A new study has revealed that potential vaccines against elephantiasis might make the infection spread more easily through communities.
The conclusion is based on the finding that parasitic worms can adjust their survival strategy based on their host's immune response.
Tiny filaria worms carried by mosquitoes block the lymph vessels that normally drain fluid from limbs or genitals, which then swell to grotesque proportions.
Simon Babayan at the University of Edinburgh, UK, and colleagues, have discovered that some vaccines may make the worms worse, reports New Scientist.
When filaria worms in mice sense that the mouse is mounting a strong immune reaction, they change their life cycle, producing more offspring in the blood earlier.
This helps the worm ensure that it will be picked up and transmitted by another mosquito despite the immune attack.
Unfortunately, experimental vaccines rely on the very immune reactions that warn the worms, said Babayan.
People who get such a vaccine may defeat their own infection, but the worms' early response means they will pass on more infections.
Babayan said potential vaccines should be tested for whether their targets adapt to them in this way.