Malaria

Overview

Malaria is a disease caused by a protozoan parasite, Plasmodium.

Singapore was certified malaria-free by the World Health Organization in November 1982.

Pathogen(s)

Four different Plasmodium species:

• P. falciparum

• P. vivax

• P. ovale

• P. malariae 

In recent years, P knowlesi, a parasite of Old-World monkeys has been identified as the fifth major human malaria parasite. It is an emerging infection in Southeast Asia and can cause serious life-threatening complications. In rare cases, it can cause death.

Transmission

Main mode of transmission is via bite of infective Anopheles mosquito.

Incubation period: Ranges from 7 to 30 days in most cases. Also varies according to species:

• P. falciparum: 9 to 14 days

• P. vivax and P. ovale: 12 to 18 days (up to 6 to 12 months for some P. vivax strains)

• P. malariae: 18 to 40 days

• P. knowlesi: 9 to 12 days

Infectious period: Infectious to mosquitoes if parasites (infective gametocytes) are present in the blood.

Clinical features

The most common early symptoms of malaria are fever, headache and chills.

In severe disease, acute kidney injury, acute respiratory distress syndrome, mental confusion, severe anemia, seizures, coma, and death can occur. 

The 2025 WHO malaria guidelines define severe malaria by the presence of any of the following features:

• Clinical

  • Impaired consciousness or unrousable coma

  • Prostration, i.e. generalised weakness where the patient is unable to sit, stand or walk without assistance

  • Multiple convulsions – more than two episodes in 24 hours Deep breathing, respiratory distress (acidotic breathing)

  • Circulatory collapse or shock

  • Significant bleeding

  • Pulmonary oedema (radiological)

• Laboratory

  • Hypoglycaemia (blood glucose < 2.2 mmol/l or < 40 mg/dl)

  • Metabolic acidosis (plasma bicarbonate < 15 mmol/l)

  • Severe malarial anaemia (Hb ≤ 5 g/dl or haematocrit of ≤ 15% in children < 12 years of age; Hb <7g/dl or haematocrit of <20% in adults) with a parasite count > 10 000/μL for P. falciparum

  • Jaundice (Plasma or serum bilirubin > 50 µmol/L (3 mg/dL) with a parasite count > 100 000/μL for P. falciparum or >20 000/μL for P. knowlesi

  • Hyperparasitaemia

    • P. falciparum: parasitaemia > 10% of red blood cells

    • P. knowlesi: parasite density > 100 000/μl

  • Renal impairment (serum creatinine > 265 μmol/l or blood urea > 20mmol/l)

Severe P. vivax malaria is defined using the same criteria as above, but with no parasite density thresholds. Severe P. knowlesi malaria is defined using the same criteria as above, with species-specific parasite density thresholds for jaundice and hyperparasitaemia as specified above.

Risk factors

Risk factors include:

• Living in or travelling to malaria-affected areas

Diagnosis

• Laboratory confirmation of malaria parasites via microscopic examination of blood films (repeat 12 hourly for 48 hours if the diagnosis is considered likely and initial films are negative).

• Identification of the species-specific malaria parasite via PCR.

• Rapid diagnostic tests (RDTs) offer a useful alternative to microscopy in situations where reliable microscopic diagnosis is not available. 

Treatment and management

Cases should be treated in hospital until parasitaemia has cleared.

Precaution, prevention, and control

Standard precautions apply in healthcare settings.

Prevention measures include:

• Starting appropriate chemoprophylaxis before travel.

• Avoiding exposure between dusk and dawn as this is when the female anopheline mosquito is active.

• Staying in rooms which are well-screened from insects from the exterior.

• Wearing long, protective clothing that covers most of one’s body.

• Using effective mosquito repellent (e.g. those containing DEET, Picaridin or IR3535 as the active ingredient) and reapplying every four to six hours on exposed skin.

There is currently no approved vaccine against malaria in Singapore.

Notification

Who should notify:

• Medical practitioners

• Laboratories

When to notify:

• On clinical suspicion or laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification for more information. 

Notification timeline:

• As soon as possible. No later than 24 hours from the time of diagnosis.

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the number of malaria cases in Singapore.

Please refer to the latest WHO malaria guidelines (2025) for more details.