Why don't the scientists do something really helpful like the complete eradication of fleas and other dangerous parasites?

Fleas aren’t part of the food chain but cause endless misery to animals and humans? Considering the leaps forward that science has made in gene manipulation etc. Instead of making luminous pigs and other sad projects why don’t they do this? I’m sure pet owners would contribute funds.
If ever a pandemic could be spread again by fleas it would be devastating. (The extinct human flea once spread the plague I believe).