title: High proportion of knowlesi malaria in recent malaria cases in Malaysia.
abstract: BACKGROUND
  Plasmodium knowlesi is a simian parasite that has been recognized as the fifth species causing human malaria. Naturally-acquired P. knowlesi infection is widespread among human populations in Southeast Asia. The aim of this epidemiological study was to determine the incidence and distribution of malaria parasites, with a particular focus on human P. knowlesi infection in Malaysia.
  
  
  METHODS
  A total of 457 microscopically confirmed, malaria-positive blood samples were collected from 22 state and main district hospitals in Malaysia between September 2012 and December 2013. Nested PCR assay targeting the 18S rRNA gene was used to determine the infecting Plasmodium species.
  
  
  RESULTS
  A total of 453 samples were positive for Plasmodium species by using nested PCR assay. Plasmodium knowlesi was identified in 256 (56.5%) samples, followed by 133 (29.4%) cases of Plasmodium vivax, 49 (10.8%) cases of Plasmodium falciparum, two (0.4%) cases of Plasmodium ovale and one (0.2%) case of Plasmodium malariae. Twelve mixed infections were detected, including P. knowlesi/P. vivax (n = 10), P. knowlesi/P. falciparum (n = 1), and P. falciparum/P. vivax (n = 1). Notably, P. knowlesi (Included mixed infections involving P. knowlesi (P. knowlesi/P. vivax and P. knowlesi /P. falciparum)) showed the highest proportion in Sabah (84/115 cases, prevalence of 73.0%), Sarawak (83/120, 69.2%), Kelantan (42/56, 75.0%), Pahang (24/25, 96.0%), Johor (7/9, 77.8%), and Terengganu (4/5, 80.0%,). In contrast, the rates of P. knowlesi infection in Selangor and Negeri Sembilan were found to be 16.2% (18/111 cases) and 50.0% (5/10 cases), respectively. Sample of P. knowlesi was not obtained from Kuala Lumpur, Melaka, Perak, Pulau Pinang, and Perlis during the study period, while a microscopically-positive sample from Kedah was negative by PCR.
  
  
  CONCLUSIONS
  In addition to Sabah and Sarawak, which have been known for high prevalence of P. knowlesi infection, the findings from this study highlight the widespread distribution of P. knowlesi in many Peninsular Malaysia states.
authors.forename: Ruhani
authors.initials: R
authors.lastname: Yusof
authors.affiliation: Department of Parasitology, Faculty of Medicine, Tropical Infectious Disease Research and Education Center (TIDREC), University of Malaya, 50603 Kuala Lumpur, Malaysia. lauyeeling@um.edu.my.
authors.forename: Yee Ling
authors.initials: YL
authors.lastname: Lau
authors.forename: Rohela
authors.initials: R
authors.lastname: Mahmud
authors.forename: Mun Yik
authors.initials: MY
authors.lastname: Fong
authors.forename: Jenarun
authors.initials: J
authors.lastname: Jelip
authors.forename: Hie Ung
authors.initials: HU
authors.lastname: Ngian
authors.forename: Sahlawati
authors.initials: S
authors.lastname: Mustakim
authors.forename: Hani Mat
authors.initials: HM
authors.lastname: Hussin
authors.forename: Noradilah
authors.initials: N
authors.lastname: Marzuki
authors.forename: Marlindawati
authors.initials: M
authors.lastname: Mohd Ali
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D004275:DNA, Ribosomal / Q000235:genetics; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008288:Malaria / Q000453:epidemiology* / Q000469:parasitology*; D008296:Malaysia / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D010961:Plasmodium / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D055815:Young Adult
chemical_list: D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S