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1.
Malar J ; 14: 520, 2015 Dec 23.
Article in English | MEDLINE | ID: mdl-26701778

ABSTRACT

BACKGROUND: Highly sensitive, scalable diagnostic methods are needed to guide malaria elimination interventions. While traditional microscopy and rapid diagnostic tests (RDTs) are suitable for the diagnosis of symptomatic malaria infection, more sensitive tests are needed to screen for low-density, asymptomatic infections that are targeted by interventions aiming to eliminate the entire reservoir of malaria infection in humans. METHODS: A reverse transcription polymerase chain reaction (RT- PCR) was developed for multiplexed detection of the 18S ribosomal RNA gene and ribosomal RNA of Plasmodium falciparum and Plasmodium vivax. Simulated field samples stored for 14 days with sample preservation buffer were used to assess the analytical sensitivity and specificity. Additionally, 1750 field samples from Southeastern Myanmar were tested both by RDT and ultrasensitive RT-PCR. RESULTS: Limits of detection (LoD) were determined under simulated field conditions. When 0.3 mL blood samples were stored for 14 days at 28 °C and 80% humidity, the LoD was less than 16 parasites/mL for P. falciparum and 19.7 copies/µL for P. vivax (using a plasmid surrogate), about 10,000-fold lower than RDTs. Of the 1739 samples successfully evaluated by both ultrasensitive RT-PCR and RDT, only two were RDT positive while 24 were positive for P. falciparum, 108 were positive for P. vivax, and 127 were positive for either P. vivax and/or P. falciparum using ultrasensitive RT-PCR. CONCLUSIONS: This ultrasensitive RT-PCR method is a robust, field-tested screening method that is vastly more sensitive than RDTs. Further optimization may result in a truly scalable tool suitable for widespread surveillance of low-level asymptomatic P. falciparum and P. vivax parasitaemia.


Subject(s)
Asymptomatic Infections , Blood/parasitology , Malaria, Falciparum/diagnosis , Malaria, Vivax/diagnosis , Plasmodium falciparum/isolation & purification , Plasmodium vivax/isolation & purification , Reverse Transcriptase Polymerase Chain Reaction/methods , DNA, Protozoan/genetics , DNA, Ribosomal/genetics , Humans , Myanmar , Plasmodium falciparum/genetics , Plasmodium vivax/genetics , RNA, Protozoan/genetics , RNA, Ribosomal, 18S/genetics , Sensitivity and Specificity
2.
J Infect Dis ; 212(11): 1778-86, 2015 Dec 01.
Article in English | MEDLINE | ID: mdl-26019283

ABSTRACT

BACKGROUND: Hemoglobin C trait, like hemoglobin S trait, protects against severe malaria in children, but it is unclear whether hemoglobin C trait also protects against uncomplicated malaria. We hypothesized that Malian children with hemoglobin C trait would have a lower risk of clinical malaria than children with hemoglobin AA. METHODS: Three hundred children aged 0-6 years were enrolled in a cohort study of malaria incidence in Bandiagara, Mali, with continuous passive and monthly active follow-up from June 2009 to June 2010. RESULTS: Compared to hemoglobin AA children (n = 242), hemoglobin AC children (n = 39) had a longer time to first clinical malaria episode (hazard ratio [HR], 0.19; P = .001; 364 median malaria-free days vs 181 days), fewer episodes of clinical malaria, and a lower cumulative parasite burden. Similarly, hemoglobin AS children (n = 14) had a longer time to first clinical malaria episode than hemoglobin AA children (HR, 0.15; P = .015; 364 median malaria-free days vs 181 days), but experienced the most asymptomatic malaria infections of any group. CONCLUSIONS: Both hemoglobin C and S traits exerted a protective effect against clinical malaria episodes, but appeared to do so by mechanisms that differentially affect the response to infecting malaria parasites.


Subject(s)
Genetic Predisposition to Disease/epidemiology , Genetic Predisposition to Disease/genetics , Hemoglobin C/genetics , Malaria, Falciparum/epidemiology , Malaria, Falciparum/genetics , Child , Child, Preschool , Cohort Studies , Female , Hemoglobin, Sickle/genetics , Humans , Incidence , Infant , Infant, Newborn , Male , Mali/epidemiology
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