What is malaria and what causes it besides bacteria? What is the name of the causal agent for malaria, which drug is used to cure it and how do the pathogens become resistant to the drugs?
There are many questions in there! Malaria is actually caused by a single-celled animal, called a protozoan; it’s not a bacterial disease. There are different species of these protozoans, which form a genus called Plasmodium; the different species cause different types of malaria, for example Plasmodium falciparum, the most deadly and severe form, and Plasmodium vivax, which is widespread throughout the world but is a less acute infection. These different forms of malaria are each treated with different medications, depending on what is most effective and available; P. vivax, for example, can be treated with chloroquine, whereas in many places, P. falciparum has become resistant to this drug. In areas where resistance to chloroquine has emerged, other drugs are used; in Africa, artemisinin-based combination therapies (ACTs) are commonly used against chloroquine-resistant P. falciparum. Other drugs used to treat malaria include quinine compounds such as quinine sulphate, mefloquine, sulfadoxine-pyrimethamine and medications combining proguanil with atovaquone (marketed as Malarone).
The emergence of resistance to these drugs is a worrying phenomenon with respect to malaria; it is such a widespread and deadly disease, that the consequences of failed treatment are very high. Resistance can be caused by many factors, at the level of the drug, the human host, the mosquito host and also the malaria parasite itself. For example, poor drug compliance during treatment can lead to a failure to clear an infection completely, allowing the remaining parasites, which were less susceptible to the drug, to survive and reproduce. With successive generations, natural selection will lead to the evolution of strains of malaria parasites which are firmly resistant to that drug. The same process occurs when mass drug administration programmes, for example in areas of high malaria endemicity, give people sub-therapeutic doses of medication (in other words, doses of the drug that are too low to kill the parasite). Another problem is when people are not checked for their infection status after having been treated for malaria; if treatment fails for some reason, they will still have parasites in their blood, and should be treated again to ensure that all the malaria has been killed. If this doesn’t happen, the parasites can carry on reproducing, as in the processes described above. For these reasons, it is crucially important for people to be given accurate doses of medication, to ensure that they complete the full course of treatment, and that once treatment has been completed, they are accurately tested as negative for the malaria parasite. Finally, there are factors related to the affinity of the malaria parasite to its vector mosquito hosts which can lead to the emergence of drug resistant strains. For example, it has been shown that strains of malaria which are resistant to chloroquine are better able to survive and reproduce inside their mosquito hosts, leading to a greater population size of resistant parasites compared to drug-susceptible ones. It is for these reasons that malaria treatment and control programmes are now being very careful with the ways in which they administer drugs and monitor infections, in order to limit any further reisstance developing; similarly, pharmaceutical and biochemical researchers are constantly on the look-out for new compounds or methods of killing malaria parasites, which can be developed into new forms of treatment.