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. 2015 Sep 10;10(9):e0137458.
doi: 10.1371/journal.pone.0137458. eCollection 2015.

Hotspots of Malaria Transmission in the Peruvian Amazon: Rapid Assessment Through a Parasitological and Serological Survey

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Free PMC article

Hotspots of Malaria Transmission in the Peruvian Amazon: Rapid Assessment Through a Parasitological and Serological Survey

Angel Rosas-Aguirre et al. PLoS One. .
Free PMC article

Abstract

Background: With low and markedly seasonal malaria transmission, increasingly sensitive tools for better stratifying the risk of infection and targeting control interventions are needed. A cross-sectional survey to characterize the current malaria transmission patterns, identify hotspots, and detect recent changes using parasitological and serological measures was conducted in three sites of the Peruvian Amazon.

Material and methods: After full census of the study population, 651 participants were interviewed, clinically examined and had a blood sample taken for the detection of malaria parasites (microscopy and PCR) and antibodies against P. vivax (PvMSP119, PvAMA1) and P. falciparum (PfGLURP, PfAMA1) antigens by ELISA. Risk factors for malaria infection (positive PCR) and malaria exposure (seropositivity) were assessed by multivariate survey logistic regression models. Age-specific seroprevalence was analyzed using a reversible catalytic conversion model based on maximum likelihood for generating seroconversion rates (SCR, λ). SaTScan was used to detect spatial clusters of serology-positive individuals within each site.

Results: The overall parasite prevalence by PCR was low, i.e. 3.9% for P. vivax and 6.7% for P. falciparum, while the seroprevalence was substantially higher, 33.6% for P. vivax and 22.0% for P. falciparum, with major differences between study sites. Age and location (site) were significantly associated with P. vivax exposure; while location, age and outdoor occupation were associated with P. falciparum exposure. P. falciparum seroprevalence curves showed a stable transmission throughout time, while for P. vivax transmission was better described by a model with two SCRs. The spatial analysis identified well-defined clusters of P. falciparum seropositive individuals in two sites, while it detected only a very small cluster of P. vivax exposure.

Conclusion: The use of a single parasitological and serological malaria survey has proven to be an efficient and accurate method to characterize the species specific heterogeneity in malaria transmission at micro-geographical level as well as to identify recent changes in transmission.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Study area in San Juan district, Loreto department, Northern Peruvian Amazon. Eight communities in three sites were included.
Site A: Aguaje (AG), Agua Blanca (AB) and Pampachica (PA); Site B: El Milagro (EM), Villa Buen Pastor (BP) and San Carlos (SC); and Site C: San Lucas (SL), El Triunfo (ET).
Fig 2
Fig 2. Flowchart of study participants.
Fig 3
Fig 3. Distribution of P. falciparum infected and exposed individuals by study site (A, B, C) with respective significant spatial clusters for P. falciparum seropositivity.
Fig 4
Fig 4. Distribution of P. vivax infected and exposed individuals by study site (A, B, C) with respective significant spatial clusters for P. vivax seropositivity.
Fig 5
Fig 5. P. vivax and P. falciparum age-seroprevalence curves for individuals under 30 years old in each site.
Black dots represent observed prevalence, whilst the blue lines represent the maximum likelihood model. Seroconversion rates (λ, (95%CI)) are plotted on the graphs. Two seroconversion rates (λ1 and λ2) are plotted in graphs if likelihood ratio tests indicate change at a certain point in calendar time.
Fig 6
Fig 6. Evolution of the annual malaria incidence in Loreto department: 1990–2013.
Information on annual malaria cases was obtained from the Regional Health Direction of Loreto. Numbers in the timeline point out important events that influenced malaria incidence: 1) First report P. falciparum in Loreto (1990), 2) first reports of chloroquine resistance (CQR) in P. falciparum (since 1994), 3) very strong ENSO phenomenon (1996–1998), 4) Implementation of new antimalarial treatment policy for P. falciparum and P. vivax (2001–2004), 5) Global fund-PAMAFRO project (2005–2010).

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Grant support

The study was funded by the Directorate General for Development Cooperation (DGCD) of the Belgian Government within the Third Framework Agreement of the Institutional Collaboration between the Institute of Tropical Medicine “Alexander von Humboldt” - Universidad Peruana Cayetano Heredia, Lima and the Institute of Tropical Medicine in Antwerp, Belgium (FA3-II project, 2011-2013)). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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