Clustered local transmission and asymptomatic Plasmodium falciparum and Plasmodium vivax malaria infections in a recently emerged, hypoendemic Peruvian Amazon community

Malaria Journal - Tập 4 Số 1 - 2005
OraLee H. Branch1, W. Martin Casapia2, Dionicia Gamboa3, Jean N. Hernandez2, Freddy Alava2, Norma Roncal3, Eugenia Alvarez3, Enrique J. Martínez Pérez3, Eduardo Gotuzzo3
1Department of Medicine, Geographic Medicine, University of Alabama at Birmingham, Bevill Research Building BBRB-556, Birmingham, Alabama, 35294-2170, USA
2Direccion de Salud-Loreto, Ministerio de Salud (MINSA), Iquitos, Peru
3Instituto de Medicina Tropical "Alexander Von Humboldt", Universidad Peruana Cayetano Heredia, A.P. 4314 Lima 100, Lima, Peru

Tóm tắt

Abstract Background

There is a low incidence of malaria in Iquitos, Peru, suburbs detected by passive case-detection. This low incidence might be attributable to infections clustered in some households/regions and/or undetected asymptomatic infections.

 Methods

Passive case-detection (PCD) during the malaria season (February-July) and an active case-detection (ACD) community-wide survey (March) surveyed 1,907 persons. Each month, April-July, 100-metre at-risk zones were defined by location of Plasmodium falciparum infections in the previous month. Longitudinal ACD and PCD (ACP+PCD) occurred within at-risk zones, where 137 houses (573 persons) were randomly selected as sentinels, each with one month of weekly active sampling. Entomological captures were conducted in the sentinel houses.

 Results

The PCD incidence was 0.03 P. falciparum and 0.22 Plasmodium vivax infections/person/malaria-season. However, the ACD+PCD prevalence was 0.13 and 0.39, respectively. One explanation for this 4.33 and 1.77-fold increase, respectively, was infection clustering within at-risk zones and contiguous households. Clustering makes PCD, generalized to the entire population, artificially low. Another attributable-factor was that only 41% and 24% of the P. falciparum and P. vivax infections were associated with fever and 80% of the asymptomatic infections had low-density or absent parasitaemias the following week. After accounting for asymptomatic infections, a 2.6-fold increase in ACD+PCD versus PCD was attributable to clustered transmission in at-risk zones.

 Conclusion

Even in low transmission, there are frequent highly-clustered asymptomatic infections, making PCD an inadequate measure of incidence. These findings support a strategy of concentrating ACD and insecticide campaigns in houses adjacent to houses were malaria was detected one month prior.

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Malaria Journal

Tập 4 Số 1

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