Malaria vaccine!

I’m catching up on the science news that I missed in the last few weeks and discovered this article on a research group that has developed a vaccine for malaria.

Over half of the world’s population live where they are at risk of contracting malaria. In areas where malaria is common it is an enormous drain on the economy, imposing massive health care costs and preventing people from going to work. In fact, malaria-ridden regions have a 1.3% lower gross domestic product (GDP) than nearby areas that are not plagued with the disease. Malaria is also deadly. The WHO reports that a child dies every 30 seconds from malaria.

Plasmodium falciparum and red blood cells.
Plasmodium falciparum and red blood cells.

Malaria is caused by protozoan parasites of the genus Plasmodium. Although a handful of Plasmodium species are capable of causing malaria, only one (Plasmodium falciparum) is frequently associated with lethal cases of the disease. The parasite reproduces sexually in Anopheles mosquitoes and lodges itself in the mosquito’s salivary glands after reaching maturity. When the mosquito bites a human, the parasite moves out of the mosquito’s salivary glands and into the human bloodstream.

The most impressive thing about malaria is how it manages to evade the immune system. When a Plasmodium parasite enters the body, its first stop is the liver. Here it invades liver cells and begins multiplying rapidly. The liver cells alert the immune system, but the immune system cannot respond quickly enough. The parasite is too fast. Before the immune system can rally the troops, the parasite makes approximately 40,000 copies of itself, bursts out of the liver cell, and goes in search of its next home: a red blood cell.

Unlike liver cells, red blood cells do not contain genes. Without genes the cells lack the codes and machinery necessary to synthesize proteins which would alert the immune system that it is under attack. This buys the parasite some time, but it still has the spleen to worry about…

Red blood cells (RBCs) are usually very squishy, a necessity when your job requires squeezing through tiny capillaries throughout the body. As RBCs age, they get worn out and lose some of their pliability. When they pass through the spleen, it identifies the aging cells and retires them.  The spleen would almost certainly destroy any RBC harboring a Plasmodium because the parasite changes the structure of the cell, making it far more rigid. The parasite needs to make sure that the red blood cell never makes it to the spleen.

To stop the RBC in its tracks, Plasmodium creates hook-like proteins that extend out from the RBC and attach to the blood vessels. While this action saves the parasite from ever encountering the spleen, the proteins alert the immune system to its presence.

Over its evolutionary history, this parasite has managed to exploit the immune system’s need for specificity. The immune system first identifies a foreign body by some telltale protein on a cell’s surface (e.g., the “hook” mentioned earlier). Once this protein has been identified, the immune system builds an army which will focus on attacking only those cells that display the protein they have been built to identify. Should that identifying protein change configuration, then the current army of immune cells will be unable to recognize the intruder. In this case, a new army will need to be readied that is capable of identifying the new protein.

Plasmodium reproduces quickly. It multiplies in one red blood cell and will then burst out in search of new ones. Every few generations, these clever parasites will turn on a different gene that codes for a protein hook with a slightly different configuration. By the time the immune system is capable of recognizing and attacking the parasite, the parasite has switched protein hooks and becomes unrecognizable to the army built to destroy it. In this way, malaria parasites often manage to stay ahead of the human body’s immune response.

There are drugs to prevent malaria and there are drugs to treat malaria, but both are often too expensive for people living in malaria-ridden areas to afford. Additionally, malarial drugs often have nasty side effects. Finding a vaccine would likely save lots of money in the long run and would do much to ease suffering. For many years, vaccine research has proceeded without much luck.

The advent of genetic techniques may now have paved the way for the creation of a vaccine.

The vaccine described in the article mentioned above uses a genetically modified version of the parasite. Scientists identified and knocked out 2 genes that the parasite needs during the stage when it is infecting cells in the liver. This genetic modification means that the parasite can be injected into people without posing any threat. The presence of the parasite gears up the immune system, which creates an army which is ready to attack Plasmodium as soon as it enters the body. This eliminates that lag time that the parasite had been exploiting and  gives the immune system the edge that it needs to destroy the parasite before it can cause any real damage.

The vaccine has proved to be 100% effective in animal trials and will hopefully be made available publicly in the near future. If the vaccine is affordable enough to be distributed widely then this should have huge human health and economic impacts. Third world countries that are so often plagued by malaria should save millions in health care costs and should experience increased GDP as a result of the healthier work force.  Best of all, millions of lives will be saved in the years after the vaccine becomes available.

If you thought this post was interesting, then I suggest reading Parasite Rex by Carl Zimmer. I got a lot of the information that I presented from this book, and it’s a fun read.

Malaria_geographic_distribution_2003

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6 thoughts on “Malaria vaccine!

  1. Wow, we have just managed to temporarily gain the upper hand in a long struggle with one of the great enemies of humanity. If this works, humanity will suddenly face an unprecedented reduction in tropical region mortality, and all the potential results of such an occurrence.

    Of course, I say temporary because it is only a matter of time (and in all likelihood, a very short time) before another strain of Plasmodium that acts or masks itself differently makes itself known. Something that directly attacks the spleen maybe, thus insinuating itself rapidly into the bloodstream, overwhelming the immune system with it’s speed, comes to mind as a potential example. So while science carries the day today, we have to always keep in mind that life, in all its glorious diversity, has multiple billions of years under its belt, and always wins out in the end.

    My other concern is the societal implications for malaria prone regions, who might not be able to react to the shift in mortality rates, causing alterations to population distribution and mandating a shift in policy, something much of the malaria-stricken world (which largely overlaps with the poverty stricken, poorly governed, 3rd world) might not be able to effectively react to.

    So, good news, tempered by reality.

    P.S. Thank you for the amazing layman’s explanation of how Plasmodium works! Of all the skills the world’s scientists possess, explaining to the non-disciplinary world is SEVERELY lacking. I have never heard such an easy to follow explanation of malaria, and I have heard numerous explanations of the disease (having lived in malaria infested regions). I must say though, the child in me would much rather take malaria pills than get a shot! 😀

  2. I hope the vaccine is successful. (my aunt first told me about it) As you wrote, the parasite has a habit of finding the next genes and staying ahead of the human immune system, so it seems like a losing battle.

    It is also funny, having had malaria myself (I was in West Africa in 2007), that the 6-pill treatment after diagnosis was supposed to take care of the entire disease. it seemed funny to me as a westerner, seeing as this bug was exploding my blood cells.

    Also, when asking around, it was normal for lots of people in Niger to get malaria once a year, you know, like the flu!
    There was a great national geographic article on Malaria in summer 2007. worth a read. includes info about how it used to be rampant in north america until there was a thorough program to eradicate it. if only everywhere else…

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