Genetic variation of the mitochondrial genes, CO1 and ND5, in Aedes aegypti from various regions of peninsular Malaysia.

Aedes aegypti is the primary vector of dengue viruses in many parts of the world. In peninsular Malaysia, epidemics of dengue occur more at certain sites particularly in the west central region compared to the eastern region. In this study, we determined the genetic diversity of Ae. aegypti collected from 19 localities in 5 regions of peninsular Malaysia based on two mitochondrial DNA genes; CO1 and ND5. The total number of haplotypes obtained for CO1 and ND5 gene were 14 (C1-C14) and five (N1-N5), respectively. Haplotype genealogical network constructed using concatenated CO1-ND5 gene sequences revealed 18 haplotypes (H1-H18) that were separated into two distinct lineages. Phylogenetic analysis showed that the first lineage (C11 and C3) was more closely related to those from Brazil and France. Unique low frequencies haplotypes detected in the current sampling was closely related to those previously found in India, Pakistan and Vietnam samples, suggesting recent invasion of these haplotypes through human movement or transportation. This is the first study in Malaysia which serves as an initial preliminary phase for a much larger study throughout the country. The understanding of the population diversity of Ae. aegypti and its impact on dengue transmission will be essential for planning of effective control programmes to reduce the burden of dengue.

A large focus of naturally acquired Plasmodium knowlesi infections in human beings.

BACKGROUND: About a fifth of malaria cases in 1999 for the Kapit division of Malaysian Borneo had routinely been identified by microscopy as Plasmodium malariae, although these infections appeared atypical and a nested PCR assay failed to identify P malariae DNA. We aimed to investigate whether such infections could be attributable to a variant form of P malariae or a newly emergent Plasmodium species. METHODS: We took blood samples from 208 people with malaria in the Kapit division between March, 2000, and November, 2002. The small subunit ribosomal RNA and the circumsporozoite protein genes were sequenced for eight isolates that had been microscopically identified as P malariae. All blood samples were characterised with a genus-specific and species-specific nested PCR assay together with newly designed P knowlesi-specific primers. FINDINGS: All DNA sequences were phylogenetically indistinguishable from those of P knowlesi, a malaria parasite of long-tailed macaque monkeys, but were significantly different from other malaria parasite species. By PCR assay, 120 (58%) of 208 people with malaria tested positive for P knowlesi, whereas none was positive for P malariae. P knowlesi parasites in human erythrocytes were difficult to distinguish from P malariae by microscopy. Most of the P knowlesi infections were in adults and we did not note any clustering of cases within communities. P knowlesi infections were successfully treated with chloroquine and primaquine. INTERPRETATION: Naturally acquired P knowlesi infections, misdiagnosed by microscopy mainly as P malariae, accounted for over half of all malaria cases in our study. Morphological similarities between P knowlesi and P malariae necessitate the use of molecular methods for correct identification. Further work is needed to determine whether human P knowlesi infections in the Kapit division are acquired from macaque monkeys or whether a host switch to human beings has occurred.