Malaria

Malaria is an infection of the red blood cells, causing a sudden fever. Untreated, infection can progress rapidly and become life threatening.

It is a parasitic disease transmitted by Anopheles mosquitoes. There are five types of parasites that cause malaria:

• Plasmodium ovale
• P. malariae
• P. knowlesi
• P. vivax
• P. falciparum.

The last two are the most common.

Malaria can kill by destruction of red blood cells (anaemia) and by altering the function of vital organs such as the brain, (cerebral malaria) lungs or kidneys.

Primarily, malaria is an infection of the red blood cells, causing recurring fever of sudden onset.  Malaria caused by P. falciparum is life threatening and can cause multiple organ damage, coma and death.

How it is spread

Malaria is spread by female Anopheles mosquitoes. The parasite enters the body in mosquito saliva when a person is bitten by an infected mosquito.

The parasite first infects the liver where it begins to multiply. After some days, the resulting parasites are released into the blood stream to infect the red blood cells, where they continue to multiply, eventually bursting the red blood cells and further infecting others. If they reach high numbers they may cause severe disease or even death.

Some of the parasites in the red blood cells develop into the sexual stages (gametocytes). If these stages are ingested when a mosquito bites an infected person, they develop in the gut of the mosquito for 10 to 14 days, and then enter the salivary glands, ready for the next bite.

Where it is found

Malaria is found throughout the tropical and subtropical regions of the world. Areas of high transmission are found predominantly in rural areas in South America (e.g. Brazil), south-east Asia (e.g. Thailand, Indonesia and East Timor), Western Pacific (Papua New Guinea, Solomon Islands and Vanuatu) and throughout sub-Saharan Africa.

The last case of locally acquired malaria in the Northern Territory was in 1962 and Australia was declared free of malaria by the World Health Organisation (WHO) in 1981. However, a number of species of Anopheles mosquitoes exist in the NT and the malaria parasite could be re-introduced into local mosquitoes if infected travellers from overseas are bitten here.

The disease could become established anywhere in the Top End, down to a latitude of 19 degrees which is just north of Tennant Creek.

Symptoms

Symptoms appear about 9 to 14 days after a bite from an infected mosquito, and coincide with the rupture of the red blood cells. Symptoms are often delayed in people who have lived in malarious areas and who may have developed some immunity.

Typically malaria produces fever, rigors (shakes), sweating, headache, vomiting and other flu-like symptoms. Sometimes there is a 2 or 3 day period of reduced symptoms before a recurrence on the third or fourth day. Untreated, infection can progress rapidly and become life threatening.

Malaria can kill by destruction of red blood cells (anaemia) and by altering the function of vital organs such as the brain, (cerebral malaria) lungs or kidneys.

Malaria relapse

P. vivax and P. ovale exist as dormant forms that remain in the liver for months or years before producing the disease.

With P. falciparum, the disease can reoccur after apparent recovery, due to either inadequate treatment or infection with a drug resistant strain. P. malariae can rarely persist with very low levels of parasite in the peripheral blood for decades.

P. knowlesi produces acute illness but does not cause relapse.

Diagnosis

Malaria is diagnosed by a blood test. The blood is examined under a microscope looking for malaria parasites inside the red blood cells. All travellers from malarious areas who become ill or develop a fever should be tested.

Treatment

All cases of P. falciparum malaria in the NT are admitted to hospital because this form of malaria can rapidly become life threatening.

Cases of malaria other than P. falciparum can sometimes be treated at home if the house is adequately screened and if the patient agrees to stay indoors between dusk and dawn. This is to avoid any risk of transmission of the parasite to the local Anopheles mosquitoes.

Treatment must be given in consultation with specialist physicians.

Before travelling overseas

Check whether the countries to which you are travelling are affected by malaria by contacting your GP, Travel Health Clinic or going to WHO International Travel and Health website or the Centers for Disease Control and Prevention website.

If you are travelling to an affected country you will often need preventative medication. Contact your GP or Travel Clinic to organise anti-malarial medication for your trip. Some medication must be started 1 week prior to entry to the affected area.

How to protect yourself from mosquito bites

While in affected areas there are measures which should be taken to reduce the risk of mosquito bites:

• avoid being outdoors between dusk and dawn to avoid mosquito bites, particularly in poorly lit areas, rural areas, or the outskirts of large towns
• if accommodation is not well screened, sleep inside mosquito netting. Use insecticide treated bed nets and clothing in high risk areas
• avoid scents on the body, e.g. perfume, deodorants, and sweat, since these can attract mosquitoes
• use protective clothing in outdoor situations including covering feet, legs and arms - loose, light coloured clothing is best
• use personal repellents containing DEET or picaridin on areas of exposed skin in combination with protective clothing
• use electric insecticide devices using repellent treated pads in indoor or enclosed areas
• use mosquito coils, or candle heated or gas operated devices using insecticide treated pads for patio and veranda or relatively sheltered or low wind outdoor situations.

For more information on protection measures see Personal protection from mosquitoes.

If you return from a malarious area and develop symptoms

If you develop symptoms of malaria within 2 years of visiting a malarious area contact your GP or hospital emergency department immediately for an urgent medical assessment.

Remember to inform the medical officer of where you have travelled as this will help determine your risk of malaria and the type of treatment required.

If you have malaria, the people you have travelled with (particularly to high risk areas such as Africa, PNG, East Timor and parts of Indonesia including Flores, Lombok and surrounding islands) should also be tested.

Information for health professionals

To find out more go to the NT Health website.

Contact

For more information contact your nearest Centre for Disease Control.

For more information on mosquitoes and virus ecology contact the Centre for Disease Control Medical Entomology Unit.