Three recently isolated Thai strains of Plasmodium falciparum were tested in vitro for their response to pyrimethamine, sulfadoxine, and both compounds in combination. One isolate, FCK, was moderately tolerant to pyrimethamine whereas FCM3 and FCM5 were not affected by this compound at serum level, being 100 times less responsive than a sensitive strain from the Gambia when tested similarly. This low degree of response is evidently due to drug resistance. Sensitivity to sulfadoxine was low in the Thai isolates, but was also lower than expected in the Gambian strain. Possible causes of the poor response are discussed. Pyrimethamine in combination with sulfadoxine showed a synergistic effect; the effective doses were reduced by ten and three times, respectively.

Antimalarials↗

PubMed1982

Plasmodium falciparum in continuous culture: a new medium for the in vitro test for sulfadoxine sensitivity.

The sulfadoxine sensitivity of two strains of Plasmodium falciparum from Thailand, FCM2 and FCM5, was assessed using two types of culture medium, Waymouth formula and RPMI 1640. Growth of the parasite was completely inhibited by 0.5 mmol of sulfadoxine per litre of Waymouth formula, whereas parasite growth in RPMI was not affected at this concentration. The apparent difference in drug sensitivity was shown to be caused by competition between 4-aminobenzoic acid and sulfadoxine. This hypothesis was further confirmed by the extent to which [(14)C]-sulfadoxine was incorporated into the infected erythrocytes.

4-Aminobenzoic Acid↗

PubMed1981

Decrease in susceptibility of Plasmodium falciparum to mefloquine in continuous culture.

Chloroquine-resistant P. falciparum, line FCK from Thailand, was tested for susceptibility to mefloquine in continuous culture. The drug resulted in 50% schizont inhibition at the level of 8.0 nmol/ml of culture when tested for the first time. After three months of discontinuous exposure to mefloquine at increasing levels, the sensitivity of the parasite decreased. A concentration as high as 128 nmol/ml eventually was required for 50% inhibition of growth.

Animals↗

PubMed1980

Carbohydrate reserves and hemolymph sugars of the African giant snail, Achatina fulica in relation to parasitic infection and starvation.

In the snail, Achatina fulica, parasitized by the rat lungworm Angiostrongylus cantonensis, levels of carbohydrate in hemolymph and digestive glands were determined. The normal level of hemolymph glucose of 11.7 mg% dropped to 4.25 mg% in the infected snails, a significant difference after only one week of infection. The level of total reducing sugar in the hemolymph also decreased significantly (12.3 mg% to 3.6 mg%) in this period. Later on, the snails were capable of adapting themselves to the parasitic infection and the concentration of hemolymph sugars returned to the normal range. Starvation caused a decrease in the carbohydrate reserves of the digestive gland only when the starved snails had been previously infected.

Angiostrongylus↗

PubMed1979

Angiostrongylus cantonensis: infectivity of first stage larvae in the presence of rat fecal materials as tested by the in vitro cultivation technique.

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Animals↗

PubMed1979

Studies on susceptibility of Pila ampullacea, to the infection with the rat lungworm, Angiostrongylus cantonensis.

Experimental infections of Pila ampullacea with first stage larvae of Angiostrongylus cantonensis were carried out to determine susceptibility of this molluscan host in relation to dose level and snail host size. Snails were divided into 3 size groups and exposed to A. cantonensis first stage larval suspensions of varying concentrations. The results showed that overall, about 20% of larvae ingested by the snails developed into infective third stage larvae, but the percentage was inversely related to both the number of larvae to which snails were exposed and snail weight. The infective worms were concentrated in the foot muscle and mantle of the molluscan host.

Animals↗

PubMed1978

Effects of parasitism and stress on hemolymph protein of the African giant snail, Achatina fulica.

Effects of parasitism and stress on the protein concentration of hemolymph have been investigated using the rat lungworm Angiostromgylus cantonensis in the snail host Achatina fulica. The normal hemolymph protein concentration, averaging 1.77 g/100 ml in noninfected snails, did not show any reduction when the hosts were infected with third stage larvae. When the infected snails were bled repeatedly, protein concentration showed a significant decrease by 0.6 g/100 ml. Starved, infected snails were capable of maintaining their hemolymph protein level within the normal range. This treatment, however, in combination with frequent bleeding, caused much stress to the snails and reduced survival. The number of survivors depended on the frequency of bleeding and on the food level.

Animals↗

PubMed1978

Amino acid, heme, and sterol requirements of the nematode, Rhabditis maupasi.

Rhabditis maupasi, a nematode that occurs in the mantle cavity of Helix aspersa and related North African food snails, requires 5 amino acids (lysine, methionine, phenylalanine, tryptophane and valine) for maintenance of the stage-3 survival larvae, and 5 additional amino acids (arginine, isoleucine, leucine, threonine and, marginally, histidine) for development of these larvae into adults and for reproduction. Tyrosine is beneficial but not absolutely required for reproduction. These results were obtained with axenic R. maupasi grown in a chemically defined medium containing salts, trace metals, purines and pyrimidines, Krebs cycle intermediates, a fatty acid (butyric), vitamins, urea, and a carbohydrate (dextrose). The complete medium contained 18 amino acids; each of 18 test media was deficient in one of the amino acids. In the complete medium and in a medium lacking the "nematode nonessential" amino acids, stage-3 R. maupasi developed into adults and produced one generation of offspring. For continuous cultivation, however, the nematode also required hemin or another iron porphyrin as well as a sterol such as cholesterol.

Amino Acids↗

PubMed1976

Growth and localization of Angiostrongylus cantonensis in the molluscan host, Achatina fulica.

The development of the rat lung worm Angiostrongylus cantonensis within the giant African snail Achatina fulica is reported. In this host, ingested first stage larvae penetrate the intestinal wall into the hemocoel and migrate to the mantle where they undergo two molts and become third stage larvae within 24 days. The mantle, harboring 85% of the total number recovered is the major location of infective larvae. The kidney contains about 11% but few larvae are found in the remaining visceral organs. Host response consists of encapsulation; destruction by means of phagocytosis was not observed.

Animals↗

PubMed1974

Rhabditis maupasi: occurrence in food snails and cultivation.

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Animals↗

PubMedDate not supplied

Clinical response and susceptibility in vitro of Plasmodium vivax to the standard regimen of chloroquine in Thailand.

The clinical effectiveness of the standard regimen of chloroquine (CQ) (a total dose of 1500 mg, given over 48 h at 0, 6, 24 and 48 h) for the treatment of Plasmodium vivax malaria in Thailand was investigated in 57 patients in an endemic area of Thailand (Chantaburi Province, eastern Thailand). For radical treatment, an additional course of a tissue schizontocidal agent, primaquine, was given following the complete course of CQ. With this regimen, satisfactory whole blood concentration-time profiles of CQ and its major metabolite desethylchloroquine (DECQ) were achieved. Mean whole blood levels of CQ and DECQ always much exceeded the reported therapeutic level of CQ (90 ng/mL) during the first 7 d of treatment. All patients responded well to the treatment; in most cases, complete and rapid clearance of parasitaemia was observed within the first 48 h. No reappearance of the parasitaemia was detected in peripheral blood films of any patient within 14 d of the evaluation period. In 6 patients, however, reappearance of P. vivax parasitaemia was observed after 30 d; 2 of them had not completed the course of primaquine. There was no difference in whole blood concentrations of CQ and DECQ, admission parasitaemia, susceptibility of the isolates to chloroquine in vitro, and parasite clearance time between patients with or without reappearance of parasitaemia. A prominent trend of deteriorating sensitivity of the parasite to the drug was, however, suggested.

Adult↗