Mixed-species malaria infection in high transmission areas of Thailand

Background: Mixed-species malaria infections examined by microscopy of Giemsa-stained thick blood films (GS-TBF) during 1996-2007 in Thailand were 0.3-0.5. However, there were reports of higher mixed-species infection rates detected by polymerase chain reaction (PCR) method. This study was conducted in order to ascertain the relative frequency of mixed-species malaria infection and possible determinants in top 10 malaria high transmission provinces of Thailand. Methods: This study was a survey of mixed Plasmodium species incidence in the top 10 malaria transmission provinces of Thailand. A total of 836 malaria patients were examined. The number of samples in each province was proportionate to the number of malaria patients in that province. A real-time PCR based on SYBR Green I detection system was used to detect and differentiate Plasmodium species. Results: Preliminary results from GS-TBF examined by the microscopists at the malaria clinics in the selected areas showed that 380 (45.5%) of 836 patients were infected by Plasmodium falciparum; 450 (53.8%), 2 (0.2%) and 4 (0.5%) were infected by P. vivax, P. malariae and mixed P. falciparum and P. vivax, respectively. Real-time PCR results of the corresponding samples from filter papers showed that 353 (42.2%) were infected by Plasmodium falciparum; 446 (53.4%), 1 (0.1%), 2 (0.2%), 32 (3.8%), 1 (0.1%) and 1 (0.1%) were infected by P. vivax, P. malariae, P. ovale, mixed P. falciparum and P. vivax, mixed P. falciparum and P. malariae and mixed P. vivax and P. ovale, respectively. Conclusion: Mixed-infection rates detected by real-time PCR were 8.48 (4.07/0.48) times higher than those detected by GS-TBS. Demographic factors including age, sex, occupation, place where contracted the disease and recurrence of the infection were not different between the groups with mono-species infection and mixed-species infection.

Drug Sensitivity of Plasmodium falciparum and Plasmodium vivax in the area of Mae Sot, Tak Province, northwestern Thailand

In vitro studies on the drug response of <I>Plasmodium falciparum</I> were conducted as from 1998 in the district of Mae Sot in northwestern Thailand near the border to Myanmar. In vitro studies on the drug response of <I>Plasmodium vivax</I> started in 2001 in the same area. For <I>P. falciparum</I> the investigations showed a very high degree of resistance. The sensitivity to mefloquine declined significantly between 198 and 2005, whereas the sensitivity to artemisinin and to quinine increased during the same period. Sensitivity to lumefantrine and atovaquone is still in the therapeutically feasible range. The sensitivity of <I>P. vivax</I> to chloroquine has declined between 2000 and 2004. Mefloquine and lumefantrine have been identified as potential replacement drugs. The activity of monodesbutyl-benflumetol proved to be higher than that of structurally related lumefantrine.