Last Review Date: November 6, 2017
Malaria is an infectious disease caused by Plasmodium parasites. The are spread by the bite of infected female Anopheles mosquitos. There are five types of Plasmodium (P) species which infect humans; P. malariae, P. falciparum, P. vivax, P. ovale and P. knowlesi.
Very rarely, transmission can also occur through infection, blood transfusion and sharing of needles or syringes.
When a human is bitten by an infected mosquito the parasites enter the blood stream and travel to the liver. After infection there is usually an incubation period of 7-30 days, after which the parasites enter red blood cells and develop. Some people don’t develop symptoms for several months, particularly if they took inadequate doses of anti-malarial medication. P. vivax and P. ovale cause relapsing disease as the parasite can stay dormant in the liver, before re-entering the blood stream months, and even years, after the initial infection. Infection by P. falciparum can cause life-threatening disease, as can P knowlesi.
The World Health Organisation declared Australia malaria-free in 1981, however several hundred cases are diagnosed in Australia each year. These people generally contract the disease while travelling, most commonly in Papua New Guinea. There were also seven cases of locally acquired malaria in the Torres Strait in 2010-11.
Ninety percent of all malaria deaths occur in sub-Saharan Africa. Malaria also exists in regions of Central and South America, parts of the Caribbean, Africa, Asia (including South Asia, Southeast Asia, and the Middle East), Eastern Europe and the South Pacific.
Worldwide, the World Health Organisation estimated there were 212 million new cases of malaria and 429,000 deaths (down 30% from 2012) in 2015.
Malaria often presents as a flu-like illness with fevers, chills, sweats, headaches, aches and . Some people develop gastrointestinal symptoms of nausea, vomiting and diarrhoea. and symptoms develop when the parasites change from the liver stage and enter red blood cells to undergo multiplication. After a few days the red blood cells burst to release the parasites.
A large spleen may be present, but there may be few other signs that can be detected by a physical examination.
Complicated malaria, primarily caused by P. falciparum, is life-threatening. It can affect the brain, kidneys, lungs and red blood cells and can result in multi-organ failure. When it affects the brain it is called cerebral malaria.
Thick and thin blood films
Ideally, three blood tests of both thick and thin blood films should be collected 12-24 hours apart to diagnose malaria. These tests are currently the ‘gold standard’ for malaria detection and identification.
Thick films are sensitive tests for diagnosing malaria infection. A large number of red blood cells are looked at under the microscope to find parasites within the cells. The number of infected red blood cells can also be calculated so that the parasite load is known.
Thin films are done with fewer blood cells examined per slide, but these tests allow identification of the type of Plasmodium species causing the infection. This is essential for correct treatment.
Rapid diagnostic tests
These tests detect a malaria () in the patient’s blood, and signify a positive result by a colour change on the testing strip. They are sometimes called ‘dipstick’ tests.
Different rapid diagnostic tests are available, and they may detect only Plasmodium falciparum, or may detect other species.
These tests are most commonly used in remote areas where there is not access to accurate microscopy (so that blood films cannot be used). In Australia and other countries where malaria is not commonly seen, these tests are used in laboratories where there is insufficient experience to allow accurate microscopy. This allows rapid and accurate diagnosis and early treatment of malaria, which is essential to improve patient outcomes. In Australia further tests are usually then done to confirm the diagnosis, often in a central laboratory.
The polymerase chain reaction amplifies malaria and allows detection and identification of the Plasmodium species. This test can be used to confirm the diagnosis in laboratories where there is a lack of microscopy experience. It is also useful in cases of low parasite loads or mixed infections, where microscopy may be less accurate. The cost of these techniques limits their use in many regions where malaria is endemic.
It is important that everyone visiting or moving to countries where there may be exposure to malaria seek medical advice. This includes immigrants who return to their country of origin to visit friends and relatives.
All travellers should use personal protection methods to avoid mosquito bites, particularly from dawn to dusk. Light-coloured, loose fitting, long sleeved clothing should be worn and mosquito repellent with adequate DEET should be used. Mosquito nets for sleeping are recommended if accommodation does not have air conditioning or screens. impregnated clothing and nets can be used by those at high risk.
Anti-malarial medication can be used after consideration of each individual’s risk. Factors that must be considered include specific areas of travel, season of travel, type and length of travel and each person’s medical history. The type of medication recommended will depend on patterns of drug resistance and the individual’s history.
It is very important that the anti-malarial medications be used as directed, including continuing the course for the prescribed amount of time after exposure to malaria finishes (up to four weeks, depending on the medication used).
Travellers who develop symptoms of malaria during or after travel should seek medical assessment as soon as possible, as early diagnosis and treatment is essential.
Treatment is guided by the species of Plasmodium causing the infection, the geographical area in which the infection was acquired (and local patterns of drug resistance) and how sick the patient is. Pregnant and breastfeeding women and children require special consideration.
Patients with uncomplicated malaria can be treated with oral medication, however more severe disease requires medication.
Infections with P. vivax and P. ovale can relapse as the form of the parasite can remain dormant in the liver, and they therefore require additional treatment.
On this site
Tests: Blood films
Elsewhere on the web
National Notifiable Diseases Surveillance System, Department of Health and Ageing
Centers for Disease Control and Prevention (US): About Malaria, Biology
Centers for Disease Control and Prevention (US): Traveler's health - Malaria
eMedicine Infections Diseases: Malaria
World health Organization: Malaria
NOTE: This article is based on research that utilises the sources cited here as well as the collective experience of the Lab Tests Online-AU Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Additional sources used in current review
K Knope [et al.]. Arboviral diseases and malaria in Australia, 2010/11: Annual report of the National Arbovirus and Malaria Advisory Committee. Commun Dis Intell. 2013; 37:E1-E20.
World Health Organisation. World Malaria Report: 2013. http://www.who.int (last accessed 16 August 2014)
Sources used in current and previous reviews
Singh B, Kim Sung L, Matusop A, Radhakrishnan A, Shamsul SS, Cox-Singh J, Thomas A, Conway DJ. A large focus of naturally acquired Plasmodium knowlesi infections in human beings. Lancet. 2004 Mar 27; 363(9414):1017-24.
GJ Fitzsimmons ... [et al.]. Arboviral diseases and malaria in Australia, 2007/08: Annual report of the National Arbovirus and Malaria Advisory Committee. Commun Dis Intell. 2009; 33: 155-169
Peter Van den Eede, Hong Nguyen Van, Chantal Van Overmeir, Indra Vythilingam, Thang Ngo Duc, Le Xuan Hung, Hung Nguyen Manh, Jozef Anné, Umberto D'Alessandro, Annette Erhart. Human Plasmodium knowlesi infections in young children in central Vietnam. Malaria Journal. 2009; 8:249
Peter Massey, David N Durrheim, Rick Speare. Inadequate chemoprophylaxis and the risk of malaria. Australian Family Physician. 2007 (Dec) 36(12): 1058–1060
Stephanie P. Johnston, Norman J. Pieniazek, Maniphet V. Xayavong, Susan B. Slemenda, Patricia P. Wilkins, and Alexandre J. da Silva. PCR as a Confirmatory Technique for Laboratory Diagnosis of Malaria. J Clin Microbiol. 2006 (Mar) 44(3): 1087–1089
Cox-Singh J, Davis TM, Lee KS, Shamsul SS, Matusop A, Ratnam S, Rahman HA, Conway DJ, Singh B. Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening. Clin Infect Dis. 2008; 46(2):165-71
Trish Batchelor, Tony Gherardin. Prevention of malaria in travelers. Australian Family Physician. 2007(May) 36(5): 289–384
Murray CK and Bennett JW. Rapid Diagnosis of Malaria. Interdisciplinary Perspectives on Infectious Diseases Volume 2009, Article ID 415953, 7 pages. Available online at http://www.hindawi.com/journals/ipid/. Accessed January 2011.
Cox-Singh J, Hiu J, Lucas SB, Divis PC, Zulkarnaen M, Chandran P, Wong KT, Adem P, Zaki SR, Singh B, Krishna S. Severe malaria - a case of fatal Plasmodium knowlesi infection with post-mortem findings: a case report. Malaria Journal. 2010 (Jan 11) 9:10.