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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

Fever in relation to P. falciparum and P. vivax densities
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Fig6: Fever in relation to P. falciparum and P. vivax densities

Mentions: A total of 10/152 (7 %) participants with P. falciparum infections detected by HVUSqPCR were febrile on the day of the survey in contrast to 14/323 (4 %) with P. vivax infections, 112/3412 (3 %) without parasitaemia and 0/48 with mixed infections (comparison P. falciparum and negatives: p = 0.038; comparison P. vivax and negatives p = 0.3 and comparison P. falciparum and P. vivax p = 0.4). The geometric mean (95 %CI) parasite density in the 47 febrile patients was 3729 (755–18,420) parasites/mL, compared to 1151 (905–1464) parasites/mL in afebrile individuals. For both P. falciparum or P. vivax was it impossible to determine a clearly delineated pyrogenic parasite density threshold (Fig. 6).Fig. 6


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)

Fever in relation to P. falciparum and P. vivax densities
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig6: Fever in relation to P. falciparum and P. vivax densities
Mentions: A total of 10/152 (7 %) participants with P. falciparum infections detected by HVUSqPCR were febrile on the day of the survey in contrast to 14/323 (4 %) with P. vivax infections, 112/3412 (3 %) without parasitaemia and 0/48 with mixed infections (comparison P. falciparum and negatives: p = 0.038; comparison P. vivax and negatives p = 0.3 and comparison P. falciparum and P. vivax p = 0.4). The geometric mean (95 %CI) parasite density in the 47 febrile patients was 3729 (755–18,420) parasites/mL, compared to 1151 (905–1464) parasites/mL in afebrile individuals. For both P. falciparum or P. vivax was it impossible to determine a clearly delineated pyrogenic parasite density threshold (Fig. 6).Fig. 6

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