Avian pulmonary proteinosis (PP) is a serious respiratory condition in birds where too much pulmonary surfactant accumulates in the lungs.
Pulmonary surfactant is a mixture of lipids and proteins in the lungs that is necessary for normal breathing but is normally cleared and replaced. Chickens with pulmonary proteinosis are unable to clear this surfactant so it continues to build up over time, leading to heart problems and respiratory failure.
Avian pulmonary proteinosis differs from pulmonary alveolar proteinosis (PAP), a similar lung condition of mammals due to the unique lung anatomy of birds.
In mammals, air flows through the trachea into alveoli (grape-like clusters of tiny air sacs within the lungs) where gas exchange occurs. Oxygen moves through the alveoli where it is exchanged into the blood capillaries for carbon dioxide. Alveolar macrophages are responsible for clearing old surfactant that lines the alveoli.
Birds have a different respiratory system to mammals. When air flows through the trachea into the lungs of a bird, it passes through tubular structures called parabronchi (instead of alveoli) which are the sites of gas exchange. Air sacs allow for a continuous, one way flow of air during inspiration and expiration.
There is little research available on the exact cause of avian pulmonary proteinosis in birds but based on research on mammals, potential factors include:
- Environmental exposure: Inhalation of dust, chemicals, allergens and/or toxins. Some of these may include metals (copper, aluminum, nickel, titanium), stone or sand, epoxy, paint, polyvinyl chloride (PVC, marine vinyl), cement, cellulose, kaolin, quartz, indium, smoke, talc, textiles, wood, diesel, welding, fiberglass, and zirconium.
- Genetic predisposition
- Underlying infections: There may be a possible association with the Marek's disease virus.
Chickens with avian pulmonary proteinosis are more likely to develop heart problems secondary to hypoxia and pulmonary hypertension due to the strain on their respiratory system. When severe, it can lead to respiratory failure and death. Unfortunately, most cases are discovered during necropsy due to the lack of awareness of this condition and difficulty diagnosing.
