malaria clinical cases detected by PCD in Loreto are concentrated among only 10–20% of the total communities of the department 6.…”

Unstable Malaria Transmission in the Southern Peruvian Amazon and Its Association with Gold Mining, Madre de Dios, 2001–2012

“…Malaria transmission in the Amazon is promoted by several factors: anthropogenically-driven habitat change-for example, agriculture, logging, and mining-resulting in changes in vector breeding sites including urbanization 14,15 ; immigration of nonimmune humans into rural settlements in new frontier sites 16,17 ; and asymptomatic carriers. 18 Gold mining leads to several of these conditions, including habitat modification 19,20 and human settlements in the Amazon frontier.…”

Comparative Vector Bionomics and Morphometrics of Two Genetically Distinct Field Populations of Anopheles darlingi Root from Belize, Central America and Zungarococha, Peru, South America

“…In addition, of those workers tested for malaria, 88% of positive cases were asymptomatic at the time of sampling. These EIR rates are much higher than those of other peri-Iquitos studies focusing on deforested areas, bringing attention to potential malaria hot spots and transmission from frequently exposed asymptomatic workers to families and communities located in areas with much lower transmission rates (139). This reinforces the potential danger for the spread of malaria if An.…”

“…A study by Parker et al (2013) showed extremely high levels of malaria transmission in remote areas of human occupation. Sites along the Mazan River, utilized by many laborers to fish, extract wood, and harvest palm leaves used in thatched roof construction, showed entomological inoculation rates (EIR) as high as 5.3 infective bites/person/night (EIRs showed a seasonality).…”