EHP Library Malaria Bulletin, Nov 20-Dec 3, 2000

Full Text Reports/Articles

MIM Pan-African Malaria Conference, March 1999, South Africa – Proceedings

Social Sciences and Malaria

1 – Health Policy 2000 Nov 17;54(2):143-159

Economic burden of malaria illness on households versus that of all other illness episodes: a study in five malaria holo-endemic Nigerian communities.

Onwujekwe O, Chima R, Okonkwo P

Health Policy Research Unit, Department of Pharmacology and Therapeutics, College of Medicine, University of Nigeria, Enugu Campus, PMB 01129, Enugu, Nigeria

We compared the financial and economic costs of malaria attack to that of a combination of other illness episodes on households in five malaria holo-endemic rural communities. The data was collected from household heads or their representatives using pre-tested interviewer-administered questionnaire. Information was collected on the amount of money household spent to treat both malaria and other illnesses respectively, together with the time lost due to both the groups of illnesses within 1 month prior to the interview. The findings showed that the cost of treating malaria illness accounted for 49.87% of curative health care costs incurred by the households. Average malaria expenditure was $1.84 per household per month, while it was $2.60 per month for the combination of other illness episodes. The average person-days lost due to malaria and the combination of other illnesses were almost equal. If the financial costs of treating malaria and other illnesses are combined, this cost will deplete 7.03% of the monthly average household income, with treatment of malaria illness alone depleting 2.91%. Thus, malaria is a big contributor to the economic burden of disease, in malaria holo-endemic communities. Community-effective malaria control programs are needed to reduce this burden on the households.

2 – Bull World Health Organ 2000;78(10):1207-21

Malnutrition as an underlying cause of childhood deaths associated with infectious diseases in developing countries.

Rice AL, Sacco L, Hyder A, Black RE

Department of International Health, Johns Hopkins University, School of Public Health, Baltimore, MD 21205, USA. [email protected]

INTRODUCTION: Recent estimates suggest that malnutrition (measured as poor anthropometric status) is associated with about 50% of all deaths among children. Although the association between malnutrition and all-cause mortality is well documented, the malnutrition-related risk of death associated with specific diseases is less well described. We reviewed published literature to examine the evidence for a relation between malnutrition and child mortality from diarrhoea, acute respiratory illness, malaria and measles, conditions that account for over 50% of deaths in children worldwide. METHODS: MEDLINE was searched for suitable review articles and original reports of community-based and hospital-based studies. Findings from cohort studies and case-control studies were reviewed and summarized. RESULTS: The strongest and most consistent relation between malnutrition and an increased risk of death was observed for diarrhoea and acute respiratory infection. The evidence, although limited, also suggests a potentially increased risk for death from malaria. A less consistent association was observed between nutritional status and death from measles. Although some hospital-based studies and case-control studies reported an increased risk of mortality from measles, few community-based studies reported any association. DISCUSSION: The risk of malnutrition-related mortality seems to vary for different diseases. These findings have important implications for the evaluation of nutritional intervention programmes and child survival programmes being implemented in settings with different disease profiles.

3 – J Ethnopharmacol 2000 Dec 1;73(3):487-493

The potential of Artemisia annua L. as a locally produced remedy for malaria in the tropics: agricultural, chemical and clinical aspects.

Mueller MS, Karhagomba IB, Hirt HM, Wemakor E

Hopital Nebobongo, Nebobongo, Congo

The plant Artemisia annua L. (Asteraceae) is listed in the Chinese pharmacopoeia as a remedy for various fevers including malaria, and contains the well-established antimalarial compound artemisinin. In this study, a hybrid form of A. annua was successfully cultivated in Central Africa. The aerial parts of the plant contained 0.63-0.70% artemisinin per dry weight, and approximately 40% of this artemisinin could be extracted by simple tea preparation methods. Five malaria patients who were treated with A. annua tea showed a rapid disappearance of parasitaemia within 2-4 days. An additional trial with 48 malaria patients showed a disappearance of parasitaemia in 44 patients (92%) within 4 days. Both trials showed a marked improvement of symptoms. In our opinion, these results justify further examinations of the antimalarial effect of A. annua preparations.

4 – Journal of Ethnopharmacology 2000,
73/1-2 (293-297)

Evaluation of some Moroccan medicinal plant extracts for larvicidal activity
Markouk M.; Bekkouche K.; Larhsini M.; Bousaid M.; Lazrek H.B.; Jana M.
H.B. Lazrek, 
Email: [email protected]

The larvicidal properties of 16 extracts of four Moroccan medicinal
plants: Calotropis procera (Wild.), Cotula cinerea (L.), Solanum sodomaeum
(L.) and Solanum elaeagnifolium (CAV.) were tested against Anopheles
labranchiae mosquito larvae. Among the extracts tested, nine exhibited high
larvicidal activity with LCinf 5inf 0 (24 h) ranging from 28 to 325 ppm.
(C) 2000 Elsevier Science Ireland Ltd.

PubMed – Nov 20-Dec 3, 2000

5 – Microbes Infect 2000 Oct 1;2(12):1461-1477The apical organelles of malaria merozoites: host cell selection, invasion, host immunity and immune evasion.

Preiser P, Kaviratne M, Khan S, Bannister L, Jarra W

Division of Parasitology, The National Institute for Medical Research, The Ridgeway, Mill Hill, NW7 1AA, London, UK

Malaria is caused by protozoan parasites belonging to the phylum Apicomplexa. These obligate intracellular parasites depend on the successful invasion of an appropriate host cell for their survival. This article is a broad overview of the molecular strategies employed by the merozoite, an invasive form of the malaria parasite, to successfully invade a suitable red blood cell.

6 – Am J Med Sci 2000 Nov;320(5):337-41

Transfusion-associated falciparum malaria successfully treated with red blood cell exchange transfusion.

Tejura B, Sass DA, Fischer RA, Daskal I, Eiger G

Department of Medicine, Albert Einstein Medical Center, Philadelphia, Pennsylvania 19141, USA.

Falciparum malaria is frequently associated with significant morbidity and mortality. The use of exchange transfusion as a therapeutic modality for severe cases of malaria has been described previously. We describe a case of a 49 year-old African American gentleman with a history of hemoglobin-SC disease who presented with a severe case of Plasmodium falciparum malaria 3 weeks after having received an infected blood transfusion. His peripheral smear showed the presence of numerous intraerythrocytic ring forms and “banana-shaped” gametocytes with a high-grade parasitemia, estimated at 18%. He was treated with antimalarial chemotherapy and also underwent a 12-unit red blood cell exchange transfusion, decreasing his parasite load to < 1%, as determined on repeat smear. It is prudent to be aware of the efficacy of this adjunctive treatment, especially with ever-increasing travel and a resultant increase in the prevalence of tropical diseases in the United States.

7 – Eur J Immunol 2000 Nov;30(11):3079-88

Generation and characterization of malaria-specific human CD8(+) lymphocyte clones: effect of natural polymorphism on T cell recognition and endogenous cognate antigen presentationby liver cells.

Bonelo A, Valmori D, Triponez F, Tiercy JM, Mentha G, Oberholzer J, Champagne P, Romero JF, Esposito F, Nebie I, Barbey C, Romero P, Herrera S, Corradin G, Lopez JA

Institute of Biochemistry, University of Lausanne, Epalinges, Switzerland.

CD8(+) cytolytic T lymphocytes (CTL) play a fundamental role in the clearance of malaria parasites from the liver in mouse models. In humans, however, only low levels of parasite-specific CD8(+) T lymphocytes have been observed in individuals living in endemic areas. In the present study, we identified high levels of circulating CD8(+) T lymphocytes specific for a previously described HLA-A2-restricted CTL epitope of the circumsporozoite (CS) protein of Plasmodium falciparum in an adult living in Burkina Faso, as evidenced by IFN-gamma ELISPOT assay and MHC-tetramer technology. After cloning by limiting dilution culture, T cell recognition of natural CS variants of P. falciparum was studied. The results demonstrate that naturally occurring variations drastically affect residues critical for T cell recognition as only two out of nine sequences analyzed were efficiently recognized by the CTL clones. These clones were also used to analyze T cell recognition of the endogenously presented cognate antigen. We observed efficient antigen recognition of both HLA-A*0201-transfected murine antigen presenting cells and liver cells from HLA-A*0201/K(b)-transgenic mice upon infection with recombinant vaccinia virus encoding the CS protein (WR-CS). More importantly, we demonstrate for the first time efficient recognition of WR-CS-infected human liver cells.

8 – Mol Biochem Parasitol 2000 Nov 1;111(1):163-171

Origin of Plasmodium falciparum malaria is traced by mitochondrial DNA.

Conway DJ, Fanello C, Lloyd JM, Al-Joubori BM, Baloch AH, Somanath SD, Roper C, Oduola AM, Mulder B, Povoa MM, Singh B, Thomas AW

Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St, WC1E 7HT, London, UK

The origin and geographical spread of Plasmodium falciparum is here determined by analysis of mitochondrial DNA sequence polymorphism and divergence from its most closely related species P. reichenowi (a rare parasite of chimpanzees). The complete 6 kb mitochondrial genome was sequenced from the single known isolate of P. reichenowi and from four different cultured isolates of P. falciparum, and aligned with the two previously derived P. falciparum sequences. The extremely low synonymous nucleotide polymorphism in P. falciparum (pi=0.0004) contrasts with the divergence at such sites between the two species (K=0.1201), and supports a hypothesis that P. falciparum has recently emerged from a single ancestral population. To survey the geographical distribution of mitochondrial haplotypes in P. falciparum, 104 isolates from several endemic areas were typed for each of the identified single nucleotide polymorphisms. The haplotypes show a radiation out of Africa, with unique types in Southeast Asia and South America being related to African types by single nucleotide changes. This indicates that P. falciparum originated in Africa and colonised Southeast Asia and South America separately.9 – Mol Biochem Parasitol 2000 Nov 1;111(1):153-161Genotyping of Plasmodium falciparum gametocytes by reverse transcriptase polymerase chain reaction.

Menegon M, Severini C, Sannella A, Paglia MG, Sangare D, Abdel-Wahab A, Abdel-Muhsin AA, Babiker H, Walliker D, Alano P

Laboratorio di Parassitologia, Istituto Superiore di Sanita, Rome, Italy

A molecular assay has been developed for the specific detection and genetic characterisation of Plasmodium falciparum gametocytes in the blood of malaria infected individuals. The assay is based on the reverse transcription and polymerase chain reaction (RT-PCR) amplification of the messenger RNA of gene pfg377, a sexual-stage specific transcript abundantly produced in maturing gametocytes. The gene contains four regions of repetitive sequences, of which region 3 was shown to be the most polymorphic in laboratory clones and field isolates of the parasite. Analysis of samples of malaria infected blood by RT-PCR specific for region 3 has enabled identification of multiple gametocyte-producing clones within single infections. The assay is able to detect gametocytes below the threshold of microscopic detection, and is highly specific for its gametocyte targets also in the presence of a vast excess of asexual forms.

10 – Mol Biochem Parasitol 2000 Nov 1;111(1):123-130

Conservation and heterogeneity of the glutamate-rich protein (GLURP) among field isolates and laboratory lines of Plasmodium falciparum.

Stricker K, Vuust J, Jepsen S, Oeuvray C, Theisen M

Department of Clinical Biochemistry, Statens Serum Institut, Artillerivej 5, DK-2300 S, Copenhagen, Denmark

Genetic variation of the glutamate-rich protein (GLURP) of Plasmodium falciparum was analysed in 29 field isolates and 15 laboratory lines of diverse geographical origin, by DNA sequencing of the non-repetitive 5′-region (R0) of the glurp gene. Polymorphism with respect to the length of the GLURP R2 repeat region was also analysed by a polymerase chain reaction method. As reference, the nucleotide sequence of the highly polymorphic 3′-region of the circumsporozoite protein gene was determined in the same isolates. It was found that even in the presence of variations in the GLURP R2 repeat region, immunodominant parts of the GLURP R0 region are surprisingly well conserved and the conservation is most pronounced in isolates from locations with very high malaria transmission. This might indicate that the R0 structure plays an important role in the parasite.

11 – Proc Natl Acad Sci U S A 2000 Nov 21;

Anopheles gambiae salivary gland proteins as putative targets for blocking transmission of malaria parasites.

Brennan JD, Kent M, Dhar R, Fujioka H, Kumar N

Johns Hopkins University School of Hygiene and Public Health, The W. Harry Feinstone Department of Molecular Microbiology and Immunology, 615 North Wolfe Street, Baltimore, MD 21205; and Case Western Reserve University, School of Medicine, Institute of Pathology, 2085 Adelbert Road, Cleveland, OH 44106.

Anopheles gambiae is the primary vector of human malaria in sub-Saharan Africa. Invasion of Anopheles salivary glands by Plasmodium sporozoites is a necessary step in the transmission of malaria and is likely to be mediated by specific receptor-ligand interactions. We are interested in identifying putative an A. gambiae salivary gland receptor or receptors for sporozoite invasion as a possible target for blocking malaria transmission. By using monoclonal antibodies against female-specific A. gambiae salivary gland proteins, two molecules, one of 29 kDa and one of 100 kDa, were identified and characterized with respect to the age and blood-feeding process of mosquitoes. In an in vivo bioassay, the monoclonal antibody against the 100-kDa protein inhibited Plasmodium yoelii sporozoite invasion of salivary glands >/=75%. These results show that A. gambiae salivary gland proteins are accessible to monoclonal antibodies that inhibit sporozoite invasion of the salivary glands and suggest alternate targets for blocking the transmission of malaria by this most competent of malaria vectors.

PubMed – Nov 20-Dec 3, 2000

12 – J Immunol 2000 Dec 1;165 (11):6341-6346

Mapping of the Region of Complement Receptor (CR) 1 Required for Plasmodium falciparum Rosetting and Demonstration of the Importance of CR1 in Rosetting in Field Isolates.

Rowe JA, Rogerson SJ, Raza A, Moulds JM, Kazatchkine MD, Marsh K, Newbold CI, Atkinson JP, Miller LH

Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh, United Kingdom. Wellcome Trust Research Laboratories, College of Medicine, University of Malawi, Blantyre, Malawi. Department of Microbiology and Immunology, MCP Hahnemann University School of Medicine, Philadelphia, PA 19129. Institut National de la Sante et de la Recherche Medicale Unite 430, Hopital Broussais, Paris, France. Kenya Medical Research Institute-Wellcome Trust Programme, KEMRI Centre for Geographical Medicine Research Coast, Kilifi, Kenya. Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom. Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, MO 63110. National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.

The malaria parasite Plasmodium falciparum induces a number of novel adhesion properties in the erythrocytes that it infects. One of these properties, the ability of infected erythrocytes to bind uninfected erythrocytes to form rosettes, is associated with severe malaria and may play a direct role in the pathogenesis of disease. Previous work has shown that erythrocytes deficient in complement receptor (CR) 1 (CR1, CD35; C3b/C4b receptor) have greatly reduced rosetting capacity, indicating an essential role for CR1 in rosette formation. Using deletion mutants and mAbs, we have localized the region of CR1 required for the formation of P. falciparum rosettes to the area of long homologous repeat regions B and C that also acts as the binding site for the activated complement component C3b. This result raises the possibility that C3b could be an intermediary in rosetting, bridging between the infected erythrocyte and CR1. We were able to exclude this hypothesis, however, as parasites grown in C3-deficient human serum formed rosettes normally. We have also shown in this report that rosettes can be reversed by mAb J3B11 that recognizes the C3b binding site of CR1. This rosette-reversing activity was demonstrated in a range of laboratory-adapted parasite strains and field isolates from Kenya and Malawi. Thus, we have mapped the region of CR1 required for rosetting and demonstrated that the CR1-dependent rosetting mechanism occurs commonly in P. falciparum isolates, and could therefore be a potential target for future therapeutic interventions to treat severe malaria.

13 – Biol Pharm Bull 2000 Nov;23(11):1275-80

Effect of artemisinin on lipid peroxidation and fluidity of the erythrocyte membrane in malaria.

Sibmooh N, Pipitaporn B, Wilairatana P, Dangdoungjai J, Udomsangpetch R, Looareesuwan S, Chantharaksri U

Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand. Email: [email protected]

The effect of artemisinin on membrane fluidity of erythrocytes was investigated using spin labeling compounds, doxyl stearic acids. The membrane fluidity of erythrocytes from the in vitro culture and malaria patients was determined. In vitro, the erythrocytes in parasite culture showed an increase in membrane fluidity which was associated with the parasite counts and stage of parasites. Artemisinin caused reduction in membrane fluidity and the effect was more pronounced in the erythrocytes infected with schizont stage-parasites. In vivo, the elevation of plasma TBARs (thiobarbituric acid reactive substances) and reduction of membrane fluidity were evident in Plasmodium falciparum-infected patients, particularly in severe cases. The levels of plasma TBARs were related to the severity of the disease. Treatment with artemisinin alone showed no effect on plasma TBARs, and did not alter the membrane fluidity. Desferrioxamine, however, reduced oxidative damage during the infection without compromising the therapeutic effect of artemisinin. These findings suggested that the infected erythrocytes were prone to the effect of artemisinin. Addition of a chelator such as desferrioxamine is beneficial and can improve the treatment of severe malaria.

14 – Parasitology 2000 Sep;121 (Pt 3):257-72

Genetic diversity and dynamics of plasmodium falciparum and P. vivax populations in multiply infected children with asymptomatic malaria infections in Papua New Guinea.

Bruce MC, Galinski MR, Barnwell JW, Donnelly CA, Walmsley M, Alpers MP, Walliker D, Day KP

Wellcome Trust Centre for the Epidemiology of Infectious Disease, Department of Zoology, University of Oxford. Email: [email protected]

We describe the dynamics of co-infections of Plasmodium falciparum and P. vivax in 28 asymptomatic children by genotyping these species using the polymorphic loci Msp2 and Msp3alpha, respectively. The total number of Plasmodium spp. infections detected using 3 day sampling over 61 days varied between 1 and 14 (mean 6.6). The dynamics of P. falciparum and P. vivax genotypes varied greatly both within and amongst children. Periodicity in the detection of P. falciparum infections is consistent with the synchronous replication of individual genotypes. Replication synchrony of multiple co-infecting genotypes was not detected. In 4-year-old children P. falciparum genotype complexity was reduced and episodes lasted significantly longer (median duration > 60 days) when compared to children aged 5-14 years (median duration 9 days). P. vivax genotype complexity was not correlated with age but the episode duration was also longer for this species in 4-year-olds than in older children but was not as long as P. falciparum episodes. Recurrence of P. falciparum and P. vivax genotypes over weeks was observed. We interpret these major fluctuations in the density of genotypes over time as the result of the mechanism of antigenic variation thought to be present in these Plasmodium species.

15 – Parasitology 2000 Sep;121 (Pt 3):247-56

Age- and species-specific duration of infection in asymptomatic malaria infections in Papua New Guinea.

Bruce MC, Donnelly CA, Packer M, Lagog M, Gibson N, Narara A, Walliker D, Alpers MP, Day KP

Wellcome Trust Centre for the Epidemiology of Infectious Disease, Department of Zoology, University of Oxford. Email: [email protected]

The burden and duration of asymptomatic malaria infections were measured in residents of the malaria endemic village of Gonoa, Madang Province, Papua New Guinea. Plasmodium falciparum, P. vivax and P. malariae infections in people aged 4 years to adulthood were compared. Frequent sampling at 3-day intervals for up to 61 days allowed assessment of individual episodes of infection. Statistical assessment of P. falciparum detection revealed a periodicity consistent with synchronous replication of this species over periods up to 27 days. The duration of P. falciparum episodes was longer across all age groups than that of P. vivax and P. malariae. A trend for decreasing duration with age was also noted in data from each species. This was most prominent in P. falciparum infections: median duration in 4-year-olds was > 48 days compared with a median between 9 and 15 days in older children and adults. The results are consistent with the slow acquisition of immunity to antigenically diverse Plasmodium populations and suggest a faster rate of acquisition to P. vivax and P. malariae than to P. falciparum.

16 – Parasitology 2000 Sep;121 (Pt 3):237-46

Mathematical modelling of the chemotherapy of Plasmodium falciparum malaria with artesunate: postulation of ‘dormancy’, a partial cytostatic effect of the drug, and its implication for treatment regimens.

Hoshen MB, Na-Bangchang K, Stein WD, Ginsburg H

Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Israel.

Although artesunate, one of the potent derivatives of the qinghaosu family of drugs for treating falciparum malaria, is already in use in the field, its therapeutic protocol has only been developed empirically by hit-or-miss. A pharmacokinetic-pharmacodynamic (PK-PD) model, required for creating such a protocol, is not straightforward. Artesunate presents extremely fast pharmacokinetics. As a result the stage specificity of its action must be treated explicitly. Also, use of standard PK-PD modelling fails to explain the clinical results. Our PK-PD modelling of its activity leads us to the postulation of the existence of a novel effect: a small fraction of the parasites, as a result of chemotherapeutic pressure, become cytostatic, or ‘dormant’. At this stage, the parasite cycle is halted, making them unsusceptible to further dosing until wakening. This slows down the antimalarial activity of the drug, entailing either many frequent doses or an extended period of treatment and surveillance. Based on our modelling, we suggest a method for deciding on rational models of chemotherapy against falciparum malaria.

17 – Parasitology 2000 Sep;121 (Pt 3):227-35

Mathematical modelling of the within-host dynamics of Plasmodium falciparum.

Hoshen MB, Heinrich R, Stein WD, Ginsburg H

Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Israel.
Email: [email protected]

The development of malaria due to Plasmodium falciparum is a complex, multi-stage process. It is usually characterized by an exponential growth in the number of parasite-infected erythrocytes, followed by marked oscillations in this number with a period of 48 h, which are eventually dampened. This course of events has been the subject of various mathematical models. In this paper we propose a new mathematical model for the in-host asexual erythrocytic development of P. falciparum malaria. Synchronicity of the infection is shown to be an inherent feature of infection, irrespective of the duration of merozoite release from the liver. It will, therefore, cause periodic symptoms, as known in malaria patients. We also simulate the effects of an induced host immune response and show how the level of immunity affects the development of disease. The simulations fit well with the clinical observations. We show how infection can become asynchronous and discuss the effect of desynchronization on the circulating and total parasitaemia and demonstrate that synchronized broods will show parasitaemia fluctuations.

18 – Parasitology 2000 Aug;121 (Pt 2):127-33

Commitment to sexual differentiation in the human malaria parasite, Plasmodium falciparum.

Smith TG, Lourenco P, Carter R, Walliker D, Ranford-Cartwright LC

Institute of Cell, Animal and Population Biology, University of Edinburgh, Scotland.

The differentiation of the two sexes in the gametocytogenesis of Plasmodium falciparum was investigated using a plaque assay and antibodies specific for various stages and sexes of gametocytes. Immunofluorescence assays on plaques of cultured parasites grown in monolayers of erythrocytes revealed that the merozoites released from a single sexually-committed schizont became either all male or all female gametocytes. Thus, the commitment of this species to differentiate into one sex or the other is likely to occur prior to the nuclear division of the sexually-committed schizont. The characteristic female-biased gametocyte sex ratio observed for many Plasmodium species is manifested in P. falciparum by a greater percentage of schizonts that produce female gametocytes (67-71%) than those that yield males. From the plaque assay, it was determined that the number of gametocytes produced per sexually-committed schizont was similar for both sexes, indicating that allocation of parasite resources was equal for each sex of gametocyte. The timing of sexual differentiation and features of the gametocyte sex ratio is discussed in relation to previous observations on P. falciparum and related malaria parasites.

19 – Parasitology 2000 Jul;121 (Pt 1):1-7

Linkage disequilibrium between two chromosomally distinct loci associated with increased resistance to chloroquine in Plasmodium falciparum.

Duraisingh MT, von Seidlein LV, Jepson A, Jones P, Sambou I, Pinder M, Warhurst DC

Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, UK.

Chloroquine-resistance in Plasmodium falciparum is associated with polymorphisms in a locus on or near the cg2 gene on chromosome 7, and in the pfmdr1 gene on chromosome 5. In this study we typed P. falciparum DNA from uncomplicated malaria cases in The Gambia in 1990, 1995 and 1996 for size polymorphism in the omega repeat of cg2, for sequence polymorphisms in pfmdr1 at codons 86 and 184, in dhfr at codon 108 and in the msp2 gene. Chloroquine sensitivity tests were conducted in vitro. A significant but incomplete association was found between the presence of the cg2 Dd2-like omega repeat size polymorphism and in vitro resistance, and between the tyr-86 allele of pfmdr1 and in vitro resistance. Furthermore there was strong linkage disequilibrium between the pfmdr1 asn-86 allele and the cg2 not Dd2-like omega repeat allele located on different chromosomes. In contrast, no linkage disequilibrium was found between these alleles and either the dhfr ser-108 allele or the msp2 IC sequence polymorphism. No significant linkage was measured between pfmdr1 asn-86 and phe-184 although these loci are separated only by 296 base pairs. Our results suggest that genetic elements linked to the cg2 and the pfmdr1 genes are important determinants of chloroquine resistance. It can be concluded that the observed linkage disequilibrium is maintained epistatically through selection by chloroquine.
20 – Stat Methods Med Res 2000 Jun;9(3):249-58

Modelling recurrent malaria in Thailand.

Tiensuwan M

Department of Mathematics, Faculty of Science, Mahidol University, Bangkok, Thailand.
Email: [email protected]

Malaria is a common infectious disease in many tropical countries. Thailand is located geographically in the tropical zone and the transmission of malaria is found widely, for instance, in the Tak province. The objective of this study is to find risk factors for the number of experiences with malaria of malaria patients, i.e. repeated recurrences of the disease within an infected individual in the Tak province in the rainy season by using Poisson regression models. Among the models fitted, the best are chosen based on the analysis of deviance. The results of this study show that the risk factors are race, spraying insecticides in houses in an infectious area, number of days staying overnight without protection against mosquitoes of malaria patients, and whether or not any members of the family of the malaria patient have had malaria.