Plasmodium falciparum and Plasmodium vivax genotypes and efficacy of intermittent preventive treatment in Papua New Guinea

Distinctive genetic structure and selection patterns in Plasmodium vivax from South Asia and East Africa

Despite the high burden of Plasmodium vivax malaria in South Asian countries, the genetic diversity of circulating parasite populations is not well described. Determinants of antimalarial drug susceptibility for P. vivax in the region have not been characterised. Our genomic analysis of global P. vivax (n = 558) establishes South Asian isolates (n = 92) as a distinct subpopulation, which shares ancestry with some East African and South East Asian parasites. Signals of positive selection are linked to drug resistance-associated loci including pvkelch10, pvmrp1, pvdhfr and pvdhps, and two loci linked to P. vivax invasion of reticulocytes, pvrbp1a and pvrbp1b. Significant identity-by-descent was found in extended chromosome regions common to P. vivax from India and Ethiopia, including the pvdbp gene associated with Duffy blood group binding. Our investigation provides new understanding of global P. vivax population structure and genomic diversity, and genetic evidence of recent directional selection in this important human pathogen.

Rapid selection of sulphadoxine-resistant Plasmodium falciparum and its effect on within-population genetic diversity in Papua New Guinea

The ability of the human malarial parasite Plasmodium falciparum to adapt to environmental changes depends considerably on its ability to maintain within-population genetic variation. Strong selection, consequent to widespread antimalarial drug usage, occasionally elicits a rapid expansion of drug-resistant isolates, which can act as founders. To investigate whether this phenomenon induces a loss of within-population genetic variation, we performed a population genetic analysis on 302 P. falciparum cases detected during two cross-sectional surveys in 2002/2003, just after the official introduction of sulphadoxine/pyrimethamine as a first-line treatment, and again in 2010/2011, in highly endemic areas in Papua New Guinea. We found that a single-origin sulphadoxine-resistant parasite isolate rapidly increased from 0% in 2002/2003 to 54% in 2010 and 84% in 2011. However, a considerable number of pairs exhibited random associations among 10 neutral microsatellite markers located in various chromosomes, suggesting that outcrossing effectively reduced non-random associations, albeit at a low average multiplicity of infection (1.35–1.52). Within-population genetic diversity was maintained throughout the study period. This indicates that the parasites maintained within-population variation, even after a clonal expansion of drug-resistant parasites. Outcrossing played a role in the preservation of within-population genetic diversity despite low levels of multiplicity of infection.

Prevalence of malaria across Papua New Guinea after initial roll-out of insecticide-treated mosquito nets

OBJECTIVES

To assess the population prevalence of malaria in villages across Papua New Guinea (PNG) following the first roll-out of free long-lasting insecticidal nets (LLIN).

METHODS

Between October 2008 and August 2009, a household survey was conducted in 49 random villages in districts covered by the LLIN distribution campaign. The survey extended to 19 villages in sentinel sites that had not yet been covered by the campaign. In each village, 30 households were randomly sampled, household heads were interviewed and capillary blood samples were collected from all consenting household members for microscopic diagnosis of malaria.

RESULTS

Malaria prevalence ranged from 0% to 49.7% with a weighted average of 12.1% (95% CI 9.5, 15.3) in the national sample. More people were infected with Plasmodium falciparum (7.0%; 95% CI 5.4, 9.1) than with P. vivax (3.8%; 95% CI 2.4, 5.7) or P. malariae (0.3%; 95% CI 0.1, 0.6). Parasitaemia was strongly age-dependent with a P. falciparum peak at age 5-9 years and a P. vivax peak at age 1-4 years, yet with differences between geographical regions. Individual LLIN use and high community coverage were associated with reduced odds of infection (OR = 0.64 and 0.07, respectively; both P < 0.001). Splenomegaly in children and anaemia were common morbidities attributable to malaria.

CONCLUSIONS

Malaria prevalence across PNG is again at levels comparable to the 1970s. The strong association of LLIN use with reduced parasitaemia supports efforts to achieve and maintain high country-wide coverage. P. vivax infections will require special targeted approaches across PNG.

Population pharmacokinetics, tolerability, and safety of dihydroartemisinin-piperaquine and sulfadoxine-pyrimethamine-piperaquine in pregnant and nonpregnant Papua New Guinean women

The tolerability, safety, and disposition of dihydroartemisinin (DHA) and piperaquine (PQ) were assessed in 32 pregnant (second/third trimester) and 33 nonpregnant Papua New Guinean women randomized to adult treatment courses of DHA-PQ (three daily doses) or sulfadoxine-pyrimethamine (SP)-PQ (three daily PQ doses, single dose of SP). All dose adminstrations were observed, and subjects fasted for 2 h postdose. Plasma PQ was assayed by using high-performance liquid chromatography, and DHA was assessed by using liquid chromatography-mass spectrometry. Compartmental pharmacokinetic models were developed using a population-based approach. Both regimens were well tolerated. There was an expected increase in the rate-corrected electrocardiographic QT interval which was independent of pregnancy and treatment. Two pregnant and two nonpregnant women had Plasmodium falciparum parasitemia which cleared within 48 h, and no other subject became slide positive for malaria during 42 days of follow-up. Of 30 pregnant women followed to delivery, 27 (90%) delivered healthy babies and 3 (10%) had stillbirths; these obstetric outcomes are consistent with those in the general population. The area under the plasma PQ concentration-time curve (AUC0-∞) was lower in the pregnant patients (median [interquartile range], 23,721 μg · h/liter [21,481 to 27,951 μg · h/liter] versus 35,644 μg · h/liter [29,546 to 39,541 μg · h/liter]; P < 0.001) in association with a greater clearance relative to bioavailability (73.5 liters/h [69.4 to 78.4] versus 53.8 liters/h [49.7 to 58.2]; P < 0.001), but pregnancy did not influence the pharmacokinetics of DHA. The apparent pharmacokinetic differences between the present study and results from other studies of women with uncomplicated malaria that showed no effect of pregnancy on the AUC0-∞ of PQ and greater bioavailability may reflect differences in postdose fat intake, proportions of women with malaria, and/or racial differences in drug disposition.

Temporal changes in Plasmodium falciparum anti-malarial drug sensitivity in vitro and resistance-associated genetic mutations in isolates from Papua New Guinea

Background

In northern Papua New Guinea (PNG), most Plasmodium falciparum isolates proved resistant to chloroquine (CQ) in vitro between 2005 and 2007, and there was near-fixation of pfcrt K76T, pfdhfr C59R/S108N and pfmdr1 N86Y. To determine whether the subsequent introduction of artemisinin combination therapy (ACT) and reduced CQ-sulphadoxine-pyrimethamine pressure had attenuated parasite drug susceptibility and resistance-associated mutations, these parameters were re-assessed between 2011 and 2013.

Methods

A validated fluorescence-based assay was used to assess growth inhibition of 52 P. falciparum isolates from children in a clinical trial in Madang Province. Responses to CQ, lumefantrine, piperaquine, naphthoquine, pyronaridine, artesunate, dihydroartemisinin, artemether were assessed. Molecular resistance markers were detected using a multiplex PCR ligase detection reaction fluorescent microsphere assay.

Results

CQ resistance (in vitro concentration required for 50% parasite growth inhibition (IC₅₀) >100 nM) was present in 19% of isolates. All piperaquine and naphthoquine IC₅₀s were <100 nM and those for lumefantrine, pyronaridine and the artemisinin derivatives were in low nM ranges. Factor analysis of IC₅₀s showed three groupings (lumefantrine; CQ, piperaquine, naphthoquine; pyronaridine, dihydroartemisinin, artemether, artesunate). Most isolates (96%) were monoclonal pfcrt K76T (SVMNT) mutants and most (86%) contained pfmdr1 N86Y (YYSND). No wild-type pfdhfr was found but most isolates contained wild-type (SAKAA) pfdhps. Compared with 2005–2007, the geometric mean (95% CI) CQ IC₅₀ was lower (87 (71–107) vs 167 (141–197) nM) and there had been no change in the prevalence of pfcrt K76T or pfmdr1 mutations. There were fewer isolates of the pfdhps (SAKAA) wild-type (60 vs 100%) and pfdhfr mutations persisted.

Conclusions

Reflecting less drug pressure, in vitro CQ sensitivity appears to be improving in Madang Province despite continued near-fixation of pfcrt K76T and pfmdr1 mutations. Temporal changes in IC₅₀s for other anti-malarial drugs were inconsistent but susceptibility was preserved. Retention or increases in pfdhfr and pfdhps mutations reflect continued use of sulphadoxine-pyrimethamine in the study area including through paediatric intermittent preventive treatment. The susceptibility of local isolates to lumefantrine may be unrelated to those of other ACT partner drugs.

Trial registration

Australian New Zealand Clinical Trials Registry ACTRN12610000913077.

Sulphadoxine-pyrimethamine plus azithromycin for the prevention of low birthweight in Papua New Guinea: a randomised controlled trial

BACKGROUND

Intermittent preventive treatment in pregnancy has not been evaluated outside of Africa. Low birthweight (LBW, <2,500 g) is common in Papua New Guinea (PNG) and contributing factors include malaria and reproductive tract infections.

METHODS

From November 2009 to February 2013, we conducted a parallel group, randomised controlled trial in pregnant women (≤ 26 gestational weeks) in PNG. Sulphadoxine-pyrimethamine (1,500/75 mg) plus azithromycin (1 g twice daily for 2 days) (SPAZ) monthly from second trimester (intervention) was compared against sulphadoxine-pyrimethamine and chloroquine (450 to 600 mg, daily for three days) (SPCQ) given once, followed by SPCQ placebo (control). Women were assigned to treatment (1:1) using a randomisation sequence with block sizes of 32. Participants were blinded to assignments. The primary outcome was LBW. Analysis was by intention-to-treat.

RESULTS

Of 2,793 women randomised, 2,021 (72.4%) were included in the primary outcome analysis (SPCQ: 1,008; SPAZ: 1,013). The prevalence of LBW was 15.1% (305/2,021). SPAZ reduced LBW (risk ratio [RR]: 0.74, 95% CI: 0.60-0.91, P = 0.005; absolute risk reduction (ARR): 4.5%, 95% CI: 1.4-7.6; number needed to treat: 22), and preterm delivery (0.62, 95% CI: 0.43-0.89, P = 0.010), and increased mean birthweight (41.9 g, 95% CI: 0.2-83.6, P = 0.049). SPAZ reduced maternal parasitaemia (RR: 0.57, 95% CI: 0.35-0.95, P = 0.029) and active placental malaria (0.68, 95% CI: 0.47-0.98, P = 0.037), and reduced carriage of gonorrhoea (0.66, 95% CI: 0.44-0.99, P = 0.041) at second visit. There were no treatment-related serious adverse events (SAEs), and the number of SAEs (intervention 13.1% [181/1,378], control 12.7% [174/1,374], P = 0.712) and AEs (intervention 10.5% [144/1,378], control 10.8% [149/1,374], P = 0.737) was similar. A major limitation of the study was the high loss to follow-up for birthweight.

CONCLUSIONS

SPAZ was efficacious and safe in reducing LBW, possibly acting through multiple mechanisms including the effect on malaria and on sexually transmitted infections. The efficacy of SPAZ in the presence of resistant parasites and the contribution of AZ to bacterial antibiotic resistance require further study. The ability of SPAZ to improve pregnancy outcomes warrants further evaluation.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01136850 (06 April 2010).