Understanding Malaria: Should Australians be Concerned?
Published: 31 May 2020
At least 200 million people are infected with malaria every year, with an estimated 400,000 deaths annually (WHO 2020).
Malaria is an infectious disease caused by the parasite Plasmodium, which is transmitted through the bite of a female Anopheles mosquito. Occasionally it is transmitted congenitally, by blood transfusion or by syringes (NSW DoH 2016).
When female Anopheles mosquitoes feed on blood to nurture their eggs, they can pick up Plasmodium parasites from humans infected with malaria. These mosquitoes will then become vectors (carriers) and transmit Plasmodium to other people they bite. You can not contract malaria directly from another person (CDC 2020; WHO 2016).
Should Australians Worry About Malaria?
Australia was certified as being malaria-free by the World Health Organisation in 1981. (QLD DoH 2017).
Despite this, there are still reasons to be vigilant:
Every year, several hundred imported cases from travellers are recorded in Australia.
If you travel to areas where malaria occurs you are at risk of being infected if you do not take appropriate precautions. These areas include:
Tropical and subtropical parts of Asia, Africa, Central America and South America;
The Pacific Islands; and
Parts of the Middle East.
Local cases are occasionally reported in the Torres Strait in Australian territory.
The Anopheles mosquito lives in parts of the Northern Territory.
(QLD DoH 2017; NSW DoH 2016; Canna 2019)
If Australia is to remain free of malaria, it is imperative that all cases are diagnosed and treated appropriately. If you’ve been in an area where malaria has occurred within the previous 12 months and you develop a fever, you should be checked for malaria, both for your own sake and to prevent malaria getting into the community.
Types of Plasmodium
There are five main species of Plasmodium that cause malaria in humans. They differ somewhat in areas where they mainly occur, the symptoms they cause, and treatment required.
Plasmodium falciparum causes the most serious and life-threatening illness, potentially resulting in liver or kidney failure, convulsions or coma.
Plasmodium vivax generally causes a less serious illness but is able to lie dormant in humans for months or years. It causes many cases of malaria in the Asia-Pacific region.
Plasmodium ovale generally causes a less serious illness but is able to lie dormant in humans for months or years.
Plasmodium malariae generally causes a less serious illness.
Plasmodium knowlesi usually only causes malaria in monkeys, but there have been some human cases.
(MyDr 2012; Stanford Health Care 2019; The Walter and Eliza Hall Institute of Medical Research 2020)
After being bitten by an infected mosquito, the Plasmodium parasite enters the liver, where it begins to multiply. 7 to 18 days later (typically), the infection re-enters the bloodstream, invades red blood cells and reproduces (NHS 2018).
The initial flu-like symptoms are likely to include:
Feeling hot and shivery;
Nausea and vomiting; and
Muscle and joint pains.
Some people may experience recurring ‘attacks’ of malaria, where they experience cycles of symptoms that last for around 6 to 12 hours.
Shivering and chills.
Profuse sweating and fatigue.
A return to normal temperature.
(NHS 2018; Mayo Clinic 2018)
Plasmodium malariae may persist for several years and has been associated with nephrotic syndrome in children (Langford et al. 2015).
Severe malaria may cause symptoms such as:
Impaired consciousness or coma (cerebral malaria);
Unable to sit up without assistance;
Vomiting or failure to feed;
Shock or severe dehydration;
Haemoglobin in the urine;
Spontaneous bleeding (nose, gums);
Low urine volume;
Low blood glucose;
High lactate in the blood; and
Poor kidney function.
(Severe Malaria Observatory 2017; RCHM 2012)
Laboratory diagnosis of malaria is by microscopy. A blood specimen is spread as a smear and examined to confirm the presence of Plasmodium and calculate the percentage of red cells containing the parasites (CDC 2020).
Where microscopy is not possible, ‘dipstick’ tests (malaria antigen immunochromatographic test) may be used. This can detect Plasmodium falciparum but not other species (CDC 2020).
Malaria is treated with antimalarial drugs to kill the Plasmodium. The exact drug will depend on the species of Plasmodium involved and the patient (some medicines are not suitable in pregnant women or infants) (Mayo Clinic 2018).
Increasing medicine resistance is a problem, especially in certain areas, and the area in which malaria was caught needs to be considered (Mayo Clinic 2018).
In severe malaria, treatment must be started urgently. Initially, it needs to be intravenous. If the attack is not classified as severe, oral medications may be used (CDC 2020).
Plasmodium vivax and Plasmodium ovale may have dormant stages (hypnozoites) that persist in the liver and are not killed by the medication used for the acute attack. The patient may need to take primaquine (Mikolajczak et al. 2015).
Anyone travelling to a malarious region should take precautions. This includes consulting a physician to prescribe preventative antimalarial drugs (NSW DoH 2016).
No antimalarial drug is 100% effective, so taking precautions to avoid mosquito bites is also crucial. These include:
Being vigilant if spending time outdoors around dawn and dusk and into the evening;
Wearing loose, light-coloured, long-sleeved shirts and long pants when outdoors;
Applying mosquito repellent to exposed skin and on clothing;
Avoiding perfumes, colognes or aftershaves;
Sleeping in screened or air-conditioned rooms if possible, and using a mosquito net if not; and
Using ‘knockdown’ sprays, mosquito coils and plug-in vaporising devices.