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Malaria: The 500,000-Year-Old 'Fever' That Won't Die

Jul 20, 2010 (Fresh Air from WHYY)

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Malaria, the mosquito-borne infectious disease, has been almost entirely eradicated in the United States for the past 60 years, but continues to infect millions of people around the globe, mainly in parts of sub-Saharan Africa and in subtropical areas.

Each year, between 300 million and 500 million people are afflicted with malaria. The main typical symptoms are fever and chills, but several complications — which can lead to convulsions, hallucinations and even death — occur in a small percentage of cases.

In The Fever: How Malaria Has Ruled Humankind for 500,000 Years, journalist Sonia Shah weaves together a social history of the disease, which has plagued humans for thousands of years and shows no sign of slowing down, despite being treatable with drugs.

In an interview on Fresh Air, Shah tells Terry Gross that prompt treatment and knowing where the infected mosquitoes live and breed are the best ways to avoid malarial infection.

"The trick is knowing where those mosquitoes are living, and building our habitats far away enough so they don't bite us — and [then] protecting ourselves during the times that they bite," Shah explains. "These are things that entomologists have figured out in many places. ... [And] the [malarial] treatments we have actually kill the parasites in our bodies so that we're not infective anymore. So if we get prompt treatment, [we] can also start to end malaria, and of course that is what we've done here in the United States. Prompt treatment and changing the way we live actually has protected us."

Interview Highlights

On the malaria parasite that infiltrates mosquitoes

"The parasite is called Plasmodium. It's a protozoan. It's a very wily little creature. It transmogrifies into about seven different forms during its life cycle which vary not just in how they look but also in their physiology. It reproduces sexually and asexually, but all of this takes place inside the bodies of mosquitoes for half their life, and the other half of [the Plasmodium's] life is spent inside whatever host they're targeting. And different malaria species target different hosts. So for us, there's at least five malaria parasite species — these species of Plasmodium that infect humankind. And what they do is they come into our bodies in the saliva of a mosquito. They hide in our liver for a while, but what they're really after is the hemoglobin in our red blood cells, so that's what they feast upon, and then they leave to go on and infect another person. So it's this cycle of being infected by malaria parasites and having them feed on our red blood cells — the hemoglobin in our red blood cells — that makes us sick from malaria."

How malaria spread

"Africans carrying malaria parasites walked out of Africa in prehistoric times and they infected Asia and Europe with malaria parasites, and then when Europeans came over to the New World, they brought malaria parasites over with them to the New World. Probably the Americas were not affected with malaria before the Europeans came over because people had to walk over the Bering land bridge, and that was cold — and that took time — and probably parasites would have died out in their bodies before mosquitoes could pick them up. But once we started sailing over, that's a lot faster. Malaria parasites can stay dormant in the body for many months, and there's actually other malaria parasites that can stay dormant in the body for up to 70 years, so if you can wait that long between mosquitoes biting you, you can pass on malaria."

How the symbiotic relationship between the mosquito and the malaria parasite developed

"Mosquitoes and the parasite probably evolved together. So the parasite has vestigial machinery inside of it that suggests that it once photosynthesized. So it was probably some kind of algae floating in the water. So it probably partnered up with mosquitoes pretty early on, since mosquito eggs are hatched inside the water and the larvae are formed in bodies of water. So they probably were together for a lot longer than the parasite started infecting us. But mosquitoes take these blood meals. As we all know, the itchy bites that we get are from the female mosquito trying to suck our blood. And the reason they are taking blood is not for food for themselves, but to nourish their eggs. So that's, evolutionarily speaking, such a hugely important thing to do — to secure the next generation. So the mosquito will actually risk her life to get a few drops of blood to feed her eggs because, of course, taking that blood meal for a tiny little mosquito is incredibly dangerous. Not only can they be easily swatted away and killed by the animals that they take blood from, but once they take the blood, they get filled up with such a huge volume of blood that they can't fly — and obviously, it needs to be able to fly to avoid predators and things. So it risks its life to do that. So that makes the parasite's exploitation of the mosquito's behavior in this so wily because the mosquito's not going to give up its blood meal. It's more than food. It's reproduction."

On the possibility of a malarial outbreak in the United States

"It's not that the parasites aren't here. It's that, if you got that sick you would spike a 103-104 fever and you would run to the hospital right away and you would get prompt treatment. ... The idea is that malaria could come back to the United States, but only if our public health system really fails."

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