Parasites and Pesticides: An Uncomfortable Truth

Yesterday, I found a rather odd tree frog on the side of our house. It appeared to have two sets of front limbs, which is quite rare and indicative of a potential parasite, the trematode.

See anything strange here?

Just for comparison...

I further investigated causes for deformed limbs in frogs and found an interesting article from Earth Observatory discussing Dr. Joseph Kiesecker's experiments on pesticide and parasite exposure to tadpoles (so, yes, this does fall into the category of aquatic ecology).

http://earthobservatory.nasa.gov/Newsroom/view.php?id=22544

From this article I learned that agricultural pesticides that are washed into aquatic systems (ag runoff) may negatively impact tadpole immune systems. The weakened tadpoles are thus more susceptible to infection from trematodes and are more likely to form cysts that may result in limb deformities. The scary part is, the concentration of pesticide necessary to initiate this effect is equal to or less than the acceptable amount present in drinking water, aka, if you live in an agricultural area you may be consuming these types of pesticides.

 So, how do these trematodes get to the tadpoles, and why do they cause these deformities? Well, the trematode utilizes several hosts in order to reach its definitive host, a wading bird. The infected frogs have deformities so that they are easier for these birds (herons for example), to catch and consume.

Trematode Life Cycle

So, I bet you're wondering just how precise these trematodes are at finding their hosts? Unfortunately, if you've ever had swimmer's itch, you've been infected by this trematode. Trust me, I got it a time or two while collecting snails, it's not the end of the world. If you were in a tropical system though, you might run the risk of getting Schistosomiasis, a potentially fatal infection that kills millions each year. And that's why I prefer waders to bare skin in stagnant waters.