62 research outputs found
Declining Artesunate-Mefloquine Efficacy against Falciparum Malaria on the Cambodia–Thailand Border
Emerging resistance in Southeast Asia raises concern over possible spread or similar evolution of resistance to other artemisinin-based combination therapies in Africa
Key Knowledge Gaps for Plasmodium vivax Control and Elimination
There is inadequate understanding of the biology, pathology,
transmission, and control of Plasmodium vivax, the
geographically most widespread cause of human malaria. During
the last decades, study of this species was neglected, in part
due to the erroneous belief that it is intrinsically benign. In
addition, many technical challenges in culturing the parasite
also hampered understanding its fundamental biology and
molecular and cellular responses to chemotherapeutics. Research
on vivax malaria needs to be substantially expanded over the
next decade to accelerate its elimination and eradication. This
article summarizes key knowledge gaps identified by researchers,
national malaria control programs, and other stakeholders
assembled by the World Health Organization to develop strategies
for controlling and eliminating vivax malaria. The priorities
presented in this article emerged in these technical
discussions, and were adopted by expert consensus of the
authors. All involved understood the priority placed upon
pragmatism in this research agenda, that is, focus upon tools
delivering better prevention, diagnosis, treatment, and
surveillance of P. vivax
A new method for detection of pfmdr1 mutations in Plasmodium falciparum DNA using real-time PCR
BACKGROUND: Surveillance for drug-resistant Plasmodium falciparum should be a component of malaria control programmes. Real-time PCR methods for the detection of parasite single-nucleotide polymorphisms (SNPs) and gene amplification could be useful survellance tools. METHODS: A real-time PCR assay has been developed that identifies single nucleotide polymorphisms (SNPs) at amino acids 86, 184, 1034 and 1042 in the P. falciparum multi-drug resistant (pfmdr 1) gene that may be associated with anti-malarial drug resistance. RESULTS: This assay has a sensitivity and specificity of 94% and 100% when compared to traditional PCR methods for genotyping. Only 54 of 68 (79%) paired pre- and post-culture DNA samples were concordant at all four loci. CONCLUSION: Real-time PCR is a sensitive and specific method to detect SNP's in pfmdr 1. Genotypes of parasites after in vitro culture may not reflect that seen in vivo
pfmdr1 GENOTYPING AND IN VIVO MEFLOQUINE RESISTANCE ON THE THAI-MYANMAR BORDER
Molecular markers have been proposed as a method of monitoring malaria drug resistance and could potentially be used to prolong the life span of antimalarial drugs. Single nucleotide polymorphisms (SNPs) in the Plasmodium falciparum gene pfmdr1 and increased gene copy number have been associated with in vitro drug resistance
but have not been well studied in vivo. In a prospective cohort study of malaria patients receiving mefloquine treatment
on the Thai-Myanmar border, there was no significant association between either pfmdr1 SNPs or in vitro drug sensitivity
and mefloquine resistance in vivo. Increased pfmdr1 gene copy number was significantly associated with recrudescence
(relative risk 2.30, 95% CI 1.27–4.15). pfmdr1 gene copy number may be a useful surveillance tool for
mefloquine-resistant falciparum malaria in Thailand
HEMATOLOGIC AND CLINICAL INDICES OF MALARIA IN A SEMI-IMMUNE POPULATION OF WESTERN THAILAND
This study examines hematologic profiles of persons with acute Plasmodium falciparum or P. vivax
infection in Maesod on Thailand’s western border with Myanmar compared with febrile, non-parasitemic persons also
reporting to malaria clinics. Nine hundred seventy-nine subjects were malaria-negative, 414 were infected with P.
falciparum, and 646 were infected with P. vivax. Persons with patent parasitemia tended to have significantly lower white
blood cell, red blood cell, platelet, and hemoglobin levels than those who were malaria-negative. For the first time, a
parallel trend in thrombocytopenia with parasitemia was found to be associated with both P. falciparum, and P. vivax
infection. Using logistic regression, persons with platelet counts < 150,000/µL were 12−15 times more likely to have
malaria than persons with platelet counts ≥ 150,000/µL. This study supplements previous literature on the hematologic
effects of malaria and helps define those alterations for a semi-immune population. Thrombocytopenia is identified as
a key indicator of malaria in these febrile patients
Delayed Plasmodium falciparum clearance following artesunate-mefloquine combination therapy in Thailand, 1997-2007
Abstract Background There is concern that artesunate resistance is developing in Southeast Asia. The purpose of this study is to investigate the prevalence of parasitaemia in the few days following treatment with artesunate-mefloquine (AM), which is an indirect measure of decreased artesunate susceptibility. Methods This is a retrospective analysis of 31 therapeutic efficacy studies involving 1,327 patients treated with AM conducted by the Thai National Malaria Control Programme from 1997–2007. Results The prevalence of patients with parasitaemia on day 2 was higher in the east compared to the west (east: 20%, west: 9%, OR 2.47, 95% CI: 1.77, 3.45). In addition, the prevalence of day-2 parasitaemia increased over time (OR for each year = 1.10, 95% CI: 1.03, 1.19). After controlling for initial parasitaemia and age, year and region remained important determinants of day-2 parasitaemia (OR for region = 3.98, 95%CI 2.63, 6.00; OR for year = 1.28, 95%CI: 1.17, 1.39). The presence of parasitaemia on day 2 and day 3 were specific, but not sensitive predictors of treatment failure. Discussion Delayed resolution of parasitaemia after AM treatment increased in eastern Thailand between 1997 and 2007, which may be an early manifestation of decreased artesunate susceptibility. However, clinical and parasitological treatment failure after 28 days (which is related to both mefloquine and artesunate decreased susceptibility) is not changing over time. The presence of parasitaemia on day 2 is a poor indicator of AM 28-day treatment failure
MEASURING ALLELIC HETEROGENEITY IN PLASMODIUM FALCIPARUM BY A HETERODUPLEX TRACKING ASSAY
We developed a novel Plasmodium falciparum genotyping strategy based on the heteroduplex tracking
assay (HTA) method commonly used to genotype viruses. Because it can detect both sequence and size polymorphisms,
we hypothesized that HTA is more sensitive than current methods. To test this hypothesis, we compared the ability of
HTA and a nested polymerase chain reaction (PCR) to detect genetic diversity in 17 Thai samples. The HTA detected
more MSP1 sequence variants in eight isolates (47%), less sequence variants in three isolates (18%), and an equal
number of sequence variants in six isolates (35%), suggesting that HTA is equal to or more sensitive than the nested
PCR. This study is a proof of concept that HTA is a sensitive allelic discrimination method able to determine genetic
diversity in P. falciparum and warrants its use in studies of antimalarial drug efficacy
Molecular Surveillance for Multidrug-Resistant Plasmodium falciparum, Cambodia
We conducted surveillance for multidrug-resistant Plasmodium falciparum in Cambodia during 2004–2006 by assessing molecular changes in pfmdr1. The high prevalence of isolates with multiple pfmdr1 copies found in western Cambodia near the Thai border, where artesunate–mefloquine therapy failures occur, contrasts with isolates from eastern Cambodia, where this combination therapy remains highly effective
PFMDR1 AND IN VIVO RESISTANCE TO ARTESUNATE-MEFLOQUINE IN FALCIPARUM MALARIA ON THE CAMBODIAN–THAI BORDER
Artemisinin combination therapies (ACTs) have recently been adopted as first-line therapy for Plasmodium
falciparum infections in most malaria-endemic countries. In this study, we estimated the association between
artesunate-mefloquine therapy failure and genetic changes in the putative transporter, pfmdr1. Blood samples were
acquired from 80 patients enrolled in an 2004 in vivo efficacy study in Pailin, Cambodia, and genotyped for pfmdr1 copy
number and haplotype. Having parasites with three or more copies of pfmdr1 before treatment was strongly associated
with recrudescence (hazard ratio [HR] = 8.30; 95% CI: 2.60–26.43). This relationship was maintained when controlling
for initial parasite density and hematocrit (HR = 7.91; 95% CI: 2.38–26.29). Artesunate-mefloquine treatment selected
for increased pfmdr1 copy number, because isolates from recurrent episodes had higher copy numbers than the paired
enrollment samples (Wilcoxon rank test, P = 0.040). pfmdr1 copy number should be evaluated further as a surveillance
tool for artesunate-mefloquine resistance in Cambodia
Misclassification of Drug Failures in Plasmodium falciparum Clinical Trials in Southeast Asia
Most trials of antimalarials occur in areas where reinfections are possible. For Plasmodium falciparum, reinfections are distinguished from recrudescences by PCR analysis of 3 polymorphic genes. However, the validity of this approach has never been rigorously tested. We tested for misclassification in 6 patients from clinical trials in Thailand and Cambodia who were classified as reinfected by the standard PCR protocol. Using heteroduplex tracking assays and direct DNA sequencing, we found that 5 of 6 (83%) patients were misclassified. Misclassification in this manner overestimates the efficacy of antimalarials and delays recognition of decreasing therapeutic efficacy, thus delaying potential policy changes
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