Sarcocystis falcatula is a parasite that can be transmitted to birds by opossums. The opossum eats an infected animal and it can be passed to birds Even if a wild possums goes nowhere near a bird it can be transmitted by flies. However, a possums, I believe can be treated for this parasite before they enter your home. Contact a veterinarian before considering a possum as a pet.
Learn more about possums as a pet
Pet opossums or Pet Possum