Multicellular structures in thin free liquid films induced by thermocapillary effect.

HYPOTHESIS: Multicellular convective structures that are induced in a fluid exposed to temperature difference are commonly observed in nature and in daily life. Different types of basic flow patterns are induced in a free liquid film by thermocapillary effect, whereas the formation of such multicellular structures has not been hitherto unravelled. EXPERIMENTS: A thin film of high-Prandtl-number liquid is prepared in a rectangular aperture of the order of 0.1 mm in thickness sustained by its surface tension. A designated temperature difference is imposed between the end surfaces of the aperture to generate a thermocapillary-driven convection in the free liquid film. We monitor the induced thermal flow patterns to evaluate the cell numbers and their wavelength by experimental and numerical approaches. FINDINGS: The multicellular structure is established by the thermocapillary effect in the free liquid films. The cell number increases in a stepwise manner as the liquid-film width increases. When the cell number increases, another pair of the cells always newly emerges. We determine the wavelength in a non-dimensional manner, and present the variation of the wavelength against the aspect ratio corresponding to the liquid-film width. The results are compared to those of convectional Marangoni-Bénard convection.

Health and well-being in small island communities: a cross-sectional study in the Solomon Islands.

OBJECTIVES: This study explored the health problems of inhabitants of small South Pacific Islands under the influence of climate change, focusing on three communities in the Solomon Islands. DESIGN: Cross-sectional study of the Solomon Islands' populations. SETTING: A field survey was conducted in Taro Island, a small, urbanised island with a whole-community relocation plan; Manuopo community of Reef Islands, a small remote island on an atoll environment and Sasamungga, an intermediately urbanised community on a larger island. The Sasamungga community was used for comparison. PARTICIPANTS: Each community's participants were recruited through local health authorities, and 113, 155 and 116 adults (aged 18+ years) from Taro, Manuopo and Sasamungga, respectively, participated voluntarily. METHODS: Each participant's body height, weight and body mass index were measured. A drop of blood was sampled for malaria testing; glycated haemoglobin and C reactive protein levels, measured from another drop of blood, were markers for diabetes and inflammation, respectively. The Primary Care Screening Questionnaire for Depression measured depressive mental states. PRIMARY AND SECONDARY OUTCOME MEASURES: Regarding health status, the dependent variables-communicable diseases, non-communicable diseases and mental state-and independent variables-differences in communities and socioeconomic status-were measured through health check-ups and interviews of individual participants. RESULTS: Taro Island inhabitants had a higher risk of obesity (OR 1.13, 95% CI 1.02 to 1.27, p=0.0189), and Manuopo inhabitants had a higher risk of depression (1.25, 95% CI 1.08 to 1.44, p=0.0026) than Sasamungga inhabitants. Manuopo inhabitants recognised more serious problems of food security, livelihood, place to live and other aspects of daily living than other communities' inhabitants. CONCLUSIONS: The three small island communities' observation identified different health problems: the urbanised community and remote community had a high risk of non-communicable diseases and mental disorders, respectively. These health problems should be monitored continuously during future climate-related changes.

Intermittency and Critical Scaling in Annular Couette Flow.

The onset of turbulence in subcritical shear flows is one of the most puzzling manifestations of critical phenomena in fluid dynamics. The present study focuses on the Couette flow inside an infinitely long annular geometry where the inner rod moves with constant velocity and entrains fluid, by means of direct numerical simulation. Although for a radius ratio close to unity the system is similar to plane Couette flow, a qualitatively novel regime is identified for small radius ratio, featuring no oblique bands. An analysis of finite-size effects is carried out based on an artificial increase of the perimeter. Statistics of the turbulent fraction and of the laminar gap distributions are shown both with and without such confinement effects. For the wider domains, they display a cross-over from exponential to algebraic scaling. The data suggest that the onset of the original regime is consistent with the dynamics of one-dimensional directed percolation at onset, yet with additional frustration due to azimuthal confinement effects.

Laminar-Turbulent Intermittency in Annular Couette-Poiseuille Flow: Whether a Puff Splits or Not.

Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette-Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0.1 and imposed a constant pressure gradient providing practically zero shear on the inner cylinder such that the base flow was approximated to that of a circular pipe flow. Localized turbulent puffs, that is, axial uni-directional intermittencies similar to those observed in the transitional circular pipe flow, were observed in the annular Couette-Poiseuille flow. Puff splitting events were clearly observed rather far from the global critical Reynolds number, near which given puffs survived without a splitting event throughout the observation period, which was as long as 104 outer time units. The characterization as a directed-percolation universal class was also discussed.

Enhancement of Meniscus Pump by Multiple Particles.

We numerically investigate the behavior of a droplet spreading on a smooth substrate with multiple obstacles. As experimental works have indicated, the macroscopic contact line or the three-phase boundary line of a droplet exhibits significant deformation resulting in a local acceleration by successive interactions with an array of tiny obstacles settled on the substrate (Mu et al., Langmuir 2019, 35). We focus on the menisci formation and the resultant pressure and velocity fields inside a liquid film in a two-spherical-particle system to realize an optimal design for the effective liquid-transport phenomenon. Special attention is paid to the meniscus formation around the second particle, which influences the liquid supply related to the pressure difference around the first particle as a function of the distance between the two particles. We find that the meniscus around the first particle plays an additional role as the reservoir of the liquid supplied toward the second particle, which is found to enhance the total pumping effect.

Pumping effect of heterogeneous meniscus formed around spherical particle.

HYPOTHESIS: A disturbance such as a microparticle on the pathway of a spreading droplet has shown the tremendous ability to accelerate locally the motion of the macroscopic contact line (Mu et al., 2017). Although this ability has been linked to the particle-liquid interaction, the physical mechanisms behind it are still poorly understood despite its academic interest and the scope of numerous industrial applications in need of fast wetting. EXPERIMENTS: In order to better understand the mechanisms behind the particle-liquid interaction, we numerically investigate the pressure and velocity fields in the liquid film. The results are compared to experiments assessing the temporal shape variation of the liquid-film meniscus from which pressure difference around the particle is evaluated. FINDINGS: The particle-induced acceleration of the film front depends both on the shape of the meniscus that forms around the particle foot and the liquid "reservoir" in the film that can be pumped thanks to the presence of the particle. The study validates the presence of three stages of pressure difference between the upstream and downstream regions of the meniscus around the particle, which leads to the local acceleration/deceleration of the macroscopic contact line. We indicate that asymmetric meniscus around the particle foot produces a net pressure force driving liquid and accelerating the liquid-film front.

Effect of pecuniary costs and time costs on choice of healthcare providers among caregivers of febrile children in rural Papua New Guinea.

BACKGROUND: User fees, transportation costs, and time costs impair access to healthcare by rural communities in low and middle income countries. However, effects of time costs on demand for healthcare are less understood than effects of user fees for health providers. In addition, prospective patients might not know about all health services available. This study aims to investigate how the family caregivers of febrile children respond to the pecuniary costs and time costs in their choice of health providers in rural Papua New Guinea. METHODS: Using an original questionnaire, we surveyed households in the catchment area surrounding Dagua Health Center in East Sepik Province, Papua New Guinea, during February-March 2015. We estimated the probability of choosing one among four categories of providers (i.e., the health center, aid posts, village health volunteers [VHVs], or home-treatment) via a mixed logit model in which we restrict alternatives to those for which family caregivers knew cost information. RESULTS: Of 1173 family caregivers, 96% sought treatment for febrile children from four categories of providers. Almost all knew the location of the health center and a health volunteer, but only 50% knew the location of aid posts. Analysis by discrete choice model showed that pecuniary costs and time costs were inversely associated with the probability of choosing any type of provider. We then changed pecuniary costs and time costs counterfactually to calculate and compare the probability of choosing each provider. Time costs affected the choice more than pecuniary costs, and individual heterogeneity appeared among caregivers with respect to pecuniary costs. When pecuniary or time costs of VHVs are altered, substitution between VHVs and home-treatment appeared. CONCLUSIONS: Our findings suggest that policies to increase awareness of aid posts and reduce time costs in addition to treatment fees for each category of healthcare provider could help developing economies to improve access to essential healthcare services.

Factors associated with children's health facility visits for primaquine treatment in rural Papua New Guinea.

BACKGROUND: To control and eventually eliminate vivax malaria, radical treatment with primaquine (PQ) is essential after completion of blood-stage treatment. Although in many malaria-endemic countries, village health volunteers (VHVs) are engaged in diagnostic treatment of malaria in remote communities, they principally provide blood-stage treatment. In such a situation, access to PQ following blood-stage treatment can be a barrier to complete treatment. However, studies on access to PQ treatment have been scarce and limited in health facility-based settings. This study aimed to identify factors associated with access to PQ treatment in rural Papua New Guinea (PNG) from the community case management perspective. METHODS: A community-based, cross-sectional survey was conducted to collect sociodemographic information on children under 15 years of age, their households, and their caretakers in East Sepik Province, PNG. Data collection lasted from February to March, 2015. Information on the diagnoses of potential non-falciparum malaria and prescription of PQ in preceding year (January to December 2014) were obtained from child health-record books. Then, multilevel logistic regression model was used to determine the factors associated with formal health facility visits for PQ treatment among children with potential non-falciparum malaria. RESULTS: Of 420 episodes diagnosed as potential non-falciparum malaria, 46 (11%) were immediately given PQ. The rest were instructed to visit formal health facilities (HFs) for PQ, and the patients obtained PQ during the second visit to HFs was 44%. Consequently, the overall proportion of PQ prescription was 50%. Logistic regression analysis suggested that among the patients who were instructed to visit HFs for PQ treatment, the initial visit to VHV and higher transportation costs to HF were inversely associated with PQ prescription during the second visit to an HF. CONCLUSIONS: Few children received PQ treatment during the second visit to HFs following diagnosis of potential non-falciparum malaria. These findings suggest a need to establish a policy to reduce structural and economic barriers and improve rural inhabitant access to PQ treatment.

Valuation Of Implanted-Stent Impact On Coronary Artery Trifurcation Blood Flow By Using CFD.

We investigated the influence of stent implanted in left main coronary artery trifurcation on blood flow by means of CFD. We simulated various stent positions and arrangement patterns considering KBT. The velocity and WSS (wall shear stress) distribution were found to depend on the stent arrangements. In addition, a strut position inhibiting the inflow velocity peaks into the branched (LCX) vessel exhibited a strong impact, which provided suppression of WSS on the high-lateralside surface of the LCX entrance. By KBT, such an impact of stent implantation can be avoided.

Numerical Demonstration of In-Tube Liquid-Column Migration Driven by Photoisomerization.

Droplet manipulation by light-induced isomerization was numerically demonstrated and investigated regarding the driving mechanism. Such a non-invasive manipulation of a droplet in a microchannel can be realized, for example, by the use of watery solution of photoresponsive surfactant that exhibits the isomerization. Due to variable fluid properties between the cis and trans isomers, one-side light irradiation on a liquid column in a tube would lead to some kind of imbalance between the two ends of the liquid column and then drive droplet migration. The present numerical simulations of air⁻liquid two-phase flow and its scalar transport of the isomer, considering the variable static contact angle, agreed quantitatively with the experimental results in terms of the migration speed. This fact supports the contention that the droplet migration is more likely to be driven by an imbalance in the wettability, or the contact angle. The migration speed was found to be less dependent on the liquid-column length, but proportional to the tube diameter.

Antimalarial drug prescribing by healthcare workers when malaria testing is negative: a qualitative study in Madagascar.

BACKGROUND: Despite the World Health Organization and the National Malaria Program of Madagascar recommending that antimalarial drugs only be prescribed for patients with positive results on malaria rapid diagnostic tests, healthcare workers continue to prescribe these drugs for cases with negative test results. We explored why and how primary healthcare workers in Madagascar continue to prescribe antimalarial drugs despite this guidance. METHODS: We purposively selected 14 medical doctors and 2 nurses from 11 primary health facilities (6 public, 5 private) in Toliara, Madagascar, and interviewed them regarding their antimalarial prescribing behaviors. Semi-structured interviews were conducted, focusing on why and how antimalarials were prescribed for clients with negative rapid diagnostic test results. Interviews were audio-recorded and transcribed verbatim, and the responses were manually coded until consistent themes emerged. RESULTS: The narrative of healthcare workers regarding their continued prescribing of antimalarials despite negative test results revealed the following: (1) they prescribe antimalarials without positive test results due to their faith to give top priority to clients including the ethical value of beneficence, hope to maintain clinician's independence, and belief in drug effectiveness; (2) they use antimalarials despite negative test results due to the availability of alternative ways to procure antimalarials; and (3) they carefully select cases to prescribe and determine specific antimalarials despite negative test results by considering the client's physical condition, preference, and economic status. Our results indicate that healthcare workers prioritized clinician autonomy to give the best care they believed for each client they received, which led to conflict with policy administrators that urged clinicians to follow the national policy and guidelines. Moreover, healthcare workers had access to multiple sources of antimalarial drugs, and there was a lack of consistency in the program provisions that allowed alternative routes for prescribing outside of official policy. CONCLUSIONS: We have shown how a national malarial treatment policy was translated into practice in Madagascar and have highlighted the barriers that may prevent policy success. We must attend to each of these barriers if we are to promote optimal use of antimalarial drugs.

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.

Comparison of Health Service Utilization for Febrile Children Before and After Introduction of Malaria Rapid Diagnostic Tests and Artemisinin-Based Combination Therapy in Rural Papua New Guinea.

BACKGROUND: In Papua New Guinea (PNG), a malaria treatment policy using rapid diagnostic tests (RDTs) plus artemisinin-based combination therapy (ACT) was widely introduced to rural communities in 2012. The objectives of the study were to evaluate the effect of this RDT/ACT introduction to a rural PNG population on health service utilization and to compare factors associated with health service utilization before and after the RDT/ACT introduction. METHODS: Household surveys with structured questionnaires were conducted before and after the introduction of RDT/ACT in a catchment area of a health center in East Sepik Province, PNG. We interviewed caregivers with children less than 15 years of age and collected data on fever episodes in the preceding 2 weeks. Using propensity score matching, febrile children before the introduction of RDT/ACT were matched to febrile children after the introduction. Then, the adjusted difference in the proportion of health service utilization [i.e., the average treatment effect (ATE) of the introduction of RDT/ACT on health service utilization] was estimated. We also employed a multilevel Poisson regression model to investigate factors influencing the use of health services. RESULTS: Of 4,690 children, 911 (19%) were reported to have a fever episode. The unadjusted proportion of health service utilization was 51.7 and 57.2% before and after the RDT/ACT introduction, respectively. After matching, no significant difference in the health service utilization was observed before and after the introduction of RDT/ACT (ATE: 0.063, 95% confidence interval -0.024 to 0.150). Multilevel regression analysis showed that the consistent factors associated with a higher utilization of health services were severe illness and being female. CONCLUSION: The utilization of health services was not significantly different before and after the introduction of RDT/ACT. Villagers may have neither sufficient informations on the new protocol nor high acceptance of RDT/ACT. The observed gender bias in health service utilization could be due to female caregivers' preferences toward girls.

Difference in vascular response between sirolimus-eluting- and everolimus-eluting stents in ostial left circumflex artery after unprotected left main as observed by optical coherence tomography.

BACKGROUND: Kissing-balloon technique (KBT) is commonly performed during percutaneous coronary intervention of distal unprotected left main coronary artery (ULM) aiming at obtaining optimal opening of the side branch (left circumflex artery; LCX) ostium. Nonetheless, detailed evaluation of vascular response to stents in LCX ostium is lacking. We therefore evaluated the vascular response to different drug-eluting stents (DES) in ostial LCX after ULM by means of optical coherence tomography (OCT). METHODS: We prospectively enrolled 38 consecutive patients with ULM disease, who were treated with single-stent procedure using DES, crossover the ULM-left anterior descending artery (LAD) followed by KBT. Twelve patients were treated with sirolimus-eluting stents (SES) and 26 patients were treated with everolimus-eluting stents (EES). OCT was conducted at post-PCI and 9-month follow-up. We evaluated the DES-vessel interactions and number of stent struts at the side branch (LCX) ostium (SO) at post-PCI, and compared the narrowing of ostial area at LCX between SES and EES. RESULTS: Post-procedure, the number of stent struts at SO was significantly higher in SES compared to EES (median 14.47% vs 0.19%, p<0.001). The narrowing of LCX ostial area at follow-up was more pronounced in SES compared with EES (29.16% vs 2.46%, respectively, p<0.001). Linear regression analysis showed a high correlation between the number of stent struts in LCX ostium and ostial area narrowing (r=0.771, p<0.001). CONCLUSIONS: OCT showed differences between EES- and SES-vessel interactions at ULM bifurcation PCI. Number of LCX ostium struts at post-PCI impacted the narrowing of ostial area at 9-month follow-up.

Village health volunteers' individual social capital and caretakers' health service utilization for febrile children in Malaria-endemic villages in Papua New Guinea.

Background: Little is known about the association between the social capital of village health volunteers (VHVs) and their performance in relation to malarial care. Methods: Data came from 337 children and 13 VHVs working in Dagua, Papua New Guinea. The outcome variable was whether caretakers brought their children to health care services on the incidence of a febrile episode. The social capital of VHVs was assessed by inquiring about relationships with people in 25 social positions/roles. Results: Caretakers were more likely to bring their febrile children to health care services when they lived in a village whose VHVs frequently discussed their activities with people in positions/roles outside their village (prevalence ratio [PR]=1.47 [95% confidence interval {CI} 1.22 to 1.78]). On the other hand, caretakers were less likely to do so when their VHVs had known people in informal positions/roles inside their village (PR=0.85 [95% CI 0.77 to 0.93]) and when they discussed their activities with people in formal positions/roles inside their village (PR=0.76 [95% CI 0.61 to 0.95]). Conclusions: Our results suggest that the social interactions of VHVs with people in positions/roles outside the village may benefit residents while those with people in positions/roles inside the village might not necessarily benefit them.

Little Polymorphism at the K13 Propeller Locus in Worldwide Plasmodium falciparum Populations Prior to the Introduction of Artemisinin Combination Therapies.

The emergence and spread of artemisinin-resistant Plasmodium falciparum is of huge concern for the global effort toward malaria control and elimination. Artemisinin resistance, defined as a delayed time to parasite clearance following administration of artemisinin, is associated with mutations in the Pfkelch13 gene of resistant parasites. To date, as many as 60 nonsynonymous mutations have been identified in this gene, but whether these mutations have been selected by artemisinin usage or merely reflect natural polymorphism independent of selection is currently unknown. To clarify this, we sequenced the Pfkelch13 propeller domain in 581 isolates collected before (420 isolates) and after (161 isolates) the implementation of artemisinin combination therapies (ACTs), from various regions of endemicity worldwide. Nonsynonymous mutations were observed in 1% of parasites isolated prior to the introduction of ACTs. Frequencies of mutant isolates, nucleotide diversity, and haplotype diversity were significantly higher in the parasites isolated from populations exposed to artemisinin than in those from populations that had not been exposed to the drug. In the artemisinin-exposed population, a significant excess of dN compared to dS was observed, suggesting the presence of positive selection. In contrast, pairwise comparison of dN and dS and the McDonald and Kreitman test indicate that purifying selection acts on the Pfkelch13 propeller domain in populations not exposed to ACTs. These population genetic analyses reveal a low baseline of Pfkelch13 polymorphism, probably due to purifying selection in the absence of artemisinin selection. In contrast, various Pfkelch13 mutations have been selected under artemisinin pressure.

CFD analysis of strut influence on blood flow in stent-implanted left main coronary artery bifurcation.

We numerically studied blood flows in a simulated branching pipe of coronary artery bifurcation, which is affected by stent implantation. We found that stent struts provide effects as guide vanes and blockages on the flow into circumflex branch. The former effect increases the flow rate and shear stress on the arteriosclerosis-prone site. The blockage effect may overwhelm the guide effect depending on a strut position against the inflow.

The Choice of Healthcare Providers for Febrile Children after Introducing Non-professional Health Workers in a Malaria Endemic Area in Papua New Guinea.

BACKGROUND: Disease burden of malaria in Papua New Guinea (PNG) is the highest in Asia and the Pacific, and prompt access to effective drugs is the key strategy for controlling malaria. Despite the rapid economic growth, primary healthcare services have deteriorated in rural areas; the introduction of non-professional health workers [village health volunteers (VHVs)] is expected to improve antimalarial drug deliveries. Previous studies on PNG suggested that distance from households negatively affected the utilization of health services; however, price effect on healthcare demand decisions has not been explored. Empirical studies on household's affordability as well as accessibility of healthcare services contribute to policy implications, such as efficient introduction of out-of-pocket costs and effective allocation of health facilities. Therefore, we investigate price responsiveness and other determinants of healthcare provider choice for febrile children in a malaria endemic rural area wherein VHVs were introduced. METHODS: Cross-sectional surveys were conducted using a structured questionnaire distributed in a health center's catchment area of East Sepik Province in the 2011/2012 rainy seasons. Caretakers were interviewed and data on fever episodes of their children in the preceding 2 weeks were collected. Mixed logit model was employed to estimate the determinants of healthcare provider choice. RESULTS: Among 257 fever episodes reported, the main choices of healthcare providers were limited to self-care, VHV, and a health center. Direct cost and walking distance negatively affected the choice of a VHV and the health center. An increase of VHV's direct cost or walking distance did not much affect predicted probability of the health center, but rather that of self-care, while drug availability and illness severity increased the choice probability of a VHV and the health center. CONCLUSION: The results suggest that the net healthcare demand increases with the introduction of a VHV. Allocations from the government's budget are required to sustain VHV activities because the introduction of a small user fee could impede the utilization of a VHV. A large travel cost related to the choice of the health center suggests that resource allocation is required for the expansion of formal healthcare providers to adequately operate a referral system.

Motion capture and manipulation of a single synthetic molecular rotor by optical microscopy.

Single-molecule imaging and manipulation with optical microscopy have become essential methods for studying biomolecular machines; however, only few efforts have been directed towards synthetic molecular machines. Single-molecule optical microscopy was now applied to a synthetic molecular rotor, a double-decker porphyrin (DD). By attaching a magnetic bead (ca. 200 nm) to the DD, its rotational dynamics were captured with a time resolution of 0.5 ms. DD showed rotational diffusion with 90° steps, which is consistent with its four-fold structural symmetry. Kinetic analysis revealed the first-order kinetics of the 90° step with a rate constant of 2.8 s(-1). The barrier height of the rotational potential was estimated to be greater than 7.4 kJ mol(-1) at 298 K. The DD was also forcibly rotated with magnetic tweezers, and again, four stable pausing angles that are separated by 90° were observed. These results demonstrate the potency of single-molecule optical microscopy for the elucidation of elementary properties of synthetic molecular machines.

Large-scale survey for novel genotypes of Plasmodium falciparum chloroquine-resistance gene pfcrt.

BACKGROUND: In Plasmodium falciparum, resistance to chloroquine (CQ) is conferred by a K to T mutation at amino acid position 76 (K76T) in the P. falciparum CQ transporter (PfCRT). To date, at least 15 pfcrt genotypes, which are represented by combinations of five amino acids at positions 72-76, have been described in field isolates from various endemic regions. To identify novel mutant pfcrt genotypes and to reveal the genetic relatedness of pfcrt genotypes, a large-scale survey over a wide geographic area was performed. METHODS: Sequences for exon 2 in pfcrt, including known polymorphic sites at amino acid positions 72, 74, 75 and 76, were obtained from 256 P. falciparum isolates collected from eight endemic countries in Asia (Bangladesh, Cambodia, Lao P.D.R., the Philippines and Thailand), Melanesia (Papua New Guinea and Vanuatu) and Africa (Ghana). A haplotype network was constructed based on six microsatellite markers located -29 kb to 24 kb from pfcrt in order to examine the genetic relatedness among mutant pfcrt genotypes. RESULTS: In addition to wild type (CVMNK at positions 72-76), four mutant pfcrt were identified; CVIET, CVIDT, SVMNT and CVMNT (mutated amino acids underlined). Haplotype network revealed that there were only three mutant pfcrt lineages, originating in Indochina, Philippines and Melanesia. Importantly, the Indochina lineage contained two mutant pfcrt genotypes, CVIET (n = 95) and CVIDT (n = 14), indicating that CVIDT shares a common origin with CVIET. Similarly, one major haplotype in the Melanesian lineage contained two pfcrt genotypes; SVMNT (n = 71) and CVMNT (n = 3). In Africa, all mutant pfcrt genotypes were the CVIET of the Indochina lineage, probably resulting from the intercontinental migration of CQ resistance from Southeast Asia. CONCLUSIONS: The number of CQ-mutant lineages observed in this study was identical to that found in previous studies. This supports the hypothesis that the emergence of novel CQ resistance is rare. However, in the mutant pfcrt genotypes, amino acid changes at positions 72, 74 and 75 appear to have recently been generated at least several times, producing distinct pfcrt mutant genotypes. The occurrence of new mutations flanking K76T may yield stronger resistance to CQ and/or a higher fitness than the original pfcrt mutant.