In vivo parasitological measures of artemisinin susceptibility

Delayed Plasmodium falciparum clearance following artesunate-mefloquine combination therapy in Thailand, 1997-2007

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.

Open-label trial with artemether-lumefantrine against uncomplicated Plasmodium falciparum malaria three years after its broad introduction in Jimma Zone, Ethiopia

BACKGROUND

In Jimma Zone, Ethiopia, the first-line treatment of uncomplicated falciparum malaria has been changed from sulphadoxine-pyrimethamine (SP) to artemether-lumefantrine (AL) in 2006. The objective of this study was to assess the effectiveness of AL in Jimma Zone two to three years after its broad introduction.

METHODS

An open-label, single-arm, 42-day study of AL against falciparum malaria was conducted in four areas with moderate transmission in Jimma Zone between November 2008 and January 2009 and between August and December 2009. Patients (one-81 years) with uncomplicated Plasmodium falciparum mono-infection were consecutively enrolled. Follow-up visits were at day 2, 3, 7, 28 and 42 or any other day if symptoms reoccurred. Primary and secondary endpoints were PCR-corrected and uncorrected cure rates (molecular differentiation between recrudescence and re-infection) on days 28 and 42. Other secondary endpoints were gametocytaemia at day 7 and day 28, parasitaemia at day 2 and 3, and re-infection rates at day 28 and day 42.

RESULTS

Of 348 enrolled patients, 313 and 301 completed follow-up at day 28 and at day 42, respectively. No early treatment failure occurred. For per protocol analysis, PCR-uncorrected cure rates at day 28 and 42 were 99.1% (95% CI 98.0-100.0) and 91.1% (95% CI 87.9-94.3), respectively. PCR-corrected cure rates at day 28 and 42 were 99.4% (95% CI 98.5-100.0) and 94.7% (95% CI 92.2-97.2), respectively. PCR-corrected cure rate at day 42 for children ≤ 5 years was 90.6% (95% CI 82.4-98.7) only. Adverse events were in general mild to moderate. Incidence of new infections was 3.4% during 42 days, no new infections with Plasmodium vivax were observed. Microscopically detected gametocytaemia was reduced by 80% between day 0 and day 7.

CONCLUSION

In general, AL was effective and well tolerated in Jimma Zone, Ethiopia. However, the PCR-corrected recrudescence rate per-protocol at day 42 for children ≤ 5 years was 9.4%. Therefore, further development should be monitored on a regular basis as recommended by WHO.

Emergence of artemisinin-resistant malaria on the western border of Thailand: a longitudinal study

BACKGROUND

Artemisinin-resistant falciparum malaria has arisen in western Cambodia. A concerted international effort is underway to contain artemisinin-resistant Plasmodium falciparum, but containment strategies are dependent on whether resistance has emerged elsewhere. We aimed to establish whether artemisinin resistance has spread or emerged on the Thailand-Myanmar (Burma) border.

METHODS

In malaria clinics located along the northwestern border of Thailand, we measured six hourly parasite counts in patients with uncomplicated hyperparasitaemic falciparum malaria (≥4% infected red blood cells) who had been given various oral artesunate-containing regimens since 2001. Parasite clearance half-lives were estimated and parasites were genotyped for 93 single nucleotide polymorphisms.

FINDINGS

3202 patients were studied between 2001 and 2010. Parasite clearance half-lives lengthened from a geometric mean of 2·6 h (95% CI 2·5-2·7) in 2001, to 3·7 h (3·6-3·8) in 2010, compared with a mean of 5·5 h (5·2-5·9) in 119 patients in western Cambodia measured between 2007 and 2010. The proportion of slow-clearing infections (half-life ≥6·2 h) increased from 0·6% in 2001, to 20% in 2010, compared with 42% in western Cambodia between 2007 and 2010. Of 1583 infections genotyped, 148 multilocus parasite genotypes were identified, each of which infected between two and 13 patients. The proportion of variation in parasite clearance attributable to parasite genetics increased from 30% between 2001 and 2004, to 66% between 2007 and 2010.

INTERPRETATION

Genetically determined artemisinin resistance in P falciparum emerged along the Thailand-Myanmar border at least 8 years ago and has since increased substantially. At this rate of increase, resistance will reach rates reported in western Cambodia in 2-6 years.

FUNDING

The Wellcome Trust and National Institutes of Health.

Emergence of artemisinin-resistant malaria on the western border of Thailand: a longitudinal study

BACKGROUND

Artemisinin-resistant falciparum malaria has arisen in western Cambodia. A concerted international effort is underway to contain artemisinin-resistant Plasmodium falciparum, but containment strategies are dependent on whether resistance has emerged elsewhere. We aimed to establish whether artemisinin resistance has spread or emerged on the Thailand-Myanmar (Burma) border.

METHODS

In malaria clinics located along the northwestern border of Thailand, we measured six hourly parasite counts in patients with uncomplicated hyperparasitaemic falciparum malaria (≥4% infected red blood cells) who had been given various oral artesunate-containing regimens since 2001. Parasite clearance half-lives were estimated and parasites were genotyped for 93 single nucleotide polymorphisms.

FINDINGS

3202 patients were studied between 2001 and 2010. Parasite clearance half-lives lengthened from a geometric mean of 2·6 h (95% CI 2·5-2·7) in 2001, to 3·7 h (3·6-3·8) in 2010, compared with a mean of 5·5 h (5·2-5·9) in 119 patients in western Cambodia measured between 2007 and 2010. The proportion of slow-clearing infections (half-life ≥6·2 h) increased from 0·6% in 2001, to 20% in 2010, compared with 42% in western Cambodia between 2007 and 2010. Of 1583 infections genotyped, 148 multilocus parasite genotypes were identified, each of which infected between two and 13 patients. The proportion of variation in parasite clearance attributable to parasite genetics increased from 30% between 2001 and 2004, to 66% between 2007 and 2010.

INTERPRETATION

Genetically determined artemisinin resistance in P falciparum emerged along the Thailand-Myanmar border at least 8 years ago and has since increased substantially. At this rate of increase, resistance will reach rates reported in western Cambodia in 2-6 years.

FUNDING

The Wellcome Trust and National Institutes of Health.

Efficacy of fixed-dose combination artesunate-amodiaquine versus artemether-lumefantrine for uncomplicated childhood Plasmodium falciparum malaria in Democratic Republic of Congo: a randomized non-inferiority trial

Background

In 2005, the Democratic Republic of Congo (DRC) adopted artesunate and amodiaquine (ASAQ) as first-line anti-malarial treatment. In order to compare the efficacy of the fixed-dose formulation ASAQ versus artemether-lumefantrine (AL), a randomized, non-inferiority open-label trial was conducted in Katanga.

Methods

Children aged six and 59 months with uncomplicated Plasmodium falciparum malaria were enrolled and randomly allocated into one of the two regimens. The risk of recurrent parasitaemia by day 42, both unadjusted and adjusted by PCR genotyping to distinguish recrudescence from new infection, was analysed.

Results

Between April 2008 and March 2009, 301 children were included: 156 with ASAQ and 145 with AL. No early treatment failures were reported. Among the 256 patients followed-up at day 42, 32 patients developed late clinical or parasitological failure (9.9% (13/131) in the ASAQ group and 15.2% (19/125) in the AL group). After PCR correction, cure rates were 98.3% (95%CI, 94.1-99.8) in the ASAQ group and 99.1% (95%CI, 94.9-99.9) in the AL group (difference −0.7%, one sided 95% CI −3.1). Kaplan-Meier PCR-adjusted cure rates were similar. Both treatment regimens were generally well tolerated.

Conclusion

Both ASAQ and AL are highly effective and currently adequate as the first-line treatment of uncomplicated falciparum malaria in this area of Katanga, DRC. However, in a very large country, such as DRC, and because of possible emergence of resistance from other endemic regions, surveillance of efficacy of artemisinin-based combination treatments, including other evaluations of the resistance of ASAQ, need to be done in other provinces.

Trial registration

The protocol was registered with the clinicaltrials.gov, open clinical trial registry under the identifier number NCT01567423.

No evidence for spread of Plasmodium falciparum artemisinin resistance to Savannakhet Province, Southern Laos

We conducted an open-label, randomized clinical trial to assess parasite clearance times (PCT) and the efficacy of 4 mg/kg (group 1, n = 22) and 2 mg/kg (group 2, n = 22) of oral artesunate for three days followed by artemether-lumefantrine in patients with uncomplicated Plasmodium falciparum malaria at Xepon Interdistrict Hospital, Savannakhet Province in southern Laos. Slides were read in duplicate. The overall mean (95% confidence interval; range) PCT in hours was 23.2 (21.2–25.3; 12–46) and 22.4 (20.3–24.5; 12–46) for the first and second microscopists, respectively (P = 0.57). Ten (23%) patients remained parasitemic on day 1 after treatment (4 [18%] in group 1 and 6 [27%] in group 2; P = 0.47). No patient had patent asexual parasitemia on the second and third days of treatment. The 42-day polymerase chain reaction–corrected cure rates were 100% in both treatment groups. Serious adverse events did not develop during or after treatment in any patients. In conclusion, no evidence of P. falciparum in vivo resistance to artesunate was found in southern Laos.

Malaria in the Greater Mekong Subregion: heterogeneity and complexity

The Greater Mekong Subregion (GMS), comprised of six countries including Cambodia, China's Yunnan Province, Lao PDR, Myanmar (Burma), Thailand and Vietnam, is one of the most threatening foci of malaria. Since the initiation of the WHO's Mekong Malaria Program a decade ago, malaria situation in the GMS has greatly improved, reflected in the continuous decline in annual malaria incidence and deaths. However, as many nations are moving towards malaria elimination, the GMS nations still face great challenges. Malaria epidemiology in this region exhibits enormous geographical heterogeneity with Myanmar and Cambodia remaining high-burden countries. Within each country, malaria distribution is also patchy, exemplified by 'border malaria' and 'forest malaria' with high transmission occurring along international borders and in forests or forest fringes, respectively. 'Border malaria' is extremely difficult to monitor, and frequent malaria introductions by migratory human populations constitute a major threat to neighboring, malaria-eliminating countries. Therefore, coordination between neighboring countries is essential for malaria elimination from the entire region. In addition to these operational difficulties, malaria control in the GMS also encounters several technological challenges. Contemporary malaria control measures rely heavily on effective chemotherapy and insecticide control of vector mosquitoes. However, the spread of multidrug resistance and potential emergence of artemisinin resistance in Plasmodium falciparum make resistance management a high priority in the GMS. This situation is further worsened by the circulation of counterfeit and substandard artemisinin-related drugs. In most endemic areas of the GMS, P. falciparum and Plasmodium vivax coexist, and in recent malaria control history, P. vivax has demonstrated remarkable resilience to control measures. Deployment of the only registered drug (primaquine) for the radical cure of vivax malaria is severely undermined due to high prevalence of glucose-6-phosphate dehydrogenase deficiency in target human populations. In the GMS, the dramatically different ecologies, diverse vector systems, and insecticide resistance render traditional mosquito control less efficient. Here we attempt to review the changing malaria epidemiology in the GMS, analyze the vector systems and patterns of malaria transmission, and identify the major challenges the malaria control community faces on its way to malaria elimination.

Malaria in the Greater Mekong Subregion: heterogeneity and complexity

The Greater Mekong Subregion (GMS), comprised of six countries including Cambodia, China's Yunnan Province, Lao PDR, Myanmar (Burma), Thailand and Vietnam, is one of the most threatening foci of malaria. Since the initiation of the WHO's Mekong Malaria Program a decade ago, malaria situation in the GMS has greatly improved, reflected in the continuous decline in annual malaria incidence and deaths. However, as many nations are moving towards malaria elimination, the GMS nations still face great challenges. Malaria epidemiology in this region exhibits enormous geographical heterogeneity with Myanmar and Cambodia remaining high-burden countries. Within each country, malaria distribution is also patchy, exemplified by 'border malaria' and 'forest malaria' with high transmission occurring along international borders and in forests or forest fringes, respectively. 'Border malaria' is extremely difficult to monitor, and frequent malaria introductions by migratory human populations constitute a major threat to neighboring, malaria-eliminating countries. Therefore, coordination between neighboring countries is essential for malaria elimination from the entire region. In addition to these operational difficulties, malaria control in the GMS also encounters several technological challenges. Contemporary malaria control measures rely heavily on effective chemotherapy and insecticide control of vector mosquitoes. However, the spread of multidrug resistance and potential emergence of artemisinin resistance in Plasmodium falciparum make resistance management a high priority in the GMS. This situation is further worsened by the circulation of counterfeit and substandard artemisinin-related drugs. In most endemic areas of the GMS, P. falciparum and Plasmodium vivax coexist, and in recent malaria control history, P. vivax has demonstrated remarkable resilience to control measures. Deployment of the only registered drug (primaquine) for the radical cure of vivax malaria is severely undermined due to high prevalence of glucose-6-phosphate dehydrogenase deficiency in target human populations. In the GMS, the dramatically different ecologies, diverse vector systems, and insecticide resistance render traditional mosquito control less efficient. Here we attempt to review the changing malaria epidemiology in the GMS, analyze the vector systems and patterns of malaria transmission, and identify the major challenges the malaria control community faces on its way to malaria elimination.

Recent clinical and molecular insights into emerging artemisinin resistance in Plasmodium falciparum

PURPOSE OF REVIEW

Artemisinin-based combination therapies (ACTs) have been deployed globally with remarkable success for more than 10 years without having lost their malaria treatment efficacy. However, recent reports from the Thai-Cambodian border reveal evidence of emerging resistance to artemisinins. The latest published clinical and molecular findings are summarized herein.

RECENT FINDINGS

Clinical studies have identified delayed parasite clearance time as the most robust marker of artemisinin resistance. Resistance has only been documented from South-east Asia and has been observed in isolates that show no significant decrease in drug susceptibility in vitro. Genetic investigations have yet to uncover robust molecular markers. In-vitro studies have identified parasite quiescence or dormancy mechanisms that protect early 'ring-stage' intra-erythrocytic parasites against short-term artemisinin exposure. This might be achieved by reducing the rate of hemoglobin degradation, important for artemisinin bioactivation.

SUMMARY

Should ACTs fail, no suitable alternatives exist as first-line treatments of P. falciparum malaria. Intensified efforts are essential to monitor the spread of resistance, define therapeutic and operational strategies to counter its impact, and understand its molecular basis. Success in these areas is critical to ensuring that recent gains in reducing the burden of malaria are not lost.

Standardizing the measurement of parasite clearance in falciparum malaria: the parasite clearance estimator

Background

A significant reduction in parasite clearance rates following artesunate treatment of falciparum malaria, and increased failure rates following artemisinin combination treatments (ACT), signaled emergent artemisinin resistance in Western Cambodia. Accurate measurement of parasite clearance is therefore essential to assess the spread of artemisinin resistance in Plasmodium falciparum. The slope of the log-parasitaemia versus time relationship is considered to be the most robust measure of anti-malarial effect. However, an initial lag phase of numerical instability often precedes a steady exponential decline in the parasite count after the start of anti-malarial treatment. This lag complicates the clearance estimation, introduces observer subjectivity, and may influence the accuracy and consistency of reported results.

Methods

To address this problem, a new approach to modelling clearance of malaria parasites from parasitaemia-time profiles has been explored and validated. The methodology detects when a lag phase is present, selects the most appropriate model (linear, quadratic or cubic) to fit log-transformed parasite data, and calculates estimates of parasite clearance adjusted for this lag phase. Departing from previous approaches, parasite counts below the level of detection are accounted for and not excluded from the calculation.

Results

Data from large clinical studies with frequent parasite counts were examined. The effect of a lag phase on parasite clearance rate estimates is discussed, using individual patient data examples. As part of the World Wide Antimalarial Resistance Network's (WWARN) efforts to make innovative approaches available to the malaria community, an automated informatics tool: the parasite clearance estimator has been developed.

Conclusions

The parasite clearance estimator provides a consistent, reliable and accurate method to estimate the lag phase and malaria parasite clearance rate. It could be used to detect early signs of emerging resistance to artemisinin derivatives and other compounds which affect ring-stage clearance.

Declining responsiveness of Plasmodium falciparum infections to artemisinin-based combination treatments on the Kenyan coast

Background

The emergence of artemisinin-resistant P. falciparum malaria in South-East Asia highlights the need for continued global surveillance of the efficacy of artemisinin-based combination therapies.

Methods

On the Kenyan coast we studied the treatment responses in 474 children 6–59 months old with uncomplicated P. falciparum malaria in a randomized controlled trial of dihydroartemisinin-piperaquine vs. artemether-lumefantrine from 2005 to 2008. (ISRCTN88705995)

Results

The proportion of patients with residual parasitemia on day 1 rose from 55% in 2005–2006 to 87% in 2007–2008 (odds ratio, 5.4, 95%CI, 2.7–11.1; P<0.001) and from 81% to 95% (OR, 4.1, 95%CI, 1.7–9.9; P = 0.002) in the DHA-PPQ and AM-LM groups, respectively. In parallel, Kaplan-Meier estimated risks of apparent recrudescent infection by day 84 increased from 7% to 14% (P = 0.1) and from 6% to 15% (P = 0.05) with DHA-PPQ and AM-LM, respectively. Coinciding with decreasing transmission in the study area, clinical tolerance to parasitemia (defined as absence of fever) declined between 2005–2006 and 2007–2008 (OR body temperature >37.5°C, 2.8, 1.9–4.1; P<0.001). Neither in vitro sensitivity of parasites to DHA nor levels of antibodies against parasite extract accounted for parasite clearance rates or changes thereof.

Conclusions

The significant, albeit small, decline through time of parasitological response rates to treatment with ACTs may be due to the emergence of parasites with reduced drug sensitivity, to the coincident reduction in population-level clinical immunity, or both. Maintaining the efficacy of artemisinin-based therapy in Africa would benefit from a better understanding of the mechanisms underlying reduced parasite clearance rates.

Trial Registration

Controlled-Trials.com ISRCTN88705995

Efficacy and effectiveness of mefloquine and artesunate combination therapy for uncomplicated Plasmodium falciparum malaria in the Peruvian Amazon

We evaluated the efficacy and effectiveness of mefloquine (MQ) plus artesunate (AS) to treat patients with uncomplicated malaria in the Peruvian Amazon Basin in April 2005-March 2006. Patients ≥ 1 year of age with fever (axillary temperature ≥ 37.5°C) or history of fever and Plasmodium falciparum monoinfection were included. Patients received antimalarial treatment with MQ (12.5 mg/kg/day for two days) and AS (4.0 mg/kg/day for three days) either by directly observed therapy or without directly observed therapy. After a 28-day follow-up, treatment efficacy and effectiveness were assessed on the basis of clinical and parasitologic outcomes. Ninety-six patients were enrolled in each study group; nine patients were lost to follow-up. All patients, except for one in the observed group, demonstrated adequate clinical and parasitologic response; none had detectable parasitemia on day 3. The efficacy of MQ + AS efficacy was 98.9% (95% confidence interval = 94.1-100.0%) and the effectiveness was 100.0% (95% confidence interval = 95.9-100.0%). Our study shows that MQ + AS is highly efficacious in the Peruvian Amazon.

Risk factors for Plasmodium falciparum hyperparasitaemia in malarious children

Background

Hyperparasitaemia is a feature of childhood severe malaria but there is little information on the risk factors for hyperparasitaemia in malarious children

Methods

The risk factors associated with Plasmodium falciparum hyperparasitaemia, defined as asexual parasitaemia > 250,000/μl, at presentation were evaluated in 3338 malarious children enrolled prospectively between 2008 and 2010 in an endemic area of southwestern Nigeria.

Results

At enrolment, 97 (3%) of 3338 malarious children had hyperparasitaemia. In a multiple regression model, 3 factors were found to be independent risk factors for the presence of hyperparasitaemia at enrolment: an age ≤ 11 years (Adjusted odds ratio [AOR] = 2.85, 95% confidence interval [CI] 1.23-6.61, P = 0.014), fever (AOR = 2.02, 95% CI 1.23-3.29, P = 0.005), and enrolment after year 2008 (AOR = 0.42, 95% CI 0.24-0.73, P = 0.002). Duration of illness ≤ 3 d was associated with increased risk of hyperparasitaemia. There was no association between season and hyperparasitaemia. Compared to non-hyperparasitaemia, hyperparasitaemia was associated with an increased risk of progression to cerebral malaria (P < 0.0001). The risk of progression in hyperparasitaemic children was higher in < 5-year olds (P = 0.02).

Conclusion

Young age and presence of fever are independent risk factors for hyperparasitaemia which is associated with an increased risk of progression to cerebral malaria. The findings have implications for case and community management of childhood hyperparasitaemia and for malaria control efforts in sub-Saharan Africa where severe malaria is relatively common.

The parasite clearance curve

Parasite clearance rates are important measures of anti-malarial drug efficacy. They are particularly important in the assessment of artemisinin resistance. The slope of the log-linear segment in the middle of the parasite clearance curve has the least inter-individual variance and is the focus of therapeutic assessment. The factors affecting parasite clearance are reviewed. Methods of presentation and the approaches to analysis are discussed.

In vivo efficacy of artemether-lumefantrine against uncomplicated Plasmodium falciparum malaria in Central Ethiopia

Background

In vivo efficacy assessments of the first-line treatments for Plasmodium falciparum malaria are essential for ensuring effective case management. In Ethiopia, artemether-lumefantrine (AL) has been the first-line treatment for uncomplicated P. falciparum malaria since 2004.

Methods

Between October and November 2009, we conducted a 42-day, single arm, open label study of AL for P. falciparum in individuals >6 months of age at two sites in Oromia State, Ethiopia. Eligible patients who had documented P. falciparum mono-infection were enrolled and followed according to the standard 2009 World Health Organization in vivo drug efficacy monitoring protocol. The primary and secondary endpoints were PCR uncorrected and corrected cure rates, as measured by adequate clinical and parasitological response on days 28 and 42, respectively.

Results

Of 4426 patients tested, 120 with confirmed falciparum malaria were enrolled and treated with AL. Follow-up was completed for 112 patients at day 28 and 104 patients at day 42. There was one late parasitological failure, which was classified as undetermined after genotyping. Uncorrected cure rates at both day 28 and 42 for the per protocol analysis were 99.1% (95% CI 95.1-100.0); corrected cure rates at both day 28 and 42 were 100.0%. Uncorrected cure rates at day 28 and 42 for the intention to treat analysis were 93.3% (95% CI 87.2-97.1) and 86.6% (95% CI 79.1-92.1), respectively, while the corrected cure rates at day 28 and 42 were 94.1% (95% CI 88.2-97.6) and 87.3% (95% CI 79.9-92.7), respectively. Using survival analysis, the unadjusted cure rate was 99.1% and 100.0% adjusted by genotyping for day 28 and 42, respectively. Eight P. falciparum patients (6.7%) presented with Plasmodium vivax infection during follow-up and were excluded from the per protocol analysis. Only one patient had persistent parasitaemia at day 3. No serious adverse events were reported, with cough and nausea/vomiting being the most common adverse events.

Conclusions

AL remains a highly effective and well-tolerated treatment for uncomplicated falciparum malaria in the study setting after several years of universal access to AL. A high rate of parasitaemia with P. vivax possibly from relapse or new infection was observed.

Trial Registration

NCT01052584

Drug-Resistant Malaria: The Era of ACT

As drug-resistant falciparum malaria has continued to evolve and spread worldwide, artemisinin-based combination therapies (ACT) have become the centerpiece of global malaria control over the past decade. This review discusses how advances in antimalarial drug resistance monitoring and rational use of the array of ACTs now available can maximize the impact of this highly efficacious therapy, even as resistance to artemisinins is emerging in Southeast Asia.

Therapeutic efficacies of artemisinin-based combination therapies in Nigerian children with uncomplicated falciparum malaria during five years of adoption as first-line treatments

The therapeutic efficacies of 3-day regimens of artesunate-amodiaquine and artemether-lumefantrine during 5 years of adoption as first-line treatments were evaluated in 811 ≤ 12-year-old malarious children. Compared with artemether-lumefantrine, amodiaquine-artesunate significantly reduced the proportion of children with fever and parasitemia 1 day after treatment (day 1; P < 0.008 for both). The proportion of parasitemic children on day 2 and gametocytemia on presentation and carriage reduced significantly over the years (P < 0.000001 and P < 0.03, respectively; test for trend). Overall efficacy was 96.5% (95% confidence interval [CI] = 94.5-98.6) and remained unchanged over the years (P = 0.87; test for trend). Kinetics of parasitemias after treatments were estimated by a non-compartmental model. Declines of parasitemias were monoexponential, with a mean elimination half-life of 1.09 hours (95% CI = 1.0-1.16). Parasitemia half-lives and efficacy were similar for both regimens and in all ages. Artesunate-amodiaquine and artemether-lumefantrine remain efficacious treatments of uncomplicated falciparum malaria in Nigerian children 5 years after adoption.

Artesunate dose escalation for the treatment of uncomplicated malaria in a region of reported artemisinin resistance: a randomized clinical trial

BACKGROUND

The emergence of artemisinin resistance has raised concerns that the most potent antimalarial drug may be under threat. The currently recommended daily dose of artesunate (AS) is 4 mg/kg, and is administered for 3 days together with a partner antimalarial drug. This study investigated the impact of different AS doses on clinical and parasitological responses in malaria patients from an area of known artemisinin resistance in western Cambodia.

METHODS

Adult patients with uncomplicated P. falciparum malaria were randomized into one of three 7-day AS monotherapy regimens: 2, 4 or 6 mg/kg/day (total dose 14, 28 and 42 mg/kg). Clinical, parasitological, pharmacokinetic and in vitro drug sensitivity data was collected over a 7-day inpatient period and during weekly follow-up to 42 days.

RESULTS

143 patients were enrolled (n = 75, 40 and 28 to receive AS 2, 4 and 6 mg/kg/day respectively). Cure rates were high in all treatment groups at 42 days despite almost half the patients remaining parasitemic on Day 3. There was no impact of increasing AS dose on median parasite clearance times, median parasite clearance rates or on the proportion of patients remaining parasitemic on Day 3. However at the lowest dose used (2 mg/kg/d) patients with parasitemia >10,000/µL had longer median (IQR) parasite clearance times than those with parasitemia <10,000/µL (63 (48-75) vs. 84 (66-96) hours, p<0.0001). 19% of patients in the high-dose arm developed neutropenia (absolute neutrophil count <1.0×10(9)/L) by Day 14 and resulted in the arm being halted early.

CONCLUSION

There is no pharmacodynamic benefit of increasing the daily dose of AS (4 mg/kg) currently recommended for short-course combination treatment of uncomplicated malaria, even in regions with emerging artemisinin resistance, as long as the partner drug retains high efficacy.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00722150.

Artesunate versus quinine in the treatment of severe falciparum malaria in African children (AQUAMAT): an open-label, randomised trial

BACKGROUND

Severe malaria is a major cause of childhood death and often the main reason for paediatric hospital admission in sub-Saharan Africa. Quinine is still the established treatment of choice, although evidence from Asia suggests that artesunate is associated with a lower mortality. We compared parenteral treatment with either artesunate or quinine in African children with severe malaria.

METHODS

This open-label, randomised trial was undertaken in 11 centres in nine African countries. Children (<15 years) with severe falciparum malaria were randomly assigned to parenteral artesunate or parenteral quinine. Randomisation was in blocks of 20, with study numbers corresponding to treatment allocations kept inside opaque sealed paper envelopes. The trial was open label at each site, and none of the investigators or trialists, apart from for the trial statistician, had access to the summaries of treatment allocations. The primary outcome measure was in-hospital mortality, analysed by intention to treat. This trial is registered, number ISRCTN50258054.

FINDINGS

5425 children were enrolled; 2712 were assigned to artesunate and 2713 to quinine. All patients were analysed for the primary outcome. 230 (8·5%) patients assigned to artesunate treatment died compared with 297 (10·9%) assigned to quinine treatment (odds ratio [OR] stratified for study site 0·75, 95% CI 0·63-0·90; relative reduction 22·5%, 95% CI 8·1-36·9; p=0·0022). Incidence of neurological sequelae did not differ significantly between groups, but the development of coma (65/1832 [3·5%] with artesunate vs 91/1768 [5·1%] with quinine; OR 0·69 95% CI 0·49-0·95; p=0·0231), convulsions (224/2712 [8·3%] vs 273/2713 [10·1%]; OR 0·80, 0·66-0·97; p=0·0199), and deterioration of the coma score (166/2712 [6·1%] vs 208/2713 [7·7%]; OR 0·78, 0·64-0·97; p=0·0245) were all significantly less frequent in artesunate recipients than in quinine recipients. Post-treatment hypoglycaemia was also less frequent in patients assigned to artesunate than in those assigned to quinine (48/2712 [1·8%] vs 75/2713 [2·8%]; OR 0·63, 0·43-0·91; p=0·0134). Artesunate was well tolerated, with no serious drug-related adverse effects.

INTERPRETATION

Artesunate substantially reduces mortality in African children with severe malaria. These data, together with a meta-analysis of all trials comparing artesunate and quinine, strongly suggest that parenteral artesunate should replace quinine as the treatment of choice for severe falciparum malaria worldwide.

FUNDING

The Wellcome Trust.

Measuring the efficacy of anti-malarial drugs in vivo: quantitative PCR measurement of parasite clearance

BACKGROUND

Artemisinin-based combination therapy, currently considered the therapy of choice for uncomplicated Plasmodium falciparum malaria in endemic countries, may be under threat from newly emerging parasite resistance to the artemisinin family of drugs. Studies in Southeast Asia suggest some patients exhibit an extended parasite clearance time in the three days immediately following treatment with artesunate monotherapy. This phenotype is likely to become a more important trial endpoint in studies of anti-malarial drug efficacy, but currently requires frequent, closely spaced blood sampling in hospitalized study participants, followed by quantitation of parasite density by microscopy.

METHODS

A simple duplex quantitative PCR method was developed in which distinct fluorescent signals are generated from the human and parasite DNA components in each blood sample. The human amplification target in this assay is the β tubulin gene, and the parasite target is the unique methionine tRNA gene (pgmet), which exhibits perfect sequence identity in all six Plasmodium species that naturally infect humans. In a small series of malaria cases treated as hospital in-patients, the abundance of pgmet DNA was estimated relative to the human DNA target in daily peripheral blood samples, and parasite clearance times calculated.

RESULTS

The qPCR assay was reproducibly able to replicate parasite density estimates derived from microscopy, but provided additional data by quantification of parasite density 24 hours after the last positive blood film. Robust estimates of parasite clearance times were produced for a series of patients with clinical malaria.

CONCLUSIONS

Large studies, particularly in Africa where children represent a major proportion of treated cases, will require a simpler blood sample collection regime, and a method capable of high throughput. The duplex qPCR method tested may fulfil these criteria, and should now be evaluated in such field studies.

Antimalarial exposure delays Plasmodium falciparum intra-erythrocytic cycle and drives drug transporter genes expression

BACKGROUND

Multi-drug resistant Plasmodium falciparum is a major obstacle to malaria control and is emerging as a complex phenomenon. Mechanisms of drug evasion based on the intracellular extrusion of the drug and/or modification of target proteins have been described. However, cellular mechanisms related with metabolic activity have also been seen in eukaryotic systems, e.g. cancer cells. Recent observations suggest that such mechanism may occur in P. falciparum.

METHODOLOGY/PRINCIPAL FINDINGS

We therefore investigated the effect of mefloquine exposure on the cell cycle of three P. falciparum clones (3D7, FCB, W2) with different drug susceptibilities, while investigating in parallel the expression of four genes coding for confirmed and putative drug transporters (pfcrt, pfmdr1, pfmrp1 and pfmrp2). Mefloquine induced a previously not described dose and clone dependent delay in the intra-erythrocytic cycle of the parasite. Drug impact on cell cycle progression and gene expression was then merged using a non-linear regression model to determine specific drug driven expression. This revealed a mild, but significant, mefloquine driven gene induction up to 1.5 fold.

CONCLUSIONS/SIGNIFICANCE

Both cell cycle delay and induced gene expression represent potentially important mechanisms for parasites to escape the effect of the antimalarial drug.