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 (varies by 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

Symptoms include:

Fever
Chills
Rigors

Signs include:

Hepatosplenomegaly (sometimes)

Severe falciparum malaria is defined by presence of any of the following features:

Clinical
- Impaired consciousness or unrousable coma
- Prostration, i.e. generalised weakness so that the patient is unable walk or sit up without assistance
- Failure to feed
- Multiple convulsions – more than two episodes in 24 hours
- Deep breathing, respiratory distress (acidotic breathing)
- Circulatory collapse or shock, systolic blood pressure < 70 mm Hg in adults and < 50 mm Hg in children
- Clinical jaundice plus evidence of other vital organ dysfunction
- Haemoglobinuria
- Abnormal spontaneous bleeding
- Pulmonary oedema (radiological)
Laboratory
- Hypoglycaemia (blood glucose < 2.2 mmol/l or < 40 mg/dl)
- Metabolic acidosis (plasma bicarbonate < 15 mmol/l)
- Severe normocytic anaemia (Hb < 5 g/dl, packed cell volume < 15%)
- Haemoglobinuria
- Hyperparasitaemia (> 2%/100 000/μl in low intensity transmission areas or > 5% or 250 000/μl in areas of high stable malaria transmission intensity)
- Hyperlactataemia (lactate > 5 mmol/l)
- Renal impairment (serum creatinine > 265 μmol/l)

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
Wearing long-sleeves and light-coloured clothing
Using mosquito repellent containing 10% to 30% DEET
Using mosquito coils
Treating clothes with permethrin-based products
Sleeping under mosquito netting and staying in well-screened or air-conditioned rooms

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 confirmed malaria cases in Singapore.