horses need to be dewormed seasonally as much as humans, cats, and dogs, etc, one infected horse can contaminate an entire field with hydatid sand, hydatid eggs, a few dozen different parasite eggs and worse that transmit easily to humans.
If people use animals they must care for the animals and deworm them seasonally.
I could be in error but I think the plague in NYC at turn of century was created by hydatid, pinworm, ascarid, threadworm eggs,etc etc from infectious horse droppings all over the city streets and roads.
If you are going to use an animal you must be responsible and deworm it seasonally.