Those of you with cats will know about Toxoplasmosis. It's a nasty parasitic infection that our feline friends get from eating bad meat.
Toxoplasmosis can survive in soil over a year. That means that being careful not to step on cats' mess is not going to make a difference; you cannot see the stuff in the soil.
Toxoplasmosis that is brought into the house and onto your floor can infect small children. This can lead to fever, pneumonia and damaged vision.
Just insist on all shoes being removed at your door. It's not rocket science.