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EHP Library Malaria Bulletin No. 20:  August 24-September 6, 2001

Social Sciences and Malaria

Trends Parasitol 2001 Sep;17(9):438-445
The development of Malaria Early Warning Systems for Africa.

Thomson MC, Connor SJ.

MALSAT Research Group, Liverpool School of Tropical Medicine, Pembroke place, L35QA, Liverpool, UK

Current efforts to predict malaria epidemics focus on the role weather anomalies can play in epidemic prediction. Alongside weather monitoring and seasonal climate forecasts, epidemiological, social and environmental factors can also play a role in predicting the timing and severity of malaria epidemics. Such factors can be incorporated into a framework for malaria early warning.

J Trop Pediatr 2001 Aug;47(4):230-238

Treatment of childhood fevers and other illnesses in three rural Nigerian communities.

Salako LA, Brieger WR, Afolabi BM, Umeh RE, Agomo PU, Asa S, Adeneye AK, Nwankwo BO, Akinlade CO.

Nigerian Institute of Medical Research and Training, Yaba, Lagos.

The seeking of healthcare for childhood illnesses was studied in three rural Nigerian communities of approximately 10,000 population each. The aim was to provide a baseline understanding of illness behaviour on which to build a programme for the promotion of prepackaged chloroquine and cotrimoxazole for early and appropriate treatment of childhood fevers at the community level. A total of 3117 parents of children who had been ill during the 2 weeks prior to interview responded to questions about the nature of the illness and the actions taken. Local illness terms were elicited, and the most prevalent recent illness and the actions taken. Local illness terms were elicited, and the most prevalent recent illnesses were 'hot body' (43.9 per cent), malaria, known as iba (17.7 per cent), and cough (7.4 per cent). The most common form of first-line treatment was drugs from a patent medicine vendor or drug hawker (49.6 per cent). Only 3.6 per cent did nothing. Most who sought care (77.5 per cent) were satisfied with their first line of action, and did not seek further treatment. The average cost of an illness episode was less than US$2.00 with a median of US$1.00. Specifically, chloroquine tablets cost an average of US 29 cents per course. Analysis found a configuration of signs and symptoms associated with chloroquine use, to include perception of the child having malaria, high temperature and loss of appetite. The configuration positively associated with antibiotic use consisted of cough and difficult breathing. The ability of the child's care-givers, both parental and professional, to make these distinctions in medication use will provide the foundation for health education in the promotion of appropriate early treatment of childhood fevers in the three study sites.


Proc Natl Acad Sci U S A 2001 Sep 4
Full-text at: http://www.pnas.org

Immune mimicry in malaria: Plasmodium falciparum secretes a functional histamine-releasing factor homolog in vitro and in vivo.

MacDonald SM, Bhisutthibhan J, Shapiro TA, Rogerson SJ, Taylor TE, Tembo M, Langdon JM, Meshnick SR.

Divisions of Allergy and Clinical Immunology and Clinical Pharmacology, Department of Medicine, The Johns Hopkins Medical Institutions, Baltimore, MD 21224; Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI 48104; Malaria Research Project and Wellcome Trust Research Laboratories, Queen Elizabeth Central Hospital, Blantyre, Malawi; Department of Medicine, University of Melbourne, Parkville 3050, Australia; and Department of Internal Medicine, College of Osteopathic Medicine, Michigan State University, East Lansing, MI 48824.

The Plasmodium falciparum translationally controlled tumor protein (TCTP) is a homolog of the mammalian histamine-releasing factor (HRF), which causes histamine release from human basophils and IL-8 secretion from eosinophils. Histamine, IL-8, and eosinophils have been reported to be elevated in patients with malaria. This study was undertaken to determine whether malarial TCTP is found in the plasma of malaria-infected patients and to determine whether it has HRF biologic activity. Malarial TCTP was found in lightly infected human volunteers and in heavily infected Malawian children, but not in uninfected patients. Recombinant malarial TCTP, like HRF, stimulated histamine release from basophils and IL-8 secretion from eosinophils in vitro. Whereas malarial TCTP was less active than HRF, the concentrations that were effective in vitro could be achievable in vivo. These data suggest that malarial TCTP, present in human plasma during a malarial illness, may affect host immune responses in vivo.

Proc Natl Acad Sci U S A 2001 Sep 4
Full-text at: http://www.pnas.org
Identification of a malaria new susceptibility locus (Char4) in recombinant congenic strains of mice.

Fortin A, Cardon LR, Tam M, Skamene E, Stevenson MM, Gros P.

Department of Biochemistry, McGill University, Montreal, QC, Canada H3G 1Y6; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, United Kingdom; and Research Institute of the McGill University Health Centre, Montreal General Hospital, 1650 Cedar Avenue, Montreal, QC, Canada H3G 1A4.

The genetic component of susceptibility to malaria is complex, both in humans and in the mouse model of infection. Two murine loci on chromosomes 8 (Pchr/Char2) and 9 (Char1) have previously been mapped in F(2) crosses, and play an important role in regulating blood parasitemia and survival to infection with Plasmodium chabaudi. These loci explain only part of the interstrain phenotypic variance, and their penetrance and expressivity vary in different inbred strains. Novel loci regulating response to P. chabaudi infection were investigated by using an alternative strategy based on a newly derived set of AcB/BcA recombinant congenic strains bred from malaria-susceptible A/J (A) and resistant C57BL/6J (B6). One of the AcB strains, AcB55, is shown to be highly resistant to infection despite 83% susceptible A genomic composition, including susceptibility alleles at Char1 and Pchr/Char2. Early onset of parasite clearance in AcB55 is associated with lower peak parasitemia and absence of mortality. Linkage analysis in an informative (AcB55 x A)F(2) population, using peak parasitemia as a quantitative trait, located a new B6-derived resistance locus on chromosome 3 (lod score = 6.57) that we designate Char4. A second, suggestive linkage on chromosome 10 (lod score = 2.53) shows additive effect with Char4 on peak parasitemia. Char4 maps to a small congenic B6 fragment in AcB55 that should facilitate the search for candidate genes. Our findings provide an entry point for parallel association studies in humans between the syntenic 4q21-4q25 region and susceptibility to disease in endemic areas of malaria.

Vaccine 2001 Sep 14;19(32):4595-4602
A prime-boost immunisation regimen using DNA followed by recombinant modified vaccinia virus Ankara induces strong cellular immune responses against the Plasmodium falciparum TRAP antigen in chimpanzees.

Schneider J, Langermans JA, Gilbert SC, Blanchard TJ, Twigg S, Naitza S, Hannan CM, Aidoo M, Crisanti A, Robson KJ, Smith GL, Hill AV, Thomas AW.

Molecular Immunology Group, Institute of Molecular Medicine, Nuffield Department of Medicine, University of Oxford, John Radcliffe Hospital, OX3 9DU, Oxford, UK

Two chimpanzees were vaccinated intramuscularly against malaria using plasmid DNA expressing the pre-erythrocytic antigens thrombospondin related adhesion protein (PfTRAP) and liver stage specific antigen-1 (PfLSA-1) of Plasmodium falciparum together with GM-CSF protein. A recombinant modified vaccinia virus Ankara (MVA) expressing PfTRAP was injected intramuscularly 6 weeks later to boost the immune response. This sequence of antigen delivery induced a specific and long-lasting T cell and antibody response to PfTRAP as detected by ELISPOT assay and ELISA. Antibody responses were detected after four DNA injections, and were boosted by injection of recombinant MVA expressing PfTRAP. Interferon-gamma secreting antigen-specific T cells were detected in both animals, but only after boosting with recombinant MVA. By screening a panel of PfTRAP-derived peptides, an epitope was identified that was recognized by cytotoxic T lymphocytes in one of the chimpanzees studied. T cells specific for this epitope were present in PBMCs and liver-infiltrating lymphocytes at a frequency of between 1 in 200 and 1 in 500. The high immunogenicity of this prime-boost regimen in chimpanzees supports further assessment of this delivery strategy for the induction of protection against P. falciparum malaria in humans.

J Parasitol 2001 Aug;87(4):928-930
Development of a method for the in vitro production of Plasmodium vivax ookinetes.

Suwanabun N, Sattabongkot J, Tsuboi T, Torii M, Maneechai N, Rachapaew N, Yim-amnuaychok N, Punkitchar V, Coleman RE.

Department of Entomology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.

We developed a method for the in vitro production of mature Plasmodium vivax ookinetes. Gametocytemic blood was collected from 98 P. vivax-infected patients reporting to malaria clinics in Maesod and Maekasa Districts, Tak Province, Thailand. Briefly, gametogenesis was induced using xanthurenic acid and parasites were separated by density gradient centrifugation and then cultured in RPMI-1640, pH 7.8-8.2. At the same time that blood was collected, 200 Anopheles dirus mosquitoes were allowed to feed on each patient. Mosquito midguts were removed 2-36 hr postfeeding, and gut contents were smeared onto glass slides, as were cultured samples from varying time points. Slides were stained with Giemsa, and the in vitro and mosquito development of ookinetes compared. Mature ookinetes were produced in 48.0% (47/98) of in vitro cultures, with a total yield ranging from 10 to 248,500 (mean = 15,523, median = 600) ookinetes produced per 5 ml blood. The temporal development and the morphology of the P. vivax ookinetes produced in vitro was similar to that observed in the A. dirus mosquitoes. The method that we describe is simple, can be used at remote sites without sophisticated equipment, and yields high numbers of clean ookinetes. This method of producing mature P. vivax ookinetes will be a useful tool for studies on ookinetes in P. vivax endemic regions.

J Parasitol 2001 Aug;87(4):912-915
Contemporaneous and successive mixed Plasmodium falciparum and Plasmodium vivax infections are associated with Ascaris lumbricoides: an immunomodulating effect?

Nacher M, Singhasivanon P, Gay F, Silachomroon U, Phumratanaprapin W, Looareesuwan S.

Cellulaire et Moleculaire des Infections Parasitaires, Faculte de medecine Pitie-Salpetriere, Paris, France.

Following an investigation suggesting a protective role for Ascaris against cerebral malaria, possibly through immunomodulation, we examined whether Ascaris had any impact on mixed Plasmodium falciparum and Plasmodium vivax infections. We studied a cross section of 928 patient files between 1991 and 1999. Forty patients had contemporaneous mixed infections and 40 patients had P. falciparum infections, followed by P. vivax infections. There was a significant association between Ascaris infection and risk of having both contemporaneous or successive mixed P. falciparum and P. vivax infections (adjusted odds ratios respectively 6 [2-18] P = 0.001 and 3.6 [1.2-11.1] P = 0.02). There was a positive linear trend between the burden of Ascaris and the risk of mixed infections P < 0.0001. These results suggested the possibility that pre-existing Ascaris infection may increase tolerance of the host to different Plasmodium spp., thus facilitating their coexistence.

Saudi Med J 2000 Mar;21(3):257-265
Ketotifen in treatment of uncomplicated falciparum malaria.

Ibrahim AM, Elhag ER, Mustafa SE.

Department of Biochemistry, Faculty of Medicine, University of Khartoum, PO Box 102, Khartoum, Sudan; Email: [email protected]

OBJECTIVE: The present in vivo study evaluates the potential use of ketotifen, a tricyclic antihistaminic drug, in treatment of Sudanese patients with uncomplicated Plasmodium falciparum malaria (19-38 years). METHODS: Four groups of patients (each has 15) were randomly selected and treated by chloroquine (25mg/kg wt) in comparison with regimen combinations of ketotifen (0.13mg/kg body wt) with chloroquine, ketotifen with Fansidar (33.3mg/kg body wt) and ketotifen with both chloroquine and Fansidar. RESULTS: Prior to treatment all patients had a parasite density that varied from 1x103-3.46x104/mL blood. On day 2, the highest level of parasitaemia was recorded in patients treated with chloroquine only. Other patients had a significantly lower parasitaemia (P<0.05) with an average range of 111-243 parasites/300 leucocytes. On day 3 no parasites were detected in groups treated by ketotifen and Fansidar or by ketotifen in combination with Fansidar and chloroquine. The mean time of parasite clearance was minimum (<32 h) amongst patients that had choloroquine administered with ketotifen alone or with both Fansidar and ketotifen. The cumulative percentage of cases with recrudescence was >39% in groups that had the chloroquine regimen alone or the combination of chloroquine with ketotifen. A single case of recrudescence was also diagnosed on day 28 in the group treated with ketotifen plus fansidar but no recrudescence occurred in the group treated with the combination of the three drugs. CONCLUSION: This study indicates the possible role of ketotifen in treatment for falciparum malaria particularly when administered in combination with chloroquine and fansidar.

Am J Epidemiol 2001 Sep 1;154(5):459-465
Effects of Malaria during Pregnancy on Infant Mortality in an Area of Low Malaria Transmission.

Luxemburger C, McGready R, Kham A, Morison L, Cho T, Chongsuphajaisiddhi T, White NJ, Nosten F.

Shoklo Malaria Research Unit, Mae Sod, Thailand. Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, John Radcliffe Hospital, Oxford, United Kingdom. London School of Hygiene and Tropical Medicine, London, United Kingdom.

Malaria during pregnancy reduces birth weight, and low birth weight is a major determinant of infant mortality. The authors estimated the impact of malaria during pregnancy on infant mortality in a Karen population living in Thailand. Between 1993 and 1996, a cohort of 1,495 mothers and their infants was followed weekly from admission of the mother to antenatal clinics until the first birthday of the infant. Both falciparum malaria and vivax malaria during pregnancy were associated with low birth weight but did not shorten gestation. Febrile illness in the week before delivery was associated with premature birth. Preterm and full-term low birth weight and fever in the week before delivery were associated with neonatal mortality. Maternal fevers close to term were also associated with the deaths of infants aged between 1 and 3 months, whereas no risk factors could be identified for deaths that occurred later in infancy. Thus, malaria during pregnancy increased neonatal mortality by lowering birth weight, whereas fever in the week before birth had a further independent effect in addition to inducing premature birth. The prevention of malaria in pregnancy and, thus, of malaria-attributable low birth weight should increase the survival of young babies.

 BMC Infect Dis 2001;1(1):10
An assessment of the usefulness of a rapid immuno-chromatographic test, "Determinetrade mark malaria pf" in evaluation of intervention measures in forest villages of central India.

Singh N, Shukla M.

Malaria Research Centre (Field Station) Medical College Building, Jabalpur (MP), India. Emasil: [email protected]

BACKGROUND: Plasmodium falciparum malaria, is a major health problem in forested tribal belt of central India. Rapid and accurate methods are needed for the diagnosis of P. falciparum. We performed a blinded evaluation of the recently introduced Determinetrade mark malaria pf test (Abbott, Laboratories, Japan) compared with microscopy and splenomegaly in children in epidemic prone areas of district Mandla to assess the impact of intervention measures. METHODS: Children aged 2-10 yrs with and without fever were examined for spleen enlargement by medical specialist by establishing a mobile field clinic. From these children thick blood smears were prepared from finger prick and read by a technician. Simultaneously, rapid tests were performed by a field lab attendant. The figures for specificity, sensitivity and predictive values were calculated using microscopy as gold standard. RESULTS: In all 349 children were examined. The sensitivity and specificity for Determine rapid diagnostic test were 91 and 80% respectively. The positive predictive values (PPV), negative predictive values (NPV) and accuracy of the test were respectively 79, 91 and 85%. On the contrary, the sensitivity and specificity of spleen in detecting malaria infection were 57 and 74 % respectively with PPV of 73%, NPV 59 % and an accuracy of 65%. CONCLUSIONS: Determinetrade mark malaria rapid diagnostic test is easier and quicker to perform and has other advantages over microscopy in not requiring prior training of personnel or quality control. Thus, highlighting the usefulness of a rapid antigen test in assessing prevailing malaria situation in remote areas.

Trends Parasitol 2001 Sep;17(9):419-425
New World monkey efficacy trials for malaria vaccine development: critical path or detour?

Gray Heppner D, Cummings JF, Ockenhouse C, Kester KE, Lyon JA, Gordon DM.

Malaria Vaccine Program, Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Silver 20910, Spring, MD, USA

Neither GMP malaria antigens nor GMP vaccines have been compared for efficacy in monkeys and humans. It is too risky to base categorical (go/no go) development decisions on results obtained using partially characterized (non-GMP) antigens, adjuvants that are too toxic for human use or unvalidated primate models. Such practices will lead to serious errors (e.g. failure to identify and stop flawed efforts, rejection of effective vaccine strategies) and unjustifiable delays. Successful malaria vaccine development will emphasize definitive field trials in populations at risk of malaria to define and improve vaccine efficacy.

Trends Parasitol 2001 Sep;17(9):415-419
Are trials in New World monkeys on the critical path for blood-stage malaria vaccine development?

Stowers AW, Miller LH.

Malaria Vaccine Development Unit, Laboratory of Parasitic Diseases, National Institute of Allergy and Infections Diseases, National Institutes of Health, 20852, Rockville, MD, USA

The development of malaria blood-stage vaccines is gathering momentum: there are several new funding initiatives, one multiantigen formulation is currently being tested and at least one other blood-stage vaccine is expected to begin trials in 2001. However, there is no consensus over the best way to select which form of an antigen to take into clinical testing. There is thus a danger that less-effective vaccines might be tested in the field in the order of their availability, rather than merit. Here, we argue that first proving efficacy in the New World monkey challenge model would accelerate development.

Clin Infect Dis 2001 Oct 1;33(7):1015-1021
Atovaquone-Proguanil versus Mefloquine for Malaria Prophylaxis in Nonimmune Travelers: Results from a Randomized, Double-Blind Study.

Overbosch D, Schilthuis H, Bienzle U, Behrens RH, Kain KC, Clarke PD, Toovey S, Knobloch J, Nothdurft HD, Shaw D, Roskell NS, Chulay JD.

Harbor Hospital and Institute of Tropical Medicine, Rotterdam, The Netherlands.

Concerns about the tolerability of mefloquine highlight the need for new drugs to prevent malaria. Atovaquone-proguanil (Malarone; GlaxoSmithKline) was safe and effective for prevention of falciparum malaria in lifelong residents of malaria-endemic countries, but experience in nonimmune people is limited. In a randomized, double-blind study, nonimmune travelers received malaria prophylaxis with atovaquone-proguanil (493 subjects) or mefloquine (483 subjects). Information about adverse events (AEs) and potential episodes of malaria was obtained 7, 28, and 60 days after travel. AEs were reported by an equivalent proportion of subjects who had received atovaquone-proguanil or mefloquine (71.4% versus 67.3%; difference, 4.1%; 95% confidence interval, -1.71 to 9.9). Subjects who received atovaquone-proguanil had fewer treatment-related neuropsychiatric AEs (14% versus 29%; P=.001), fewer AEs of moderate or severe intensity (10% versus 19%; P=.001), and fewer AEs that caused prophylaxis to be discontinued (1.2% versus 5.0%; P=.001), compared with subjects who received melfoquine. No confirmed diagnoses of malaria occurred in either group. Atovaquone-proguanil was better tolerated than was mefloquine, and it was similarly effective for malaria prophylaxis in nonimmune travelers.

Nature 2001 Aug 30;412(6850):875-876
MalariaCooperative silencing elements in var genes.

Deitsch KW, Calderwood MS, Wellems TE.

Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892-0425, USA.

Each Plasmodium falciparum malaria parasite carries about 50 var genes from a diverse family that encode variable adhesion proteins on the infected red blood cells of the host, but individual parasites single out just one var gene for expression and silence all the others. Here we show that this silencing is established during the DNA-synthesis phase (S phase) of the cell cycle and that it depends on the cooperative interaction between two elements in separate control regions of each var gene (the 5'-flanking region and the intron). This finding should help to clarify the mechanisms by which parasites coordinate the silencing and activation of var genes that are responsible for antigenic variation in malaria.

Proc Natl Acad Sci U S A 2001 Aug 28
Full-text at: http://www.pnas.org

Induction of CD4+ T cell-dependent CD8+ type 1 responses in humans by a malaria DNA vaccine.

Wang R, Epstein J, Baraceros FM, Gorak EJ, Charoenvit Y, Carucci DJ, Hedstrom RC, Rahardjo N, Gay T, Hobart P, Stout R, Jones TR, Richie TL, Parker SE, Doolan DL, Norman J, Hoffman SL.

Malaria Program, Naval Medical Research Center, 503 Robert Grant Avenue, Silver Spring, MD 20910; Henry M. Jackson Foundation, Rockville, MD 20852; United States Army Medical Research Institute of Infectious Diseases, Fort Detrick, MD 21702; Vical Incorporated, San Diego, CA 92121; Bioject Inc., Portland, OR 97224; and School of Hygiene and Public Health, Johns Hopkins University, Baltimore, MD 21205-2129.

We assessed immunogenicity of a malaria DNA vaccine administered by needle i.m. or needleless jet injection [i.m. or i.m./intradermally (i.d.)] in 14 volunteers. Antigen-specific IFN-gamma responses were detected by enzyme-linked immunospot (ELISPOT) assays in all subjects to multiple 9- to 23-aa peptides containing class I and/or class II restricted epitopes, and were dependent on both CD8(+) and CD4(+) T cells. Overall, frequency of response was significantly greater after i.m. jet injection. CD8(+)-dependent cytotoxic T lymphocytes (CTL) were detected in 8/14 volunteers. Demonstration in humans of elicitation of the class I restricted IFN-gamma responses we believe necessary for protection against the liver stage of malaria parasites brings us closer to an effective malaria vaccine.

Redox Rep 2001;6(3):137-142
The role of cerebral oedema in the pathogenesis of cerebral malaria.

Sanni LA.

Division of Parasitology, National Institute for Medical Research, London, UK. Email: [email protected]

It has been suggested that sequestration of parasitized red blood cells might contribute to the pathogenesis of cerebral malaria (CM), by hypoxia causing either: (i) compensatory vasodilatation with a resultant increase in the brain volume; or (ii) enhancing cytokine-induced nitric oxide (NO) production via induction of inducible NO synthase (iNOS). Available evidence suggests that cerebral oedema is the initiating and probably the most important factor in the pathogenesis of murine CM. The relevance of this model in the study of the pathogenesis of CM has been questioned. However, a closer look at published reports on both human and murine CM, in this review, suggests that the pathogenesis of the murine model of CM might reflect more closely the CM seen in African children than that seen in Asian adults. It is also proposed that the role of iNOS induction during CM is protective: that the primary purpose of iNOS induction is to inhibit the side effects of brain indoleamine 2,3-dioxygenase (IDO) induction and quinolinic acid accumulation during hypoxia.

Proc R Soc Lond B Biol Sci 2001 Sep 7;268(1478):1855-1860
Very large long-term effective population size in the virulent human malaria parasite Plasmodium falciparum.

Hughes AL, Verra F.

Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.

It has been proposed that the virulent human malaria parasite Plasmodium falciparum underwent a recent severe population bottleneck. In order to test this hypothesis, we estimated the effective population size of this species from the patterns of nucleotide substitution at 23 nuclear protein-coding loci, using a variety of methods based on coalescent theory. Both simple methods and phylogenetically based maximum-likelihood methods yielded the conclusion that the effective population size of this species has been of the order of at least 10(5) for the past 300 000-400 000 years.

Exp Biol Med (Maywood) 2001 Sep;226(8):746-752
On the Mechanism of Hemozoin Production in Malaria Parasites: Activated Erythrocyte Membranes Promote beta-Hematin Synthesis.

Orjih AU.

Faculty of Allied Health Sciences, Kuwait University, Salaibikhat 90805, Kuwait.

The ferriprotoporphyrin IX (FP) molecules released by intraerythrocytic malaria parasites during hemoglobin digestion are converted to beta-hematin and are stored in the parasites' food vacuoles. It has been demonstrated in cell-free medium that the incorporation of FP into beta-hematin under physiological conditions requires a catalyst from parasite lysates or pre-formed beta-hematin. In the present studies, lysates of Plasmodium falciparum-infected erythrocytes were suspended in 1 M NaOH and were washed with phosphate buffer, pH 7.6. When the cell extracts were incubated with hematin in 0.5 M sodium acetate buffer, pH 5, for 20 hr at 37 degrees C, a large quantity of beta-hematin was formed. To determine whether parasite components were necessary for the beta-hematin formation, normal erythrocyte ghosts were similarly treated with 1 M NaOH and then incubated with hematin. In repeated experiments it was found that, on the average, 70% of the hematin was converted to beta-hematin. Membranes treated with HCl or CH(3)COOH also promoted the formation of beta-hematin, while untreated membranes were ineffective. The possibility that metabolic activities in the food vacuoles of malaria parasites may activate membrane fragments, from hemoglobin vesicles, to promote beta-hematin formation is discussed in this paper.

Insect Mol Biol 2001 Aug;10(4):347-356
Effects of malaria infection on vitellogenesis in Anopheles gambiae during two gonotrophic cycles.

Ahmed AM, Maingon R, Romans P, Hurd H.

Centre for Applied Entomology and Parasitology, School of Life Sciences, Keele University, Keele, Staffordshire, ST5 5BG, UK, Department of Zoology, University of Toronto, Toronto, Ontario, M5S 3G5, Canada.

We report changes in the abundance of vitellogenin (Vg) mRNA, and concentration of haemolymph Vg and ovarian vitellin (Vn) in Anopheles gambiae following infection with Plasmodium yoelii nigeriensis. A parasite-induced reduction in Vg mRNA abundance was first detected 24 h after feeding on an infective blood meal, when ookinetes were invading the midgut. During a second gonotrophic cycle post-infection, developing oocysts reduced Vg mRNA abundance by up to 33% and the effect was detected from 2 h post blood meal. Concentrations of Vg were initially reduced by infection during the second cycle, as predicted from Vg mRNA measurements. However, after 24 h, excess Vg had accumulated in the haemolymph. This accumulation may be due to impaired uptake, since ovarian vitellin accumulation was significantly decreased by infection during both gonotrophic cycles.
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Last modified September 07, 2001