We wrote recently about the first effective vaccine against malaria, which should be widely available in a few years. However, malaria continues to take a terrible toll, 409,000 deaths in 2019, 94% (384,000) in sub-Saharan Africa (1 in 600 infections).
While Covid has killed many more worldwide, the age profiles of the most vulnerable are reversed. Covid kills mainly over-80s while malaria kills mostly under-5s. Their deaths, about 250,000 per year, dwarf counted total Covid deaths in sub-Saharan Africa, which are under 30,000.
Pregnant women also have a higher risk of miscarriage and prematurity. In Nigeria, where a third of African malaria deaths occur, almost all Nigerians are at risk, with 30% of child and 11% of maternal deaths due to the disease.
Incidence of malaria worldwide
Once prevalent over 53% of the Earth’s surface, since 1900 the area subject to malaria has halved, with global mortality down by 90%.
This is due to campaigns to eradicate malarial mosquitoes, measures to prevent infection, and improved treatments. China is the latest country to be declared malaria-free. Europe was declared malaria-free again (!) in 2015: it had been malaria-free in 1975 but the disease re-emerged for political and socioeconomic reasons, population movements following the First Gulf War, and interruption of prevention measures. Even in Africa, where the highly virulent Plasmodium falciparum parasite prevails, deaths have fallen by 40% in the last 20 years. However, the WHO reports that efforts to curb malaria in Africa have stalled and may be reversed as a result of Covid.
Malaria may cause more excess death in Africa than Covid itself. A 25% reduction in anti-malaria efforts could lead to perhaps 46,000 additional malaria deaths per year, mostly children (according to the BMJ).
How to eliminate malaria
Only concerted, combined approaches can fully eradicate malaria. Ronald Ross established the role of mosquitoes in malaria by 1897 and this knowledge began to inform anti-malaria measures. US Army Surgeon-General William Gorgas was the first to tackle malaria with mixed measures. Charged with eliminating malaria and yellow fever in Havana and, in 1904, during construction of the Panama Canal, he had ponds and swamps drained, fumigated buildings, introduced screens to keep mosquitoes out of buildings, and provided mosquito nets.
Thirty years later, Mussolini inaugurated the Bonifica Integrale scheme in the Pontine marshes, known for malaria since antiquity. First, the marshes were drained and replaced with agricultural land, killing residual larvae with Paris green. Then healthy housing was built for 60,000 settlers. Thirdly, malaria infections were treated with quinine, while people were educated about the causes and prevention of malaria. This reduced the death rate from malaria in Italy by over 80% by World War 2. Post-war campaigns eradicated malaria in Italy by 1971.
Other multi-pronged approaches include use of Paris green, mosquitofish and oil in breeding areas in Corsica in 1929 and, in the plains of Palestine (1922-26), drainage of marshes, quinine as treatment and prophylactic, cleaning water channels, and spraying of oil and Paris green, virtually eliminating malaria.
Reconquest of malaria in Europe after its re-emergence in the 1990s required a similar combination of approaches: commitment of governments, support from WHO experts, adequate funding, detection and surveillance of cases, integrated control measures, community involvement, cross-border collaboration, and education of at-risk populations.
The problem of malaria in Africa
Two Nigerian medical sociologists describe some of the problems with anti-malaria efforts in Africa and argue for concerted approaches as in Europe and America, incorporating environmental considerations.
Funding is crucial: money from donor countries rose from 2000, with malaria deaths falling by 40%, until 2016, when funding fell to about half that required. The worst-affected countries have lower GDPs, partly due to malaria’s economic impact.
Then there’s politics: colonialism’s legacy is a patchwork of states often delineated by rivers, mountains or straight lines on a map, with ethnic groups split or forced together. Many are dictatorships or kleptocracies, often linked to dominant ethnic groups, bringing separatism and civil wars, and militating against the organisation (or even the will) needed to bring health services to all.
The use of insecticide-treated nets (ITNs) is a success story: over half of children and pregnant women slept under these in 2019, compared with 3% in 2000, substantially reducing mortality. However, ITNs need replacing regularly, and some mosquitoes have developed resistance (ITNs may also be misused, e.g. as fishing nets).
Prevention of infection with prophylactic drugs is important for pregnant women but these still reach only a third of African women at risk.
Mosquito breeding in stagnant water is still a major problem, exacerbated by dam construction. Swamps and ponds near villages, poor sanitation, and cramped wooden housing all exacerbate the risk of infection, but dealing with these is expensive.
Climate change may worsen the malaria threat since low temperatures limit mosquito survival. Mosquitoes will colonise higher altitude regions with warming and increased rainfall.
The best approach, say the sociologists, is to combine ITNs and prophylaxis (and drug treatments for sufferers) with measures to restrict breeding by improving sanitation, removing waste heaps, undergrowth near dwellings, removing ponds and stagnant water from villages, and improving housing to limit insect entry.
The message is that malaria can be eliminated, not with vaccines, but by a combination of concerted physical, chemical and medical methods.
Responses to malaria
Malaria exerted extreme selection pressure on humans to evolve mutations to increase life expectancy in the young where it was most prevalent, resulting in several gene variants, most commonly those associated with thalassaemia and sickle cell anaemia. They alter red blood cells, making it more difficult for Plasmodium to infect or survive in them but, for sickle cell and thalassaemia, two mutant genes (one from each parent) cause severe illness.
The effective treatment, cinchona bark, was discovered by missionaries in South America in the 1600s. Its active ingredient, quinine, kills malarial parasites; alternatives such as chloroquine have since been developed. These also prevent infection but the parasite can evolve resistance. The ancient Chinese remedy, sweet wormwood, contains artemisinin which also kills malarial parasites.
Mosquitoes need stagnant water, such as ponds, swamps, marshlands, and rice paddies for their larval stage. Draining these or spraying with oil reduces breeding opportunities.
Screens to prevent mosquitoes entering dwellings are relatively expensive and rely on the absence of gaps. Nets have long been used to exclude biting insects at night. ITNs prevent about 50% of infections, reducing child deaths by 18%; their use may have prevented about a billion infections since 2000.
Paris green, which contains copper and arsenic, kills mosquito larvae: it was used to eradicate malarial mosquitoes in Italy in 1934 and in north-east Brazil in 1940. The most successful insecticide, DDT, was used to eradicate malaria in parts of Italy by spraying inside houses and outbuildings, and then in the USA (1947-52). Predictably, resistance to insecticides has evolved, limiting their effectiveness.