Isoenzyme variation in schizonts of Plasmodium vivax from Burma

The treatment of falciparum malaria

Effective treatment for falciparum malaria has been available for over 300 years, and for most of this time physicians have argued over the best doses and the methods of administering antimalarial drugs. A reasonable consensus has since emerged on the treatment of uncomplicated malaria, but there is still disagreement over the management of severe infections, and as a consequence there have been confusing and dangerous discrepancies in treatment recommendations. In this review, Nicholas White discusses the confusion, offering a rational basis for the clinical treatment of both uncomplicated and severe falciparum malaria.

The genetic diversity of Plasmodium vivax populations

Little is known of the genetic diversity and population structure of Plasmodium vivax, a debilitating and highly prevalent malaria parasite of humans. This article reviews the known polymorphic genetic markers, summarizes current data on the population structure of this parasite and discusses future prospects for using knowledge of the genetic diversity to improve control measures.

Spotaneous Rupture of Spleen Due to Plasmodium Vivax Malaria

Spontaneous rupture of the spleen is a rare complication of Plasmodium vivax malaria which may be under diagnosed. Recently we encountered such a case in an expatriate a few days after arriving from his country. The presentation was of fever; abdominal pain and vomiting. Computed tomographic scan and ultrasound were not helpful in making an initial diagnosis but the development of hypotension and a significant drop in hemoglobin later pointed to the diagnosis. The rupture was sufficiently severe to necessitate splenectomy. The case is described, treatment options are discussed and pertinent literature is reviewed.

"One-pot" synthesis and antimalarial activity of formamidine derivatives of 4-anilinoquinoline

Amodiaquine (AQ) is an antimalarial which is effective against chloroquino-resistant strains of Plasmodium falciparum but whose clinical use is severely restricted because of associated hepatotoxicity and agranulocytosis. "One-pot" synthesis of formamidines likely to be transformed into AQ derivatives is reported. Compared with AQ, the new compounds were devoid of in vitro cytotoxicity upon human embryonic lung cells and mouse peritoneal macrophages. One showed a potent in vivo activity in mice infected with P berghei. Transformation of this compound by reductive amination led to a new type of AQ derivatives that displayed an in vitro activity similar to that of AQ but did not lead to toxic quinone-imines.

Comparative clinical characteristics and response to oral antimalarial therapy of children with and without Plasmodium falciparum hyperparasitaemia in an endemic area

The clinical characteristics and the responses to oral antimalarial therapy of 104 children presenting consecutively with or without Plasmodium falciparum hyperparasitaemia (HP) were investigated in an endemic area. At presentation, although the 52 children with HP were significantly younger and had significantly higher heart rates than the 52 without, there were no significant differences between the two groups in their symptoms or in any other clinical feature of their malaria. Responses to oral antimalarial drugs were similar in both groups. Analysis of the disposition kinetics of parasitaemia, using a non-compartmental model similar to that used in characterizing drug disposition, showed that the two groups had similar half-lives of parasitaemia (t1/2pd), volumes of blood completely cleared of parasites per unit time (CLBpd), and parasite-clearance-time:t1/2pd ratios. Three children in the HP group, all aged < 3 years, progressed to cerebral malaria within 8 h of presentation, and another HP child presented with isolated trunkal ataxia, indicative of cerebellar involvement. No child in the non-HP group had any of the features of severe malaria. Although the clinical characteristics and responses to oral therapy of children with and without HP are therefore very similar, young children with HP appear to have an increased risk of developing other features of severe malaria.

Severe thrombocytopenia suggesting immunological mechanisms in two cases of vivax malaria

Case 1: A 27-year-old woman, referred to our hospital because of relapsing fever after travel to Thailand, was given a diagnosis of vivax malaria. Clinical investigation revealed thrombocytopenia, elevated platelet-associated IgG (PAIgG), and negative antibody against Plasmodium vivax antigen. After antimalarial treatment, the levels of both the platelets and PAIgG returned to normal. Case 2: A 28-year-old Sri Lankan man was admitted to our hospital with a complaint of fever. The patient had thrombocytopenia, elevated PAIgG, and positive antibody against Plasmodium vivax antigen. He contracted malaria in Sri Lanka about 6 months prior to this admission. After treatment, the platelet count and PAIgG level returned to normal. In these two cases, high levels of PAIgG may have been involved in the development of the thrombocytopenia. In the first patient, in particular, the thrombocytopenia was thought to be induced by some immunological mechanism prior to the detection of antimaralial antibodies in serum.

Structure-based design of parasitic protease inhibitors

To streamline the preclinical phase of pharmaceutical development, we have explored the utility of structural data on the molecular target and synergy between computational and medicinal chemistry. We have concentrated on parasitic infectious diseases with a particular emphasis on the development of specific noncovalent inhibitors of proteases that play a key role in the parasites' life cycles. Frequently, the structure of the enzyme target of pharmaceutical interest is not available. In this setting we have modeled the structure of the relevant enzyme by virtue of its sequence similarity with proteins of known structure. For example, we have constructed a homology-based model of falcipain, the trophozoite cysteine protease, and used the computational ligand identification algorithm DOCK to identify in compuo enzyme inhibitors including oxalic bis(2-hydroxy-1-naphthyl-methylene)hydrazide (1) [Ring, C. S.; Sun, E.; McKerow, J. H.; Lee, G.; Rosenthal, P. J., Kuntz, I. D.; Cohen, F. E., Proc. Natl Acad. Sci. U.S.A. 1993, 90, 3583]. Compound 1 inhibits falcipain (IC50 6 microM) and the organism in vitro as judged by hypoxanthine uptake (IC50 7 microM). Following this lead, to date, we have identified potent bis arylacylhydrazides (IC50 150 nM) and chalcones (IC50 200 nM) that are active against both chloroquine-sensitive and chloroquine-resistant strains of malaria. In a second example, cruzain, the crystallographically determined structure of a papain-like cysteine protease, resolved to 2.35 A, was available. Aided by DOCK, we have identified a family of bis-arylacylhydrazides that are potent inhibitors of cruzain (IC50 600 microM). These compounds represent useful leads for pharmaceutical development over strict enzyme inhibition criteria in a structure-based design program.

Development of resistance to chloroquine by Plasmodium vivax in Myanmar

Fifty patients with Plasmodium vivax infection were treated with the standard regimen of chloroquine phosphate (1500 mg over 3 d) followed by primaquine (45 mg immediately and then weekly for 8 weeks); 43 patients had sensitive infections but recrudescences of parasitaemia occurred between days 3 and 14 with RI, RII and RIII patterns in one, 3 and 3 patients, respectively. All the chloroquine-resistant cases were again treated with chloroquine (1500 mg) and no further recrudescence or relapse was detected on days 21 and 28. This study indicates that chloroquine is losing its efficacy against P. vivax in Myanmar.

Activation of the coagulation cascade in severe falciparum malaria through the intrinsic pathway

The mechanisms involved in the activation of the coagulation cascade in severe falciparum malaria were studied in 22 adult patients (19 male, three female) aged 18-45 (mean +/- SD 31 +/- 11) years. Of these, nine had multiple vital organ dysfunction, and bleeding occurred in four patients, two of whom died. During acute illness the reduction in plasma antithrombin III (AT III) concentrations and elevation in thrombin-AT III complexes were associated with significant reductions in factor XII and prekallikrein activities, and an increase in the C1 inhibitor antigen/activity ratio. Serial plasminogen activity remained within the normal range in all patients while protein C activity was significantly reduced. All patients had markedly elevated plasma polymorphonuclear leucocyte elastase (PMN-elastase) levels with mild depletion of alpha-2 macroglobulin but normal concentrations of alpha-1 antitrypsin. There was no correlation between PMN-elastase concentrations and any of the coagulation parameters or concentrations of proteinase inhibitors. These results suggest that the intrinsic pathway of the clotting cascade is activated in severe malaria. This may cause activation of the complement system and release of bradykinin and PMN-elastase and could contribute to the pathogenesis of severe malaria.

Rosetting

Why do some individuals get severe falciparum malaria while others don't? Rosetting (the binding of uninfected erythrocytes to Plasmodium falciparum-infected erythrocytes), together with endothelial cytoadherence, has been shown to play a crucial role in the obstruction of the microvosculoture in P. falciparum malaria. Here, Mats Wahlgren, Victor Fernandez, Carin Scholonder and Johan Carlson review the literature surrounding rosetting.

Culture model for the study of cerebral malaria: antibodies from Plasmodium falciparum-infected comatose patients inhibit the dendritic development of Purkinje cells

The in vitro development of kitten Purkinje cells was inhibited by sera or IgG from cerebral malaria (CM) patients but not by sera from acute non-complicated malaria (NCM) cases. This inhibitory effect, quantified by computer-assisted methods, concerned the dendritic (though not the axonal) development and was found to be related to the presence of CM sera of self-reactive antibodies of the IgG class. These results suggest that protection acquired against the major complication of Plasmodium falciparum malaria may correspond to the repression of an abnormal stimulation of autoreactive B cells.

Altered plasma lipid pattern in falciparum malaria

Plasma levels of HDL, LDL, total cholesterol and triglycerides were measured in 60 patients with falciparum malaria (37 severe cases and 23 mild) and in 83 healthy individuals, to study malaria-induced changes in plasma lipids. Triglyceride levels were lower in the patients than in the controls but the difference was significant only for those with severe malaria (P < 0.001). In contrast, the levels of all the other plasma lipids were significantly higher (P < 0.001) in those with severe malaria than in those with mild malaria, and in the mild malaria cases compared with the controls. Initially LDL cholesterol was estimated by the Friedwald formula, but this gave negative values in a few cases of severe malaria. Plasma lipoproteins were therefore also measured by nephelometry; the estimated levels of S particles, corresponding to LDL, were then found to be lower in all malaria cases than in the controls (P < 0.001) but never negative. Interestingly, levels of L particles in the patients with severe malaria were significantly elevated compared with the other patients and controls (P < 0.001), indicating impaired metabolism of chylomicrons. Plasma albumin, considered a negative acute phase protein (i.e. its level decreases as a consequence of the acute phase response), was reduced significantly and was directly correlated to HDL cholesterol levels (r = 0.715 and r = 0.895, respectively) in both mild and severe malaria. Follow-up of 22 of the severe malaria cases three weeks after treatment indicated that, while triglycerides had returned to similar levels to those in the controls, total cholesterol levels were still elevated and could give misleading results if lipid profiles were used, immediately after malaria infection, to assess an individual's risk of developing atherosclerosis.

Disposition of quinine in plasma, red blood cells and saliva after oral and intravenous administration to healthy adult Africans

The pharmacokinetics of quinine has been studied in ten healthy adult Africans after intravenous infusion and oral ingestion of a 500 mg dose. Blood and saliva samples were collected over 48 h and quinine in plasma, red cells and saliva was determined by HPLC. Quinine was rapidly and almost completely absorbed after an oral dose, with absorption half-life of 0.53 h, a tmax of 1-3 h and a bioavailability of 88%. Analysis of the i.v. data gave an apparent volume of distribution of 3.6 l.kg-1 and a plasma clearance of 0.19 l.kg-1.h-1. The concentration-time curves for plasma, red cells and saliva had declining phases were approximately parallel, giving a similar half-life that in all three media. The half-lives after the i.v. infusion also did not different from those after oral administration. The dose was well tolerated by both methods of administration.

Hyperparasitaemia: not a reliable indicator of severity or poor prognosis in falciparum malaria in children in endemic African countries

Hyperparasitaemia as an indicator of severity or poor prognosis in falciparum malaria and response to oral antimalarial therapy were evaluated in an outpatient study of 77 consecutive African children from an endemic area. At presentation, clinical illness was graded as mild in 37, moderate in 14 and severe in 26. There was no evidence of renal, hepatic or cerebral complications. Clinical response to oral antimalarial drugs was characterized by rapid and uneventful recovery from illness in all but one patient who required hospital admission with prompt clearance of parasitaemia and fever within 96 hours. It is concluded that greater than 5% parasitaemia may be well tolerated by semi-immune African children. Semi-immune subjects with hyperparasitaemia and no other evidence of severe or complicated disease in an endemic area may well be treated with oral antimalarials providing the infecting strain is fully sensitive to the drug chosen and the drug is rapidly absorbed.

Cerebral malaria in children

Cerebral malaria is a rapidly progressive encephalopathy with up to 50% mortality. A cardinal feature is the massing of red cells containing mature Plasmodium falciparum within the cerebral capillaries. Adhesion of these parasitised red cells to endothelium, an event which may initiate cerebral malaria, is being studied at the molecular level. However, the relevance of these studies to the pathophysiology and treatment of human cerebral malaria is uncertain. Although chloroquine is still widely used to treat falciparum malaria, resistance has spread to most of the endemic zone. Quinine is emerging as the only effective treatment for cerebral malaria, though resistance to this drug threatens to become a problem. Alternative drugs are urgently needed.

Tumor-necrosis factor and other cytokines in cerebral malaria: experimental and clinical data

Evidence is presented here that tumor necrosis factor/cachectin (TNF), is of crucial importance in the pathogenesis of cerebral malaria. First, the central lesion of CM, hemorrhagic necrosis of cerebral vessels, corresponds to lesions observed during other pathological conditions associated with high serum TNF levels, such as endotoxemic shock or administration of TNF. Second, in both mouse and human, there is a close correlation between high serum TNF levels and CM. At least in mouse, high TNF levels and CM depend upon T lymphocytes of the CD4+ phenotype. Third, passive immunization against mouse TNF significantly prolongs the survival of P. berghei-infected CBA/Ca mice, and prevents the development of neurologic signs. Treatment with the anti-TNF antibody also prevents hemorrhagic necrosis of brain vessels. Fourth, in the mouse model, a cytokine cascade including at least GM-CSF, IL-3 and IFN-gamma is required for the elevation of TNF level. This cascade appears to involve two components: (a) a quantitative component: increased accumulation of macrophages results from the concomitant release of IL-3 and GM-CSF, and (b) a qualitative component: macrophage number has not only to be raised, but macrophages need to be activated by IFN-gamma. Fifth, metabolic parameters of CM and its main lesion in both mouse and human, i.e. the hemorrhagic necrosis of small brain vessels, correspond to the known properties of TNF.

Electrophoretic variants of enzymes in isolates of Plasmodium falciparum, P. malariae and P. vivax from Thailand

A new electrophoretic variant of glucose phosphate isomerase (GPI), which we now denote GPI-3, has been found in isolates of Plasmodium falciparum from 6 patients, all of whom acquired the infection in the same region (in or near Prachinburi province) of Thailand. In other regions, from which 453 isolates have been tested, only GPI-1 and/or GPI-2 have been found. Two isolates of P. malariae from patients at Kanchanaburi showed a band of GPI activity on cellulose acetate gels at a cathodal position quite distinct from that of any previously known GPI variants in other human malaria parasites. Thirty-nine isolates of P. vivax from 3 regions of Thailand have been examined for variants of GPI and lactate dehydrogenase (LDH). Three forms of GPI were found, corresponding approximately in band positions to GPI-1, 2 and 3 of P. falciparum. The position of the band of LDH activity in P. vivax was the same in all the isolates examined, and different from that of LDH-1 in P. falciparum.

Plasmodium vivax: enzyme polymorphism in isolates of Indian origin

185 isolates of Plasmodium vivax were collected from patients visiting the malaria clinic run by the National Malaria Eradication Programme, Delhi, India. Percoll gradient centrifugation was used to concentrate P. vivax parasites from 0.4 to 0.5 ml of blood collected by finger prick. The parasite concentrate from each isolate was electrophoretically analysed for lactate dehydrogenase (LDH), NADP-dependent glutamate dehydrogenase (GDH), glucose phosphate isomerase (GPI) and adenosine deaminase (ADA). Variations were observed in GPI, GDH and ADA systems. Four electrophoretic forms of GPI and 5 each of GDH and ADA were observed. Electrophoretic mobilities of the different isoenzymic forms in P. vivax were identical to those reported for P. falciparum, indicating that the 2 species cannot be differentiated on the basis of electrophoretic patterns of the 4 enzyme systems studied.

Management of severe malarial infection

Severe malaria is a major cause of infant and childhood death in the tropics. Effective management relies on rapid diagnosis, prompt administration of parenteral schizonticidal antimalarial drugs, careful fluid balance, prevention of convulsions and early recognition of complications such as hypoglycemia, metabolic acidosis, anemia, pulmonary edema, renal failure, bleeding and supervening bacterial sepsis. The mortality of treated cerebral malaria remains 20%. New, more rapidly acting antimalarials and earlier referral of children with complicated infections should reduce this unacceptable death rate.