Malaria

What is malaria?
Malaria is a common and serious tropical disease caused by a type of parasite (protozoan) transmitted to human beings by biting mosquitoes. There are four kinds of malaria that can infect humans: Plasmodium falciparum, P. vivax, P. ovale, and P. malariae. P. falciparum is the most severe form of malaria, and it and P. vivax are the most commonly encountered.

Where does malaria occur?
Malaria is a public health problem in more than 100 countries; over 2 billion people live in malarious parts of the world. More than 90% of cases occur in tropical Africa, but it is also found in the Indian subcontinent, Southeast Asia, Central and South America, Hispaniola (Haiti and the Dominican Republic), the Middle East, and Oceania. For travellers and tourists, Africa south of the Sahara probably represents the area of greatest risk of malaria. 

How common is malaria?
The World Health Organization estimates that there were between 150 and 300 million cases of malaria in 2015, causing more than 400 thousand deaths. There were 81 malaria cases notified in Ireland in 2015. All cases in Ireland have been associated with overseas travel and immigrants returning from malaria-risk areas. Malaria is a notifiable disease in Ireland.

How do you get malaria?
Humans get malaria from the bite of a malaria-infected mosquito. Those at risk include people living in or travelling through a malaria-infected area. Mosquitoes feed on blood, and when a mosquito bites an infected person, it swallows malaria parasites in the person's blood. The malaria parasites grow in the mosquito for a week or so, and if the mosquito then bites again, the parasites are passed on to another person. 

The parasites then travel to the person's liver, where they multiply. Once they have built up in number, the parasites leave the liver and enter red blood cells; it is at this stage that the person begins to feel unwell. This generally happens after 2 to 3 weeks depending on the type of malaria but occasionally can take up to 9 months. The red blood cells when full, burst and the parasites are free to attack other red blood cells. At the same time, toxins from the parasite are released into the blood, making the person feel unwell. If a feeding mosquito bites an infected person at this point, it is likely to ingest blood that contains malarial parasites, and within a week that mosquito will be infectious if it goes on to bite another person (Further information on the mosquito's lifecycle can be found in the World Health Organization's Roll Back Malaria Factsheet).

What are the signs and symptoms of malaria?
Malaria produces an illness that resembles influenza, with fever, chills, headache, muscle aches, and tiredness. Nausea, vomiting, and diarrhoea are not uncommon. The most severe form of malaria, that caused by Plasmodium falciparum, if not promptly treated, may cause kidney failure, seizures, mental confusion, coma, and death. Anaemia and jaundice may occur, and haemoglobin from the burst red blood cells may be passed out in the urine, causing it to become dark in colour (Blackwater fever). 

How soon will a person feel unwell after being bitten by an infected mosquito?
Most people begin to feel unwell from 10 days to 4 weeks after being infected; in some cases the illness may take as long as a year to develop. Uncommonly, malaria caused by P. vivax and P. ovale (but not the more serious P. falciparum) can relapse months or even years after travelling to a malaria-infected country. Parasites can remain dormant in the liver for several months up to 4 years after an infected mosquito bites a person. This can happen even if the person took their anti-malarial treatment as directed. Fortunately, this form of malaria responds very well to anti-malarial medication.

It is therefore important that any traveller who becomes ill with a fever or flu-like illness while travelling and up to 1 year after returning home should immediately seek professional medical care. You should let your doctor know that you have visited a malaria-risk area.

How is malaria diagnosed?
Malaria is clinically suspected in anyone who gives a history of travel in affected areas and who has suggestive symptoms. It is diagnosed by identifying the parasites through a microscope in a thin smear of the patient's blood.

What is the treatment for malaria?
Malaria can be cured with prescription drugs. The type of drugs and length of treatment depend on which kind of malaria is diagnosed, where the patient was infected, the age of the patient, and how severely ill the patient was at start of treatment.

If I have had malaria, or have been visiting or living in malaria-endemic country, will I have developed immunity to malaria?
If you have had malaria or have been living in malaria-endemic country, you may have developed partial immunity. In malaria-endemic areas with high levels of transmission, newborn children are protected in their first months of life by the antibodies of their immune mothers. After that, they gradually develop their own immunity over the years. The immunity is reversible: fully "immune" adults who leave malarious areas lose virtual all their immunity with the space of 1 to 2 years. In areas with only seasonal or epidemic malaria where disease is infrequent, adequate protective immunity may never build up. In persons with sickle cell anaemia or the sickle cell trait, the abnormal haemoglobin S offers some protection against Plasmodium falciparum infection.

How do I avoid catching it?

• For further advice see the World Health Organization's factsheet on malaria.
• Protection from biting mosquitoes is the first line of defence against malaria in endemic areas. The following measures are effective in reducing the risk of mosquito bites:
  • If possible, avoid going out between dusk and dawn when mosquitoes commonly bite.
  • Wear long-sleeved clothing and long trousers and closed shoes when going out at night, and avoid dark colours, which attract mosquitoes.
  • Apply insect repellent to exposed skin, choosing one with DEET or dimethyl phthalate.
  • Stay in a well-constructed and well-maintained building in the most developed part of town.
  • Use screens over doors and windows. If accommodation allows entry of mosquitoes, use a mosquito net over the bed.
  • Use anti-mosquito sprays or insecticide dispensers that contain tablets impregnated with pyrethroids, or burn pyrethroid mosquito coils in bedroom at night.
• There is additional information on how to protect yourself and your family from mosquito bites.

As well as effective treatments for patients who contract malaria, there are effective prophylactic medications that can be taken to prevent the development of malaria. These medications may have to be taken for up to 7 days BEFORE you enter the malarious area and for up to 4 weeks AFTER you leave the area. 

The type of prophylaxis depends on the area, local species of malaria, local pattern of anti-malarial drug resistance (which is increasing) and personal characteristics such as allergies and contraindications, including (for some drugs) pregnancy. Your doctor can recommend which is the most suitable for you to take, in light of the area to which you are travelling and your own personal medical history. Your doctor can advise you about the advisability of travelling if pregnant and of bringing very small children, especially to areas where malaria parasites have become resistant to chloroquine. 

Unfortunately, no anti-malarial prophylaxis medication gives complete protection. Malaria may be contracted despite taking anti-malarial prophylaxis. If it is taken exactly as prescribed by your doctor, without missing doses, there is a high likelihood of avoiding malaria. 

If you do not take prophylactic medication as advised and for the recommended time periods before and after travel, you will be considerably more likely to develop disease and it may be more difficult to treat as a result.

Very importantly, the effects of precautions add up; taking medication properly, using insect repellent frequently, wearing suitable clothing, particularly in the mornings and evenings and using a mosquito net, will dramatically reduce your chances of being bitten and going on to develop malaria.

To prevent Malaria
• Take your antimalarial medication as prescribed.
• Prevent mosquito bites
• If you become unwell, immediately seek medical attention

Where are the malaria hotspots around the world?
The distribution of the different kinds of malaria can vary slightly from time to time as can the types of drugs used to prevent and treat it. Your GP will be able to advise you as to the most appropriate preventive medication to take.

What is 'airport malaria'?
Very occasionally, mosquitoes can be carried on board aircraft and on landing in a country where malaria is not normally seen, can bite people living close to the airport. This unusual form of malaria is known as 'airport malaria'. Between 1969 and 1999, 12 countries reported to the World Health Organization, a total of 87 cases of malaria in people living near an airport. France has reported most cases (26) but Belgium (16 cases) and the UK (14 cases) also see a considerable number of cases of this unusual phenomenon. Theoretically, airport malaria is possible close to any airport where the climatic conditions allow mosquitoes to survive and feed for even a few hours after emerging from the aircraft.

Updated: 28 March 2017