The most common avenue of transmission is mosquitoes, but it may also transmit via inhalation or ingestion. If a bird has an open wound or scratch, the virus has an entry point.
Outdoor aviaries that are susceptible to droppings drying and the ‘dust’ becoming airborne or with birds that forage the ground are prime examples.
With Poxvirus you’ll find nodules on the unfeathered areas of the bird, including around the beak, cere, eyes, legs and feet. The nodules may break open and become scabby areas. Poxvirus victims are prone to secondary, opportunistic infections from bacteria and/or fungus.
Wet Poxvirus is an internal presentation of this virus often with growths not only in the mouth and into the esophagus and further into the bird’s system, but also in or on the eyes.
Papilloma virus also produces growths on birds, usually a wart-like projection first seen on or around the vent area. It can, however, present just about anywhere.
The only treatment for papillomas so far is removal, usually cauterization, as they appear. By maintaining this treatment many birds find many more years left of a good, quality life save for the times this surgery is necessary.
Papillomas that start on the cloaca/vent may also show up, eventually, in the oral cavity. Usually this is at the base of the tongue to begin with, but may also include the esophagus. Lachrymal involvement is also seen (the eye area/tear ducts).
Oral papillomas may cause dyspnea (loss of balance).
Internal papillomatosis (IPP) will involve the bile ducts of the liver.
What you have to keep reminding yourself is that just because you might not see all these symptoms and your bird is acting fine, not showing signs of pain like a mammal would - doesn't mean it's fine. Birds are experts at what is called "masking", hiding symptoms, illness, infection, weakness and other problems until they are so progressed that they can't hide them anymore, or at least keep it up consistently.
That's why some owners will see symptoms and suddenly the bird seems ok again. By the time the symptoms return, it's much worse - so getting your bird to professional care at the very first inclination of something wrong is usually the most productive of recovery at the most reasonable cost.
You mention that you've had a problem before with bumble foot or scaley feet. These are aggravating little mites that might seem eradicated and then show up somewhere else, exactly like you're seeing.
Knemidokoptic (Mange) Mites cause white or grayish, crusty lesions/growths on non-feathered areas of the bird. Corners of the mouth, feet, legs and cere are commonly affected. In advanced cases the feet can look deformed from them. Sometimes a bird won’t have symptoms other than feather loss and itching.
Certified Avian Specialist
Cert. Avian Specialist; Int. Assoc.Animal Behavior Consult; Pet Ind. Joint Advisory Council; author