I googled some info about them here's the link:
The Nasty and Deadly Breeding Method of Chigoe (Sand) Fleas - Flea Crawl
Here's your regular nasty flea info:
Ever-Present Enemy of the Human Species: Fleas - Flea Crawl
I think it's just better to be protected and not take a chance. The vet also said that if the dog injests a fea, they can get tape worms from it. Sounds absurd but that's what they said.