Malaria and Plasmodium

Malaria is caused by tiny Plasmodium parasites. These parasites are spread to people through the bites of an infected female Anopheles mosquito. There are five species of parasites that are known to cause malaria in humans: Plasmodium vivax, Plasmodium malariae, Plasmodium falciparum, Plasmodium ovale curtisi and Plasmodium ovale wallikeri and Plasmodium knowlesi.

Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale and Plasmodium malariae together account for nearly all human infections, with Plasmodium falciparum accounting for the overwhelming majority of malaria deaths. However, an increasing number of cases of severe malaria in Southeast Asia have recently been attributed to Plasmodium knowlesi.

But nature has always more tricks up its sleeve, because other species of Plasmodium have increasingly been isolated from humans, including Plasmodium brasilianum, Plasmodium inui, Plasmodium rhodiani, Plasmodium schweitzi, Plasmodium semiovale and Plasmodium simium.

And that's not all because the parasite is very good at adapting and mutating. Over time it has been able to counter any poison we use to combat the disease. We call that poison medicine.

Plasmodium falciparum has developed resistance to nearly all antimalarials in current use, although the geographical distribution of resistance to any single antimalarial drug varies greatly. Plasmodium vivax has been shown to be resistant to chloroquine and/or primaquine in some areas. Chloroquine-resistant Plasmodium falciparum has been described everywhere malaria is transmitted except for malarious areas of Central America (northwest of the Panama Canal), the island of Hispaniola, and limited areas of the Middle East and Central Asia. Mefloquine resistance is frequent in some areas of South-East Asia and has been reported in the Amazon region of South America and sporadically in Africa.

Sulfadoxinepyrimethamine resistance occurs frequently in South-East Asia and South America. It was initially almost 100% effective in curing malaria when introduced in 1977, but within five years was curing only 10% of cases due to drug resistance.

What's left, you might ask. Artemisinin is a drug that is produced from sweet wormwood (Artemisia annua). It possesses the most rapid action of all current drugs against Plasmodium falciparum. When used correctly in combination with other anti-malarial drugs, artemisinin is nearly 95% effective in curing malaria and the parasite is highly unlikely to become drug resistant, says the WHO hopefully[1].

Now we leave the realm of fantasy and discover that the parasite increasingly develops resistance to Artemisinin[2].

[1] WHO: WHO calls for an immediate halt to provision of single-drug artemisinin malaria pills – 2006. See here. 
[2] Tilley et al: Artemisinin Action and Resistance in Plasmodium falciparum in Trends in Parasitology - 2016