Introduction. Malaria is currently one of the most prevalent parasite-transmitted diseases caused by parasites of the genus Plasmodium. Misidentification of human malaria parasites especially P. knowlesi based on microscopic examination is very common. The objectives of this paper were to accurately identify the incidence of human malaria parasites in the interior division of Sabah, Malaysian Borneo, based on small subunit ribosomal RNA (ssrRNA) and to determine the misidentification rate in human malaria parasites. Methods. Nested PCR was used to detect the presence of human malaria parasites. A total of 243 blood spot samples from patients who had requested for blood film for malaria parasite (BFMP) analyses were used in this study. Results. Nested PCR findings showed that there was no P. malariae infection while the highest prevalent malaria parasite was P. knowlesi, followed by P. vivax, P. falciparum, and mixed infection. Only 69.5% of the 243 samples giving consistent nested PCR and microscopic results. Conclusion. The preliminary findings from molecular detection of malaria showed that P. knowlesi was the most prevalent Plasmodium species in the interior division of Sabah. The findings from this paper may provide a clearer picture on the actual transmission of different Plasmodium species in this region.

Plasmodium knowlesi had been recognized as the fifth human malaria parasite due to its wide distribution of naturally acquired infection among the human populations in many parts of Southeast Asia. The aim of this molecular epidemiological study was to determine the incidence of human malaria parasites with special attention to P.knowlesi in four districts in the interior division of Sabah, Malaysian Borneo. Nested-PCR assays were used to identify the presence of Plasmodium species in the DNA extracted from 243 dried blood spots collected for six months in year 2010 from patients suspected to have malaria. A total of 107 (44%) of the samples were positive for Plasmodium sp. based on genus-specific nested-PCR detection. Among these Plasmodium positive samples, there were 63 (58.9%) single P.knowlesi infection and two cases of mixed-species infection with P.knowlesi (1 P.knowlesi/P.falciparum and 1 P.knowlesi/P.vivax).DNA sequencing of 20 randomly selected P.knowlesi isolates from this study showed that these isolates were similar with the sexual type of naturally acquired P.knowlesi in human. P.knowlesi was the most prevalent Plasmodium sp. in this region and it had been consistently found in all the four study sites with the highest incidence in the Tenom district which accounted for 53.8% (35 cases) of all P.knowlesi cases reported in this region. This preliminary study provides a clearer picture on the actual transmission of the fifth human malaria parasites in the interior division of Sabah. The high incidence and widespread of potentially fatal P.knowlesi infection in this region should pose an important concern where proper treatment and management is needed timely.Index Terms-Malaysian Borneo, Molecular epidemiology, Malaria, Plasmodium knowlesi.