Integrating Parasitological and Entomological Observations to Understand Malaria Transmission in Riverine Villages in the Peruvian Amazon

Abstract

Background Remote rural riverine villages account for most of the reported malaria cases in the Peruvian Amazon. As transmission decreases due to intensive standard control efforts, malaria strategies in these villages will need to be more focused and adapted to local epidemiology. Methods By integrating parasitological, entomological, and environmental observations between January 2016 and June 2017, we provided an in-depth characterization of malaria transmission dynamics in 4 riverine villages of the Mazan district, Loreto department. Results Despite variation across villages, malaria prevalence by polymerase chain reaction in March 2016 was high (>25% in 3 villages), caused by Plasmodium vivax mainly and composed of mostly submicroscopic infections. Housing without complete walls was the main malaria risk factor, while households close to forest edges were more commonly identified as spatial clusters of malaria prevalence. Villages in the basin of the Mazan River had a higher density of adult Anopheles darlingi mosquitoes, and retained higher prevalence and incidence rates compared to villages in the basin of the Napo River despite test-and-treat interventions. Conclusions High heterogeneity in malaria transmission was found across and within riverine villages, resulting from interactions between the microgeographic landscape driving diverse conditions for vector development, housing structure, and human behavior.

Quantifying the effect of human population mobility on malaria risk in the Peruvian Amazon

“…We determined that travel to Mazan city (approx. 3 km from study area) increases the risk of malaria infection, compatible with previous reports that also highlight that the vector is present in the peridomestic zones of the community and in greater frequency in all villages in the watershed of the Mazan river [ 44 , 47 ]. It is also important to note that Mazan is the main city in the entire watershed, so all the other communities interact there for different reasons.…”

“…This is particularly important in populations with low parasite densities or close to the limit of detection of diagnostic methods due to the fitness of the immune response in consequence to constant infections [ 43 ]. The results obtained in this study are comparable to the 54.3% previously obtained in the district of Mazan [ 33 ], 40.9% and 31.8% in the village of Libertad [ 19 , 44 ], Primero de Enero village with 44.4% [ 19 ] and in villages that belong to other river basins, such as the Napo river basin, where the Urco Miraño village had a prevalence of 30.7% [ 19 , 44 ]. Further studies are needed to determine the generalizability of the results of this study to the entire Loreto region, mainly due to the high heterogeneity in malaria endemicity and HPM patterns.…”

Malaria transmission structure in the Peruvian Amazon through antibody signatures to Plasmodium vivax

“…The high seroprevalence in Iquitos and Mazán is consistent with recent intense exposure in both sites [ 5 , 19 , 28 ]. Our serological markers have been validated for detecting recent exposure in low transmission settings [ 13 ], but in high transmission settings, seropositivity may be due to either recent infection or cumulative lifetime exposure [ 14 ].…”

“…Open houses have been associated as a high risk factor for P . vivax in Mazán [ 16 , 19 ] and in other studies in the Amazon [ 26 ]. 16% of HH in Iquitos and 8% of HH in Mazán were open houses (0–3 walls) ( p = 0.004).…”

“…Malaria transmission in Maynas is perennial, with a peak between February and July [ 17 ]. While in 2017, Iquitos and Mazán were considered medium- and high-risk districts for malaria transmission, respectively [ 18 ], intensified malaria control during 2017 significantly reduced transmission and parasite prevalence in Mazán villages [ 19 ].…”