Birds carry a variety of diseases such as Ornithosis, Listeria and Ecoli that can be transmitted to humans from both the droppings and also the birds themselves. Pigeon droppings can lead to respiratory complaints such as psittacosis. Parasites such as mites, ticks, fleas and beetles are linked to birds, so you may find you’ll also suffer from a parasite infestation if the bird problem is left unattended.