On World Malaria Day (25.04.2024)
Malaria is considered by many to be the tropical disease par excellence. With an annual mortality rate of more than half a million, the parasite infection transmitted by mosquitoes is still one of the leading causes of the low life expectancy of children and pregnant women in affected regions.
It is often forgotten that malaria was also widespread in Europe until the middle of the last century, in the Balkans, Italy, Greece, the Caucasus and the south of France, and even in the USA. The widespread use of the insecticide DDT, which is now banned in many countries, after 1945 and the draining of breeding sites, which had already begun in the 1930s, made it possible to eradicate the disease in Europe.
Due to these successes, the World Health Organization (WHO) launched a large-scale campaign to eradicate malaria worldwide in the 1960s. However, this failed and malaria transmission even returned to areas where it had completely disappeared, such as Sri Lanka. The reasons for this included the increasing resistance of the pathogens, the plasmodia, to the few available drugs such as chloroquine, but also the increasing ineffectiveness of DDT on the transmitting mosquitoes. Basically, however, the failure of the campaign can be attributed to the lack of accompanying research. In comparison, the eradication of the worm disease river blindness, which is also transmitted by mosquitoes, was much more effective. In this case, the World Bank program also included research measures, which enabled rapid adjustments to the program.
At the end of the 1980s, malaria research underwent a renaissance, as a result of which surprisingly effective new long-term remedies were developed: the first to be tested were mosquito nets impregnated with new types of insect repellents, the pyrethrenoids, which actually made it possible to significantly reduce malaria mortality among children in many regions of Africa and Asia. It has also been learned to use newer insecticides more selectively and sparingly. New medicines were developed, mostly based on the worm herb Artemisia, which was already well known in folk medicine. Derivatives of the substance artemisinin, which was discovered in the People's Republic of China and further developed in many places, made it possible to counteract chloroquine resistance, at least for the time being, in combination with other active substances. Intermittent drug treatment protocols have become established in the fight against pregnancy malaria.
Fig.1: Spread and decline of malaria since 1900 (from Lancet Infectious Diseases 2004,4,327-336)
The biggest breakthrough, however, is the development of two vaccines against malaria: RTS, S/AS101 from the USA/Belgium and R21/Matrix-M from Oxford.
Both have been approved by drug agencies and are now being tested for long-term efficacy through large-scale vaccination campaigns in some countries. Not long ago, it looked as if the control or even eradication of malaria was within reach. Unfortunately, however, it should be noted that the good progress made at the beginning of the first decade is on the decline again.
While 897,000 people died of malaria in 2000, the figure was only 568,000 in 2019, but by 2022 it was already 608,000, a significant increase. The COVID-19 pandemic played a key role in this: resources were diverted and the fragile healthcare systems in many developing countries were devastated, meaning that many sick people could no longer be treated. In the long term, however, climate change plays a role; the rise in temperature helps the spread of mosquitoes, and the numerous floods do the same.
New species of vector mosquitoes such as Anopheles stephensi are conquering new habitats in dilapidated parts of the city. The newer and rather expensive insecticides are also gradually losing their effectiveness and plasmodia are also likely to become more resistant to artemisinins. The effect of the rapid tests is also limited; mutants of the plasmodia have increasingly been observed which do not carry the antigen detected in the test and therefore give false negative results. Some of these negative elements therefore appear to be known from earlier tests.
However, this should not be a reason for pessimism. In fact, malaria research today is stronger than ever with the help of a new generation of researchers in the fields of field epidemiology, parasitology and malaria molecular biology, even with declining funding. However, the crucial question of how to permanently integrate the fight against malaria, which is best equipped with novel tools, into the fragile and weakened health systems of low-income countries must also be addressed and should not be neglected in the upcoming reform projects of the post-pandemic period.
Guest article by Dr. Michel Pletschette, MSc, DTMH, Senior Researcher, Department of Infectious Diseases and Tropical Medicine, LMU Klinikum München
Dr. med. univ. Michel Pletschette, MSc, DTMH
Senior Researcher, Abteilung für Infektions- und Tropenmedizin, LMU Klinikum München
