Bryan Greenhouse

Selection of Plasmodium falciparum pfmdr1 Alleles following Therapy with Artemether-Lumefantrine in an Area of Uganda where Malaria Is Highly Endemic

ABSTRACT Polymorphisms in the Plasmodium falciparum pfmdr1 gene were assayed in pretreatment samples and in samples from patients reinfected following therapy with artemether-lumefantrine. The pfmdr1 alleles 86N, 184F, and 1246D significantly increased in prevalence after treatment. All samples had a single pfmdr1 copy. Treatment with artemether-lumefantrine selects for polymorphisms that may alter antimalarial drug response.

Artemether-Lumefantrine versus Dihydroartemisinin-Piperaquine for Treatment of Malaria: A Randomized Trial

Objectives: To compare the efficacy and safety of artemether-lumefantrine (AL) and dihydroartemisinin-piperaquine (DP) for treating uncomplicated falciparum malaria in Uganda. Design: Randomized single-blinded clinical trial. Setting: Apac, Uganda, an area of very high malaria transmission intensity. Participants: Children aged 6 mo to 10 y with uncomplicated falciparum malaria. Intervention: Treatment of malaria with AL or DP, each following standard 3-d dosing regimens. Outcome measures: Risks of recurrent parasitemia at 28 and 42 d, unadjusted and adjusted by genotyping to distinguish recrudescences and new infections. Results: Of 421 enrolled participants, 417 (99%) completed follow-up. The unadjusted risk of recurrent falciparum parasitemia was significantly lower for participants treated with DP than for those treated with AL after 28 d (11% versus 29%; risk difference [RD] 18%, 95% confidence interval [CI] 11%–26%) and 42 d (43% versus 53%; RD 9.6%, 95% CI 0%–19%) of follow-up. Similarly, the risk of recurrent parasitemia due to possible recrudescence (adjusted by genotyping) was significantly lower for participants treated with DP than for those treated with AL after 28 d (1.9% versus 8.9%; RD 7.0%, 95% CI 2.5%–12%) and 42 d (6.9% versus 16%; RD 9.5%, 95% CI 2.8%–16%). Patients treated with DP had a lower risk of recurrent parasitemia due to non-falciparum species, development of gametocytemia, and higher mean increase in hemoglobin compared to patients treated with AL. Both drugs were well tolerated; serious adverse events were uncommon and unrelated to study drugs. Conclusion: DP was superior to AL for reducing the risk of recurrent parasitemia and gametocytemia, and provided improved hemoglobin recovery. DP thus appears to be a good alternative to AL as first-line treatment of uncomplicated malaria in Uganda. To maximize the benefit of artemisinin-based combination therapy in Africa, treatment should be integrated with aggressive strategies to reduce malaria transmission intensity.

Artemether-Lumefantrine Versus Dihydroartemisinin-Piperaquine for Falciparum Malaria: A Longitudinal, Randomized Trial in Young Ugandan Children

BACKGROUND Artemisinin-based combination therapies are now widely recommended as first-line treatment for uncomplicated malaria. However, which therapies are optimal is a matter of debate. We aimed to compare the short- and longer-term efficacy of 2 leading therapies in a cohort of young Ugandan children. METHODS A total of 351 children aged 6 weeks to 12 months were enrolled and followed up for up to 1 year. Children who were at least 4 months of age, weighted at least 5 kg, and had been diagnosed as having their first episode of uncomplicated malaria were randomized to receive artemether-lumefantrine or dihydroartemisinin-piperaquine. The same treatment was given for all subsequent episodes of uncomplicated malaria. Recrudescent and new infections were distinguished by polymerase chain reaction genotyping. Outcomes included the risk of recurrent malaria after individual treatments and the incidence of malaria treatments for individual children after randomization. RESULTS A total of 113 children were randomized to artemether-lumefantrine and 119 to dihydroartemisinin-piperaquine, resulting in 320 and 351 treatments for uncomplicated falciparum malaria, respectively. Artemether-lumefantrine was associated with a higher risk of recurrent malaria after 28 days (35% vs 11%; P = .001]). When the duration of follow-up was extended, differences in the risk of recurrent malaria decreased such that the overall incidence of malaria treatments was similar for children randomized to artemether-lumefantrine, compared with those randomized to dihydroartemisinin-piperaquine (4.82 vs 4.61 treatments per person-year; P = .63). The risk of recurrent malaria due to recrudescent parasites was similarly low in both treatment arms. CONCLUSIONS Artemether-lumefantrine and dihydroartemisinin-piperaquine were both efficacious and had similar long-term effects on the risk of recurrent malaria. Clinical trials registration. NCT00527800.

Estimating the annual entomological inoculation rate for Plasmodium falciparum transmitted by Anopheles gambiae s.l. using three sampling methods in three sites in Uganda.

BackgroundThe Plasmodium falciparum entomological inoculation rate (Pf EIR) is a measure of exposure to infectious mosquitoes. It is usually interpreted as the number of P. falciparum infective bites received by an individual during a season or annually (aPf EIR). In an area of perennial transmission, the accuracy, precision and seasonal distribution (i.e., month by month) of aPf EIR were investigated. Data were drawn from three sites in Uganda with differing levels of transmission where falciparum malaria is transmitted mainly by Anopheles gambiae s.l. Estimates of aPf EIR derived from human-landing catches – the classic method for estimating biting rates – were compared with data from CDC light traps, and with catches of knock down and exit traps separately and combined.MethodsEntomological surveillance was carried out over one year in 2011/12 in three settings: Jinja, a peri-urban area with low transmission; Kanungu, a rural area with moderate transmission; and Nagongera, Tororo District, a rural area with exceptionally high malaria transmission. Three sampling approaches were used from randomly selected houses with collections occurring once a month: human-landing collections (eight houses), CDC light traps (100 houses) and paired knock-down and exit traps each month (ten houses) for each setting. Up to 50 mosquitoes per month from each household were tested for sporozoites with P. falciparum by ELISA. Human biting rate (HBR) data were estimated month by month. P. falciparum Sporozoite rate (Pf SR) for yearly and monthly data and confidence intervals were estimated using the binomial exact test. Monthly and yearly estimates of the HBR, the Pf SR, and the Pf EIR were estimated and compared.ResultsThe estimated aPf EIR values using human-landing catch data were 3.8 (95% Confidence Intervals, CI 0-11.4) for Jinja, 26.6 (95% CI 7.6-49.4) for Kanungu, and 125 (95% CI 72.2-183.0) for Tororo. In general, the monthly Pf EIR values showed strong seasonal signals with two peaks from May-June and October-December, although the precise timing of the peaks differed between sites. Estimated HBRs using human-landing catches were strongly correlated with those made using CDC light traps (r2 = 0.67, p < 0.001), and with either knock-down catches (r2 = 0.56, p < 0.001) and exit traps (r2 = 0.82, p < 0.001) or the combined catches (r2 = 0.73, p < 0.001). Using CDC light trap catch data, the Pf SR in Tororo was strongly negatively correlated with monthly HBR (r2 = 0.44, p = 0.01). In other sites, no patterns in the Pf SR were discernible because either the number P. falciparum of sporozoite positive mosquitoes or the total number of mosquitoes caught was too low.ConclusionsIn these settings, light traps provide an alternative method for sampling indoor-resting mosquitoes to human-landing catches and have the advantage that they protect individuals from being bitten during collection, are easy to use and are not subject to collector bias. Knock-down catches and exit traps could also be used to replace human-landing catches. Although these are cheaper, they are subject to collector bias.

Malaria Transmission, Infection, and Disease at Three Sites with Varied Transmission Intensity in Uganda: Implications for Malaria Control

The intensification of control interventions has led to marked reductions in malaria burden in some settings, but not others. To provide a comprehensive description of malaria epidemiology in Uganda, we conducted surveillance studies over 24 months in 100 houses randomly selected from each of three subcounties: Walukuba (peri-urban), Kihihi (rural), and Nagongera (rural). Annual entomological inoculation rate (aEIR) was estimated from monthly Centers for Disease Control and Prevention (CDC) light trap mosquito collections. Children aged 0.5-10 years were provided long-lasting insecticidal nets (LLINs) and followed for measures of parasite prevalence, anemia and malaria incidence. Estimates of aEIR were 2.8, 32.0, and 310 infectious bites per year, and estimates of parasite prevalence 7.4%, 9.3%, and 28.7% for Walukuba, Kihihi, and Nagongera, respectively. Over the 2-year study, malaria incidence per person-years decreased in Walukuba (0.51 versus 0.31, P = 0.001) and increased in Kihihi (0.97 versus 1.93, P < 0.001) and Nagongera (2.33 versus 3.30, P < 0.001). Of 2,582 episodes of malaria, only 8 (0.3%) met criteria for severe disease. The prevalence of anemia was low and not associated with transmission intensity. In our cohorts, where LLINs and prompt effective treatment were provided, the risk of complicated malaria and anemia was extremely low. However, malaria incidence was high and increased over time at the two rural sites, suggesting improved community-wide coverage of LLIN and additional malaria control interventions are needed in Uganda.

In Vitro Sensitivities of Plasmodium falciparum to Different Antimalarial Drugs in Uganda

ABSTRACT The control of malaria is challenged by resistance of Plasmodium falciparum to multiple drugs. New combination regimens are now advocated for the treatment of uncomplicated falciparum malaria, but the extent of resistance to newer agents is incompletely understood. We measured the in vitro sensitivity of P. falciparum parasites cultured from children enrolled in a drug efficacy trial in Kampala, Uganda, from 2006 to 2008. Sensitivities were measured by comparing levels of histidine-rich protein-2 in parasites incubated with different concentrations of drugs with those in untreated controls. The cultured parasites exhibited a wide range of sensitivities to chloroquine (CQ); monodesethylamodiaquine (MDAQ), the major active metabolite of amodiaquine; and quinine (QN). Mean 50% inhibitory concentration (IC50) results were above standard cutoffs for resistance for CQ and MDAQ. Parasites were generally sensitive to dihydroartemisinin (DHA), lumefantrine (LM), and piperaquine (PQ). For CQ, MDAQ, and QN but not the other drugs, activities against individual strains were highly correlated. We also assessed known resistance-mediating polymorphisms in two putative transporters, pfcrt and pfmdr1. When parasites that were least and most sensitive to each drug were compared, the pfmdr1 86Y mutation was significantly more common in parasites that were most resistant to CQ and MDAQ, and the pfmdr1 D1246Y mutation was significantly more common in parasites that were most resistant to MDAQ and QN. In summary, we demonstrated in parasites from Kampala a range of sensitivities to older drugs; correlation of sensitivities to CQ, MDAQ, and QN; and good activity against nearly all strains for DHA, LM, and PQ.

Epidemiology of subpatent Plasmodium falciparum infection: implications for detection of hotspots with imperfect diagnostics

BackgroundAt the local level, malaria transmission clusters in hotspots, which may be a group of households that experience higher than average exposure to infectious mosquitoes. Active case detection often relying on rapid diagnostic tests for mass screen and treat campaigns has been proposed as a method to detect and treat individuals in hotspots. Data from a cross-sectional survey conducted in north-western Tanzania were used to examine the spatial distribution of Plasmodium falciparum and the relationship between household exposure and parasite density.MethodsDried blood spots were collected from consenting individuals from four villages during a survey conducted in 2010. These were analysed by PCR for the presence of P. falciparum, with the parasite density of positive samples being estimated by quantitative PCR. Household exposure was estimated using the distance-weighted PCR prevalence of infection. Parasite density simulations were used to estimate the proportion of infections that would be treated using a screen and treat approach with rapid diagnostic tests (RDT) compared to targeted mass drug administration (tMDA) and Mass Drug Administration (MDA).ResultsPolymerase chain reaction PCR analysis revealed that of the 3,057 blood samples analysed, 1,078 were positive. Mean distance-weighted PCR prevalence per household was 34.5%. Parasite density was negatively associated with transmission intensity with the odds of an infection being subpatent increasing with household exposure (OR 1.09 per 1% increase in exposure). Parasite density was also related to age, being highest in children five to ten years old and lowest in those > 40 years. Simulations of different tMDA strategies showed that treating all individuals in households where RDT prevalence was above 20% increased the number of infections that would have been treated from 43 to 55%. However, even with this strategy, 45% of infections remained untreated.ConclusionThe negative relationship between household exposure and parasite density suggests that DNA-based detection of parasites is needed to provide adequate sensitivity in hotspots. Targeting MDA only to households with RDT-positive individuals may allow a larger fraction of infections to be treated. These results suggest that community-wide MDA, instead of screen and treat strategies, may be needed to successfully treat the asymptomatic, subpatent parasite reservoir and reduce transmission in similar settings.

Antibodies to Plasmodium falciparum Antigens Predict a Higher Risk of Malaria But Protection From Symptoms Once Parasitemic

BACKGROUND Associations between antibody responses to Plasmodium falciparum antigens and protection against symptomatic malaria have been difficult to ascertain, in part because antibodies are potential markers of both exposure to P. falciparum and protection against disease. METHODS We measured IgG responses to P. falciparum circumsporozoite protein, liver-stage antigen 1, apical-membrane antigen 1 (AMA-1), and merozoite surface proteins (MSP) 1 and 3, in children in Kampala, Uganda, and measured incidence of malaria before and after antibody measurement. RESULTS Stronger responses to all 5 antigens were associated with an increased risk of clinical malaria (P < .01) because of confounding with prior exposure to P. falciparum. However, with use of another assessment, risk of clinical malaria once parasitemic, stronger responses to AMA-1, MSP-1, and MSP-3 were associated with protection (odds ratios, 0.34, 0.36, and 0.31, respectively, per 10-fold increase; P < .01). Analyses assessing antibodies in combination suggested that any protective effect of antibodies was overestimated by associations between individual responses and protection. CONCLUSIONS Using the risk of symptomatic malaria once parasitemic as an outcome may improve detection of associations between immune responses and protection from disease. Immunoepidemiology studies designed to detect mechanisms of immune protection should integrate prior exposure into the analysis and evaluate multiple immune responses.

Selection of Known Plasmodium falciparum Resistance-Mediating Polymorphisms by Artemether-Lumefantrine and Amodiaquine- Sulfadoxine-Pyrimethamine but Not Dihydroartemisinin- Piperaquine in Burkina Faso

ABSTRACT Artemether-lumefantrine (AL), dihydroartemisinin-piperaquine (DP), and amodiaquine-sulfadoxine-pyrimethamine (AQ-SP) offer excellent antimalarial efficacy but may select for parasite polymorphisms that decrease drug sensitivity. We evaluated the selection of known polymorphisms in genes encoding putative transporters (pfcrt and pfmdr1) and SP targets (pfdhfr and pfdhps) in parasites that caused new infections within 42 days of therapy for uncomplicated falciparum malaria in Burkina Faso. In 559 children in 2006, 42-day genotype-uncorrected failures were seen in 31.2% with AL, 11.8% with AQ-SP, and 7.6% with DP. After prior AL therapy, selection of wild-type sequences was seen for K76T in pfcrt (72.7% mixed or mutant results pretreatment versus 52.1% in new infections; P = 0.008) and N86Y (36.0% versus 18.7%; P = 0.025) and Y184F (66.7% versus 45.8%; P = 0.009) in pfmdr1. After prior AQ-SP therapy, selection of mutant sequences was seen for N51I (30.8% versus 61.5%; P = 0.05), C59R (28.2% versus 76.9%; P = 0.002), and S108N (30.8% versus 76.9%; P = 0.005) in pfdhfr. After prior DP therapy, selection was not seen for K76T (72.7% versus 77.8%; P = 0.96) in pfcrt or N86Y (36.0% versus 33.3%; P = 0.84), Y184F (66.7% versus 77.8%; P = 0.39), or D1246Y (9.3% versus 0%; P = 0.42) in pfmdr1. In 378 additional treatments with DP in 2007, 42-day uncorrected failure was seen in 10.9%. After prior DP, selection was again not seen for K76T (66.7% mixed or mutant results versus 59.5%; P = 0.43) in pfcrt or N86Y (38.7% versus 40.5%; P = 0.85), Y184F (67.6% versus 73.0%; P = 0.54), or D1246Y (3.6% versus 8.1%; P = 0.50) in pfmdr1. Despite its chemical similarity, piperaquine did not select for the same polymorphisms as chloroquine or AQ, suggesting different mechanisms of resistance.

Urban malaria: primary caregivers knowledge attitudes practices and predictors of malaria incidence in a cohort of Ugandan children.

Objectives To assess malaria‐related knowledge, attitude and practices (KAP) among primary caregivers, to identify associations between primary caregivers’ characteristics and positive KAP towards malaria, and to identify independent predictors of childhood malaria incidence in an urban setting.