Abstract
To monitor the incidence of Plasmodium knowlesi infections and determine whether other simian malaria parasites are being transmitted to humans, we examined 1,047 blood samples from patients with malaria at Kapit Hospital in Kapit, Malaysia, during June 24, 2013–December 31, 2017. Using nested PCR assays, we found 845 (80.6%) patients had either P. knowlesi monoinfection (n = 815) or co-infection with other Plasmodium species (n = 30). We noted the annual number of these zoonotic infections increased greatly in 2017 (n = 284). We identified 6 patients, 17–65 years of age, with P. cynomolgi and P. knowlesi co-infections, confirmed by phylogenetic analyses of the Plasmodium cytochrome c oxidase subunit 1 gene sequences. P. knowlesi continues to be a public health concern in the Kapit Division of Sarawak, Malaysian Borneo. In addition, another simian malaria parasite, P. cynomolgi, also is an emerging cause of malaria in humans.
Highlights
Plasmodium spp. were identified in the late 1800s, and >30 species have been described in primates, including humans, apes, and monkeys [1,2]
Throughout the 5-year study, we observed a remarkable increase in Plasmodium knowlesi malaria cases
The increasing incidence of P. knowlesi in the Kapit Division, in 2017; the few patients infected with human malaria parasites, P. falciparum, P. vivax, P. ovale, and P. malariae, during June 2013–December 2016; and the lack of indigenous cases in Kapit in 2017 reflect the recent malaria situation in Malaysian Borneo and Peninsular Malaysia [11]
Summary
Plasmodium spp. were identified in the late 1800s, and >30 species have been described in primates, including humans, apes, and monkeys [1,2]. After the large focus on human P. knowlesi infections in the Kapit Division of Sarawak state in 2004 [3], extended studies on wild long-tailed macaques (Macaca fascicularis) and pig-tailed macaques (M. nemestrina) in the area found these species harbor 6 simian malaria parasites: P. inui, P. knowlesi, P. cynomolgi, P. coatneyi, P. fieldi, and P. simiovale [12,18]. Besides P. knowlesi, 2 other simian parasites, P. inui and P. cynomolgi, have zoonotic capabilities that have been proven through accidental and experimental infections [1,19,20,21]. P. cynomolgi was reported to infect humans during an accidental transmission in a laboratory in the United States in 1956 and later by experimental trials [1,19]. RESEARCH determine whether human infections with P. cynomolgi and P. inui occurred in the Kapit Division of Sarawak, Malaysian Borneo
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