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The epidemiology of subclinical malaria infections in South-East Asia: findings from cross-sectional surveys in Thailand-Myanmar border areas, Cambodia, and Vietnam.

Imwong M, Nguyen TN, Tripura R, Peto TJ, Lee SJ, Lwin KM, Suangkanarat P, Jeeyapant A, Vihokhern B, Wongsaen K, Van Hue D, Dong le T, Nguyen TU, Lubell Y, von Seidlein L, Dhorda M, Promnarate C, Snounou G, Malleret B, Rénia L, Keereecharoen L, Singhasivanon P, Sirithiranont P, Chalk J, Nguon C, Hien TT, Day N, White NJ, Dondorp A, Nosten F - Malar. J. (2015)

Bottom Line: A history of fever, male sex, and age of 15 years or older were independently associated with parasitaemia in a multivariate regression model stratified by site.Light microscopy and RDTs identified only a quarter of all parasitaemic participants.The asymptomatic Plasmodium reservoir is considerable, even in low transmission settings.

View Article: PubMed Central - PubMed

Affiliation: Mahidol Oxford Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. noi@tropmedres.ac.

ABSTRACT

Background: The importance of the submicroscopic reservoir of Plasmodium infections for malaria elimination depends on its size, which is generally considered small in low transmission settings. The precise estimation of this reservoir requires more sensitive parasite detection methods. The prevalence of asymptomatic, sub-microscopic malaria was assessed by a sensitive, high blood volume quantitative real-time polymerase chain reaction method in three countries of the Greater Mekong Sub-region.

Methods: Cross-sectional surveys were conducted in three villages in western Cambodia, four villages along the Thailand-Myanmar border and four villages in southwest Vietnam. Malaria parasitaemia was assessed by Plasmodium falciparum/pan malaria rapid diagnostic tests (RDTs), microscopy and a high volume ultra-sensitive real-time polymerase chain reaction (HVUSqPCR: limit of detection 22 parasites/mL). All villagers older than 6 months were invited to participate.

Results: A census before the surveys identified 7355 residents in the study villages. Parasite prevalence was 224/5008 (4 %) by RDT, 229/5111 (5 %) by microscopy, and 988/4975 (20 %) when assessed by HVUSqPCR. Of these 164 (3 %) were infected with P. falciparum, 357 (7 %) with Plasmodium vivax, 56 (1 %) with a mixed infection, and 411 (8 %) had parasite densities that were too low for species identification. A history of fever, male sex, and age of 15 years or older were independently associated with parasitaemia in a multivariate regression model stratified by site.

Conclusion: Light microscopy and RDTs identified only a quarter of all parasitaemic participants. The asymptomatic Plasmodium reservoir is considerable, even in low transmission settings. Novel strategies are needed to eliminate this previously under recognized reservoir of malaria transmission.

No MeSH data available.


Related in: MedlinePlus

The correlations between anaemia, fever and age. Younger participants were more likely to be febrile and anaemic (Hb < 11 g/dL)
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Fig3: The correlations between anaemia, fever and age. Younger participants were more likely to be febrile and anaemic (Hb < 11 g/dL)

Mentions: The population of the 11 participating villages were comparable in age distributions; the median age of the participants was 21 years with 37 % of the participants under 15-year-old (Table 1; data disaggregated by village are shown in Additional file 3). Of the 741 children under 72 months who participated in the study 57 (8 %) were febrile (tympanic temperature >37.5 °C) on the day of the examination. In the Vietnamese sites the proportion of febrile children was 1 % in contrast to 10 % in the Thailand–Myanmar border areas and the Cambodian sites (p = 0.001; Table 1). Moderate anaemia (Hb <8 g/dL) was present in 5 % of children in the Vietnamese sites, 3 % of children in the Thailand–Myanmar border areas and 2 % in the Cambodian sites (p < 0.009). Younger age was associated with a higher prevalence of fever and anaemia compared to older age (p < 0.0001; Fig. 3). The prevalence of fever increased with the severity of anaemia: 3 % in participants with an Hb ≥11 g/dL, 5 % with 8 ≤ Hb < 11 g/dL and 9 % in the group with Hb <8 g/dL (2 d.f.; p = 0.002).Table 1


The epidemiology of subclinical malaria infections in South-East Asia: findings from cross-sectional surveys in Thailand-Myanmar border areas, Cambodia, and Vietnam.

Imwong M, Nguyen TN, Tripura R, Peto TJ, Lee SJ, Lwin KM, Suangkanarat P, Jeeyapant A, Vihokhern B, Wongsaen K, Van Hue D, Dong le T, Nguyen TU, Lubell Y, von Seidlein L, Dhorda M, Promnarate C, Snounou G, Malleret B, Rénia L, Keereecharoen L, Singhasivanon P, Sirithiranont P, Chalk J, Nguon C, Hien TT, Day N, White NJ, Dondorp A, Nosten F - Malar. J. (2015)

The correlations between anaemia, fever and age. Younger participants were more likely to be febrile and anaemic (Hb < 11 g/dL)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4590703&req=5

Fig3: The correlations between anaemia, fever and age. Younger participants were more likely to be febrile and anaemic (Hb < 11 g/dL)
Mentions: The population of the 11 participating villages were comparable in age distributions; the median age of the participants was 21 years with 37 % of the participants under 15-year-old (Table 1; data disaggregated by village are shown in Additional file 3). Of the 741 children under 72 months who participated in the study 57 (8 %) were febrile (tympanic temperature >37.5 °C) on the day of the examination. In the Vietnamese sites the proportion of febrile children was 1 % in contrast to 10 % in the Thailand–Myanmar border areas and the Cambodian sites (p = 0.001; Table 1). Moderate anaemia (Hb <8 g/dL) was present in 5 % of children in the Vietnamese sites, 3 % of children in the Thailand–Myanmar border areas and 2 % in the Cambodian sites (p < 0.009). Younger age was associated with a higher prevalence of fever and anaemia compared to older age (p < 0.0001; Fig. 3). The prevalence of fever increased with the severity of anaemia: 3 % in participants with an Hb ≥11 g/dL, 5 % with 8 ≤ Hb < 11 g/dL and 9 % in the group with Hb <8 g/dL (2 d.f.; p = 0.002).Table 1

Bottom Line: A history of fever, male sex, and age of 15 years or older were independently associated with parasitaemia in a multivariate regression model stratified by site.Light microscopy and RDTs identified only a quarter of all parasitaemic participants.The asymptomatic Plasmodium reservoir is considerable, even in low transmission settings.

View Article: PubMed Central - PubMed

Affiliation: Mahidol Oxford Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. noi@tropmedres.ac.

ABSTRACT

Background: The importance of the submicroscopic reservoir of Plasmodium infections for malaria elimination depends on its size, which is generally considered small in low transmission settings. The precise estimation of this reservoir requires more sensitive parasite detection methods. The prevalence of asymptomatic, sub-microscopic malaria was assessed by a sensitive, high blood volume quantitative real-time polymerase chain reaction method in three countries of the Greater Mekong Sub-region.

Methods: Cross-sectional surveys were conducted in three villages in western Cambodia, four villages along the Thailand-Myanmar border and four villages in southwest Vietnam. Malaria parasitaemia was assessed by Plasmodium falciparum/pan malaria rapid diagnostic tests (RDTs), microscopy and a high volume ultra-sensitive real-time polymerase chain reaction (HVUSqPCR: limit of detection 22 parasites/mL). All villagers older than 6 months were invited to participate.

Results: A census before the surveys identified 7355 residents in the study villages. Parasite prevalence was 224/5008 (4 %) by RDT, 229/5111 (5 %) by microscopy, and 988/4975 (20 %) when assessed by HVUSqPCR. Of these 164 (3 %) were infected with P. falciparum, 357 (7 %) with Plasmodium vivax, 56 (1 %) with a mixed infection, and 411 (8 %) had parasite densities that were too low for species identification. A history of fever, male sex, and age of 15 years or older were independently associated with parasitaemia in a multivariate regression model stratified by site.

Conclusion: Light microscopy and RDTs identified only a quarter of all parasitaemic participants. The asymptomatic Plasmodium reservoir is considerable, even in low transmission settings. Novel strategies are needed to eliminate this previously under recognized reservoir of malaria transmission.

No MeSH data available.


Related in: MedlinePlus