Abstract
BackgroundPlasmodium knowlesi and Plasmodium cynomolgi are two malaria parasites naturally transmissible between humans and wild macaque through mosquito vectors, while Plasmodium inui can be experimentally transmitted from macaques to humans. One of their major natural hosts, the long-tailed macaque (Macaca fascicularis), is host to two other species of Plasmodium (Plasmodium fieldi and Plasmodium coatneyi) and is widely distributed in Southeast Asia. This study aims to determine the distribution of wild macaques infected with malarial parasites by examining samples derived from seven populations in five countries across Southeast Asia.MethodsPlasmodium knowlesi, P. cynomolgi, P. coatneyi, P. inui and P. fieldi, were detected using nested PCR assays in DNA samples from 276 wild-caught long-tailed macaques. These samples had been derived from macaques captured at seven locations, two each in the Philippines (n = 68) and Indonesia (n = 70), and one each in Cambodia (n = 54), Singapore (n = 40) and Laos (n = 44). The results were compared with previous studies of malaria parasites in long-tailed macaques from other locations in Southeast Asia. Fisher exact test and Chi square test were used to examine the geographic bias of the distribution of Plasmodium species in the macaque populations.ResultsOut of 276 samples tested, 177 were Plasmodium-positive, with P. cynomolgi being the most common and widely distributed among all long-tailed macaque populations (53.3 %) and occurring in all populations examined, followed by P. coatneyi (20.4 %), P. inui (12.3 %), P. fieldi (3.4 %) and P. knowlesi (0.4 %). One P. knowlesi infection was detected in a macaque from Laos, representing the first documented case of P. knowlesi in wildlife in Laos. Chi square test showed three of the five parasites (P. knowlesi, P. coatneyi, P. cynomolgi) with significant bias in prevalence towards macaques from Malaysian Borneo, Cambodia, and Southern Sumatra, respectively.ConclusionsThe prevalence of malaria parasites, including those that are transmissible to humans, varied among all sampled regional populations of long-tailed macaques in Southeast Asia. The new discovery of P. knowlesi infection in Laos, and the high prevalence of P. cynomolgi infections in wild macaques in general, indicate the strong need of public advocacy in related countries.
Highlights
Plasmodium knowlesi and Plasmodium cynomolgi are two malaria parasites naturally transmissible between humans and wild macaque through mosquito vectors, while Plasmodium inui can be experimentally trans‐ mitted from macaques to humans
In 1965, the first case of a human naturally infected with knowlesi malaria was reported [10] and human infections in nature were considered extremely rare until in 2004, when 120 of 208 malaria patients at Kapit Hospital in Sarawak, Malaysian Borneo were found to be infected with P. knowlesi using nested Polymerase chain reaction (PCR) assays [11]
The present study demonstrates that two macaque malaria parasites naturally transmissible to humans, P. cynomolgi, and P. inui, exist among all the 7 sampled regional populations of wild long-tailed macaques
Summary
Plasmodium knowlesi and Plasmodium cynomolgi are two malaria parasites naturally transmissible between humans and wild macaque through mosquito vectors, while Plasmodium inui can be experimentally trans‐ mitted from macaques to humans One of their major natural hosts, the long-tailed macaque (Macaca fascicularis), is host to two other species of Plasmodium (Plasmodium fieldi and Plasmodium coatneyi) and is widely distributed in Southeast Asia. Since 1930, three other species of Plasmodium that typically infect wild macaques in Southeast Asia had been known to be transmissible to humans This was first demonstrated by passage with blood infected with Plasmodium knowlesi [3], and later with Plasmodium cynomolgi [4] and Plasmodium inui [5]. These recent discoveries of humans infected with what were previously thought to be non-human malarias implied the potential larger distribution of human cases that may have not yet been confirmed and highlighted the potentially high risks of more zoonotic malaria infections
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