In vitro susceptibility studies of Plasmodium falciparum isolates and clones against type II antifolate drugs.

Six clones were derived from each Plasmodium falciparum isolate obtained from Malaysia, Africa and Thailand and were characterized against type II antifolate drugs, cycloguanil and pyrimethamine using the modified in vitro microtechnique. Results showed that these isolates were of a heterogeneous population, with 50% inhibitory concentrations of Gombak A clones at 0.0151-0.1450 and 0.0068-0.1158 microM, Gambian clones at 0.0056-0.1792 and 0.0004-0.0068 microM and TGR clones at 0.0103-0.0703 and 0.0776-0.3205 microM against cycloguanil and pyrimethamine, respectively. All clones displayed similar susceptibilities as their parent isolates except A/D3, A/D5, A/G4 and A/H7 clones which were sensitive to cycloguanil at 0.0735, 0.0151, 0.0540 and 0.0254 microM but Gm/B2 clone was resistant at 0.1792 microM, respectively. However, A/D3, TGR/B4, TGR/B7, TGR/C4, TGR/C7 and TGR/H2 clones were resistant to pyrimethamine at 0.1158, 0.1070, 0.1632, 0.1580, 0.2409 and 0.3205 microM, respectively. Further results indicated that they were pure clones compared to their parent isolates as their drug susceptibility studies were statistically different (p < 0.05).

Short report: development of a new diagnostic method for Plasmodium falciparum infection using a reverse transcriptase-polymerase chain reaction.

We describe here a reverse transcriptase-polymerase chain reaction method for the detection of malaria parasites. Ten in vitro-cultured isolates of Plasmodium falciparum and 16 specimens from patients infected with P. falciparum were used to examine the specificity and sensitivity of the test. The sensitivity of the test was 0.3 parasites per microliter of blood. Specificity was determined by matching the sequences of the specimens' DNA to published sequences of 18S ribosomal RNA genes in the species-specific region. The test proved to be very sensitive and specific for the detection of P. falciparum infection.

Quantitative assessment of antimalarial activities from Malaysian Plasmodium falciparum isolates by modified in vitro microtechnique.

Malaysian, TGR (Thailand), and Gambian (West African) Plasmodium falciparum isolates were cultured in vitro by the candle jar method and were characterized for their susceptibilities to present antimalarial drugs by the modified in vitro microtechnique. Results showed that 93 and 47% of the Malaysian isolates were resistant at 50% inhibitory concentrations of 0.1415 to 0.7737 and 0.1025 to 0.1975 microM, respectively, while the rest were susceptible to choloroquine and cycloguanil at 0.0376 and 0.0306 to 0.0954 microM, respectively. All isolates were susceptible to mefloquine, quinine, and pyrimethamine at 0.0026 to 0.0172, 0.0062 to 0.0854, and 0.0149 to 0.0663 microM, respectively. In contrast, the Gambian isolate was susceptible to multiple drugs at 0.0024 to 0.0282 microM; TGR was resistant to chloroquine at 0.8147 microM but was susceptible to mefloquine, quinine, cycloguanil, and pyrimethamine at 0.0024, 0.0096, 0.0143, and 0.0495 microM, respectively.

Toxocariasis--an unlikely cause of Palm Island mystery disease.

After the suggestion was made that the "Palm Island mystery disease" might have been an epidemic of visceral larva migrans that was caused by the flying fox parasite, Toxocara pteropodis, work was undertaken to elucidate this nematode's life-cycle and pathogenicity. Studies of infections in various laboratory animals have shown unexpectedly variable susceptibility patterns, with mice harbouring most larvae for the longest time period. However, in all susceptible animals (which include mice, guinea-pigs and suckling rats), the larvae demonstrated marked hepatotropism. Experimental infections in monkeys demonstrated that primates are susceptible to this infection, but large doses of 20,000 infective eggs produced blood eosinophilia and focal granulomatous hepatitis without clinical disease or biochemical abnormalities in the blood. It is concluded that humans are susceptible to larval infections with this nematode, but that clinical manifestations would be unlikely to develop.

Effect of diethylcarbamazine citrate on Angiostrongylus malaysiensis infection in rats.

The aim of the study was to observe the effect of diethylcarbamazine citrate (DEC) on Angiostrongylus malaysiensis infection in albino rats. An attempt was made to vary the dose of DEC and treat infected animals at the larval and adult stages of infection. The doses were varied with an aim at finding an effective dosage. Animals were treated also during the pre-infection period to observe if the drug had any prophylactic properties. The results obtained show that DEC given after infection was effective only when its administration was initiated on day 42 of the infection corresponding to the mature adult stage of the parasite. In addition, it had some prophylactic activity against the infection.

New hosts of Breinlia booliati with observations on its distribution in Southeast Asia.

Breinlia booliati Singh & Ho, 1973 first described from Peninsular Malaysia has been shown to infect a large range of murids ranging in distribution from southern Thailand, Peninsular Malaysia, Sarawak to Ciloto, Indonesia. Probably further work will reveal a greater host range as well as its geographical distribution. The vectors involved in its transmission need to be elucidated.

Distribution and ecological consideration of Breinlia booliati infecting wild rodents in Malaysia.

Seven of the 18 species of lowland forest terrestrial and semi-arboreal murids were found naturally infected with Breinlia booliati. Of these, two species, Rattus sabanus and R. cremoriventer, were found to be the most preferred hosts. None of the murids from the highland, field or human-inhabited areas was infected. This could have been due more to the greater scarcity of the vectors in these habitats than to the susceptibility of the hosts. The absence of this parasite in the squirrels examined may be attributed either to host specificity or to the normal activity cycles or vertical stratification of the vectors, separating them in space and/or time from the squirrels. The pattern of dispersion of the parasite is influenced by the wide distribution of suitable hosts, and the hypothesis that the parasite is of forest origin is discussed.