The development of effective malaria vaccines may be hindered by extensive genetic diversity in the surface proteins being employed as vaccine antigens. Understanding of the extent and dynamics of ...genetic diversity in vaccine antigens is needed to guide rational vaccine design and to interpret the results of vaccine efficacy trials conducted in malaria endemic areas. Molecular epidemiological, population genetic, and structural approaches are being employed to try to identify immunologically relevant polymorphism in vaccine antigens. The results of these studies will inform choices of which alleles to include in multivalent or chimeric vaccines; however, additional molecular and immuno-epidemiological studies in a variety of geographic locations will be necessary for these approaches to succeed. Alternative means of overcoming antigenic diversity are also being explored, including boosting responses to critical conserved regions of current vaccine antigens, identifying new, more conserved and less immunodominant antigens, and developing whole-organism vaccines. Continued creative application and integration of tools from multiple disciplines, including epidemiology, immunology, molecular biology, and evolutionary genetics and genomics, will likely be required to develop broadly protective vaccines against Plasmodium and other antigenically complex pathogens.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Our goal is to develop a vaccine that sustainably prevents Plasmodium falciparum (Pf) malaria in ≥80% of recipients. Pf sporozoites (PfSPZ) administered by mosquito bites are the only immunogens ...shown to induce such protection in humans. Such protection is thought to be mediated by CD8⁺ T cells in the liver that secrete interferon-γ (IFN-γ). We report that purified irradiated PfSPZ administered to 80 volunteers by needle inoculation in the skin was safe, but suboptimally immunogenic and protective. Animal studies demonstrated that intravenous immunization was critical for inducing a high frequency of PfSPZ-specific CD8⁺, IFN-γ-producing T cells in the liver (nonhuman primates, mice) and conferring protection (mice). Our results suggest that intravenous administration of this vaccine will lead to the prevention of infection with Pf malaria.
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Chloroquine-Resistant Malaria Wellems, Thomas E.; Plowe, Christopher V.
The Journal of infectious diseases,
09/2001, Volume:
184, Issue:
6
Journal Article
Peer reviewed
Open access
The development of chloroquine as an antimalarial drug and the subsequent evolution of drug-resistant Plasmodium strains had major impacts on global public health in the 20th century. In P. ...falciparum the cause of the most lethal human malaria, chloroquine resistance is linked to multiple mutations in PfCRT, a protein that likely functions as a transporter in the parasite’s digestive vacuole membrane. Rapid diagnostic assays for PfCRT mutations are already employed as surveillance tools for drug resistance. Here, we review recent field studies that support the central role of PfCRT mutations in chloroquine resistance. These studies suggest chloroquine resistance arose in ⩾4 distinct geographic foci and substantiate an important role of immunity in the outcomes of resistant infections after chloroquine treatment. P. vivax which also causes human malaria, appears to differ from P. falciparum in its mechanism of chloroquine resistance. Investigation of the resistance mechanisms and of the role of immunity in therapeutic outcomes will support new approaches to drugs that can take the place of chloroquine or augment its efficiency
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Antifolate antimalarial drugs interfere with folate metabolism, a pathway essential to malaria parasite survival. This class of drugs includes effective causal prophylactic and therapeutic agents, ...some of which act synergistically when used in combination. Unfortunately, the antifolates have proven susceptible to resistance in the malaria parasite. Resistance is caused by point mutations in dihydrofolate reductase and dihydropteroate synthase, the two key enzymes in the folate biosynthetic pathway that are targeted by the antifolates. Resistance to these drugs arises relatively rapidly in response to drug pressure and is now common worldwide. Nevertheless, antifolate drugs remain first-line agents in several sub-Saharan African countries where chloroquine resistance is widespread, at least partially because they remain the only affordable, effective alternative. New antifolate combinations that are more effective against resistant parasites are being developed and in one case, recently introduced into use. Combining these antifolates with drugs that act on different targets in the parasite should greatly enhance their effectiveness as well as deter the development of resistance. Molecular epidemiological techniques for monitoring parasite drug resistance may contribute to development of strategies for prolonging the useful therapeutic life of this important class of drugs.
In 1993, Malawi became the first African country to replace chloroquine with sulfadoxine-pyrimethamine nationwide in response to high rates of chloroquine-resistant falciparum malaria. To determine ...whether withdrawal of chloroquine can lead to the reemergence of chloroquine sensitivity, the prevalence of the pfcrt 76T molecular marker for chloroquine-resistant Plasmodium falciparum malaria was retrospectively measured in Blantyre, Malawi. The prevalence of the chloroquine-resistant pfcrt genotype decreased from 85% in 1992 to 13% in 2000. In 2001, chloroquine cleared 100% of 63 asymptomatic P. falciparum infections, no isolates were resistant to chloroquine in vitro, and no infections with the chloroquine-resistant pfcrt genotype were detected. A concerted national effort to withdraw chloroquine from use has been followed by a return of chloroquine-sensitive falciparum malaria in Malawi. The reintroduction of chloroquine, ideally in combination with another antimalarial drug, should be considered in areas where chloroquine resistance has declined and safe and affordable alternatives remain unavailable
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Falciparum malaria remains a major cause of disease and death among children and pregnant women in sub-Saharan Africa. During the second half of the 20th century, chloroquine was the antimalarial ...treatment of choice, because it was safe, inexpensive, and highly effective against susceptible malaria parasites. Chloroquine resistance arose more than 40 years ago in Southeast Asia and South America, and in these regions chloroquine has now been largely abandoned as a treatment for falciparum malaria. Increasing rates of chloroquine resistance contribute to the rising morbidity and mortality from malaria in Africa.
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Given the lack of affordable alternatives, chloroquine remains . . .
To assess the relationship between mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) and clinical pyrimethamine-sulfadoxine resistance, polymerase ...chain reaction surveys and analyses for new mutations were conducted in four countries with increasing levels of pyrimethamine-sulfadoxine resistance: Mali, Kenya, Malawi, and Bolivia. Prevalence of mutations at DHFR codon 108 and a new mutation at DHPS 540 correlated with increased pyrimethamine-sulfadoxine resistance (P < .05). Mutations at DHFR 51, DHFR 59, and DHPS 437 correlated with resistance without achieving statistical significance. Mutations at DHFR 164 and DHPS 581 were common in Bolivia, where pyrimethamine-sulfadoxine resistance is widespread, but absent in African sites. Two new DHFR mutations, a point mutation at codon 50 and an insert at codon 30, were found only in Bolivia. DHFR and DHPS mutations occur in a progressive, stepwise fashion. Identification of specific sets of mutations causing in vivo drug failure may lead to the development of molecular surveillance methods for pyrimethamine-sulfadoxine resistance.
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Molecular assays for monitoring sulfadoxine-pyrimethamine-resistant Plasmodium falciparum have not been implemented because of the genetic and statistical complexity of the parasite mutations that ...confer resistance and their relation to treatment outcomes. This study analyzed pretreatment dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) genotypes and treatment outcomes in a double-blind, placebo-controlled trial of sulfadoxine-pyrimethamine and chlorproguanildapsone treatment for uncomplicated P. falciparum malaria. Multiple logistic regression was used to identify mutations that were predictive of treatment failure and to identify interactions and confounding factors. Infections caused by parasites with 3 DHFR mutations and 2 DHPS mutations (the "quintuple mutant") were associated with sulfadoxine-pyrimethamine treatment failure but not with chlorproguanil-dapsone treatment failure. The presence of a single DHFR mutation (Arg-59) with a single DHPS mutation (Glu-540) accurately predicted the presence of the quintuple mutant. If this model is validated in other populations, it will finally be possible to use molecular markers for surveillance of antifolate-resistant P. falciparum malaria in Africa.
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As chloroquine resistance spreads across Africa, the dihydrofolate reductase (DHFR) inhibitors pyrimethamine and proguanil are being used as alternative first-line drugs for the treatment and ...prevention of Plasmodium falciparum malaria. Resistance to these drugs is conferred by point mutations in parasite DHFR. These point mutations can be detected by polymerase chain reaction (PCR) assays, but better methods for sample collection, DNA extraction, and a diagnostic PCR are needed to make these assays useful in malaria-endemic areas. Here we report methods for collecting fingerstick blood onto filter paper strips that are air-dried, then stored and transported at room temperature. Cell lysis and DNA extraction are accomplished by boiling in Chelex-100. We also report a nested PCR technique that has improved sensitivity and specificity. These procedures readily detect mixed infections of parasites with both sensitive and resistant genotypes (confirmed by direct sequencing) and are reliable at parasite densities less than 250/mm3 in field surveys.
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