Airsacculitis, also known as air sacculitis, aerosacculitis, air sac disease, air sac infection, air sac syndrome and simply sac disease, is a common inflammatory condition of air sacs that occurs in birds and is caused by various microbial (mostly bacterial) taxa. Having multiple different causative agents, the condition is widely distributed around the world.
Since the disease is highly infectious it is especially dangerous for domesticated birds (poultry) bred on big farms. Occurrence of airsacculitis in big flocks can mean high economic loss, as infected poultry needs to be carefully observed, with all of the infected tissue disposed of and not used for human food. In severe cases of the disease whole infected bird carcasses need to be disposed.
Usually the disease affects younger birds, aged between 6 and 12 weeks. The most characteristic sign of airsacculitis is an inflamed mucous membrane of bird air sacs, which swells and becomes red, with infected birds exhibiting different symptoms, such as coughing, lethargy, swelling of the neck, difficult breathing, appetite and weight loss etc.
The same term is used for bacterial infection and subsequent inflammation of laryngeal air sacs in non-human primates.
In birds
Anatomical background
The respiratory system of birds differs significantly from that found in mammals. Birds have relatively small lungs that are rigid and not contractile like those of mammals, in which lungs expand and contract during the breathing cycle. Another critical difference is the absence of so-called air sacs in mammals. Such structures help birds to regulate air flow through their respiratory system. Birds also lack the diaphragm.
Signs and symptoms
Airsacculitis is an inflammatory condition, that appears as a consequence of infection with various species of microbes, mostly bacteria. The condition itself resembles mammal bronchitis and pneumonia, even though different body parts are infected and inflamed.
In a few cases the condition is asymptomatic. Infected birds usually appear sick; lower part of their neck can swell and animals experience difficulties breathing. They may cough, lose their appetite and subsequently their weight, often exhibit nasal discharge, apparent clogged nares, ruffled feathers, have watery eyes and appear lethargic. Affected adult females (hens) lay fewer eggs, while juveniles exhibit stunted growth.
When doing an autopsy congestion of air sacs, throat and nares is evident. Air sacs are red, swollen and produce a lot of liquid.
Cause
The cause of airsacculitis is a bacterial infection of air sacs. The common disease causative agents are species, such as pathogenic Escherichia coli, Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS), Mycoplasma meleagridis (MM), Ornithobacterium rhinotracheale (ORT) and Bordetella avium. Airsacculitis can also be caused by other microbes, such as fungi and in rare cases even viruses. Only rarely airsacculitis is a consequence of improper vaccine or its administration.
This disease is highly infectious in birds, but the infectivity is dependent on the causative agent itself. Specific bacteria species (particularly E. coli), causing the airsacculitis in birds, can be transmitted to people. In some cases this disease can be latent, meaning bacteria remain dormant in survivors and potentially attack non-infected birds after a while.
Diagnosis and treatment
Typical symptoms should be observed. The disease can be diagnosed with a help of radiography and endoscopy. After a close inspection (e.g. an air sac biopsy) veterinarians usually prescribe antibiotics for the exact infectious agent. It is also important to diagnose any additional (comorbid) diseases. Abscess and granuloma can be removed surgically.
To prevent the disease poultry should be kept in dry and warm (not chilled or over-heated) conditions, with appropriate sanitation, source of clean water and an access to enough fresh air (ventilation).
Prognosis
Prognosis is usually favorable, with poultry experiencing moderate pain for some time. It has been reported that commonly about 2/3 of infected birds recover after exhibiting symptoms for some time. Prompt care increases the likelihood of survival. In specific birds unwanted feather-plucking can occur as a consequence of infection and inflammation.