The geography of Plasmodium knowlesi malaria

Mosquito modelling and zoonotic malaria

The Plasmodium knowlesi parasite, found in wild monkey populations, is a potentially serious public health concern yet almost nothing is known about its geographical extent. It is known to cause severe and fatal disease in humans and is the most common cause of clinical malaria in high transmission regions of Malaysia where it is more likely to cause severe malaria than P. falciparum. However, P. knowlesi-specific molecular diagnostic techniques are rarely used and this parasite species is often mis-diagnosed as one of the four human malarias. When MAP’s work on this malaria parasite started, sporadic human cases had been reported from Brunei, Cambodia, Kalimantan in Indonesia, Myanmar, the Andaman and Nicobar Islands of India, the Philippines, Singapore, Thailand and Viet Nam as well as most parts of Malaysia. More recent reports also now include Sumatra in Indonesia and Laos.

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The potential range of Plasmodium knowlesi malaria

The ranges of each known or putative host species (specifically, three macaque species) and each known or putative vector species were updated to identify areas where the host and vector species are both present. This information was combined with geographical information on confirmed P. knowlesi infections in these species and in humans to classify subnational regions of southeast Asia according to the current evidence for potential P. knowlesi transmission to humans. The resulting map is available with the PLoS NTD paper and at the MAP website.

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Geographical distributions of the host and vector species of Plasmodium knowlesi

Reports of occurrence of each host and vector species were geopositioned and used in a species distribution model to estimate the relative probability of occurrence of each species. The distributions of these species and the chance that they occupy habitats where humans live or work are believed to be influenced by deforestation. This project, therefore, constructed data on the cover of intact and disturbed forests for use in the species distribution models. Of the macaque host species, M. nemestrina was mainly predicted to occur in forested areas whereas M. fascicularis was predicted to occur in vegetation mosaics, cropland, wetland and urban areas in addition to forested areas. Of the vector species, the Leucosphyrus Complex was predicted to occur in areas with disturbed, but not intact, forest cover whereas the Dirus Complex was predicted to occur in areas with 10–100 % tree cover as well as vegetation mosaics and cropland. This has potential implications for the distribution of P. knowlesi malaria risk because Leucosphyrus Complex mosquitoes and M. nemestrina are only found in the southern part of the disease range whereas Dirus Complex mosquitoes are only found in the northern part. Macaca fascicularis is found across the disease range but not as far north as the human infections recorded at the Myanmar/China border. The maps generated by this work are available with the Parasites & Vectors paper and at the MAP website.

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The geographical distribution of Plasmodium knowlesi infection risk

Data on the locations of confirmed infections in humans, hosts (macaques) and vectors were used in a joint model of infections within these three groups. This model was used to predict the relative probability of infections occurring in humans and to construct a risk map for the region. The available data on infections outside Malaysia is weak and the resulting map should be viewed as a guide to areas where surveillance should be strengthened in order to confirm geographical variation in the risk of P. knowlesi malaria. This region of Asia is making strong progress in eliminating the other human malarias and the P. knowlesi map was used to highlight areas where P. knowlesi infections are most likely to persist after the other human malarias have been eliminated. The resulting map is available on the Explorer Tool.

Data on the locations of confirmed infections in humans, hosts (macaques) and vectors were used in a joint model of infections within these three groups. This model was used to predict the relative probability of infections occurring in humans and to construct a risk map for the region. The available data on infections outside Malaysia is weak and the resulting map should be viewed as a guide to areas where surveillance should be strengthened in order to confirm geographical variation in the risk of P. knowlesi malaria. This region of Asia is making strong progress in eliminating the other human malarias and the P. knowlesi map was used to highlight areas where P. knowlesi infections are most likely to persist after the other human malarias have been eliminated. The resulting map is available with the PLoS NTD paper and at the MAP website.

Related Publications

URLDOIShearer FM., Huang Z., Weiss DJ., Wiebe A., Gibson HS., Battle KE., Pigott DM., Brady OJ., Putaporntip C., Jongwutiwes S., et al,

Estimating geographical variation in the risk of zoonotic Plasmodium knowlesi infection in countries eliminating malaria

PLoS Neglected Tropical Diseases. August 2016 10(8): e0004915.
URLDOIMoyes CL., Shearer FM., Huang Z., Wiebe A., Gibson HS., Nijman V., Mohd-Azlan J., Brodie JF., Malaivijitnond S., Linkie M., et al,

Predicting the geographical distributions of the macaque hosts and mosquito vectors of Plasmodium knowlesi malaria in forested and non-forested areas

Parasites & Vectors. April 2016 9: 242.
URLDOIMoyes CL., Henry AJ., Golding N., Huang Z., Singh B., Baird JK., Newton PN., Huffman M., Duda KA., Drakeley CJ., et al,

Defining the geographical range of the Plasmodium knowlesi reservoir

PLoS Neglected Tropical Diseases. March 2014 8(3): e2780.