Avian Pulmonary Proteinosis

Avian pulmonary proteinosis (PP) is a serious respiratory disorder in birds characterized by the excessive buildup of pulmonary surfactant in the lungs.

Pulmonary surfactant is a mixture of lipids and proteins that plays a vital role in normal breathing. Under typical conditions, it is continuously broken down and replaced. In chickens with pulmonary proteinosis, this clearance process fails, allowing surfactant to accumulate over time. As it builds up, it interferes with normal lung function and can ultimately contribute to respiratory failure and secondary heart complications.

Although similar in name, avian pulmonary proteinosis differs from pulmonary alveolar proteinosis (PAP) seen in mammals due to key differences in lung anatomy.

In mammals, air travels through the trachea into tiny, grape-like air sacs called alveoli, where gas exchange occurs. Oxygen passes into the bloodstream while carbon dioxide is removed. Specialized cells called alveolar macrophages help clear old surfactant from these structures.

Birds, however, have a distinct respiratory system. Air moves through the trachea into the lungs and passes through tubular structures called parabronchi, where gas exchange takes place. Additionally, birds have air sacs that enable a continuous, one-way flow of air during both inhalation and exhalation.

The exact cause of avian pulmonary proteinosis remains unclear, and research in birds is limited. However, insights from mammalian studies suggest several possible contributing factors, including environmental exposures (such as dust, chemicals, toxins, and certain metals), genetic predisposition, and underlying infections—potentially including Marek’s disease virus.

Chickens affected by this condition are at increased risk of developing heart problems due to chronic low oxygen levels (hypoxia) and pulmonary hypertension. In severe cases, the disease can progress to respiratory failure and death. Unfortunately, avian pulmonary proteinosis is often only identified during necropsy, as it is not widely recognized and can be difficult to diagnose in living birds.