Discover Magazine Blog 5/24/12
The enemy of my enemy is my friend—especially if I’m a frog and my
enemies are competing parasites. A recent study in PNAS found that frogs populations exposed to a more diverse set of flukes actually had lower rates of
infection, with fewer frogs in the group afflicted with tiny hitchhikers.
Researchers at the University of Colorado-Boulder bred Pacific chorus
frogs in a lab and put their tadpoles in different tanks with anywhere from one
to six different types of flukes. On average, 40% of the frogs that came
into contact with only a single fluke species developed infections, while 34%
of frogs exposed to four flukes and 23% of frogs exposed to six flukes were
infected (the numbers for two, three flukes followed a roughly similar trend).
Additionally, some of the fluke species make frogs sicker than others, and
oddly enough, the frogs exposed to a greater variety of flukes had a lower
proportion of infections from these dangerous species.
Most research on host-parasite interactions has focused one host–one
parasite, but as this study shows, it’s a lot more complicated in the natural
world. Preserving biodiversity—even biodiversity of creatures, whether flukes
or microbes, that we’re not fond of—might be an important part of keeping
disease down. Why that is isn’t exactly clear—the scientists who did this
study, for instance, aren’t sure why frogs were better off with lots of flukes
around.
But it could be analogous to what happens in humans who have the
biodiversity of their gut microbes disturbed by antibiotics. Once healthy, or
at least relatively harmless, microbes are wiped out, it’s easy for dangerous
bacteria like C. difficile to take over their real estate and cause life-threatening disease. Something similar seems to happen
with viruses: having certain viruses in your body
can keep you from getting infected by other, more harmful pathogens.
In fighting off infections, thus, it could help to have allies among the
enemy.
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