Sand Fleas themselves are not contagious because they are not a disease or virus but instead sand fleas are fleas that inhabit the sand.
The sand flea rarely does bite humans but sometimes they can and will bite a hum that is walking barefoot in the sand on beaches or laying on the beach.
Sand Fleas also rarely come home with you and all you need to do is wash them off with water or stick your feet or hands in the ocean to clean the sand fleas off.
I always wear sandals when on the beach because when I went barefoot before I did get some sand fleas on my feet.
They did bite me but the bite was not really harmful and went away within a few weeks.
You're unlikely to get sick or catch any contagious disease from sand fleas or sand flea bites but getting bitten by the sand flea still is not fun.