Antimalarial resistance is the ability in the microorganisms that cause the disease malaria to withstand the effects of drugs used to treat the disease. It is an example of the broader phenomenon of drug resistance, the evolutionary adaptation of species of disease-causing microorganisms to give them a greater ability to survive the treatments used to cure them. Malaria is a disease caused by being infected with a single cell of the Plasmodium genus, which is transmitted to humans though the bite of a mosquito carrying these organisms. The disease malaria is a significant health problem in much of the world and has been one of the primary targets of many initiatives in impoverished countries, making the development of antimalarial resistance an important global health concern.
There are number of Plasmodium species that cause malaria in various species, though the great majority of malaria in humans is caused by the species Plasmodium falciparum. Malaria produces symptoms such as vomiting, convulsions, and anemia and commonly causes a characteristic alternating cycle of fever and chills in the sufferer. It is potentially fatal and can also cause cause brain damage, especially in infected children, damage to the retinas, and stillbirth or low birth-weight in infected pregnant women. Malaria is an extremely common disease, especially in tropical or subtropical regions where the heat and moisture of the climate is highly friendly to mosquitoes, with an estimated 250 million infections and 1 million deaths annually.
Like other forms of drug resistance, antimalarial resistance develops because of the evolutionary pressures placed on species of the Plasmodium genus by human medicine. When a new antimalarial drug comes into use, it tends to be highly effective because the species it targets has never had to face that threat and is not equipped to withstand it, because there was previously no survival benefit to such an ability. As the new drug is used, this changes and any individual members of the species that happen to be less susceptible to the drug than is typical of the species will have a greater chance than their less resistant fellows to survive and reproduce, which means that the next generation will be descended primarily from them and so carry the genes of the organisms most able to survive the drug. New resistance-increasing genetic mutations that occur in subsequent generations, which would have been useless or even detrimental prior to the arrival of the drug, will now be advantageous to the organisms that carry them and so become more likely to be passed down.
This process repeats as long as the drug is used, with each subsequent generation descended from the most resistant members of the previous one and genes that promote antimalarial resistance consequently becoming more common. As a result, the antimalarial drug becomes less and less effective. The antimalarial drugs to which malaria is resistant can vary from region to region, depending on the history of infection and treatment in that area.
This is a very important impetus behind the development of new drugs, because the ability of modern medicine to reduce the loss of human health and life caused by malaria depends on the creation of drugs that the disease has not adapted to. The more a drug is used, the more rapidly resistance is likely to develop due to the selective pressure, so initiatives to fight malaria typically place a great deal of focus on preventing mosquitoes from spreading the infection to humans in the first place by killing disease-carrying mosquito populations with pesticides, engineering projects to eliminate the swampy areas where mosquitoes breed, or keeping mosquitoes away from humans through chemical insect repellents or physical barriers.