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Causative Agents

Plasmodium falciparum, P. vivax, P. ovale and 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 SE Asia and is capable of causing serious life threatening complications and death in a minority of cases.

Incubation Period

1 to 4 weeks (months for non-falciparum Plasmodium)

Infectious Period

Until parasites cleared from blood.


Transmission via bite of infected female Anopheles mosquito. Vertical transmission and by blood transfusion or organ transplant also possible.


Approximately 100-300 cases per annum in Singapore (80% vivax); almost all are imported.

One hundred and seventy laboratory-confirmed cases were reported in 2009, an increase of 13.2% compared to the 152 cases reported in 2008. 16.8% of the cases were reportedly acquired locally, an increase of 16.1% compared to the previous year. There were six cases of simian malaria involving five locals and one foreigner. Three of the local residents acquired their infection while trekking in Malaysia at separate occasions while two were infected during jungle trainings at Brunei.

Endemic in SE Asia, particularly rural areas.

Chloroquine-resistant falciparum malaria is widespread in the region; occasional cases of chloroquine-resistant vivax have also been reported.


Fever, chills, rigors


Hepatosplenomegaly sometimes present

Severe falciparum malaria

Defined by presence of any of the following features:

  • Clinical
    • impaired consciousness or unrousable coma
    • prostration, i.e. generalized weakness so that the patient is unable walk or sit up without assistance
    • failure to feed
    • multiple convulsions – more than two episodes in 24 h
    • 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)

  • Examination of thick and thin blood films (repeat 12 hourly for 48 hours if the diagnosis is considered likely and initial films are negative).
  • Rapid diagnostic tests (RDTs) offer a useful alternative to microscopy in situations where reliable microscopic diagnosis is not available
  • Anaemia, thrombocytopenia and leucopenia are common.
  • FBC, electrolytes, glucose, LFTs, clotting screen and a CXR should be performed in all patients with acute falciparum malaria to assess severity (see above criteria).

A legally notifiable disease in Singapore. Notify Ministry of Health (Form MD 131 or electronically via CD-LENS) not later than 24 hours from the time of diagnosis.

  • Cases should be treated in hospital until parasitaemia has cleared.
  • Non-falciparum malaria: chloroquine 600 mg stat, then 300 mg X 3 daily doses. Primaquine 15mg daily for 2 weeks to eliminate hepatic stage (check G6PD levels first).
  • Falciparum malaria, mild: Artemisinin-based combination therapies preferred. Alternative choice is oral quinine 600 mg tds for 7 days, together with doxycycline 100 mg bd for 7 days.
  • Falciparum malaria, severe (as defined above): a medical emergency. Treatment is urgent and experience with severe malaria is essential. Intravenous (IV) artesunate plus clindamycin or doxycycline is treatment of choice for severe malaria. Intravenous quinine plus doxycycline is an alternative.  Meticulous fluid management, regular monitoring of blood sugar and supportive therapy for organ dysfunction as required. Exchange transfusion may be considered  for high parasitaemia with complications, but the indications and level of parasitaemia are controversial.

The best community-based control in malaria endemic countries is impregnated bed- nets.

  • For personal protective measures for travellers to endemic areas:
    • Avoid exposure between dusk and dawn as this is when the female anopheline mosquito is active.
    • Wear long-sleeves light-coloured clothing.
    • Use mosquito repellent containing 10% to 30% DEET.
    • Use mosquito coils.
    • Consider treating clothes with permethrin-based products.
    • Sleep under impregnated mosquito netting and keep to well-screened or air- conditioned rooms.
  • Control: epidemic vector control measures will be implemented when local transmission is detected.

  • Mefloquine: 250mg (salt) per week, beginning 1 week before departure and continued for 4 weeks after leaving the endemic area. Advantage: weekly dosing; reasonable pricing. Disadvantage: neuropsychiatric side effects.
  • Doxycycline: 100mg daily beginning 1 to 2 days before entering the affected area and for 4 weeks after leaving the area. Advantage: cheap. Disadvantage: daily dosing. Side effects: photosensitivity, vaginal thrush and oesophagitis.
  • Atovaquone/proguanil (Malarone): 1 adult tablet once daily beginning 1 to 2 days before entering affected area and for 7 days after leaving the area. Advantage: few side effects, short duration of intake before and after travel. Disadvantage: expensive, daily intake.
  • Chloroquine/proguanil is a less optimal alternative.


  1. Lee YCA, Tang CS, Ang LW et al. Epidemiological characteristics of imported and locally- acquired malaria in Singapore. Ann Aca Med Singapore 2009;38:840-9.
  2. Cox-Singh J, Davis TM, Lee KS, et al. Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening. Clin Infect Dis 2008;46:165-71.
  3. Ng OT, Ooi EE, Lee CC, et al. Naturally acquired human Plasmodium knowlesi infection, Singapore. Emerg Infect Dis 2008;14:814-6.
  4. WHO. Guideline for the Treatment of Malaria - 2nd edition, 2010. World Health Organization.
  5. International Travel and Health 2010. World Health Organization.

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