Fleas are a nuisance, they are attracted to movement they can bite you, mice, rats, pets and other people , they carry and can transmit disease.
It was the flea that transmitted the bubonic plague pandemic, ( black Death )
Fleas transmitted the disease from rats to people in Europe, this killed over 50 Million People .
Plaque infested fleas were dropped out of planes during WW2 as a biological weapon, to spread disease among our allied troops.
You don’t need pets to have fleas.
Fleas are easily transported into your home, they will jump onto you when you are walking and then you bring them inside your home.
Just that easy!