The scab of the air sacs is a disease parasitic infection which affects the respiratory tract and is caused by mites white. The causative agent is Cytodites nudus. 

When present in small amounts, this mite is considered non-pathogenic. However, if the infection is massive, it can result in granulomatous pneumonia, which can be confused with other respiratory diseases. 

The mites tend to live in the bronchi, lungs, alveoli, and even in the cavities aerial of the bones. 

Mite air bags, Cytodites nudusspecies sarcoptiformes (now called Acaridida); live as endoparásito in the bronchi, lungs and air sacs of chickens and birds (especially birds and pheasants), from where it penetrates the peritoneum; its food is a serous fluid, which is absorbed through the oral appliance, which is transformed into the suction tube.

It is a chronic disease that sometimes goes unnoticed. When the number of parasites is small, the form in which it occurs is not known; when the number is large, there is some cloudiness in the alveoli, and are produced slight difficulty in breathing and sneezing, so that the eggs deposited by these mites in the airway may be expelled. 

The mite is small, viviparous, 0.6 mm long, and egg-shaped; it lacks basic and locomotive organs, is white in color, has a soft exoskeleton, and a few light-colored bristles. It is transmitted to poultry by pigeons and wild birds, causing severe respiratory distress. The most severe symptoms in affected animals only occur in large-scale outbreaks. 

In extreme cases, it can be seen wasting of the birds, peritonitis, pneumonia, and death.