Malaria Tropica Research Articles

Parasite-host interaction in malaria: genetic clues and copy number variation

In humans, infections contribute highly to mortality and morbidity rates worldwide. Malaria tropica is one of the major infectious diseases globally and is caused by the protozoan parasite Plasmodium falciparum. Plasmodia have accompanied human beings since the emergence of humankind. Due to its pathogenicity, malaria is a powerful selective force on the human genome. Genetic epidemiology approaches such as family and twin studies, candidate gene studies, and disease-association studies have identified a number of genes that mediate relative protection against the severest forms of the disease. New molecular approaches, including genome-wide association studies, have recently been performed to expand our knowledge on the functional effect of human variation in malaria. For the future, a systematic determination of gene-dosage effects and expression profiles of protective genes might unveil the functional impact of structural alterations in these genes on either side of the host-parasite interaction.

Synthesis of Novel Diazabicycles and their Antiprotozoal Activities

We describe the synthesis of new diaryl substituted diazabicyclo[3.2.1]octanes from diazepanes which were prepared by the reduction of diazepanones. The formation of the bicyclic system was optimized by microwave irradiation and the structures of the new compounds were established by single crystal structure analysis and NMR spectroscopy. All new compounds were tested for their potencies against Plasmodium falciparum K1 and Trypanosoma b. rhodesiense, the causative organisms of malaria tropica and the East African form of sleeping sickness.

SARs of the antiprotozoal action of 6,7-diaryl-bicyclo[2.2.2]octan-2-ols

Several 4-amino-6,7-diarylbicyclo[2.2.2]octan-2-ols bearing varying substituents on the aromatic rings were synthesized following a manual method for applying the Hansch approach. All new compounds were tested for their activity against the causative organisms of East African sleeping sickness and malaria tropica. Structure activity relationships are discussed.

Die Malaria im Römischen Kaiserreich: eine bemerkenswerte Textstelle in den Digesten

The significance of malaria for the decadence and the final fall of the Western Roman Empire is discussed controversially. It seems verisimilar that Central Europe was free of malaria at the end of the last ice age, and it is undisputed that the Apennine peninsula was a substantially depopulated, endemic malaria area around 600 A.D. The immigration of three of the four Plasmodium species infectious for man took place most likely at different era and with very different effects on the antique societies. A text passage in the Digesta of Justinian (D 21.1.1.8), written by the post classical jurist Ulpian (approx. 170-223 A.D.), illuminates selectively in region and period the malaria situation of the social underclass in and around Rome, a city with a population over a million at that time. The quotation indicates, shortened, "that an old Quartana, about which one does not have to worry any longer, is not an argument for a warranty for defects in case of slaves bought at the market". From this annotation one can deduce that at the turn of the second to the third century A.D. Quartana recrudescence represented the medical normality for people from the social underclass in Rome and the surrounding area. Thus, while at that time Plasmodium malariae seemed to be a common part of the human parasite fauna in Latium, Malaria tropica and Malaria tertiana did not yet unfold their depopulating, economically and socially devastating effects; this happened several centuries later, although the existence of at least one effective vector is proven.

Plasmodium falciparumin Ancient Egypt

To the Editor: Malaria is a disease caused by parasites of the genus Plasmodium. The infection is transmitted to humans through the bites of female mosquitoes of the genus Anopheles. Four species of Plasmodium are pathogenic to humans, and each leads to different clinical features: P. falciparum causes severe malaria with undulating high fever (malaria tropica); P. malariae, P. vivax, and P. ovale cause less severe clinical courses of disease with the manifestations of malaria quartana (P. malariae) and malaria tertiana (P. vivax and P. ovale). Literary evidence for malaria infection dates back to the early Greek period when Hippocrates described the typical undulating fever (1), highly suggestive of plasmodial infection. Although it is believed that malaria widely affected early pre-Hippocrates populations, until now only 1 study, which used molecular analysis, clearly identified P. falciparum in a Roman infant dating back to the 5th century AD (2). Two other studies used molecular analysis to identify more recent plasmodial DNA in ancient human remains, i.e., from 100–400 years ago (3,4). A substantial number of nonspecific amplifications in these previous studies raised concerns as to the specificity of current molecular markers for ancient malaria (3,4). In this report, we describe the unambiguous identification of ancient DNA (aDNA) for P. falciparum in ancient Egyptian mummy tissues from ≈4,000 years ago. We analyzed 91 bone tissue samples from ancient Egyptian mummies and skeletons. The Egyptian material derived from the Predynastic to Early Dynastic site of Abydos (n = 7; 3500–2800 BC), a Middle Kingdom tomb in Thebes West (n = 42; 2050–1650 BC), and various tomb complexes in Thebes West, which were built and used between the Middle and New Kingdom until the Late Period (n = 42; c. 2050–500 BC). All samples were first tested for Plasmodium spp. DNA by using the heminested PCR for the 18S rDNA primer targets usually used for malaria identification (5). Direct sequencing was performed on those with positive amplification products. Thereby, a high number of amplification products of various sizes (including the expected size) were detected. However, on sequencing, all amplicons provided nonspecific products. Consequently, in a second set, all material was tested for the P. falciparum chloroquine-resistance transporter gene (pfcrt gene) (6,7), which was also further characterized by direct sequencing. In this second set of experiments, 2 of the 91 ancient Egyptian samples tested positive for the 134-bp fragment of the pfcrt region of P. falciparum (Figure). The specificity of the amplification was verified by sequencing, which showed 99% sequence concordance. The result was verified by parallel analysis in 2 independent laboratories; observations were fully concordant. The 2 positive samples originated from 2 different tomb complexes dating from the New Kingdom until Late Period (1500–500 BC). Each sample was obtained from adults who had osteopathologic evidence of chronic anemia. No positive results were found for the earlier samples from the Predynastic to Early Dynastic or Middle Kingdom periods. Figure PCR amplification of a 134-bp fragment of ancient DNA of Plasmodium falciparum in Egyptian mummies. Lane 1, molecular marker; lanes 10 and 11, 2 negative controls. One (lane 6) of 8 samples shows a positive amplification product (arrow). Specificity of ... Previously, immunologic tests have been used to investigate the presence and incidence of malaria in ancient Egyptian mummies (8,9). Because >40% of all samples and 92% of samples from persons with bone lesions suggestive of chronic anemia tested positive for the P. falciparum histidine-rich protein-2 antigen, doubts as to the specificity of those tests have been raised. Our study unambiguously identified P. falciparum aDNA in Egyptian mummy samples, thereby proving a specific infection by falciparum malaria in ancient Egypt. With respect to the infection incidence, our molecular analysis suggests a more realistic frequency than had been previously suggested by paleoimmunologic methods. Consequently, the aDNA analysis is superior with respect to the reaction specificity, so that the latter should not further be used for that purpose. This report adds another infectious disease to the spectrum of paleomicrobiology in ancient Egypt, thereby further explaining the previously postulated influence of infectious diseases on the low life expectancy for ancient Egyptian populations (10). Molecular detection of pathogen aDNA can be used not only to identify a certain disease, but it may also provide information on disease frequency, evolutionary origin, and pathways.

Acyl derivatives of 5-amino-2-azabicyclo[3.2.2]nonanes

5-Amino-2-azabicyclo[3.2.2]nonanes possess activity against the causative organisms of Human African trypanosomiasis and Malaria tropica. Their newly prepared N-acyl derivatives were inactive against Trypanosoma b. rhodesiense, but some of them showed good antiplasmodial activity against a multiresistant strain of Plasmodium falciparum. The results are compared to the activities of the N-unsubstituted compounds and N-sulfonyl analogues. The diastereomeric character of the formed amides was elucidated by NMR spectroscopy.

Imported malaria in children: a national surveillance in the Netherlands and a review of European studies

Falciparum malaria or malaria tropica is one of the leading causes of childhood mortality worldwide. Malaria-related deaths occur mainly in sub-Saharan Africa, where an estimated 365 million clinical cases of Plasmodium falciparum malaria occur each year. In Europe, imported malaria cases occur due to returning travellers or immigration mostly from African countries. Children are more at risk than adults. The objective of this study was to identify high risk groups for imported childhood malaria in Europe in order to guide development of strategies for prevention, early recognition and management. In the period May 2003-January 2005 we reviewed all cases of paediatric malaria in the Netherlands notified by the Dutch Paediatric Surveillance System (Nederland Signalerings Centrum Kindergeneeskunde, NSCK) and the literature on imported malaria in children in Europe published between 1996 and 2006. Malaria occurred mainly in children of long-term (n = 15, 47%) and new (n = 8, 25%) immigrants and was mostly acquired in sub-Saharan Africa. The dominant species was P. falciparum. Only one quarter of children had used adequate malaria chemoprophylaxis. Complicated disease occurred in 10 (31%) of cases. We also reviewed the literature and found 6082 reported cases of imported malaria among children in Europe; among these, four died and only one was reported to develop neurological sequelae. Imported malaria in children remains an important problem and is unlikely to decrease unless the reasons for inadequate prophylaxis are addressed.

Antiprotozoal Activities of Epimeric Aminobicycles

We synthesized several 4-aminobicyclo[2.2.2] octan-2-ols and 4-amino-2-azabicyclo[3.2.2]nonanes from epimerized 4-amino-bicyclo[2.2.2]octan-2-ones. The new compounds were tested for their activity against Trypanosoma b. rhodesiense, the causative organism of East African sleeping sickness, and Plasmodium falciparum K1, a multiresistant protozoan parasite which causes Malaria tropica. The results are compared to the activities of their formerly synthesized stereoisomers and structure–activity relationships are discussed.

New 4-Amino-2-azabicyclo[3.2.2]nonane Derivatives and their Antiprotozoal Potencies

Several 2-substituted 4-amino-2-azabicyclo [3.2.2]nonane derivatives were synthesized. The new compounds were investigated for their activities against the causative organism of East African sleeping sickness, Trypanosoma b. rhodesiense, and a protozoan parasite which causes Malaria tropica, Plasmodium falciparum K1, a strain which is resistant to chloroquine and pyrimethamine. The results are compared to the activities of 2-unsubstituted 4-amino-2-azabicyclo[3.2.2]nonanes.

Baculovirus-based Vaccination Vectors Allow for Efficient Induction of Immune Responses Against Plasmodium falciparum Circumsporozoite Protein

Baculovirus vectors are able to transduce a large variety of mammalian cell types and express transgenes placed under the control of heterologous promoters. In this study, we evaluated the potential of baculovirus vectors for malaria vaccination. To induce efficient CD4(+) and CD8(+) T-cell responses, we produced a series of vectors that display the Plasmodium falciparum circumsporozoite (CS) protein in the virion envelope and/or allow for CS expression upon transduction of mammalian cells. We found that baculovirus vectors can transduce professional antigen-presenting cells and trigger their maturation, which is a prerequisite for efficient antigen presentation. Upon intramuscular injection into mice, the vector that both displayed and expressed CS induced higher anti-CS antibody titers (of the immunoglobulin (IgG)1 and IgG2a type) and a higher frequency of interferon-gamma-producing T cells specific to CS, than the vectors which either only displayed or only expressed CS. The baculovirus CS display/expression vector was also superior in inducing CS-specific CD4(+) and CD8(+) T-cell responses in vitro using human peripheral blood mononuclear cells from naive donors. This, together with the absence of pre-existing immunity to baculoviruses in humans, the absence of viral gene expression in mammalian cells, and the relative low immunogenicity of baculovirus virions, makes these vectors promising tools for vaccination. Furthermore, the ability to produce large amounts in serum-free medium at a low cost adds a further advantage to this vector system.

Regioselectively modified sulfated cellulose as prospective drug for treatment of malaria tropica

Adhesion of Plasmodium falciparum infected erythrocytes (IE) to placental chondroitin-4-sulfate (CSA) has been linked to the severe disease outcome of pregnancy-associated malaria. Consequently, sulfated polysaccharides with inhibitory capacity may be considered for therapeutic strategies as anti-adhesive drugs. During in vitro screening a regioselectively modified cellulose sulfate (CS10) was selected as prime candidate for further investigations because it was able to inhibit adhesion to CSA expressed on CHO cells and placental tissue, to de-adhere already bound infected erythrocytes, and to bind to infected erythrocytes. Similar to the undersulfated placental CSA preferred by placental-binding infected erythrocytes, CS10 is characterized by a clustered sulfate pattern along the polymer chain. In further evaluation of its effects on P. falciparum interactions with host erythrocytes, we now show that CS10 inhibits the in vitro asexual growth of parasites in erythrocytes. Furthermore, we show that CS10 interferes with C1 of the classical complement pathway but not with MBL of the lectin pathway. In order to gain insights into the possible interactions of CS10 with known parasite receptors at the molecular level, we designed 3D-structures of characteristic stretches of CS10. CS10 fragments with clustered sulfate groups showed complex patterns of hydrophobic and hydrophilic patches most likely suitable for interactions with protein binding partners. The significance of CS10 interactions with the complement system as well as its anti-malarial effect for prospective drug application are discussed.

Hydrazones and new Oximes of 4-Aminobicyclo[2.2.2]octanones and their Antiprotozoal Activities

4-Aminobicyclo[2.2.2]octan-2-ones and -ols showed activity against the causative organisms of East African sleeping sickness and Malaria tropica. Several imino derivatives of the ketones were more active. Now hydrazono analogues and 3-hydroximino derivatives of the ketones and alcohols were synthesized. The structures of the obtained isomers were elucidated by NMR spectroscopy. A single phenylhydrazone exhibited quite good antitrypanosomal activity in the range of already known imino analogues.

Antiplasmodial and antitrypanosomal activity of new esters and ethers of 4-dialkylaminobicyclo[2.2.2]octan-2-ols

Only three drugs are available for the treatment of East African trypanosomiasis. Patients suffer from painful application, severe side effects and increasing resistance against these drugs. Malaria tropica kills more than 2 million people every year mainly due to growing drug resistance. 4-Dialkylaminobicyclo[2.2.2]octan-2-ols and some of their esters have shown activity against both the causative organisms, Trypanosoma brucei rhodesiense and Plasmodium falciparum. Ethers and new esters with markedly higher lipophilicity were prepared in three-step procedures from acyclic synthons. The new compounds were screened for their antiprotozoal activities against T. b. rhodesiense (STIB 900) and P. falciparum K1 (resistant to chloroquine and pyrimethamine), and for their cytotoxicity with l-6 cells by means of in vitro microplate assays. The results were compared to those of the parent compounds indicating that higher lipophilicity increases the antiprotozoal activities. The pivalate 10a showed the highest antitrypanosomal activity. The 4-chlorobenzoate 9b exhibited good antiplasmodial activity and low cytotoxicity. The most active antiplasmodial agent was the benzhydryl ether 13c which was nearly as active as chloroquine against sensitive strains.

Structural Requirements for the Antiprotozoal Activity of 4-Aminobicyclo[2.2.2]octan-2-ols

Several 4-aminobicyclo[2.2.2]octan-2-ones and -ols were synthesized using different pathways. The new compounds were investigated for their activity against Trypanosoma b. rhodesiense, the causative organism of East African sleeping sickness and Plasmodium falciparum the protozoan parasite which causes Malaria tropica. The results are compared to the activities of known compounds and the influence of the substitution of the bicyclo[2.2.2]octane skeleton on the biological activities is discussed.

Malaria tropica in der Schwangerschaft - Ein Fallbericht

We report on a 25-year-old prima gravida in the 26th week of pregnancy with a malaria tropica infection from Kenya. A prior therapy for Lues latens seropositiva had been successful. Hospital admission was because of uncommon fever, chronic anemia and increasing thrombocytopenia. After typical attacks of fever malaria tropica was diagnosed in blood slides; because of this an intravenous therapy with chinin and clindamycin over 8 days was started. As a side effect of the chinin therapy premature labour resulted, which necessitated tocolytic treatment. The patient returned to give birth in the 40th week of pregnancy; a girl with a birth weight of 3560 g was born (APGAR score 9/10/10, pHNA 7.27). Signs of connatal lues did not show up in the first 14 days of the infant's life. In Europe malaria infections during pregnancy are rarely described in the literature. However, for a differential diagnosis of uncommon attacks of fever in pregnancy blood slides are recommended. In principle in pregnancy travel to malaria-endemic areas should be avoided. After the 16th week of pregnancy mefloquine is the current drug of choice for chemoprophylaxis.

Evidence for the involvement of Plasmodium falciparum proteins in the formation of new permeability pathways in the erythrocyte membrane

The intraerythrocytic developmental stages of the malaria parasite Plasmodium falciparum are responsible for the clinical symptoms associated with malaria tropica. The non-infected human erythrocyte is a terminally differentiated cell that is unable to synthesize proteins and lipids de novo, and it is incapable of importing a number of solutes that are essential for parasite proliferation. Approximately 12-15 h after invasion the parasitized cell undergoes a marked increase in its permeability to a variety of different solutes present in the extracellular milieu. The increase is due to the induction in the erythrocyte membrane of 'new permeability pathways' which have been characterized in some detail in terms of their transport and electrophysiological properties, but which are yet to be defined at a molecular level. Here we show that these pathways are resistant to trypsin but are abolished by treatment of intact infected erythrocytes with chymotrypsin. On resuspension of chymotrypsinized cells in chymotrypsin-free medium the pathways progressively reappear, a process that can be inhibited by cytotoxic agents, and by brefeldin A which inhibits protein secretion. Our results provide evidence for the involvement of parasite encoded proteins in the generation of the pathways, either as components of the pathways themselves or as auxiliary factors.

Central diabetes insipidus in a patient with malaria tropica

Up to 21% of severe cases of malaria tropica are associated with polyuria and are life-threatening. We describe a 39-yr-old man with malaria tropica who developed disseminated intravascular coagulation, polyuria, and a pituitary lesion. Empiric treatment with vasopressin improved the polyuria. This is the first case of malaria tropica in which central diabetes insipidus has been documented.

Plasmodium vivax: In vitro susceptibility of blood stages to synthetic trioxolane compounds and the diamidine DB75

Plasmodium vivax is an important human pathogen causing malaria in more temperate climates of the world. Similar to Plasmodium falciparum, the causative agent for malaria tropica, drug resistance is beginning to emerge for this parasite species and this hampers adequate treatment of infection. We have used a short-term ex vivo drug assay to monitor activity of OZ277 (RBx-11160), a fully synthetic anti-malarial peroxide, and the diamidine DB75 against P. vivax. For both compounds as well as the anti-malarial reference compounds artesunate, artemether, and chloroquine, the in vitro IC 50 values were determined in one-cycle hypoxanthine incorporation assays. Results from such assays were found to be very similar compared to IC 50 values obtained from one-cycle P. falciparum hypoxanthine assays. We demonstrate the anti-parasite activity of OZ277 and the reference compounds to be faster than that of DB75. These data warrant clinical testing of OZ277 against P. vivax malaria and support recent data on clinical activity against P. vivax for DB75.

Inhibition of Farnesyltransferase as a Strategy for the Development of Novel Anti-Malarials

Farnesyltransferase catalyzing the transfer of a farnesyl residue from farnesylpyrophosphate to the thiol of a cysteine side chain of proteins carrying the C-terminal CAAX-tetrapeptide sequence has been one of the prime targets in the development of novel anti-cancer agents. From numerous farnesyltransferase inhibitors that have been described, several have reached advanced stages of clinical trials. In addition to mammals, farnesyltransferases were also identified in different pathogenic protozoa including Plasmodium falciparum, the causative agent of malaria tropica. Therefore, inhibition of farnesyltransferase has also been suggested as a new strategy for the treatment of parasitic infections. The overall sequence identity of human and P. falciparum farnesyltransferase is considerably low, however, amino acid differences in the active sites are rather small. Only few inhibitors have been assayed against P. falciparum farnesyltransferase; some of them displayed high activity against the isolated enzyme but were only moderately active when assayed against blood stages of P. falciparum. A number of established farnesyltransferase inhibitors or derivatives of them are highly active against the human enzyme or against human cancer cells, but generally displayed only micromolar activity against P. falciparum blood stages. However, there are examples of various inhibitors with nanomolar in vitro activity against P. falciparum. In a mouse model, activity has also been demonstrated in vivo. This may justify further efforts in the development of specific anti-malarial farnesyltransferase inhibitors.

Mögliche Auswirkungen des Klimawandels auf die Ausbreitung der Malaria Tropica - Ergebnisse einer strategischen Simulation

The Earth's surface is presently undergoing a period of global warming-up, which increases the likelihood of a spread of malaria tropica. A reliable prognosis would be important for efficient prevention by initiating appropriate counter-measures well in time. The following paper presents simulations of the effects of climatic changes on the spread of malaria. We do not specifically aim at obtaining concrete data for a particular region; rather, we are concerned with gaining an insight into the complex interrelations between global environment changes and the spread of malaria.