Aspergillosis is a fungal infection that commonly causes respiratory disease in pet birds. It can cause both upper (nose, sinuses, eye, and trachea) and lower (lungs and air sacs – a specialized part of the respiratory tract that birds have) respiratory problems or more broadly distributed systemic infections. Aspergillus is normally an environmental contaminant and is not contagious from bird to bird.
Candida albicans is a common environmental fungus that can affect the digestive tracts of birds. It is a common cause of 'sour crop' or a crop infection (ingluvitis), especially in young birds. Candida can be a primary or secondary cause of crop infections. Often, other diseases compromise the bird's immune system and predispose a bird to secondary Candida infection (candidiasis).
The normal lens in the eye of any animal is clear and colorless. A cataract is an increase in the density or opacity of the lens; it is often observed as whiteness within the pupil. Cataracts are often seen in canaries and less often in Amazon Parrots, African Grey Parrots, and Macaws. Cataracts decrease the visual acuity of the bird and may eventually lead to blindness.
Feather loss occurs either because the bird is truly losing feathers or because the bird, or its cage-mate, is picking out its feathers. Feather-picking is often a behavioral problem, especially in the larger species of birds (such as cockatoos, macaws, and African gray parrots). However, feather loss and feather-picking can also be caused by diseases that result in irritation or pain for the bird, or damage to, or inappropriate growth of feathers. Your veterinarian may have to many perform several diagnostic tests to rule out potential causes. Treatment of feather loss depends on the cause. Feather loss and feather-picking are complicated problems; for specific advice, your bird should have a thorough work-up by a veterinarian familiar with birds.
While many owners believe parasites are common causes of skin disorders and feather loss in birds, this is usually not the case. However, Knemidokoptic mange, also called cere mites or scaly face is a relatively common disorder, particularly in some of the smaller species of birds.
Pacheco's disease is caused by a herpes virus. Many species of birds are susceptible. Cockatoos and Amazon parrots are very susceptible to the infection and usually die, whereas conures, such as the Nanday and Patagonian Conures seem to be resistant to the disease.
The polyomavirus of pet birds belongs to the family Papovavirus, the same group of viruses that causes benign skin tumors (papillomas or warts) in birds. Polyomavirus can cause benign feather lesions in budgies (the so-called French molt or Budgerigar Fledgling disease) or acute death.