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EHP Library Malaria Bulletin No. 27:  Dec 7,  2001-Jan 3, 2002

Environmental Management

Trop Med Int Health 2001 Dec;6(12):986-991

Patterns in age-specific malaria incidence in a population exposed to low levels of malaria transmission intensity.

Kleinschmidt I, Sharp B.

South African Medical Research Council, Durban, South Africa.

The population of the northern part of the province of KwaZulu Natal in South Africa has experienced low levels of malaria transmission intensity for many years. We investigated the widely held assumption that individuals in this population do not develop clinical tolerance to infection with Plasmodium falciparum. We calculated malaria incidence rates by 5-year age groups from a comprehensive small area malaria reporting system and from national census data for the period from mid-1990 to mid-1999. Incidence rates were plotted against age groups for each of the nine malaria seasons, and by quintile of crude incidence rate. These show that age-specific incidence varied considerably in areas of high incidence and in years of high incidence. In these areas malaria incidence rose with age until the late teens, and either remained constant or decreased in young adults. This finding appears to be consistent with results from settings of much higher transmission intensities which show that clinical tolerance to infection with P. falciparum in adults may be acquired as a result of a small number of infective bites in early childhood and implies that even in this relatively low transmission area, there is an asymptomatic reservoir of infection in older people. The results also show that in high incidence subregions the lowest incidences are reported for children under 5 years of age, which may be the result of greater protection offered to this age group by malaria vector control through indoor house spraying.

Social Sciences and Malaria

Trop Med Int Health 2001 Dec;6(12):1075-1083

Community perception of school-based delivery of anthelmintics in Ghana and Tanzania The Partnership for Child Development.

Brooker S, Marriot H, Hall A, Adjei S, Allan E, Maier C, Bundy DA, Drake LJ, Coombes MD, Azene G, Lansdown RG, Wen ST, Dzodozmenyo M, Cobbinah J, Obro N, Kihamia CM, Issae W, Mwanri L, Mweta MR, Mwaikemwa A, Salimu M, Ntimbwa P, Kiwelu VM, Turuka A, Nkungu DR, Magingo J.

The Partnership for Child Development, Imperial College School of Medicine, London, UK, The World Bank, Washington, DC, USA, Ghana Partnership for Child Development, Accra, Ghana, Tanzania Partnership for Child Development, Dar es Salaam, Tanzania.

This paper presents the results of an evaluation of community perception of two large-scale, government-run, school-based health programmes delivering anthelmintic drugs to primary school children, in Ghana (80 442 children in 577 schools) and Tanzania (110 000 children in 352 schools). Most teachers (96% in Ghana and 98% in Tanzania) were positive about their role in the programme, including administration of anthelmintic drugs, and parents and children fully accepted their taking on this role. The benefits of the programme were apparent to teachers, parents and children in terms of improved health and well-being of the children. Over 90% of parents in both Ghana and Tanzania indicated a willingness to pay for the continuation of drug treatment. The evaluation also highlighted areas that are critical to programme effectiveness, such as communication between schools and parents, the issue of collaboration between the health and education sectors, parents' perception of the importance of helminth infection as a serious and chronic health problem (compared with more acute and life threatening illnesses such as malaria), and who should pay for treatment of side-effects.

Trop Med Int Health 2001 Dec;6(12):992-997

Perception of chloroquine efficacy and alternative treatments for uncomplicated malaria in children in a holoendemic area of Tanzania: implications for the change of treatment policy.

Tarimo DS, Minjas JN, Bygbjerg IC.

Department of Parasitology and Medical Entomology, Muhimbili University College of Health Sciences, Dar es Salaam, Tanzania, Department of International Health, Institute of Public Health, University of Copenhagen, Copenhagen, Denmark.

Prior to policy change from chloroquine (CQ) to sulphadoxine/pyrimethamine (S/P; Fansidar) we assessed the perception of CQ efficacy and the alternative treatment options for malaria in children among parents/guardians (N=527) of under-fives attending first level health facilities on account of fever. It was hypothesized that the long experience with CQ and its antipyretic effect (lacking in S/P) might impede acceptance of S/P for wider use as first-line drug. Malarial fevers in children were most commonly treated with CQ (92.8%), followed by quinine (60.7%) and S/P (28.7%). A 63.2% knew the reasons for non-response to antimalarial treatment, and only 50% were aware that CQ could fail to treat malaria, and 57.1% knew alternative treatment options, namely quinine (52.2%) and S/P (20.5%). Generally, decreased efficacy of CQ had been noticed, and quinine was prescribed for both suspected and proven CQ failures in first level health facilities and the district hospital. S/P was judged to be more effective than quinine, but too strong for children, and was the least known drug in the study area. All formulations of S/P cost more per dose for a child and an adult than CQ. The implications of these findings on the change of malaria treatment policy are discussed.


Infect Immun 2002 Jan;70(1):102-106

Identification of Novel Plasmodium gallinaceum Zygote- and Ookinete-Expressed Proteins as Targets for Blocking Malaria Transmission.

Langer RC, Li F, Vinetz JM.

WHO Collaborating Center for Tropical Disease, Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555.

The development of transmission-blocking vaccines is one approach to malaria control. To identify novel Plasmodium zygote- and ookinete-secreted proteins as targets of blocking malaria transmission, monoclonal antibodies (MAbs) were produced against parasite-secreted proteins found in Plasmodium gallinaceum ookinete culture supernatants. Four MAbs-1A6, 2A5, 2B5, and 4B6-were identified that bound to P. gallinaceum zygotes and ookinetes in diverse patterns in terms of spatial localization on parasites, time course of antigen expression, and Western immunoblot patterns. MAbs 2A5 and 4B6 recognized more than one protein band as detected by Western immunoblot of P. gallinaceum ookinete supernatants. Beginning at 0 h postfertilization, MAb 2A5 recognized a diverse set of antigens; at 10 h postfertilization, MAb 4B6 recognized several antigens as well. MAb 1A6 recognized a single approximately 17-kDa protein, and 2B5 recognized a single approximately 32-kDa protein at 15 h postfertilization. In membrane feeding assays to assess the effect of these MAbs on P. gallinaceum infectivity for Aedes aegypti mosquitoes, the addition of MAbs 1A6 and 2B5 to infectious blood meals significantly inhibited oocyst development in the mosquito midgut. In contrast, MAb 2A5 seemed to enhance infectivity. These results demonstrate that Plasmodium ookinetes secrete proteins (in addition to previously characterized chitinases) that may be targets for blocking malaria transmission. Future investigation of ookinete-secreted neutralization-sensitive molecules should provide valuable insight into mechanisms by which ookinetes exit the blood meal, penetrate and transverse the peritrophic matrix, and invade the mosquito midgut epithelium.

Lancet 2001 Dec 8;358(9297):1927-193

Efficacy of RTS,S/AS02 malaria vaccine against Plasmodium falciparum infection in semi-immune adult men in The Gambia: a randomised trial.

Bojang KA, Milligan PJ, Pinder M, Vigneron L, Alloueche A, Kester KE, Ballou WR, Conway DJ, Reece WH, Gothard P, Yamuah L, Delchambre M, Voss G, Greenwood BM, Hill A, McAdam KP, Tornieporth N, Cohen JD, Doherty T.

Medical Research Council Laboratories, PO Box 273, The, Banjul, Gambia

Background RTS,S/AS02 is a pre-erythrocytic malaria vaccine based on the circumsporozoite surface protein of Plasmodium falciparum fused to HBsAg, incorporating a new adjuvant (AS02). We did a randomised trial of the efficacy of RTS,S/AS02 against natural P falciparum infection in semi-immune adult men in The Gambia.Methods 306 men aged 18-45 years were randomly assigned three doses of either RTS,S/AS02 or rabies vaccine (control). Volunteers were given sulfadoxine/pyrimethamine 2 weeks before dose 3, and kept under surveillance throughout the malaria transmission season. Blood smears were collected once a week and whenever a volunteer developed symptoms compatible with malaria. The primary endpoint was time to first infection with P falciparum. Analysis was per protocol.Findings 250 men (131 in the RTS,S/AS02 group and 119 in the control group) received three doses of vaccine and were followed up for 15 weeks. RTS,S/AS02 was safe and well tolerated. P falciparum infections occurred significantly earlier in the control group than the RTS,S/AS02 group (Wilcoxon's test p=0.018). Vaccine efficacy, adjusted for confounders, was 34% (95% CI 8.0-53, p=0.014). Protection seemed to wane: estimated efficacy during the first 9 weeks of follow-up was 71% (46-85), but decreased to 0% (-52 to 34) in the last 6 weeks. Vaccination induced strong antibody responses to circumsporozoite protein and strong T-cell responses. Protection was not limited to the NF54 parasite genotype from which the vaccine was derived. 158 men received a fourth dose the next year and were followed up for 9 weeks; during this time, vaccine efficacy was 47% (4-71, p=0.037).Interpretation RTS,S/AS02 is safe, immunogenic, and is the first pre-erythrocytic vaccine to show significant protection against natural P falciparum infection.

Health Econ 2001 Dec;10(8):731-749

Changing the first line drug for malaria treatment-cost-effectiveness analysis with highly uncertain inter-temporal trade-offs.

Goodman CA, Coleman PG, Mills AJ.

Health Policy Unit, London School of Hygiene and Tropical Medicine, London, UK.

Access to effective treatment would substantially reduce the burden of malaria in sub-Saharan Africa, but resistance to chloroquine, the most commonly used first line drug, is now widespread. There has been considerable debate over the level of chloroquine resistance at which a new first line drug should be adopted. Two issues make this an extremely complex decision: it involves trade-offs in costs and health outcomes over time; and many of the parameters are uncertain. A modelling approach was identified as appropriate for addressing these issues. The costs and effects of changing from chloroquine to sulphadoxine-pyrimethamine (SP) as the first line drug were modelled over 10 years, allowing for growth in drug resistance. Probabilistic sensitivity analysis was used to allow for the high levels of parameter uncertainty. The optimal year of switch was highly dependent on both empirical values, such as initial resistance and resistance growth rates, and on subjective values, such as the time preferences of policy-makers. It was not possible to provide policy-makers with a definitive threshold resistance level at which to switch, but the model can be used as an analytical tool to structure the problem, explore trade-offs, and identify areas for which data are lacking. Copyright 2001 John Wiley & Sons, Ltd.

QJM 2001 Dec;94(12):709-715

Glucose production and gluconeogenesis in adults with cerebral malaria.

van Thien H, Ackermans MT, Dekker E, Chien VO, Le T, Endert E, Kager PA, Romijn JA, Sauerwein HP.

. Bao Loc General Hospital, Lamdong Province, Vietnam, Departments of. Clinical Chemistry, Laboratory of Endocrinology and Radiochemistry, Internal Medicine, Infectious Diseases, Tropical Medicine and AIDS, and. Endocrinology and Metabolism, Academic Medical Centre, Amsterdam, The Netherlands, Director of Health Service of Lamdong Province, Vietnam, Department of Endocrinology and Metabolism, Leiden University Medical Centre, Leiden, The Netherlands.

Hypoglycaemia is an important complication in severe malaria, ascribed to an inhibition of gluconeogenesis. However, the only data available suggested that in severe malaria, total glucose production is increased. We measured glucose production and gluconeogenesis after an overnight fast in all seven patients with cerebral malaria (CM) consecutively admitted to Bao Loc General hospital over a 2-year period, and in six healthy sex- and age-matched controls. Glucose production was measured by infusion of [6,6-(2)H(2)]glucose and the contribution of gluconeogenesis by oral ingestion of (2)H(2)O. Compared to controls, plasma glucose concentration was 42% higher in CM patients (p=0.004), and glucose production was doubled (p=0.003). Gluconeogenesis contributed 100% of the total glucose in CM patients but only 58% in controls (p=0.003). The plasma concentrations of the substrates for gluconeogenesis and the glucoregulatory hormones were not different between patients and controls, except for an increase in lactate and cortisol in the patients. Cerebral malaria is associated with increases rather than decreases in plasma glucose, glucose production and gluconeogenesis, and there is no contribution of glycogenolysis to glucose production. Factors other than malaria per se are involved in the pathogenesis of hypoglycaemia associated with CM.

Science 2001 Dec 14;294(5550):2271

INFECTIOUS DISEASES: Bed Nets Prove Their Mettle Against Malaria.

Enserink M.

ATLANTA--At a meeting here last month, researchers presented results from a 2-year study showing that the use of insecticide-impregnated bed nets saves many lives, even in areas with intense malaria transmission year-round. A set of 18 papers about the trial will appear in the American Journal of Tropical Medicine and Hygiene next spring.

Mol Immunol 2001 Dec;38(6):443-455

Plasmodium vivax malaria vaccine development.

Arevalo-Herrera M, Herrera S.

Immunology Institute, Universidad del Valle, Cali, Colombia

Plasmodium vivax represents the most widespread malaria parasite worldwide. Although it does not result in as high a mortality rate as P. falciparum, it inflicts debilitating morbidity and consequent economic impact in endemic communities. In addition, the relapsing behavior of this malaria parasite and the recent resistance to anti-malarials contribute to making its control more difficult. Although the biology of P. vivax is different from that of P. falciparum and the human immune response to this parasite species has been rather poorly studied, significant progress is being made to develop a P. vivax-specific vaccine based on the information and experience gained in the search for a P. falciparum vaccine. We have devoted great effort to antigenically characterize the P. vivax CS protein and to test its immunogenicity using the Aotus monkey model. Together with other groups we are also assessing the immunogenicity and protective efficacy of the asexual blood stage vaccine candidates MSP-1 and DBP in the monkey model, as well as the immunogenicity of Pvs25 and Pvs28 ookinete surface proteins. The transmission-blocking efficacy of the responses induced by these latter antigens is being assessed using Anopheles albimanus mosquitoes. The current status of these vaccine candidates and other antigens currently being studied is described.

Mol Immunol 2001 Dec;38(6):433-442

Peptide-based subunit vaccines against pre-erythrocytic stages of malaria parasites.

Tsuji M, Zavala F.

Department of Medical and Molecular Parasitology, New York University School of Medicine, 341 East 25th Street, 10010, New York, NY, USA

Malaria currently ranks among the most prevalent infections in tropical and sub-tropical areas throughout the world with relatively high morbidity and mortality particularly in young children. The widespread occurrence and the increased incidence of malaria in many countries, caused by drug-resistant parasites (Plasmodium falciparum and P. vivax) and insecticide-resistant vectors (Anopheles mosquitoes), indicate the need to develop new methods of controlling this disease. Experimental vaccination with radiation-attenuated sporozoites can protect animals and humans against the disease, demonstrating the feasibility of developing an effective malaria vaccine. However, vaccines based on radiation-attenuated sporozoites are not feasible for large scale application due to lack of in vitro culture system. Therefore, the development of peptide-based subunit vaccines has been undertaken as an alternative approach. Synthetic peptides containing defined B- and T-cell epitopes of different antigens expressed in sporozoites and/or liver stages have been used as subunit vaccines in experimental animal models. They have been shown to be highly immunogenic and capable of inducing protective immunity mediated by antibodies, as well as CD4+ and CD8+ T-cells.

Vaccine 2001 Dec 12;20(5-6):771-788

Conversion of poorly immunogenic malaria repeat sequences into a highly immunogenic vaccine candidate.

Milich DR, Hughes J, Jones J, Sallberg M, Phillips TR.

Vaccine Research Institute of San Diego (VRISD), 3030 Science Park Road, Suite 100, 92121, San Diego, CA, USA

The recent success of a Plasmodium falciparum malaria vaccine consisting of circumsporozoite protein (CSP) T and B cell epitopes has rekindled interest in the development of a pre-erythrocytic vaccine. In order to optimize immunogenicity, well-characterized CSP-specific neutralizing B cell epitopes and a universal T cell epitope were combined with an efficient and flexible particulate carrier platform, the hepatitis B core antigen (HBcAg), to produce a novel pre-erythrocytic vaccine candidate. The vaccine candidate, V12.PF3.1, is a potent immunogen in mice eliciting unprecedented levels (greater than 10(6) titers) of sporozoite-binding antibodies after only two doses. The anti-sporozoite antibodies are long lasting, represent all IgG isotypes, and antibody production is not genetically restricted. CSP-specific CD4(+) T cells are also primed by V12.PF3.1 immunization in a majority of murine strains. Furthermore, the hybrid HBcAg-CS particles can be produced inexpensively in bacterial expression systems. These and other characteristics suggest that V12.PF3.1 represents an efficient and economical P. falciparum vaccine candidate for use separately or in combination with other formulations.

Vaccine 2001 Dec 12;20(5-6):763-770

Antibodies to Plasmodium vivax transmission-blocking vaccine candidate antigens Pvs25 and Pvs28 do not show synergism.

Hisaeda H, Collins WE, Saul A, Stowers AW.

Malaria Vaccine Development Unit, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 5640 Fisher Lane, 20852, Rockville, MD, USA

Transmission-blocking vaccines against malaria parasites target molecules expressed by sexual stage parasites to elicit antibodies that prevent the infection of the mosquito vector. Pvs25 and Pvs28, expressed on the surface of ookinetes, are potential candidates for such a vaccine and induce antibodies that block the infectivity of Plasmodium vivax in immunized animals. To improve the ability to induce transmission-blocking antibodies, Pvs25 and Pvs28 were produced as a single fusion protein by the yeast Saccharomyces cerevisiae. Mice immunized with a low dose of the chimeric molecule (Pvs25-28) developed higher antibody responses compared with mice immunized with either Pvs25 or Pvs28. In membrane feeding assays, both anti-Pvs25-28 and anti-Pvs25 antisera had similarly potent transmission-blocking activities (and both were much greater than anti-Pvs28). Furthermore, serum from mice simultaneously immunized with both Pvs25 and Pvs28, or serum mixtures of anti-Pvs25 alone and anti-Pvs28 alone did not enhance the efficacy over anti-Pvs25 serum alone, demonstrating that there is no synergism in the ability to block transmission of P. vivax between anti-Pvs25 and anti-Pvs28 antibodies.

Vaccine 2001 Dec 12;20(5-6):744-755

Enhanced activation of rhesus T cells by vectors encoding a triad of costimulatory molecules (B7-1, ICAM-1, LFA-3).

Shankar P, Schlom J, Hodge JW.

Research Scholar's Program at the NIH, Howard Hughes Medical Institute, 20892, Bethesda, MD, USA

Since the rhesus is often used as a "gatekeeper" model for the evaluation of malaria and simian immunodeficiency virus (SIV)/HIV vaccines, the identification of strategies to enhance the activation of rhesus T cells would potentially aid in the generation of more potent vaccines directed against these infectious agents. Several molecules normally found on the surface of professional human APCs are capable of providing the second signals critical for T cell activation: B7-1 (CD80), ICAM-1 (CD54), and LFA-3 (CD58). With the exception of B7, T cell costimulatory molecules in the rhesus have not been identified. We have recently designed and characterized both recombinant vaccinia and recombinant avipox vectors containing the transgenes for a triad of human T cell costimulatory molecules (B7-1, ICAM-1, LFA-3; designated TRICOM). Here, we demonstrate the enhanced activation of rhesus T cells stimulated with rhesus APCs infected with TRICOM vectors in the presence of signal 1. Infection with TRICOM vectors led to significant improvement of APC capabilities in terms of reduction of the amount of signal 1 needed to activate naive T cells, and reduction in the amount of APCs required to activate T cells using a constant amount of signal 1. Antibody blocking studies demonstrated that each of the three costimulatory molecule transgenes contributed to the enhanced proliferation of T cells. TRICOM-enhanced T cell activation was shown to correspond to increases in type 1 cytokines and a reduced level of apoptosis. TRICOM-infected autologous B cells from rhesus immunized with either an SIV vaccine or a malaria vaccine stimulated significantly greater levels of IFN-gamma in response to specific peptide than stimulation with uninfected autologous B cells or B cells infected with wild-type vector. The ability to augment immune responses using poxvirus-based vaccines containing multiple costimulatory molecule transgenes can now be addressed in the rhesus macaque model.

Mol Biochem Parasitol 2001 Dec;118(2):233-245

Determining liver stage parasite burden by real time quantitative PCR as a method for evaluating pre-erythrocytic malaria vaccine efficacy.

Witney AA, Doolan DL, Anthony RM, Weiss WR, Hoffman SL, Carucci DJ.

Malaria Program, Naval Medical Research Center, 503 Robert Grant Avenue, Room 3A4O 20910-7500, Silver Spring, MD, USA

The detection and quantitation of blood stage parasitaemia is typically used as a surrogate endpoint for estimating the efficacy of vaccines targeted against the hepatic stage, as well as the erythrocytic stage, of the parasite. However, this does not provide an adequate means of evaluating the efficacy of vaccines, which may be only partially effective at the liver-stage. This is a particular concern for effective evaluation of immune enhancement strategies for candidate pre-erythrocytic stage vaccines. Here, we have developed and validated a method for detecting and quantitating liver stage parasites, using the TaqMan(R) fluorescent real-time quantitative PCR system (PE Applied Biosystems). This method uses TaqMan(R) primers designed to the Plasmodium yoelii 18S rRNA gene and rodent GAPDH to amplify products from infected mouse liver cDNA. The technique is highly reproducible as demonstrated with plasmid controls and capable of efficiently quantitating liver-stage parasite burden following a range of sporozoite challenge doses in strains of mice, which differ in their susceptibility to sporozoite infection. We have further demonstrated the capacity of this technique to evaluate the efficacy of a range of pre-erythrocytic stage vaccines. Our data establish this quantitative real-time PCR assay to be a fast and reproducible way of accurately assessing liver stage parasite burden and vaccine efficacy in rodent malaria models.

Mol Biochem Parasitol 2001 Dec;118(2):201-210

Profiling the malaria genome: a gene survey of three species of malaria parasite with comparison to other apicomplexan species.

Carlton JM, Muller R, Yowell CA, Fluegge MR, Sturrock KA, Pritt JR, Vargas-Serrato E, Galinski MR, Barnwell JW, Mulder N, Kanapin A, Cawley SE, Hide WA, Dame JB.

Computational Biology Branch, National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, 20892, Bethesda, MD, USA

We have undertaken the first comparative pilot gene discovery analysis of approximately 25000 random genomic and expressed sequence tags (ESTs) from three species of Plasmodium, the infectious agent that causes malaria. A total of 5482 genome survey sequences (GSSs) and 5582 ESTs were generated from mung bean nuclease (MBN) and cDNA libraries, respectively, of the ANKA line of the rodent malaria parasite Plasmodium berghei, and 10874 GSSs generated from MBN libraries of the Salvador I and Belem lines of Plasmodium vivax, the most geographically wide-spread human malaria pathogen. These tags, together with 2438 Plasmodium falciparum sequences present in GenBank, were used to perform first-pass assembly and transcript reconstruction, and non-redundant consensus sequence datasets created. The datasets were compared against public protein databases and more than 1000 putative new Plasmodium proteins identified based on sequence similarity. Homologs of previously characterized Plasmodium genes were also identified, increasing the number of P. vivax and P. berghei sequences in public databases at least 10-fold. Comparative studies with other species of Apicomplexa identified interesting homologs of possible therapeutic or diagnostic value. A gene prediction program, Phat, was used to predict probable open reading frames for proteins in all three datasets. Predicted and non-redundant BLAST-matched proteins were submitted to InterPro, an integrated database of protein domains, signatures and families, for functional classification. Thus a partial predicted proteome was created for each species. This first comparative analysis of Plasmodium protein coding sequences represents a valuable resource for further studies on the biology of this important pathogen.

Mol Biochem Parasitol 2001 Dec;118(2):167-174

Phat-a gene finding program for Plasmodium falciparum.

Cawley SE, Wirth AI, Speed TP.

Department of Statistics, U.C. Berkeley, 94720, Berkeley, CA, USA

We describe and assess the performance of the gene finding program pretty handy annotation tool (Phat) on sequence from the malaria parasite Plasmodium falciparum. Phat is based on a generalized hidden Markov model (GHMM) similar to the models used in GENSCAN, Genie and HMMgene. In a test set of 44 confirmed gene structures Phat achieves nucleotide-level sensitivity and specificity of greater than 95%, performing as well as the other P. falciparum gene finding programs Hexamer and GlimmerM. Phat is particularly useful for P. falciparum and other eukaryotes for which there are few gene finding programs available as it is distributed with code for retraining it on new organisms. Moreover, the full source code is freely available under the GNU General Public License, allowing for users to further develop and customize it.

Mol Biochem Parasitol 2001 Dec;118(2):147-154

Comparative genomics in Plasmodium: a tool for the identification of genes and functional analysis.

Thompson J, Janse CJ, Waters AP.

Department of Parasitology, Leiden University Medical Centre, Postbus 9600, 2300 RC, Leiden, The Netherlands

Comparative genomics allows inferences to be drawn about the coding potential of related genomes, and the evolutionary forces that have influenced genome organisation. Early comparisons have indicated that there is significant synteny (conserved physical association of genes) between the human parasite Plasmodium falciparum and the malaria parasites of rodents, such as Plasmodium berghei. The various Plasmodium genome initiatives have now provided the opportunity to perform comparative genomics within different species of malaria parasites in more detail, allowing the discovery of orthologues and paralogues of less well conserved genes and addressing questions of conservation, evolution and structure of multi-gene families. A remarkable level of conservation is being revealed, illustrated here by a comparison of members of one of the first conserved gene families to emerge from the sequencing initiatives, the P48/45 gene family. We have identified two additional members in this family, Pf36p and Pfs38, and shown that all members are conserved in P. falciparum and P. berghei, opening the way for functional analyses in the latter more accessible rodent malaria model. In addition, it has been shown that direct comparison of a 13.6 kb contig of a chromosome of P. berghei and the orthologous region in P. falciparum reveals an unexpected high level of conservation of gene organisation and complexity. The results of this comparison highlight the value of a comparative approach to elucidate the gene content of complex loci and improve its annotation

Mol Biochem Parasitol 2001 Dec;118(2):139-145

Bioinformatics and the malaria genome: facilitating access and exploitation of sequence information.

Coppel RL.

Department of Microbiology and the Victorian Bioinformatics Consortium, P.O. Box 53, Monash University, Victoria 3800, Melbourne, Australia

The torrent of sequence information unleashed by the various genome sequencing projects, including that of Plasmodium falciparum, will lead to an unprecedented increase in the data available for research purposes. The scientific community is struggling to develop ways to assimilate this information and ensure that it is fully analysed in a way that enables rapid development of new therapeutic and diagnostic advances. This is particularly so for the field of tropical medicine where many of the scientists have had limited training in the area of Bioinformatics and may be further hampered by poor access to the sequence data. A number of collections of malaria genome sequence are available, each with their own advantages and disadvantages, however further improvements in these information resources are needed. In particular, there would be great benefit in integrating genomic sequence and functional genomics results with the large amount of pre-existing knowledge related to parasite biology and immunological interactions with the host. Attempts to achieve this include the PlasmoDB database, and the lessons learned in this effort could be of great utility to other organism-specific databases.

Mol Biochem Parasitol 2001 Dec;118(2):133-138

A status report on the sequencing and annotation of the P. falciparum genome.

Gardner MJ.

The Institute for Genomic Research, 9712 Medical Center Drive, 20850, Rockville, MD, USA

Almost 5 years ago, an international consortium of sequencing centers and funding agencies was formed to sequence the genome of the human malaria parasite Plasmodium falciparum. A novel chromosome by chromosome shotgun strategy was devised to sequence this very AT-rich genome. Two of the 14 chromosomes have been completed and the remaining chromosomes are in the final stages of gap closure. The consortium recently developed plans for the annotation and analysis of the complete genome sequence and its publication in 2002.

PMID: 11738703 [PubMed - as supplied by publisher]

Bioorg Med Chem 2002 Jan;10(1):227-232

New chemical and biological aspects of artemisinin-Derived trioxane dimers.

Posner GH, Northrop J, Paik IH, Borstnik K, Dolan P, Kensler TW, Xie S, Shapiro TA.

Department of Chemistry, School of Arts and Sciences, The Johns Hopkins University, 21218, Baltimore, MD, USA

Joining two 10-deoxoartemisinin trioxane units via a p-diacetylbenzene linker produces new C-10 non-acetal dimers and. 1H NMR spectroscopy allows unambiguous assignment of the stereochemistry at C-10 in these dimers. Successful replacement of both carbonyl oxygen atoms in these diketone dimers by fluorine atoms produces new tetrafluorinated dimers and. Each dimer was evaluated in vitro for antimalarial, antiproliferative, and antitumor activities; ketone dimers and, more than fluorinated dimers and, are promising for chemotherapy of both malaria and cancer.

BMC Microbiol 2001;1(1):31

A novel tetratricopeptide repeat (TPR) containing PP5 serine/threonine protein phosphatase in the malaria parasite, Plasmodium falciparum.

Dobson S, Kar B, Kumar R, Adams B, Barik S.

Department of Biochemistry and Molecular Biology, University of South Alabama, College of Medicine, 307 University Blvd, Mobile, Alabama, 36688-0002, USA. [email protected]

BACKGROUND: The malarial parasite, Plasmodium falciparum (Pf), is responsible for nearly 2 million deaths worldwide. However, the mechanisms of cellular signaling in the parasite remain largely unknown. Recent discovery of a few protein kinases and phosphatases point to a thriving reversible phosphorylation system in the parasite, although their function and regulation need to be determined. RESULTS: We provide biochemical and sequence evidence for a protein serine/threonine phosphatase type PP5 in Plasmodium falciparum, and named it PfPP5. The 594-amino acid polypeptide was encoded by a 1785 nucleotide long intronless gene in the parasite. The recombinant protein, expressed in bacteria, was indistinguishable from native PfPP5. Sequencing comparison indicated that the extra-long N-terminus of PfPP5 outside the catalytic core contained four tetratricopeptide repeats (TPRs), compared to three such repeats in other PP5 phosphatases. The PfPP5 N-terminus was required for stimulation of the phosphatase activity by polyunsaturated fatty acids. Co-immunoprecipitation demonstrated an interaction between native PfPP5 and Pf heat shock protein 90 (hsp90). PfPP5 was expressed in all the asexual erythrocytic stages of the parasite, and was moderately sensitive to okadaic acid. CONCLUSIONS: This is the first example of a TPR-domain protein in the Apicomplexa family of parasites. Since TPR domains play important roles in protein-protein interaction, especially relevant to the regulation of PP5 phosphatases, PfPP5 is destined to have a definitive role in parasitic growth and signaling pathways. This is exemplified by the interaction between PfPP5 and the cognate chaperone hsp90.

Trop Med Int Health 2001 Dec;6(12):1016-1022

Phenothiazines: potential alternatives for the management of antibiotic resistant infections of tuberculosis and malaria in developing countries.

Amaral L, Viveiros M, Kristiansen JE.

Unit of Mycobacteriology, Institute of Hygiene and Tropical Medicine, Universidade Nova de Lisboa, Lisboa, Portugal, Department of Clinical Microbiology, Sonderborg Sygehus, South Danish University, Sonderborg, Denmark.

The in vitro and in vivo activity of phenothiazines against antibiotic susceptible and antibiotic resistant Mycobacterium tuberculosis and malaria-causing Plasmodia is reviewed. Given the facts that pulmonary tuberculosis and malaria are the major causes of death in developing countries, that both of these infections continue to escalate in their resistance to antibiotics, that the cost for the management of these infections is beyond that afforded by most developing nations, and lastly, that new and effective agents are not forthcoming from the pharmaceutical industry, the scientific rationale for the potential use of select phenothiazines for the management of these infections is presented.

Trop Med Int Health 2001 Dec;6(12):983-985

Two cases of autochthonous Plasmodium falciparum malaria in Germany with evidence for local transmission by indigenous Anopheles plumbeus.

Kruger A, Rech A, Su XZ, Tannich E.

Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany, Klinikum Duisburg, Duisburg, Germany, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD, USA.

Autochthonous Plasmodium falciparum malaria (PFM) in Central Europe has been reported repeatedly, transmission of the parasite being attributed to blood transfusion or imported P. falciparum-infected vectors. We report two cases of PFM in German children without travel history to malaria-endemic areas. Both infections occurred during a stay in a hospital where a child from Angola with chronic P. falciparum infection was hospitalized at the time. Known routes of transmission, such as imported mosquitoes or blood transfusion, were very unlikely or could be excluded, whereas evidence was obtained for transmission by the indigenous mosquito species Anopheles plumbeus.

Clin Exp Immunol 2001 Dec;126(3):503-510

Changes in cytokine production associated with acquired immunity to Plasmodium falciparum malaria.

Rhee MS, Akanmori BD, Waterfall M, Riley EM.

Institute of Cell, Animal and Population Biology, Division of Biological Sciences, University of Edinburgh, Edinburgh, UK, Immunology Unit, Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana and Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK.

Individuals living in malaria-endemic areas eventually develop clinical immunity to Plasmodium falciparum. That is, they are able to limit blood parasite densities to extremely low levels and fail to show symptoms of infection. As the clinical symptoms of malaria infection are mediated in part by pro-inflammatory cytokines it is not clear whether the acquisition of clinical immunity is due simply to the development of antiparasitic mechanisms or whether the ability to regulate inflammatory cytokine production is also involved. We hypothesize that there is a correlation between risk of developing clinical malaria and the tendency to produce high levels of proinflammatory cytokines in response to malaria infection. In order to test this hypothesis, we have compared the ability of peripheral blood mononuclear cells from malaria-naive and malaria-exposed adult donors to proliferate and to secrete IFN-gamma in response to P. falciparum schizont extract (PfSE). In order to determine how PfSE-induced IFN-gamma production is regulated, we have also measured production of IL-12p40 and IL-10 from PfSE-stimulated PBMC and investigated the role of neutralizing antibody to IL-12 in modulating IFN-gamma production. We find that cells from naive donors produce moderate amounts of IFN-gamma in response to PfSE and that IFN-gamma production is strongly IL-12 dependent. Cells from malaria-exposed donors living in an area of low malaria endemicity produce much higher levels of IFN-gamma and this response is also at least partially IL-12 dependent. In complete contrast, cells from donors living in an area of very high endemicity produce minimal amounts of IFN-gamma. No significant differences were detected between the groups in IL-10 production, suggesting that this cytokine does not play a major role in regulating malaria-induced IFN-gamma production. The data from this study thus strongly support the hypothesis that down-regulation of inflammatory cytokine production may be a component of acquired clinical immunity to malaria but the mechanism by which this is achieved remains to be elucidated.

Br J Clin Pharmacol 2001 Dec;52(6):663-670

Population pharmacokinetics of the new antimalarial agent tafenoquine in Thai soldiers.

Edstein MD, Kocisko DA, Brewer TG, Walsh DS, Eamsila C, Charles BG.

Department of Pharmacology, Australian Army Malaria Institute, Enoggera, QLD, Australia, US Army and Thai Medical Components, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand and The Australian Centre for Paediatric Pharmacokinetics, School of Pharmacy, The University of Queensland, St Lucia, QLD, Australia.

AIMS: To describe the population pharmacokinetics of tafenoquine in healthy volunteers after receiving tafenoquine for malaria prophylaxis. METHODS: The population consisted of 135 male Thai soldiers (mean age 28.9 years; weight 60.3 kg). All soldiers were presumptively treated with artesunate for 3 days plus doxycycline for 7 days to remove any pre-existing malaria infections. After the treatment regime, 104 soldiers (drug group) received a loading dose of 400 mg tafenoquine base daily for 3 days followed by 400 mg tafenoquine monthly for 5 consecutive months. In the placebo group, 31 soldiers were infected with malaria during the study period. They were re-treated with artesunate for 3 days plus doxycycline for 7 days followed by a loading dose of 400 mg tafenoquine daily for 3 days and then 400 mg tafenoquine weekly for prophylaxis. Blood samples were randomly collected from each soldier on monthly and weekly prophylaxis. Plasma tafenoquine concentrations were measured by h.p.l.c. Population pharmacokinetic modelling was performed using NONMEM. RESULTS: A one-compartment model was found best to describe the pharmacokinetics of tafenoquine after oral administration. Age and weight influenced volume of distribution (V/F), and subjects who contracted malaria had higher clearance (CL/F), but none of these factors was considered to have sufficient impact to warrant change in dosing. The population estimates of the first-order absorption rate constant (Ka), CL/F and V/F were 0.694 h-1, 3.20 l h-1 and 1820 l, respectively. The intersubject variability in these parameters (coefficient of variation, CV%) was 61.2%, 25.3% and 14.8%, respectively. The absorption and elimination half-lives were 1.0 h and 16.4 days, respectively. The residual (unexplained) variability was 17.9%. CONCLUSIONS: The population pharmacokinetics of orally administered tafenoquine have been determined in Thai soldiers under field conditions. This information, together with its known potent antimalarial activity, portends well for the application of tafenoquine as a useful prophylactic drug or for short-term radical treatment of vivax malaria.

Br J Clin Pharmacol 2001 Dec;52(6):655-661

A comparison of oral artesunate and artemether antimalarial bioactivities in acute falciparum malaria.

Suputtamongkol Y, Newton PN, Angus B, Teja-Isavadharm P, Keeratithakul D, Rasameesoraj M, Pukrittayakamee S, White NJ.

Department of Medicine, Siriraj Hospital, Bangkok, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand, Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, John Radcliffe Hospital, Headington, Oxford, United Kingdom and Department of Immunology and Medicine, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.

AIMS: Artesunate and artemether are the two most widely used artemisinin derivatives in the treatment of uncomplicated Plasmodium falciparum malaria, but there is little information on their comparative pharmacokinetics. The aim of this study was to examine the relative oral antimalarial bioavailability and pharmacokinetics of the two derivatives. METHODS: The pharmacokinetic properties of oral artesunate and artemether (4 mg kg-1) were compared in a randomized cross-over study of 14 adult patients in western Thailand with acute uncomplicated Plasmodium falciparum malaria. Antimalarial activity was compared using a previously validated, sensitive bioassay. RESULTS: Despite a 29% lower molar dose, oral artesunate administration resulted in significantly larger mean area under the plasma antimalarial activity time curve and median maximum plasma antimalarial activity than after oral artemether (P </= 0.02). The mean (95% CI) oral antimalarial bioavailability of artemether, relative to oral artesunate, corrected for molar dose was 58 (40-76)%. The mean (95% CI) relative antimalarial bioavailability of artemether was lower on the first day of treatment, 31 (17-100)%, compared to the second day, 72 (44-118)% (P = 0.018). In vivo parasite clearance and time above the in vitro IC90 were similar for the two drugs, despite considerable differences in Cmax and AUC. CONCLUSIONS: The oral antimalarial bioavailability following artemether was significantly lower than that after artesunate. Artemether oral antimalarial bioavailability is reduced in acute malaria.

EHP is sponsored by the Office of Health, Infectious Diseases and Nutrition, 
Bureau for Global Health,  of the U.S. Agency for International Development

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Last modified April 02, 2002