Airsacculitis Also called
Air sac disease, air sac infection, air sac syndrome, sac disease
General signs -
Coughing, loss of appetite, nasal discharge, weight loss or stunted growth, ruffled feathers, difficulty breathing, clogged nares, rattling breath, lethargy, and (for mature hens) a drop in laying
Cardinal or diagnostic signs -
Generally occurs in younger birds, 6 - 12 weeks old. Post-mortem: Air-sacs, throat, and nares filled with congestion
Various bacteria infect air-sacs, including E. coli and Mycoplasma. Air sacs are a part of a chicken's respiratory system, which is rather different than the respiratory systems of mammals. In birds, for example, the respiratory system helps to regulate body temperature; also, they have no diaphragm. Air sacs move air through lungs in a one-way direction. Birds' lungs are comparatively small, and through a complex process the air sacs help to keep the air in birds' lungs more oxygen-filled. That means birds can breathe at higher altitudes than mammals. That is helpful to high-flying birds, but probably less helpful for ground-dwelling chickens... save those in high-altitude places like Silverton, Colorado.
Very communicable between birds. Exact mode of communicability depends on the particular bacteria infecting the birds.
Communicability to humans
Humans don't have air sacs. However some bacteria causing the illness can affect humans, such as E. coli. Practice good biosecurity.
One to three weeks, varying depending on the infecting bacteria
In some cases, yes. For instance, M. gallisepticum is carried by survivors and can infect other birds.
Yes. Bacteria that can cause this disease are commonly found in most environments
Home treatment and/or prevention
Sometimes this illness follows vaccination for other respiratory diseases, or in concert with them. In other words, infection from another illness can move from bronchial passages to air-sacs, for example. So keep your brooder and coop dry and as dust-free as possible, make certain your birds have plenty of fresh air and don't get chilled or over-heated.
Antibiotics are sometimes quite effective, but you'll need to have your bird examined for a few reasons. One is that you'll want a firm diagnosis so you'll know what respiratory disease your bird has, and another is that there are other illnesses that can occur at the same time as airsacculitis, and you'll need to know if your bird has more than one illness. Finally, what antibiotics to use will depend on the bacteria causing the infection/s. Some will be effective, while others will just case further stress on the system without helping.
This is a serious illness, but about 2/3 of the birds should recover---more with prompt care.
Other conditions, illnesses and/or diseases with similar signs:
Chronic Respiratory Disease, coryza, gapeworm, IB, CRD, and other illnesses affecting the respiratory system
Also consider browsing through this list of other chicken illnesses with respiratory symptoms.