Anderson, T.J., B. Haubold, J.T. Williams, J.G. Estrada-Franco, L. Richardson, R. Mollinedo, M. Bockarie, J. Mokili, S. Mharakurwa, N. French, J. Whitworth, I.D. Velez, A.H. Brockman, F. Nosten, M.U. Ferreira, and K.P. Day, Microsatellite markers reveal a spectrum of population structures in the malaria parasite plasmodium falciparum. Molecular Biology and Evolution, 2000. 17(10): p. 1467-82.[PubMed Link]
Multilocus genotyping of microbial pathogens has revealed a range of population structures, with some bacteria showing extensive recombination and others showing almost complete clonality. The population structure of the protozoan parasite Plasmodium falciparum has been harder to evaluate, since most studies have used a limited number of antigen-encoding loci that are known to be under strong selection. We describe length variation at 12 microsatellite loci in 465 infections collected from 9 locations worldwide. These data reveal dramatic differences in parasite population structure in different locations. Strong linkage disequilibrium (LD) was observed in six of nine populations. Significant LD occurred in all locations with prevalence <1% and in only two of five of the populations from regions with higher transmission intensities. Where present, LD results largely from the presence of identical multilocus genotypes within populations, suggesting high levels of self-fertilization in populations with low levels of transmission. We also observed dramatic variation in diversity and geographical differentiation in different regions. Mean heterozygosities in South American countries (0.3-0.4) were less than half those observed in African locations (0. 76-0.8), with intermediate heterozygosities in the Southeast Asia/Pacific samples (0.51-0.65). Furthermore, variation was distributed among locations in South America (F:(ST) = 0.364) and within locations in Africa (F:(ST) = 0.007). The intraspecific patterns of diversity and genetic differentiation observed in P. falciparum are strikingly similar to those seen in interspecific comparisons of plants and animals with differing levels of outcrossing, suggesting that similar processes may be involved. The differences observed may also reflect the recent colonization of non- African populations from an African source, and the relative influences of epidemiology and population history are difficult to disentangle. These data reveal a range of population structures within a single pathogen species and suggest intimate links between patterns of epidemiology and genetic structure in this organism.

Brockman, A., R.N. Price, M. van Vugt, D.G. Heppner, D. Walsh, P. Sookto, T. Wimonwattrawatee, S. Looareesuwan, N.J. White, and F. Nosten, Plasmodium falciparum antimalarial drug susceptibility on the north- western border of Thailand during five years of extensive use of artesunate-mefloquine. Transactions of the Royal Society of Tropical Medicine and Hygiene, 2000. 94(5): p. 537-44. [PubMed Link]
Following a marked decline in the efficacy in vivo of mefloquine between 1990 and 1994, a combination of artesunate (4 mg/kg/d for 3 d) and mefloquine (25 mg/kg) has been used as first line treatment of uncomplicated falciparum malaria in camps for displaced persons located along the north-western border of Thailand. Antimalarial drug susceptibility of fresh isolates of Plasmodium falciparum from this population was evaluated using a radioisotope microdilution assay between 1995 and 1999. In total, 268 isolates were collected, of which 189 were from primary infections and 79 from recrudescent infections. The geometric mean 50% inhibitory concentration (IC50) values from primary infections were: dihydroartemisinin 1.2 ng/mL, artesunate 1.6 ng/mL, artemether 4.8 ng/mL, atovaquone 0.4 ng/mL, lumefantrine 32 ng/mL, chloroquine 149 ng/mL, quinine 354 ng/mL, mefloquine 27 ng/mL and halofantrine 4.1 ng/mL. A significant positive correlation was found between the susceptibility in vitro to artesunate and quinine (r = 0.43, P < 0.001), mefloquine (r = 0.46, P < 0.001), and halofantrine (r = 0.51, P < 0.001). These levels of resistance in vitro are among the highest reported and confirm continuing high level multidrug resistance in this area. Despite intensive use of the combination between 1995 and 1999 there has been a significant improvement in mefloquine sensitivity (P < 0.001) and artesunate sensitivity (P < 0.001). This supports observations in vivo that the combination of artesunate and mefloquine has reversed the previous decline in mefloquine sensitivity.

Ezzet, F., M. van Vugt, F. Nosten, S. Looareesuwan, and N.J. White, Pharmacokinetics and pharmacodynamics of lumefantrine (benflumetol) in acute falciparum malaria. Antimicrobial Agents and Chemotherapy, 2000. 44(3): p. 697-704. [PubMed Link]
The objective of this study was to conduct a prospective population pharmacokinetic and pharmacodynamic evaluation of lumefantrine during blinded comparisons of artemether-lumefantrine treatment regimens in uncomplicated multidrug-resistant falciparum malaria. Three combination regimens containing an average adult lumefantrine dose of 1,920 mg over 3 days (four doses) (regimen A) or 2,780 mg over 3 or 5 days (six doses) (regimen B or C, respectively) were given to 266 Thai patients. Detailed observations were obtained for 51 hospitalized adults, and sparse data were collected for 215 patients of all ages in a community setting. The population absorption half-life of lumefantrine was 4.5 h. The model-based median (5th and 95th percentiles) peak plasma lumefantrine concentrations were 6.2 (0.25 and 14.8) microgram/ml after regimen A, 9. 0 (1.1 and 19.8) microgram/ml after regimen B, and 8 (1.4 and 17.4) microgram/ml after regimen C. During acute malaria, there was marked variability in the fraction of drug absorbed by patients (coefficient of variation, 150%). The fraction increased considerably and variability fell with clinical recovery, largely because food intake was resumed; taking a normal meal close to drug administration increased oral bioavailability by 108% (90% confidence interval, 64 to 164) (P, 0.0001). The higher-dose regimens (B and C) gave 60 and 100% higher areas under the concentration-time curves (AUC), respectively, and thus longer durations for which plasma lumefantrine concentrations exceeded the putative in vivo MIC of 280 microgram/ml (median for regimen B, 252 h; that for regimen C, 298 h; that for regimen A, 204 h [P, 0.0001]) and higher cure rates. Lumefantrine oral bioavailability is very dependent on food and is consequently poor in acute malaria but improves markedly with recovery. The high cure rates with the two six- dose regimens resulted from increased AUC and increased time at which lumefantrine concentrations were above the in vivo MIC.

McGready, R., A. Brockman, T. Cho, D. Cho, M. van Vugt, C. Luxemburger, T. Chongsuphajaisiddhi, N.J. White, and F. Nosten, Randomized comparison of mefloquine-artesunate versus quinine in the treatment of multidrug-resistant falciparum malaria in pregnancy. Transactions of the Royal Society of Tropical Medicine and Hygiene, 2000. 94(6): p. 689-93. [PubMed Link]
Since no effective malaria prevention measures have been identified for pregnant women living on the western border of Thailand, prompt diagnosis and efficient treatment are paramount, although drug resistance in Plasmodium falciparum has narrowed the treatment options. An open randomized comparison of supervised quinine (10 mg salt/kg every 8 h) for 7 days (Q7) versus mefloquine 25 mg base/kg (total dose) plus artesunate 4 mg/kg per day for 3 days (MAS3) was conducted in 1995- 97 in 108 Karen women with acute uncomplicated falciparum malaria in the second or third trimesters of pregnancy. The MAS3 regimen was more effective than the Q7 regimen: day 63 cure rates were 98.2% (95% CI 94.7-100) (n = 65) for MAS3 and 67.0% (95% CI 43x3-90x8) (n = 41) for Q7, P = 0x001. The MAS3 regimen was also associated with less gametocyte carriage; the average person-gametocyte-weeks for MAS3 was 2.3 (95% CI 0-11) and for Q7 was 46x9 (95% CI 26-78) per 1000 person- weeks, respectively (P < 0.001). MAS3 was significantly better tolerated. These evident advantages must be balanced against a possible increased risk of stillbirth with the use of mefloquine in pregnancy. Further randomized studies assessing the safety and efficacy of other artemisinin-containing combination regimens in pregnancy are needed urgently.

McGready, R., E. Paw, and F. Nosten, Menorrhagia caused by dengue fever. Australia and New Zealand Journal of Obstetrics and Gynaecology, 2000. 40(3): p. 354-5.[PubMed Link]

McGready, R., J. Simpson, S. Panyavudhikrai, S. Loo, E. Mercuri, L. Haataja, T. Kolatat, F. Nosten, and L. Dubowitz, Neonatal neurological testing in resource-poor settings. Annals of Tropical Paediatrics, 2000. 20(4): p. 323-36.[PubMed Link]
The aim of the study was to design and test a neurological examination for newborns that could be performed reliably by paramedical staff in resource-poor settings. The examination was adapted from a method established by Dubowitz et al., the latest version of which includes an optimality score. The final items in the test were chosen because they were culturally acceptable, could be elicited according to strict but easily comprehensible instructions and because the expected responses could be scored by the descriptions given or by diagrams in the proforma. The shortened examination was easily taught to paramedical staff who achieved a high degree of inter-observer reliability. This shortened version of the examination was piloted by comparing newborns from a Karen refugee camp on the western border of Thailand and from a large maternity hospital in Bangkok with a standardized cohort of newborns in London. The modified shortened version of the test was sufficiently sensitive to identify a number of differences between the cohorts, notably the poor vision performance and markedly reduced tone of the Karen newborns. In conclusion, the test can be used very reliably by paramedical staff and is a useful, simple and portable tool for the neurological assessment of newborn babies where resources are limited.

McGready, R. and F. Nosten, The pregnant traveller - Malaria and pregnancy. Obstetrics and Gynecology, 2000. 2(2): p. 120.[PubMed Link]

Nosten, F., M. van Vugt, R. Price, C. Luxemburger, K.L. Thway, A. Brockman, R. McGready, F. ter Kuile, S. Looareesuwan, and N.J. White, Effects of artesunate-mefloquine combination on incidence of Plasmodium falciparum malaria and mefloquine resistance in western Thailand: a prospective study. Lancet, 2000. 356: p. 297-302. [PubMed Link]
BACKGROUND: Worsening drug resistance in Plasmodium falciparum malaria is a major threat to health in tropical countries. We did a prospective study of malaria incidence and treatment in an area of highly multidrug- resistant P. falciparum malaria. METHODS: We assessed incidence of P. falciparum malaria and the in-vivo responses to mefloquine treatment over 13 years in two large camps for displaced Karen people on the northwest border of Thailand. During this time, the standard mefloquine dose was first increased, and then combined artesunate and mefloquine was introduced as first-line treatment for uncomplicated P. falciparum malaria. FINDINGS: Early detection and treatment controlled P. falciparum malaria initially while mefloquine was effective (cure rate with mefloquine [15 mg/kg] and sulphadoxine-pyrimethamine in 1985, 98% [95% CI 97-100]), but as mefloquine resistance developed, the cure rate fell (71% [67-77] in 1990). A similar pattern was seen for high-dose (25 mg/kg) mefloquine monotherapy from 1990-94. Since the general deployment of the artesunate-mefloquine combination in 1994, the cure rate increased again to almost 100% from 1998 onwards, and there has been a sustained decline in the incidence of P. falciparum malaria in the study area. In-vitro susceptibility of P. falciparum to mefloquine has improved significantly (p=0.003). INTERPRETATION: In this area of low malaria transmission, early diagnosis and treatment with combined artesunate and mefloquine has reduced the incidence of P. falciparum malaria and halted the progression of mefloquine resistance. We recommend that antimalarial drugs should be combined with artemisinin or a derivative to protect them against resistance.

Nosten, F., Prophylactic effect of Malarone against malaria:all good news? Lancet, 2000. 356: p. 1864-1865.[PubMed Link]

van Vugt, M., B.J. Angus, R.N. Price, C. Mann, J.A. Simpson, C. Poletto, S.E. Htoo, S. Looareesuwan, N.J. White, and F. Nosten, A case-control auditory evaluation of patients treated with artemisinin derivatives for multidrug-resistant Plasmodium falciparum malaria. American Journal of Tropical Medicine and Hygiene, 2000. 62(1): p. 65-9. [PubMed Link]
The artemisinin derivatives are now used widely in areas with multidrug- resistant Plasmodium falciparum malaria such as Southeast Asia, but concerns remain over their potential for neurotoxicity. Mice, rats, dogs, and monkeys treated with high doses of intramuscular artemether or arteether develop an unusual pattern of focal damage to brain stem nuclei (particularly those involved in auditory processing). To investigate whether a similar toxic effect occurs in patients treated with these compounds, clinical neurologic evaluation, audiometry and early latency auditory evoked responses were measured in a single-blind comparison of 79 patients who had been treated with > or =2 courses of oral artemether or artesunate within the previous 3 years, and 79 age- and sex-matched controls living in a malaria-endemic area on the northwestern border of Thailand. There were no consistent differences in any of these test results between the cases and controls. This study failed to detect any evidence of significant neurotoxicity in patients treated previously with oral artemether or artesunate for acute malaria.

van Vugt, M., S. Looareesuwan, P. Wilairatana, R. McGready, L. Villegas, I. Gathmann, R. Mull, A. Brockman, N.J. White, and F. Nosten, Artemether-lumefantrine for the treatment of multidrug-resistant falciparum malaria. Transactions of the Royal Society of Tropical Medicine and Hygiene, 2000. 94(5): p. 545-8.[PubMed Link]
The efficacy and safety of the 6-dose regimen of artemether- lumefantrine were assessed in an open randomized trial in children and adults presenting with acute, uncomplicated Plasmodium falciparum malaria in Thailand between November 1997 and March 1998. 200 patients were enrolled in 2 centres: 150 received artemether-lumefantrine (i.e., a median total dose of 9.6 mg/kg [interquartile range 8.7-10.7] and 57.9 mg/kg of lumefantrine [52.4-64.0]) and 50 the standard combination of artesunate (12 mg/kg over 3 d) and mefloquine (25 mg/kg). All patients had rapid initial clinical and parasitological responses. The 28 d cure rates were high: 97.7% (95% confidence interval [95% CI] 93.5- 99.5%) for artemether-lumefantrine and 100% (95% CI 92.5-100%) for artesunate-mefloquine. The 6-dose regimen of artemether-lumefantrine was better tolerated than, and as effective as, artesunate-mefloquine, the current standard treatment in this area of multidrug-resistant P. falciparum malaria.