The Ingenuity of the Malaria Parasite

Shelby Nilsen
Jul 22, 2017 · Unlisted

I hate mosquitoes. You hate mosquitoes. We all hate mosquitoes. Never mind the debate over their importance to various ecosystems, they’re simply nasty, personal bubble-bursting creatures that carry nasty, debilitating agents along with them — like malaria. I mean, just look at them.

“I’m coming for you…”

Now, after that nightmare-provoking image, what if I told you it’s not entirely their fault? Well, at least the malaria bit.

Malaria is caused by a one-celled parasite called Plasmodium that likes to hitch a first-class ride within the gut of mosquitoes.

Studies have revealed evidence that the parasite can suppress and stimulate the insect’s blood lust to further its own reproduction and dispersal at various points in its lifespan. In layman’s terms, it acts as a backseat driver. It actually has the ability to influence the mosquito’s behavior. The process goes something like this…

Missy Mosquito flies along, minding her own business, stopping as she pleases to feast on some bumbling mammalian flesh. In order to eat, she uses her long proboscis to wriggle through layers of skin cells until she hits her target, a blood vessel. As soon as she begins to drink, the human body reacts by sending an army of platelets to the puncture site to stop up the sudden leak. Missy anticipates this (maybe not consciously, but go with me on this one) and injects a special anticoagulation serum that decimates those platelets and prevents them from creating a clot. Her feast continues.

Once she has had her fill, Missy flies off. She is quite satiated and pleased with herself. Soon after, however, she begins to lose her appetite. Somewhere along the way, Missy has consumed Plasmodium gametocytes — cells that specialize in the transition from human host to mosquito. Researchers hypothesize that this lack of hunger is a result of the Plasmodium reproduction period, when the parasite becomes very protective of its space inside the mosquito’s gut. Now Missy cannot stand the thought of drinking one more drop of blood, which is quite embarrassing for an insect of her persuasion. Ten days later, though, the opposite occurs.

Missy is suddenly voraciously hungry. Unbeknownst to her (or maybe knownst, who can tell?) a plethora of Plasmodium progeny are vying for release, having reached their infectious stage of development. As the theory goes, it is in the parasite’s best interests, at this point, for Missy to have an increased hunger and desire to feed. It accomplishes this by stopping up the supply of anticoagulant located in Missy’s salivary glands. Without the anticoagulant, her victim’s platelets quickly pile up at the puncture site and clog up her proboscis, preventing her from receiving her fill of blood. Thus Missy must feed on many more hosts than usual to satisfy her appetite, causing the infection to spread much more vastly and quickly than it otherwise would.

Crazy, right? That something so small could have such a widespread effect on both poor Missy’s appetite and the human population!

But we’re not done yet.

Next, we come to the effect Plasmodium could have on YOU. Thrombocytopenia — low platelet count — is commonly observed in malaria-infected individuals. Because of this, the blood of an infected person flows much more easily into Missy’s proboscis, allowing her to ingest a greater quantity of infected blood to transmit on to others. So it is easier for Missy, now, to feed on infected hosts rather than healthy ones.

Another controversial claim proposes that the Plasmodium parasite also plays a role in enhancing an infected person’s scent to make them more appealing to Missy and her brethren. A 2005 field study conducted in Kenya and a laboratory study held in Brazil lend support to this hypothesis.

So what we’ve learned, here, is that the same microscopic entity that has the capability of making you deathly ill is also capable of transforming you into a beacon to help spread the disease to others! Nature is so intricate, and so terrifying.

Millions of people across the world are infected with vector-borne diseases like malaria. Research such as we have discussed today reflects a great need in our society to understand the minutia of how parasites such as Plasmodium affect not only their hosts but the entire ecosystem in which they thrive.

If this tale both intrigues and disgusts you, I highly recommend checking out this book authored by science journalist Kathleen McAuliffe. It will make your face do that thing it does when you watch horror movies while peeking out from underneath the covers, and you will learn some fascinating things.

Unlisted

Shelby Nilsen

Written by

Biomedical research and technology writer. Compulsive traveler armed with a pen and a pinch of snark.

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