Abstract
BackgroundPlasmodium knowlesi is a significant cause of human malaria in Sarawak, Malaysian Borneo. Only one study has been previously undertaken in Sarawak to identify vectors of P. knowlesi, where Anopheles latens was incriminated as the vector in Kapit, central Sarawak. A study was therefore undertaken to identify malaria vectors in a different location in Sarawak.MethodsMosquitoes found landing on humans and resting on leaves over a 5-day period at two sites in the Lawas District of northern Sarawak were collected and identified. DNA samples extracted from salivary glands of Anopheles mosquitoes were subjected to nested PCR malaria-detection assays. The small subunit ribosomal RNA (SSU rRNA) gene of Plasmodium was sequenced, and the internal transcribed spacer 2 (ITS2) and mitochondrial cytochrome c oxidase subunit 1 (cox1) gene of the mosquitoes were sequenced from the Plasmodium-positive samples for phylogenetic analysis.ResultsTotals of 65 anophelines and 127 culicines were collected. By PCR, 6 An. balabacensis and 5 An. donaldi were found to have single P. knowlesi infections while 3 other An. balabacensis had either single, double or triple infections with P. inui, P. fieldi, P. cynomolgi and P. knowlesi. Phylogenetic analysis of the Plasmodium SSU rRNA gene confirmed 3 An. donaldi and 3 An. balabacensis with single P. knowlesi infections, while 3 other An. balabacensis had two or more Plasmodium species of P. inui, P. knowlesi, P. cynomolgi and some species of Plasmodium that could not be conclusively identified. Phylogenies inferred from the ITS2 and/or cox1 sequences of An. balabacensis and An. donaldi indicate that they are genetically indistinguishable from An. balabacensis and An. donaldi, respectively, found in Sabah, Malaysian Borneo.ConclusionsPreviously An. latens was identified as the vector for P. knowlesi in Kapit, central Sarawak, Malaysian Borneo, and now An. balabacensis and An. donaldi have been incriminated as vectors for zoonotic malaria in Lawas, northern Sarawak.
Highlights
Plasmodium knowlesi is a significant cause of human malaria in Sarawak, Malaysian Borneo
Intravenous inoculation of sporozoites isolated from the simiophilic An. hackeri in 1961 into an uninfected rhesus monkey demonstrated that An. hackeri was the natural vector of P. knowlesi in Peninsular Malaysia [28]
Plasmodium species in Anopheles mosquitoes Deoxyribonucleic acid (DNA) extracted from the salivary glands of 65 Anopheles mosquitoes was subjected to nested Polymerase chain reaction (PCR) assays and Plasmodium DNA was only detected in samples derived from 10 An. balabacensis and 6 An. barbirostris (s.l.) collected in Long Luping
Summary
Plasmodium knowlesi is a significant cause of human malaria in Sarawak, Malaysian Borneo. Knowlesi malaria cases have been reported from different locations in Malaysia [2,3,4,5,6,7], in almost all countries in Southeast Asia [8,9,10,11,12,13,14,15,16,17] except Timor Leste, and in the Nicobar and Andaman Islands of India [18] This simian malaria parasite is the most common cause for malaria admissions to hospitals in Malaysia, where in the years 2017–2019, 10,968 cases were reported, with 87% occurring in the states of Sabah and Sarawak in Malaysian Borneo (unpublished data, Ministry of Health Malaysia) [19]. It was only in 1999, in Belaga, Sarawak that an ELISA was used for detection of sporozoites of Plasmodium spp. in mosquitoes, but the ELISA could only detect two species of Plasmodium, P. falciparum and P. vivax [29]
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