Malaria is an infection of the red blood cells caused by one or more of five species of Plasmodium parasite transmitted by Anopheles mosquitoes. The best known symptom of malaria is fever, but the most dangerous aspect of the disease is potentially fatal brain damage caused by Plasmodium falciparum.
Malaria is a mainly tropical and sub-tropical disease, with about half of the world’s population at risk of infection. Children aged under five years are most seriously affected. Frequent exposure to malaria from an early age generally builds immunity so adults who've grown up in malarious countries are less susceptible to severe malaria. Visitors to malarious countries generally have no immunity to malaria and are advised to seek medical advice before travel and take steps to avoid infection.
Annually, there are nearly 220 million cases of malaria with numbers increasing slightly in recent years. Over 90% of malaria is reported in Africa and 5% is reported in Southeast Asia. About 435,000 people die of malaria each year. Of these deaths, 90% are in Africa and 60% of those who die are children. Drug resistance is a matter of growing concern.
Species of plasmodium
Plasmodium falciparum occurs in most malarious countries and is by far the most common malaria in Africa. It causes:
- severe, non-relapsing malaria
- most malaria deaths
- potentially fatal cerebral malaria
Plasmodium ovale mostly occurs in Africa, but also seen in the Pacific and Asia. It causes less severe relapsing malaria but relapses may occur years after infection occurs.
Plasmodium malariae occurs in many malarious countries, although it's not always common. When is does occur it causes benign non-relapsing malaria which is debilitating but rarely fatal.
Plasmodium vivax Asia is found in Asia, including southeast Asia, as well as Eastern Mediterranean, Oceania and South America. It's uncommon in most of Africa, except:
It causes potentially serious relapsing malaria and these relapses may continue for long periods after infection occurs.
Plasmodium knowlesi is found in Southeast Asia and causes potentially serious non-relapsing malaria. P. knowlesi usually occurs in monkeys and is now the most common malaria in humans in some of the malarious areas.
Historically, malaria was found in Europe and the United States. Malaria seen in Europe is nearly always imported, although there are rare cases of locally transmitted infection. Together, the UK and France report approximately 50% of imported cases seen in European Union countries. The distribution of malaria has decreased in recent decades with the population of Sub-Saharan Africa experiencing most cases of the disease. In the past 20 years there have been substantial decreases in malaria cases reported from the areas below:
- Indian sub-continent
- Southeast Asia
- South America
- Central America
However, outbreaks do occur in many countries in those regions. For example, in recent months Venezuela has reported a large increase in numbers of cases. As well as Argentina, remaining low risk areas reporting rare cases are some countries in:
- Central Asia
- North Africa
- Middle East
As of 2017, Paraguay has been declared malaria free, while China reported no cases in 2017. Since 2016, the World Health Organisation (WHO) European Region has been formally free of malaria.
Travellers to malarious countries are advised to seek medical attention if they develop a fever during or after travel.