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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The only stages of malaria parasites capable of establishing an infection in a mosquito are the gametocytes that circulate in the blood of the veterbrate host. Within minutes of ingestion by a mosquito the gametocytes transform into mature gametes in the process of "exflagellation." This process is controlled in vitro solely by the change in pH in the blood as it moves from the environment of the circulation to that of the atmosphere, the pH rise being mediated by the fall in carbon dioxide tension as the blood equilibrates with the atmosphere.
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PMID:Control of gamete formation (exflagellation) in malaria parasites. 1 66

Gametogenesis in Plasmodium gallinaceum involves bicarbonate-dependent processes and requires a continuous supply of glucose (presumably as an energy source). Emergence and exflagellation of gametocytes, in vitro, occur independently of the CO2 tension but are rigidly correlated with the pH of the external medium. In bicarbonate-saline gametogenesis is initiated only if the pH exceeds 7.7. Our results suggest that gamete development of malaria parasites is stimulated when infected blood is exposed to air because the decrease in the CO2 tension of the blood causes its pH to rise.
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PMID:Gamete development in malaria parasites: bicarbonate-dependent stimulation by pH in vitro. 2 12

Chloroquine resistance has arisen in both human and murine forms of malaria. CR Plasmodium berghei in mice does not produce the malaria pigment which is characteristic of the CS form. Determinations of carbon monoxide production (i.e., host heme catabolism) by individual mice revealed that those infected with CS P. berghei produce only one fourth as much carbon monoxide as do CR infected mice at all levels of infection. These observations confirm the idea that malaria pigment is composed of precipitated host cell hemoglobin and suggest that drug resistance is accompanied by a basic alteration in parasite-mediated hemoglobin catabolism.
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PMID:Host heme catabolism in drug-sensitive and drug-resistant malaria. 33 45

The aim of this study was to find optimal conditions for the membrane feeding technique to obtain maximum infection rates of mosquitoes with Plasmodium yoelii nigeriensis. The results show that the malaria parasite Plasmodium yoelii nigeriensis is most infective to Anopheles stephensi mosquitoes on day 3 of the infection in the mice, 1 day before the peak of parasitaemia. The mortality rate of the mosquitoes fed on mice on day 3 after infection was the highest as compared to mosquitoes fed on other days after infection. Gametocytes from mice 3 days after infection were fed to mosquitoes by three different membrane feeding methods. The results indicate that feeding during the first 10 min after blood collection gave the highest infection rates. Keeping the blood meal at a pH of 7.2 yields higher infection rates than keeping it at pH of 8.5. Stirring of the blood and supplying it with CO2 is not necessary when feeding of the mosquitoes is completed within the first 10 min after collection of the blood.
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PMID:Trials to infect Anopheles stephensi with Plasmodium yoelii nigeriensis by the membrane feeding technique. 145 66

In May 1987 and January 1988 the chloroquine sensitivity of Plasmodium falciparum in the Ubombo and Ingwavuma districts of KwaZulu was determined by a modified in vitro microtest in which the patients' plasma was replaced with non-immune human AB serum and the test plates were incubated in an atmosphere of 3% oxygen, 4% carbon dioxide and 93% nitrogen. A success rate of 74% was achieved using this technique. All of 23 successfully tested isolates from malaria patients reporting to clinics and a hospital in these areas were found to be resistant to chloroquine, schizogony being inhibited at 32 pmol per well in the majority of tests. Seventy-five per cent of the isolates obtained through active surveillance in the Ubombo district were found to be resistant in varying degrees. Malarial parasites collected from clinics and a hospital in the endemic area did not change markedly in their in vitro response to chloroquine during the 8-month period May 1987-January 1988.
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PMID:In vitro confirmation of chloroquine-resistant Plasmodium falciparum malaria in KwaZulu. 305 56

Several observations suggest that iron is essential for the development of malaria parasites but there is evidence that the parasites in erythrocytes do not obtain iron from haemoglobin. The total haemin level in parasitized erythrocytes does not vary during parasite development, indicating that the iron-containing moiety of haemoglobin is not detectably metabolized. Although parasite proteases can degrade the protein part of haemoglobin in red cells, no parasite enzymes that degrade haemin have been identified. In mammalian cells, haemin is degraded to carbon monoxide and bilirubin by the enzyme haeme oxygenase. This enzyme has not been found in malaria parasites. In fact haemin has been found to be toxic to parasite carbohydrate metabolism. Thus, iron apparently cannot be liberated from haemin and instead is sequestered in infected red cells as haemozoin, the characteristic pigment associated with malarial infection. If iron bound to transferrin is the source of ferric ions for malaria parasites within mature erythrocytes, then the parasite must synthesize its own transferrin receptor and localize it on the surface of the infected cell, because the receptors for transferrin are lost during erythrocyte maturation. Our results here suggest that Plasmodium falciparum synthesizes its own transferrin receptors enabling it to take up iron from transferrin by receptor-mediated endocytosis.
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PMID:A protein on Plasmodium falciparum-infected erythrocytes functions as a transferrin receptor. 309 54

Plasmodium falciparum-infected human erythrocytes grown in vitro do not release 14CO2 when incubated in the presence of [1-14C]glutamate, despite the presence of glutamate dehydrogenase, implying the absence of alpha-ketoglutarate dehydrogenase activity and the lack of functional tricarboxylic acid cycle in the human malaria parasite. Cultures incubated with [14C]bicarbonate, however, fix CO2 into acid-stable metabolites; CO2 fixation proceeds linearly for up to two hours after an initial brief lag and may contribute appreciably to the metabolism of the parasite.
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PMID:Absence of alpha-ketoglutarate dehydrogenase activity and presence of CO2-fixing activity in Plasmodium falciparum grown in vitro in human erythrocytes. 614 96

Mosquitos were collected in three villages on the western coast of the island of Palawan, Republic of the Philippines, from June 1986 to April 1987, using 3 methods. Anopheles flavirostris, the primary malaria vector, was the most abundant of the Anopheles collected biting man, ranging from a low of 83.9% in June (16.1 collected/man/night) to 98.3% in April (29.1 collected/man/night). The number of species was greatest in the animal-baited traps with 54 species detected. The CO2-baited CDC light traps were neither effective nor economically feasible as a monitoring tool for malaria vectors at this site. People were at risk from An. flavirostris bites throughout the night except 1800-2000 which are low-risk hours. Anopheles flavirostris is slightly exophagic during most of the year, but moderately endophagic during the hot, dry season.
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PMID:A survey of the mosquitos (Diptera: Culicidae) of Napsan, Palawan, Republic of the Philippines. 790 82

The CO2-enriched atmosphere required for the short-term growth of human malaria parasites can be provided by a small, disposable environmental bag that is readily available in many laboratories. This provides an ideal alternative means for incubating malaria parasites when specially-prepared gas mixtures, air-tight incubation chambers or candle-jars are unavailable or they are too expensive or impractical to use. Such an environmental bag should encourage greater use of the WHO in vitro test for assessing the drug susceptibility of malaria parasites.
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PMID:Disposable environmental chamber for assessing the drug susceptibility of malaria parasites. 813 76

Mefloquine (MQ) is highly effective in the treatment and prophylaxis of chloroquine-resistant Plasmodium falciparum malaria. Despite its widespread use, scant information is available on the transplacental profile and time course of MQ transfer across the human placenta. Six human placentas were perfused with human plasma for 180 min using recirculating maternal and fetal circuits. The viability of the placental preparation was validated measuring oxygen and carbon dioxide balance and the rates of glucose consumption and lactate production. MQ data were compared with antipyrine, a routine marker in placental perfusions. Disappearance of MQ from the maternal circulation after a dose of 0.8 mg/liter was biexponential, with a first, rapid distribution phase into the placental tissue. The apparent first-order distribution (lambda 1) and elimination (lambda z) rate constants were 0.043 +/- 0.014 min-1 and 0.020 +/- 0.007 min-1, respectively. The fetomaternal mass ratio became constant (0.46 +/- 0.07) after 120 min of perfusion and the time needed to achieve equal concentrations on both sides of the placenta was 178 +/- 31 min. MQ clearance was 3.36 +/- 0.38 ml/min. About 40% of the MQ maternal dose was recovered in tissue and 11% appeared in the fetal circulation. These data provide support for using MQ in pregnant women for both the treatment and prophylaxis of Plasmodium malaria, although comparison with other compounds are needed.
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PMID:Mefloquine transfer during in vitro human placenta perfusion. 816 35


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