High Incidence of Plasmodium knowlesi Infection in the Interior Division of Sabah, Malaysian Borneo

Abstract

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.