ABSTRACT
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.