Malaria is a parasite of red blood cells and the world's number one infectious disease. It is caused by infection of the liver with parasites of the genus Plasmodium, transmitted by the bite of infected anopheline mosquitoes Anopheles bifurcatus. The parasites cause the rupture of red blood cells and, in its worse cases, life-threatening anaemia, coma or death. The disease is characterized clinically by recurrent paroxysms of chills, high fever, seizures, sweating and prostration. It can lead to anaemia, kidney failure or rupture of the spleen. In man, malaria is produced by four specific parasites: Plasmodium vivax, P. malariae, P. ovale and P. falciparum. Falciparum malaria is the most life-threatening and has a fatality rate in untreated cases of 25%; it is transmitted by its African mosquito vector Anopheles gambiae.
Malaria is worsening in many parts of the world. It is a major threat to health and development, is primarily an environmental and socio-economic problem. Past reliance on narrow strategies is increasingly seen as the reason for the resurgence of this debilitating disease. The P. falciparum] parasite has continued to evolve resistance to almost all drugs in use (chloroquine, sulfadoxine/pyramethamine, and mefloquine). In areas of mosquito control, research with bed nets impregnated with pyrethroid insecticide offers hope of at least partial control of transmission of the disease in certain epidemiological situations. However, many people cannot afford the mosquito nets, which cost $5-10. Patients can usually be saved if they receive prompt medical treatment, but many of them cannot afford doctor's fees or the cost of travel, in total often less than $20.
Ronald Ross discovered that mosquitoes transmit malaria in 1897. When malaria became a human disease (it is thought to originate in primates) is unclear. One thing that is clear is that it emerged long enough ago for humans to evolve innate defences.
The disease is characterized by fever and "flu-like" symptoms that may come and go, including chills, headache, muscle ache, and/or a vague feeling of illness. Vomiting or diarrhoea may also occur. There may be anaemia and jaundice (yellowing of the skin and whites of the eyes). Malaria symptoms can develop as early as seven days after first being exposed and as late as several months or even longer after leaving a malarious area, when use of preventive drugs has been stopped. If treatment is not received for Falciparum malaria, it can proceed to shock, liver and kidney failure, coma and death. While illness caused by vivax, ovale or malariae malarias is not usually life-threatening, it can pose serious risks to the very young or very old or to those with other illnesses. If these types of malaria are left untreated, episodes may recur at irregular times for months or possibly years, and the malariae form can recur more than 25 years after exposure.
Sickle cell mutation is a potentially fatal blood disorder seen mainly in Africa. This mutation in a haemoglobin gene (responsible for red pigment in blood cells) is one of a number of genetic traits that actually protect against malaria. People who have this genetic mutation are protected against malaria and thus likely to reproduce and pass on their evolutionary advantage.
A second genetic mutation that protects humans against malaria affects an essential enzyme for red blood cell function. But individuals with this mutation may also develop life-threatening anaemia (deficiency in the number or quality of red blood cells) due to the destruction of red blood cells as a side effect of treatment with some modern anti-malarial drugs.
Malaria kills more people each year than have died from AIDS in the last 15 years, according to the Malaria Foundation based in New York. Malaria is estimated to have caused 429,000 deaths in 2015.
In 1993, about 40 percent of the world's population, or about 2.5 billion people in more than 100 countries were said to be at risk from malaria, and 270 million infected. Most of the victims are children and pregnant women, with over 1 million dying each year. Malaria was thought to be under control in much of the world in the 1970s, but has become resistant to many drugs and insecticides. Outbreaks have quadrupled in recent years, with cases reported in the United States and Europe for the first time in decades. Africa bears the brunt of the problem with about 90 percent of all deaths by malaria. In India, malaria was almost wiped out between 1950 and 1970 through the country's extensive eradication programme, with annual infections falling 75 million to 100,000, and deaths from 800,000 to virtually none. Over the last two decades the trend has reversed with four epidemics since 1994.
Malaria continues to be the most important single disease in sub-Saharan Africa, and one of the most significant elsewhere in the tropics. It is endemic almost everywhere in the tropics, where approximately 2,582 million people live in 103 affected countries (over two-fifths of the world's population). The disease has claimed millions of lives in several countries over recent decades, and continues to account for a very high morbidity and mortality in the non-immune inhabitants of endemic areas. In 1990, it was estimated that 270 million people were infected. It had been estimated prior to increasing parasite resistance to antimalarial drugs that one million people die from malaria every year and at any given moment, 160 million people suffer from the disease. However, 1994 estimates were that the disease causes 200 million cases of clinical illness a year, and up to 2 million deaths. Some epidemiologists believe the death toll may be twice as high. In 1997, those estimates rose to 300 to 500 million cases per year.
Anti-malarial activities have protected only about 11% of the population, mainly in urban and peri-urban localities. Malaria has saturated the middle of the African continent where 100 million clinical cases of malaria occur each year. Following prolonged rains in 1990, epidemics had hit several highland areas, such as Botswana, Madagascar, Rwanda, Swaziland, and Zambia. The continuous increase of chloroquine resistance in Africa is now hampering control and treatment in rural areas. It is the most important single cause of febrile convulsions in children in tropical Africa, and a major cause of death in early life. Approximately 50% of children up to the age of three are infected (in some villages of western Kenya, virtually all children under age 5 have detectable Plasmodium in their bloodstream on any given day; many of these infections are subclinical, though a certain percentage progress to illness, and some of those to death.) Data from Gambia in 1987 show that malaria accounted for 10% of infant deaths and 25% of deaths of children between one and four years old. By adulthood, repeated infection produces partial immunity. In Kenyan surveys, about 40% of adults were found to have bloodstream parasites on any day.
Outside Africa, analysis of the 5.2 million cases reported to WHO in 1989 showed that 95% came from only 25 countries. India accounted for 39% of these "non-African cases", Brazil for 11%, and a further 25% (combined, in decreasing order of incidence) from Afghanistan, China, Myanmar, Sri Lanka, Thailand and Viet Nam. General trends in the total number of reported malaria cases indicated a stabilization after 1979, following the control of the major resurgence in Southeast Asia in the mid-1970s. China, in particular, has shown a steady decrease in case numbers since 1977 (some 140,000 in 1989 compared to 360,000 in 1986, and between three and four million in the late 1970s). In some countries, such as Thailand, improvement in the availability and quality of medical treatment have reduced deaths, even though the numbers of malaria cases increased. Generally, the Asian region shows a slowly declining trend in the prevalence of the disease (being the bulk of the 5.2 million cases outside Africa in 1991, compared with 6.5 million in 1982 and 10.7 million in 1977), while the rest of the western Pacific region, the eastern Mediterranean and European regions and the Region of the Americas show an increasing trend (700,000 in the Americas in 1982 compared to 280,000 in 1973).
Some areas of the world are now experiencing major malarial epidemics: Brazil (100,000 in 1977; 560,000 in 1988), Afghanistan (47,000 in 1980; 422,000 in 1986, aided by the war). Dramatically deteriorating areas of malaria control corresponded to all frontier areas of economic development, such as agriculture and mining in newly-opened jungle, and in areas of war, conflict, illegal trading and migration of refugees. In such areas, it is the most dangerous of the two main malaria parasites Plasmodium falciparum that is claiming lives. In Brazilian Amazon, falciparum malaria is killing some 6-10 thousand people a year, mainly young adults working in development projects. Malaria is appearing in some area of the South Pacific, such as the highlands of Papua New Guinea, where it has not been previously reported. Concern is that this is a consequence of climate change.
36% of the disease-specific budget of the World Bank/UNDP/WHO Special Programme for Research and Training in Tropical Diseases (TDR) is being spent on malaria to develop new tools for control and treatment. This is by far the largest disease-specific effort of this WHO-managed programme. One aspect is the careful identification and classification of particular social, economic and ecological situations that encourage malaria, and the design of specific strategies to cope with each such situation. "Types" of malaria thus identified include "African savannah malaria", "forest malaria", and "urban malaria", each requiring different approaches.
In 1997 only $85 million was spent globally on malaria research, about half the amount spent on asthma research, probably because malaria is a disease of the poor. Western drug companies doubt that 3rd world villagers would be able to pay for vaccine if they did develop it.
"Airport malaria" is the term used to describe malaria spread by mosquitoes from malarial regions hitching rides aboard aircraft. Each year in US there are 50-100 cases attributed to this source of transmission. The malarial risk to those traveling to countries in the tropics and subtropics also is increasing.
Malaria has been declared 'public enemy number one' by WHO and affects more than 500 million people in 90 countries, causing 1.5-2.7 million deaths per year (WHO 1997a).