[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/) › Plasmodium knowlesi # Plasmodium knowlesi - Parasite - Exam priority: medium A monkey malaria parasite of Southeast Asia that also infects people. It multiplies every 24 hours and can become severe quickly. Updated Nov 13, 2026 Also called: monkey malaria, fifth human malaria ## Quick facts **Type** Parasite · [Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/) **Gram / shape** Rings like P **Spread** Bite of forest Anopheles mosquitoes · Like any malaria **Causes** Knowlesi malaria · Severe knowlesi malaria On this page - The basics Key points - At a glance - Morphology - Transmission - Life cycle - In Colombia - Memory aid - What the colours mean - Clinical Virulence factors - Diseases it causes - Clinical picture - Diagnosis - Treatment Treatment - Prevention - Study Test yourself - Connections Connections ## Key points - Fifth human malaria: a zoonosis of macaques in Southeast Asia. - 24-hour cycle: daily fever and rapid rise in parasitemia. - Under the microscope it looks like P. malariae (bands) and P. falciparum (rings); PCR confirms. - Can be severe, with kidney injury; treat severe cases with IV artesunate. ## At a glance **Shape** Rings like P. falciparum; band trophozoites and schizonts like P. malariae **Family** Plasmodiidae **Type** Intracellular protozoan (sporozoan) of red blood cells **Stain** Giemsa thick and thin smear; PCR needed to name the species ## Morphology - Early rings look like P. falciparum: double chromatin dots, appliqué forms and several parasites per cell. - Older trophozoites form bands across the cell, like P. malariae. - Mature schizonts have up to 16 merozoites; infected red cells are not enlarged. ## Transmission - Bite of forest Anopheles mosquitoes of the Leucosphyrus group that have fed on infected macaques. - Human-to-human transmission by mosquitoes has not been shown in nature: it is a zoonosis. - Like any malaria, also possible by blood transfusion. **Reservoir:** Long-tailed and pig-tailed macaques (and leaf monkeys) in Southeast Asian forests **Vector:** Anopheles of the Leucosphyrus group (for example An. balabacensis in Malaysian Borneo), which bite in forests and forest edges. ### Isolation precautions What the care team adds to standard precautions. - Standard ## Life cycle - An infected Anopheles injects sporozoites while biting a macaque or a person in the forest. - Sporozoites multiply in the liver; P. knowlesi has no dormant hypnozoites. - Merozoites invade red cells and complete a cycle about every 24 hours. - Some parasites become gametocytes in the blood. - A mosquito takes up gametocytes from a monkey, and the sexual cycle ends with new sporozoites in its salivary glands. ## Virulence factors - The 24-hour blood cycle lets parasitemia rise fast, so high counts can be reached within days. - Severe disease with jaundice, kidney injury, respiratory distress and shock, mostly in adults with high parasitemia. - Thrombocytopenia is common. ## Diseases it causes - Knowlesi malaria: daily fever with chills, headache and myalgia after forest exposure in Southeast Asia. [Malaria →](https://durgical.com/en/conditions/malaria/) - Severe knowlesi malaria with acute kidney injury and high parasitemia; can be fatal if recognized late. [Acute kidney injury →](https://durgical.com/en/conditions/acute-kidney-injury/) ## Clinical picture - Most cases come from Malaysia (especially Sabah and Sarawak in Borneo), but it occurs across Southeast Asia. - Travelers who visited forests in the region can present at home weeks later. - Daily (quotidian) fever is a clue, unlike the 72-hour rhythm of P. malariae. ## Diagnosis - Thick and thin Giemsa smears show the parasite but often misread it as P. malariae (or P. falciparum in early stages). - PCR is the definitive way to identify the species. - Rapid antigen tests may detect it poorly; a 'P. malariae' with high parasitemia in a traveler from Southeast Asia is P. knowlesi until proven otherwise. ## Treatment Uncomplicated disease responds to artemisinin-based combinations or chloroquine; severe disease is treated with intravenous artesunate, as for severe falciparum malaria. No primaquine is needed for relapse because it has no hypnozoites. Drug class only; doses and regimens are set by the clinician from the current guideline. In Pharmacology: - [Artemether + lumefantrine](https://durgical.com/en/pharmacology/artemether-lumefantrine/) - [Chloroquine](https://durgical.com/en/pharmacology/chloroquine/) - [Artesunate](https://durgical.com/en/pharmacology/artesunate/) ## Prevention - Repellents, long clothing and treated nets when entering forests in Southeast Asia. - Chemoprophylaxis for travelers as for other malaria in the region. - Bed nets and indoor spraying are less useful because vectors bite outdoors in forests. ## In Colombia It does not occur in the Americas. In Colombia it matters for travelers returning from Southeast Asia; any imported malaria is reported to SIVIGILA. ## Memory aid «Knowlesi knows no rest»: it divides every day like a clock that rings at 24 hours, wears a malariae costume and lives with the monkeys. ## Test yourself Think of the answer, then tap the question to see it. ## What is the natural reservoir of Plasmodium knowlesi? Long-tailed and pig-tailed macaques in Southeast Asian forests. ## Why is P. knowlesi often missed on microscopy? Its late stages look like P. malariae and its rings like P. falciparum; PCR is needed to identify it. ## What is the length of its blood cycle and why does it matter? About 24 hours: it causes daily fever and lets parasitemia rise quickly to dangerous levels. ## Does P. knowlesi need primaquine to prevent relapses? No. It does not form hypnozoites in the liver. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/plasmodium-knowlesi/) ## What the colours mean **Gram-positive** Thick peptidoglycan wall: stains purple. **Gram-negative** Thin wall with an outer membrane: stains pink. **Acid-fast** Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain. ## Connections ## Related 5 - [Plasmodium malariae and Plasmodium ovale](https://durgical.com/en/microbiology/plasmodium-malariae-and-plasmodium-ovale/) - [Plasmodium falciparum](https://durgical.com/en/microbiology/plasmodium-falciparum/) - [Plasmodium vivax](https://durgical.com/en/microbiology/plasmodium-vivax/) - [Anopheles](https://durgical.com/en/microbiology/anopheles/) - [Babesia spp.](https://durgical.com/en/microbiology/babesia-spp/) ## Related conditions 2 - [Malaria](https://durgical.com/en/conditions/malaria/) - [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/) [← Back to the group: Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/) Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [CDC - DPDx - Malaria](https://www.cdc.gov/dpdx/malaria/index.html) (CDC, 2024); [Zoonotic Malaria – Global Overview and Research and Policy Needs](https://pmc.ncbi.nlm.nih.gov/articles/PMC4135302/) (Frontiers in Public Health (PMC), 2014); [Three Divergent Subpopulations of the Malaria Parasite Plasmodium knowlesi](https://wwwnc.cdc.gov/eid/article/23/4/16-1738_article) (Emerging Infectious Diseases (CDC), 2017). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/microbiology/plasmodium-knowlesi/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/plasmodium-knowlesi/