Artemether-lumefantrine Resistance Monitoring in Children With Uncomplicated Plasmodium Falciparum Malaria in Mali

Overview

Background: Malaria is a disease caused by a parasite. People get malaria if they are bitten by an parasite-infected mosquito. A drug called artemether-lumefantrine (AL) can treat malaria. Although iAL has helped make the malaria problem less severe in the African country of Mali, researchers want to find out if malaria parasites are becoming resistant to this drug. Objective: To test for AL-resistant parasites in children with malaria in Mali. Eligibility: AL resistance monitoring study: children aged 2 17 years who live in Kenieroba, Mali, and have malaria. Blood collection substudy: healthy volunteers aged 18 65 years. Design: Volunteers for the substudy will have blood taken up to 6 times a year. Study participants will be screened with 1 finger-prick blood sample. Girls may have a pregnancy test. Baseline visit: Participants will have a physical exam. Their vital signs and temperature will be measured. They will answer questions about their symptoms. They will give a blood sample. Participants will get 6 doses of AL over 3 days. They will take it in tablet form with milk. Some participants will also stay at the clinic for 2 days. They will have a catheter placed in a vein. They will have blood taken frequently. Participants will have follow-up visits for about 1 month. They may have: Physical exam performed Vital signs and temperature measured Symptom questionnaire administered Finger-prick blood sample and/or a regular blood sample taken Pregnancy test given Antimalarial medications other than AL provided.

Artemether-lumefantrine (AL) has replaced artesunate + amodiaquine as the frontline artemisinin (ART) combination therapy (ACT) for uncomplicated Plasmodium falciparum malaria in Mali. It is not known whether parasites are developing resistance to AL in Mali, where we are studying how naturally-acquired immunity and sickle-cell trait reduce malaria risk and parasite density in our pediatric study population. AL Resistance Monitoring Study: To monitor for emerging AL resistance in vivo and lumefantrine (LF) resistance ex vivo, we will conduct a standard WHO-recommended protocol to measure AL resistance rates over the next 4 years. We will enroll all children aged 2-17 years with uncomplicated falciparum malaria and parasite count between 2,000 and 200,000 parasites per microliter, treat them with AL on D0, D1, and D2, confirm adequate LF plasma concentrations on Day 7, and monitor for malaria symptoms and recurrent parasitemias on D0, D1, D2, D3, D7, D14, D21, and D28. In related laboratory studies, we will use blood samples taken at the times of enrollment and recrudescence to measure parasite susceptibility to LF and other antimalarial drugs ex vivo; investigate genetic and transcriptional determinants of parasite response to AL in vivo and LF ex vivo; and prepare cryopreserved parasites for future work on drug action and resistance mechanisms. Parasite Clearance Substudy: We have recently discovered an agedependent acceleration of parasite clearance rates in Malian children, and postulate that it is mediated by IgG specific for Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), the parasite s main virulence factor on the surface of infected red blood cells (iRBCs). We hypothesize that ART exposure induces the premature expression of PfEMP1 on the surface of circulating ring-iRBCs in vivo. To test this hypothesis, we will calculate parasite clearance rates in a subset of subjects with relatively high parasite densities, and relate these rates to the ability of autologous IgG to recognize ring-iRBCs over the first 8 hours of ART exposure in vivo. In this same subset of patients, we will also explore whether AL induces parasite dormancy in vivo by removing parasites at H0, H6, H24, H48, D3, D7, and D14 following AL therapy, and cloning them to quantify the number of viable parasites. Blood Collection Study: We have found that sickle-cell trait (HbAS), like naturally-acquired humoral immunity, reduces both malaria risk and parasite density in our study population, and that this protection is associated with abnormal PfEMP1 display on the iRBC surface. To elucidate the molecular mechanism of this phenotype and explore how it may synergize with naturally-acquired IgG responses, we will investigate whether the development of PfEMP1 trafficking machinery is impaired in HbAS compared to normal homozygous hemoglobin A (HbAA) red blood cells (RBCs). To test this, we will purify parasite isolates from children with malaria, inoculate them into HbAA and HbAS RBCs from healthy adult donors, and follow their intraerythrocytic development using flow cytometry and electron microscopy.