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Publication Metadata only Genetic population of Plasmodium knowlesi during pre-malaria elimination in Thailand(2021-12-01) Rungniran Sugaram; Patcharida Boondej; Suttipat Srisutham; Chanon Kunasol; Watcharee Pagornrat; Usa Boonyuen; Arjen M. Dondorp; Aungkana Saejeng; Prayuth Sudathip; Mallika Imwong; Faculty of Tropical Medicine, Mahidol University; Chulalongkorn University; Thailand Ministry of Public Health; Nuffield Department of MedicineBackground: Thailand is committed to eliminating malaria by 2024. From 2013 to 2020, the total number of malaria cases have decreased, from 37,741 to 4474 (an 88.1% reduction). However, infections with Plasmodium knowlesi, a monkey malarial pathogenPublication Open Access Clinical trials of artesunate plus sulfadoxine‑pyrimethamine for Plasmodium falciparum malaria in Afghanistan: maintained efficacy a decade after introduction(2016) Ghulam Rahim Awab; Mallika Imwong; Sasithon Pukrittayakamee; Fazel Alim; Warunee Hanpithakpong; Joel Tarning; Dondorp, Arjen M.; Day, Nicholas P. J.; White, Nicholas J.; Woodrow, Charles J.; Mahidol University. Faculty of Tropical Medicine. Mahidol-Oxford Tropical Medicine Research Unit (MORU)Background: Combination therapy with artesunate plus sulfadoxine-pyrimethamine (SP) was adopted as recommended treatment for Plasmodium falciparum infection in Afghanistan in 2003. Methods: A series of prospective clinical studies examining the efficacy of artesunate plus sulfadoxine-pyrimethamine (AS + SP) against P. falciparum were undertaken in sentinel sites in Afghanistan from 2007 to 2014, accompanied by relevant molecular studies. The first study was a randomized trial of AS + SP versus dihydroartemisinin-piperaquine, while two subsequent studies were standard therapeutic efficacy studies of AS + SP. Results: Three hundred and three patients were enrolled across four provinces in the north and east of the country. Curative efficacy was high in all the trials, with an adequate clinical and parasitological response (ACPR) of more than 95 % in all groups and trial stages. Genotyping for drug-resistance alleles at dhfr indicated fixation of the S108 N mutation and a prevalence of the C59R mutation of approximately 95 % across all sites. Other mutations in dhfr and dhps remained rare or absent entirely, although five isolates from the first trial carried the dhps triple mutant SGEGA haplotype. In the last study undertaken in 2012–2014 the K13 artemisinin resistance marker was examined; only two of 60 successfully sequenced samples carried a K13-propeller mutation. Conclusions: These data confirm maintained efficacy 10 years after introduction of artesunate plus SP as combination treatment of P. falciparum in Afghanistan. The molecular data indicate that despite a substantial fall in incidence, resistance has not developed to artemisinins, or intensified to the ACT partner drug components. Trial Registration http://www.clinicaltrials.gov/ct NCT00682578, NCT01115439 and NCT01707199Publication Open Access The epidemiology of subclinical malaria infections in South‑East Asia: findings from cross‑sectional surveys in Thailand– Myanmar border areas, Cambodia, and Vietnam(2015) Mallika Imwong; Nguyen, Thuy Nhien; Rupam Tripura; Peto, Tom J.; Lee, Sue J.; Lwin, Khin Maung; Preyanan Suangkanarat; Atthanee Jeeyapant; Benchawan Vihokhern; Klanarong Wongsaen; Hue, Dao Van; Dong, Le Thanh; Nguyen, Tam‑Uyen; Yoel Lubell; Seidlein, Lorenz von; Mehul Dhorda; Cholrawee Promnarate; Georges Snounou; Benoit Malleret; Laurent Rénia; Lilly Keereecharoen; Pratap Singhasivanon; Pasathorn Sirithiranont; Jem Chalk; Chea Nguon; Hien, Tran Tinh; Nicholas Day; White, Nicholas J.; Arjen Dondorp; Francois Nosten; Mahidol University. Faculty of Tropical Medicine. Mahidol Oxford Research UnitBackground: 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.Publication Open Access Assessment of therapeutic responses to gametocytocidal drugs in Plasmodium falciparum malaria.(2014-12-09) White, Nicholas J; Ashley, Elizabeth A; Recht, Judith; Delves, Michael J; Ruecker, Andrea; Smithuis, Frank M; Eziefula, Alice C; Bousema, Teun; Drakeley, Chris; Kesinee Chotivanich; เกศินี โชติวานิช; Mallika Imwong; มัลลิกา อิ่มวงศ์; Sasithon Pukrittayakamee; ศศิธร ผู้กฤตยาคามี; Jetsumon Prachumsri; เจตสุมน ประจำศรี; Chu, Cindy; Andolina, Chiara; Bancone, Germana; Hien, Tran T; Mayxay, Mayfong; Taylor, Walter RJ; Seidlein, Lorenz von; Price, Ric N; Barnes, Karen I; Djimdé, Abdoulaye; ter Kuile, Feiko; Gosling, Roly; Chen, Ingrid; Dhorda, Mehul J; Stepniewska, Kasia; Guérin, Philippe; Woodrow, Charles J; Dondorp, Arjen M; Day, Nicholas PJ; Nosten, Francois H; White, Nicholas J; Mahidol University. Faculty of Tropical Medicine. Department of Clinical Tropical Medicine.; Mahidol University. Faculty of Tropical Medicine. Department of Molecular Tropical Medicine and Genetics.; Mahidol University. Faculty of Tropical Medicine. Mahidol-Oxford Tropical Medicine Research Unit.; Mahidol University. Faculty of Tropical Medicine. Mahidol Vivax Research Unit.; Mahidol University. Faculty of Tropical Medicine. Shoklo Malaria Research Unit.Indirect clinical measures assessing anti-malarial drug transmission-blocking activity in falciparum malaria include measurement of the duration of gametocytaemia, the rate of gametocyte clearance or the area under the gametocytaemia-time curve (AUC). These may provide useful comparative information, but they underestimate dose-response relationships for transmission-blocking activity. Following 8-aminoquinoline administration P. falciparum gametocytes are sterilized within hours, whereas clearance from blood takes days. Gametocytaemia AUC and clearance times are determined predominantly by the more numerous female gametocytes, which are generally less drug sensitive than the minority male gametocytes, whereas transmission-blocking activity and thus infectivity is determined by the more sensitive male forms. In choosing doses of transmission-blocking drugs there is no substitute yet for mosquito-feeding studies.Publication Open Access Prevalence of antifolate resistance mutations in Plasmodium falciparum isolates in Afghanistan(2013-03-15) Awab, Ghulam R; Sasithon Pukrittayakamee; ศศิธร ผู้กฤตยาคามี; Natsuda Jamornthanyawat; นาถสุดา จามรธัญญวาท; Yamin, Fazel; Dondorp, Arjen M.; Day, Nicholas P.J.; White, Nicholas J.; Woodrow, Charles J.; Mallika Imwong; มัลลิกา อิ่มวงศ์; Mallika Imwong; Mahidol University. Faculty of Tropical Medicine. Mahidol-Oxford Tropical Medicine Research Unit (MORU); Mahidol University. Faculty of Tropical Medicine. Department of Clinical Tropical Medicine; Mahidol University. Faculty of Tropical Medicine. Department of Molecular Tropical Medicine and Genetics; Mahidol University. Center for Emerging and Neglected Infectious DiseasesBACKGROUND: Artesunate plus sulphadoxine-pyrimethamine (AS+SP) is now first-line treatment for Plasmodium falciparum infection in several south Asian countries, including Afghanistan. Molecular studies provide a sensitive means to investigate the current state of drug susceptibility to the SP component, and can also provide information on the likely efficacy of other potential forms of artemisinin-combination therapy. METHODS: During the years 2007 to 2010, 120 blood spots from patients with P. falciparum malaria were obtained in four provinces of Afghanistan. PCR-based methods were used to detect drug-resistance mutations in dhfr, dhps, pfcrt and pfmdr1, as well as to determine copy number of pfmdr1. RESULTS: The majority (95.5%) of infections had a double mutation in the dhfr gene (C59R, S108N); no mutations at dhfr positions 16, 51 or 164 were seen. Most isolates were wild type across the dhps gene, but five isolates from the provinces of Kunar and Nangarhar in eastern Afghanistan had the triple mutation A437G / K540E / A581G; all five cases were successfully treated with three receiving AS+SP and two receiving dihydroartemisinin-piperaquine. All isolates showed the pfcrt SVNMT chloroquine resistance haplotype. Five of 79 isolates had the pfmdr1 N86Y mutation, while 52 had pfmdr1 Y184F; positions 1034, 1042 and 1246 were wild type in all isolates. The pfmdr1 gene was not amplified in any sample. CONCLUSIONS: This study indicates that shortly after the adoption of AS+SP as first-line treatment in Afghanistan, most parasites had a double mutation haplotype in dhfr, and a small number of isolates from eastern Afghanistan harboured a triple mutation haplotype in dhps. The impact of these mutations on the efficacy of AS+SP remains to be assessed in significant numbers of patients, but these results are clearly concerning since they suggest a higher degree of SP resistance than previously detected. Further focused molecular and clinical studies in this region are urgently required.Publication Open Access Investigations on anopheline mosquitoes close to the nest sites of chimpanzees subject to malaria infection in Ugandan highlands(2012-04-17) Krief, Sabrina; Levrero, Florence; Krief, Jean-Michel; Supinya Thanapongpichat; สุภิญญา ธนาพงษ์ภิชาติ; Mallika Imwong; มัลลิกา อิ่มวงศ์; Snounou, Georges; Kasenene, John M.; Cibot, Marie; Gantier, Jean-Charles; Krief, Sabrina; Mahidol University. Faculty of Tropical MedicineBACKGROUND: Malaria parasites (Plasmodium sp.), including new species, have recently been discovered as low grade mixed infections in three wild chimpanzees (Pan troglodytes schweinfurthii) sampled randomly in Kibale National Park, Uganda. This suggested a high prevalence of malaria infection in this community. The clinical course of malaria in chimpanzees and the species of the vectors that transmit their parasites are not known. The fact that these apes display a specific behaviour in which they consume plant parts of low nutritional value but that contain compounds with anti-malarial properties suggests that the apes health might be affected by the parasite. The avoidance of the night-biting anopheline mosquitoes is another potential behavioural adaptation that would lead to a decrease in the number of infectious bites and consequently malaria. METHODS: Mosquitoes were collected over two years using suction-light traps and yeast-generated CO(2) traps at the nesting and the feeding sites of two chimpanzee communities in Kibale National Park. The species of the female Anopheles caught were then determined and the presence of Plasmodium was sought in these insects by PCR amplification. RESULTS: The mosquito catches yielded a total of 309 female Anopheles specimens, the only known vectors of malaria parasites of mammalians. These specimens belonged to 10 species, of which Anopheles implexus, Anopheles vinckei and Anopheles demeilloni dominated. Sensitive DNA amplification techniques failed to detect any Plasmodium-positive Anopheles specimens. Humidity and trap height influenced the Anopheles capture success, and there was a negative correlation between nest numbers and mosquito abundance. The anopheline mosquitoes were also less diverse and numerous in sites where chimpanzees were nesting as compared to those where they were feeding. CONCLUSIONS: These observations suggest that the sites where chimpanzees build their nests every night might be selected, at least in part, in order to minimize contact with anopheline mosquitoes, which might lead to a reduced risk in acquiring malaria infections.