Wednesday, 26 December 2012

CBC Ideas - Worthy Parasites

Have you ever found a tiny parasitic pea crab living
inside your oyster? Some folks like to eat these too.
Image: NOAA
My CBC Ideas documentary, Worthy Parasites: A Villain's Silver Lining, will air for the first time on Jan 8, 2013, at 9 PM.

Regular listeners of CBCs Ideas, hosted by Paul Kennedy, know that the program can explore virtually any topic in science, history, the arts, culture, religion or anything else you can think of. Interesting, provocative, and contemporary, it's been on the air for decades and it's always worth a listen.

That's why I'm thrilled and honored to be the contributor of an episode that explores how species almost everyone loathes - parasites - are actually beneficial in many ways, even essential in our world. If you think parasites have no worth, think again, and listen to my one-hour episode in January.

CBC Ideas, Worthy Parasites: A Villain's Silver Lining is available on CBC Radio One across Canada: Tuesday, January 8 at 9 p.m. (9:30 p.m. NT) and Monday, January 28 at 2 p.m. (2:30 p.m. NT). It will also be live streamed and streamed on demand on the CBC website, and available as a podcast.

You'll be surprised by all the good things parasites do for you.

Ivermectin for Bedbugs

Would you take a drug to make yourself poisonous to mosquitoes, or black flies, or wasps? How about taking Ivermectin for bedbugs? I'm not so sure about this - the most obvious problem is that one would have to be bitten before it could work!

Ivermectin for Bedbug Infestation


Bedbug bites can be very uncomfortable.
Taking Ivermectin for bed bugs would
only work if every bug bit at least
once more!
A recent article on suggested that giving people oral Ivermectin for bedbugs might be an effective way of dealing with a bedbug infestation. A very small study (three people) found that most bedbugs died if they fed on someone within a day of a dose of Ivermectin, and that 54 hours after the dose, 42% of bugs died after feeding.

Treating people who aren’t sick with drugs has precedent: it’s common for people traveling in places where mosquitoes carry malaria, for example, to take an anti-malarial drug to avoid infection. But while malaria can easily kill you, bedbugs have never been shown to transmit disease to humans.

Ivermectin is an antiparasitic and obviously an insecticide. Like all drugs, it comes with a risk of side effects, some of them quite serious. Would it really make sense to expose large numbers of people – people who aren’t infected with anything - to this drug? It seems to me that treating a dwelling with insecticides is one thing – sometimes not a very good thing – but turning people into insecticide laden bug traps is another.

Bedbug Feeding Habits

Would it even work? Past research has indicated that bedbugs don’t feed every day. A 2009 study indicated that they might feed every two to three days and that they might synchronize their feeding (in other words, the bugs in a colony all tend to feed at the same time). Ivermectin is typically given as a single dose; how would we determine when it’s feeding day for the bedbugs? If the first twenty-four hours is crucial, you’d want to make sure you took the drug on the right day. And what if some survived or didn’t feed that day? And you’d need 100% participation from people staying in the dwelling. Imagine trying to do this in an apartment building. How many doses of Ivermectin would it take?

Finally, I suspect resistance would arise fairly quickly. If 42% of bugs died after feeding at the 54 hour mark, that means 58% survived – and they’d all been exposed to the drug. If their survival was due to them having more natural resistance than the other bugs, and they passed that along to subsequent generations, we’d see more and more resistance.

Before very long, the days of using Ivermectin for bedbugs would be over.



Gale, J. (2012) “Bed Bugs Dying After Merck Drug Suggests Possible Weapon.”

Reinhardt, K., Isaac, D. and Naylor, R. (2010), Estimating the feeding rate of the bedbug Cimex lectularius in an infested room: an inexpensive method and a case study. Medical and Veterinary Entomology, 24: 46–54. doi: 10.1111/j.1365-2915.2009.00847.x