Malaria is one of the deadliest mosquito-borne diseases in the world, because according to the World Malaria Report, in 2015 alone approximately 438 thousand people died from this disease. And although it is crucial to continue the fight against malaria and focus on a future in which malaria doesn’t exist, it is also important to look back as to how malaria came to be, because that can provide answers about how to best combat it.
This disease that is called malaria is actually caused by a protozoan parasite of Plasmodium genus, which lives in mosquitoes that are of the Anopheles genus. Among the Anopheles mosquitoes are some of the most common mosquito species in Malaria hotspots like Africa – the Anopheles gambiae Anopheles funestus mosquitoes. The malaria parasite’s life cycle starts in the walls of mosquito gut, because at this stage the parasite is something called oocyst – the parasite is covered with thick and hardy shell, that get shed when people is infected with this parasite. But before a mosquito gets contagious and is able to transmit this parasite to humans, the parasite needs to experience its next and last life cycle in mosquitoes body – its need to release sporozoites that travel to mosquito salivary ducts, that way making the mosquitoes able to actually be malaria vectors and cause malaria to humans by feeding on humans.
But how did mosquitoes that have these parasites develop and which was first – the mosquito already with malaria parasite or the Plasmodium genus parasite that infected the mosquitoes?
It has been confirmed, that malaria has been around for a long time, because evidence of this disease have been found in fossils from the middle of Crataceous period, so approximately from 100 million years ago give or take a couple of million years. And both insect vectors aka mosquito like creatures like biting midges and vertebrate hosts aka the ancestors of the Plasmodium genus parasites have been found in these fossils. But how did these parasites came to be, because they had to come from somewhere to start transmitting malaria first to reptiles and nowadays to humans?
For a long time scientists believed that malaria actually developed first in the parasites, so saying that the vertebrate hosts (the egg in the “which came first, the chicken or the egg” dilemma) where the beginnings of this awful disease. However, in the last half a century or so, scientists actually have changed their tune, now saying that the insect vectors came first after all (the chicken came before the egg, if we are using the same analogy, which is true in the original “the chicken or the egg” debate, and probably true for malaria parasites and insects, too), so saying that the parasite actually evolved inside of the insects, denying that the insects somehow were infected by already developed malaria parasites.
The main scientist that started this way of thinking was Clay Huff, but a man named George Poinar continues this line of researcher, working to get more and more proof that the theory of insects coming before malaria parasites is accurate. For example some of the proof that the insects came first, and only later the malaria parasites developed in them, is that the sexual reproduction that the parasites need to move on with their life cycle, can happen only in insect, and that since the malaria parasites most likely evolved from Gregarinida taxonomic group parasites, that, too, evolved inside of insects, their successors did the same.
This kind of research is important, because it sheds light on the way malaria evolves, therefore helping to locate the malarial genome in mosquitoes and hopefully one day making mosquitoes that have this genome extinct, that way making a disease called malaria extinct, too. But as of now, the fight against malaria continues, because there is still a lot of research to be done. So don’t forget to learn more about malaria and mosquito control that is one of the best ways to avoid malaria, as well as remember that on April 25th we celebrate World Malaria Day.