Impact Factor 2021: 3.041 (@Clarivate Analytics)
5-Year Impact Factor: 2.776 (@Clarivate Analytics)
Impact Factor Rank: 10/24, Q2 (Tropical Medicine)
  • Users Online: 880
  • Print this page
  • Email this page

Table of Contents
Year : 2022  |  Volume : 15  |  Issue : 8  |  Page : 337-338

The rise of Plasmodium knowlesi cases: Implication to Malaysia’s malaria-free status

1 Department of Parasitology and Medical Entomology, Faculty of Medicine, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
2 Department of Parasitology and Medical Entomology; Infectious Disease Group, Faculty of Medicine, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia

Date of Submission28-Jul-2022
Date of Decision06-Aug-2022
Date of Acceptance09-Aug-2022
Date of Web Publication18-Aug-2022

Correspondence Address:
Zulkarnain Md Idris
Department of Parasitology and Medical Entomology; Infectious Disease Group, Faculty of Medicine, Universiti Kebangsaan Malaysia, Kuala Lumpur
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1995-7645.353920

Rights and Permissions

How to cite this article:
Muhammad AB, Azman EN, Eddie NA, Azmi NI, Yee VC, Idris ZM. The rise of Plasmodium knowlesi cases: Implication to Malaysia’s malaria-free status. Asian Pac J Trop Med 2022;15:337-8

How to cite this URL:
Muhammad AB, Azman EN, Eddie NA, Azmi NI, Yee VC, Idris ZM. The rise of Plasmodium knowlesi cases: Implication to Malaysia’s malaria-free status. Asian Pac J Trop Med [serial online] 2022 [cited 2022 Dec 7];15:337-8. Available from:

Malaria remains a major public health challenge globally. It is one of the world’s deadliest diseases, responsible for 627 000 deaths worldwide in 2020 alone[1]. In Malaysia, the Malaria Eradication Programme in Peninsular Malaysia and Malaysia Borneo in 1969 and 1967, respectively, drastically reduced the number of malaria cases in the country[2]. Subsequently, the programme was further reinforced and improved, resulting in zero indigenous human malaria species in 2018[1]. Currently, Malaysia has been identified as one of the World Health Organization (WHO) Western Pacific Region countries with zero indigenous cases for three consecutive years[1], thus eligible for the WHO certification of a malaria-free status country.

Even though the number of human malaria cases has reduced markedly, Malaysia is facing increasing cases of zoonotic malaria due to Plasmodium (P.) knowlesi. A significant increase in the number of P. knowlesi cases from 376 in 2008 to 4 130 cases was reported in 2018 [Figure 1]. Although P. knowlesi cases declined slightly in 2019 and 2021 (i.e. to 3 222 and 3 575 cases, respectively), P. knowlesi malaria resulted in six and 13 deaths in 2019 and 2021, respectively [Figure 1]. Most cases of P. knowlesi infection and death were recorded in the states of Malaysian Borneo (i.e. Sabah and Sarawak). Researchers checked the effect of climatic variables on the malaria incidence[3]. The geographical topography of Sabah and Sarawak, which have vast forested areas, consists of primary and secondary forests that are habitats for the natural reservoir hosts (i.e. macaques) and the mosquito vector Anopheles[2],[4]. It was found that there is a significant positive correlation between forest density and the number of P. knowlesi cases[5]. The density of the forest is important as it increases contact between the human hosts and the habitats of Anopheles mosquitoes, thus increasing the chance for P. knowlesi malaria transmission.
Figure 1: Reported cases of indigenous human malaria, zoonotic malaria and malaria death in Malaysia from 2000 to 2021 (Vector Borne Disease Sector, Disease Control Division, Ministry of Health Malaysia, unpublished data).

Click here to view

Furthermore, communities living in the forest and on the edges of forests or those engaged in forest-related activities such as hunting and camping are at a higher risk of contracting simian malaria due to their proximity to reservoir macaque hosts and mosquito vectors[6]. In Malaysia, previous studies have also included indigenous and tribal communities, cultivators, and forest workers among the high-risk populations of contracting P. knowlesi[4],[7]. In addition, the increasing number of naturally acquired zoonotic malaria infections in humans happens in regions where the natural hosts and vectors coexist. This factor is mainly attributed to the increased interconnectivity between humans, the reservoir macaque host, and the competent mosquito vector associated with local ecological changes such as deforestation and biodiversity loss, which eventually modify the dynamics of zoonotic malaria infection transmission[8]. Thus, understanding the effects and causes of biodiversity loss in a changing ecosystem on the risks of contracting infectious diseases, particularly zoonotic malaria, is a multi-factorial issue that must be addressed collectively.

Massive deforestation of tropical rainforests in Malaysia is also a major environmental issue in the country. The rapid expansion of the timber industries and large-scale plantations on agricultural commodities such as palm oil, rubber, and durian can result in an ecosystem imbalance, which is predicted to continue. Diversity and biological imbalance from deforestation may influence the functioning and stability of the natural ecological system (e.g. changes in mosquito oviposition sites and wildlife habitat), thus potentially increasing the threat of P. knowlesi malaria transmission and other zoonotic disease outbreaks[9]. Furthermore, deforestation results in the loss of habitat diversity, increasing forest fragmentation and decimation, which may affect the dynamics of P. knowlesi malaria transmission between macaques, vectors, and people and lead to an increase in the number of P. knowlesi cases in the deforested regions[4],[9]. Also, forest areas in Malaysia are being cleared and permanently converted into industrial land to cater to the growing demand for socio-economic reasons[10]. The modification of local forested landscapes for anthropogenic land use, such as for economic, residential and recreational use, has been proven to provide the ideal settings for mosquito populations harbouring P. knowlesi malaria parasites[11]. Finally, forest fragmentation from human activities can alter macaque population distributions and behaviours, leading to their invasion and increased proximity to human settlements.

For Malaysia’s National Malaria Elimination Strategic Plan to succeed and eventually achieve malaria-free status, Malaysia should aim to further improve the health care system and strengthen case-based surveillance in P. knowlesi affected areas. While field epidemiology remains relevant and important for the country, genomic epidemiology is likely to play a critical role in the surveillance. It may eventually help clarify issues related to transmission pathways and the most effective forms of P. knowlesi malaria control. Furthermore, with tailor-made strategies, the transmission of P. knowlesi in humans may be blocked without severely compromising the welfare of the macaque natural hosts, wildlife biodiversity and economic development of P. knowlesi malaria endemic area of the country.

Conflict of interest statement

We declare that there is no conflict of interest.


It was supported by the Geran Fundamental Fakulti Perubatan (FF- 2022-049), Universiti Kebangsaan Malaysia.

Authors’ contributions

The conceptualization was done by ZMI. The literature and drafting of the manuscript were conducted by ABM, ENA, NAE, NIA and VCTY. The editing and supervision were performed by ZMI. All authors have read and agreed to the final version of the manuscript.

  References Top

World Health Organization. World malaria report 2021. [Online]: Available from: [Accessed on 6 July 2022].  Back to cited text no. 1
Dian ND, Rahim MA, Idris ZM. Plasmodium cynomolgi: An emerging threat of zoonotic malaria species in Malaysia? Asian Pac J Trop Med 2022; 15: 4-6. doi: 10.4103/1995-7645.335698.  Back to cited text no. 2
  [Full text]  
Abbasi M, Rahimi Foroushani A, Jafari-Koshki T, Pakdad K, Vatandoost H, Hanafi-Bojd AA. The impact of climatic variables on the population dynamics of the main malaria vector, Anopheles stephensi Liston (Diptera: Culicidae), in southern Iran. Asian Pac J Trop Med 2020; 13: 448-455. doi: 10.4103/1995-7645.291038.  Back to cited text no. 3
  [Full text]  
Dian ND, Rahim MAFA, Chan S, Idris ZM. Non-human primate malaria infections: A review on the epidemiology in Malaysia. Int J Environ Res Public Health 2022; 19(13): 7888. doi: 10.3390/ijerph19137888.  Back to cited text no. 4
Barber BE, William T, Dhararaj P, Anderios F, Grigg MJ, Yeo TW, et al. Epidemiology of Plasmodium knowlesi malaria in north-east Sabah, Malaysia: Family clusters and wide age distribution. Malar J 2012; 11: 401. doi: 10.1186/1475-2875-11-401.  Back to cited text no. 5
Byrne I, Aure W, Manin BO, Vythilingam I, Ferguson HM, Drakeley CJ, et al. Environmental and spatial risk factors for the larval habitats of Plasmodium knowlesi vectors in Sabah, Malaysian Borneo. Sci Rep 2021; 11: 11810. doi: 10.1038/s41598-021-90893-1.  Back to cited text no. 6
Grigg MJ, Cox J, William T, Jelip J, Fornace KM, Brock PM, et al. Individual-level factors associated with the risk of acquiring human Plasmodium knowlesi malaria in Malaysia: A case-control study. Lancet Planet Health 2017; 1: e97-e104. doi: 10.1016/S2542-5196(17)30031-1.  Back to cited text no. 7
Stark DJ, Fornace KM, Brock PM, Abidin TR, Gilhooly L, Jalius C, et al. Long-tailed macaque response to deforestation in a Plasmodium knowlesi-endemic Area. Ecohealth 2019; 16: 638-646. doi: 10.1007/s10393-019- 01403-9.  Back to cited text no. 8
Civitello DJ, Cohen J, Fatima H, Halstead NT, Liriano J, McMahon TA, et al. Biodiversity inhibits parasites: Broad evidence for the dilution effect. Proc Natl Acad Sci 2015; 112: 8667-8671. doi: 10.1073/pnas.1506279112.  Back to cited text no. 9
Wilcove DS, Koh, LP. Addressing the threats to biodiversity from oil- palm agriculture. Biodivers Conserv 2010; 19: 999-1007. doi: 10.1007/ s10531-009-9760-x.  Back to cited text no. 10
Hawkes FM, Manin BO, Cooper A, Daim S, Homathevi R, Jelip J, et al. Vector compositions change across forested to deforested ecotones in emerging areas of zoonotic malaria transmission in Malaysia. Sci Rep 2019; 9: 13312. doi: 10.1038/s41598-019-53744-8.  Back to cited text no. 11


  [Figure 1], [Figure 1]


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

  In this article
Article Figures

 Article Access Statistics
    PDF Downloaded218    
    Comments [Add]    

Recommend this journal