Surveys on new human malaria in South East Asia

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Field survey of malaria was conducted in Thailand, Indonesia, Myanmar and China using an acridine orange (AO) staining method. Diagnostic results were compared with those by microtiter plate hybridization (MPH), and a nested PCR methods.1. In Thailand, a total of 548 samples were obtained, and many P.malariae and P.ovale infections diagnosed by the AO method were confirmed by the MPH and/or nested PCR methods. Their prevalence reached about 20% and 2.2%, respectively. In addition, three samples of P.ovale infections were AO-positive but MPH-negative. Analysis of the target sequences revealed that these isolates were the same mutated type (two nucleotide deletion and one nucleotide substitution) with that found in Vietnam. On the other hand, P.falciparum isolates were found to possess a point mutation at the target region in the 18S rRNA gene.2. In China, many P.malariae infections were also detected from the Sichuan Province by the three methods. By the nested PCR method, a long deletion from amplified PCR product was found at the probe region, indicating that this may be a new mutated type of P.malariae. Later, the same mutated form was detected from Thailand, Indonesia, and Myanmar, indicating that it is widely distributing in SEA.3. In Myanmar, many P.malariae and P.ovale infections were also detected. The mutated types of both of P.malariae and P.ovale which had been found in Vietnam was also detected. In contrast, in Indonesia only six samples of P.malariae and only two of P.ovale were found. One sample of P.malariae was the same new type, but others were normal.