The power of parasites

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First aired on Ideas (08/01/13)

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For a species that makes up half -- if not more -- of all the species on Earth, parasites have a bad reputation. They're slimy, repulsive and generally, humans try to avoid them.

But, Rosemary Drisdelle, a clinical specialist in parasitology and author of Parasites: Tales of Humanity's Most Unwelcome Guests, finds the bottom-feeders fascinating and thinks people should reconsider the stigma they've attached to them.

In her documentary Worthy Parasites: A Villain's Silver Lining, which aired Tuesday on CBC's Ideas, Drisdelle explores how the maligned creatures can actually help humans, revealing some interesting new scientific research.

During the American Civil War, she says, one doctor discovered how to use a medicinal maggot, which feeds on dead tissue and leaves healthy tissue behind, to clean soldiers' festering wounds. Now, modern medicine is rediscovering this type of therapy.

"[Some parasites] teach the immune system how to regulate itself, how to control itself," said Graham Rook, a medicinal microbiology professor at London, England's University College. He says when humans distanced themselves from the environment and parasites, huge numbers of people started suffering from chronic inflammatory disorders.

In the states and the U.K., scientists are now conducting clinical trials for how parasites can prevent the advance of certain types of multiple sclerosis. 

Rook advises those diagnosed to wait for the clinical trials to be completed before seeking out the therapy, but some people are choosing to self-inject with hook worms.

"Parasites are mislabeled, misunderstood, under appreciated," said Jasper Lawrence, who owns a company that distributes parasites to some 550 clients and has used the therapy himself. "And one day ... it's going to be radically transformed."

Drisdelle points to a few more parasitic powers:

  • Aphrodisiac: A parasitic worm infects and castrates oysters, so all of its host's energy is spent on it, making the parasite responsible for the aphrodisiac powers of juicy oysters.
  • Risk-taking: One parasite can influence risk-taking behaviour, according to a study. It shows that infected young men are much more likely to be in traffic accidents during their first few years with a license. This parasite is also linked to increases in suicide, homicide and mental health illnesses, but may be responsible for some scientific discoveries and entrepreneurial success.

Currently, few parasites are studied, said Susan Perkins, an associate curator and professor at the American Museum of Natural History, and many will be lost before scientists can discover them. 

As a key component of a healthy eco-system and with potential for medicinal powers, losing thousands of species of parasites could be detrimental.



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