Aspergillus is a fungus that is ubiquitous in the environment. It generally causes either nasal or respiratory infections and disseminated infections. Nasal infections are not suspected to disseminate. The nasal infections tend to be caused by a different species of the fungus, namely Aspergillus fumigatus
, compared to disseminated infections, which tend to be caused by Aspergillus tereus
The immune status is an important determinant as to whether a dog will contract aspergillosis. Pre-existing nasal disease and/or previous prolonged antibiotic therapy may be important in the development of nasal infections. Conditions that suppress the immune system, such as diabetes, Cushing's disease, chemotherapy, glucocorticoid therapy and hereditary immunosuppressive conditions may predispose dogs to developing disseminated aspergillosis.
Nasal aspergillosis is a relatively common disease in dogs. The disease usually remains confined to the nasal cavity or the sinuses, but marked destruction of the turbinates (delicate nasal bony structures) is always seen. Occasionally, a very invasive infection may affect the orbit (where the eyeball is located) and may even erode through the skull. Most cases of nasal aspergillosis are in dogs with normal immune systems that are in otherwise excellent health.
Nasal aspergillosis is usually seen in dolichocephalic (long-nosed) and mesocephalic (medium-nosed) breeds, but rarely in brachycephalic (short-nosed) breeds. Dogs of any age may be affected, but approximately 40 percent are 3 years old or younger, and 80 percent are 7 years of age or younger. The main features of the disease are a profuse nasal discharge consisting of blood mixed with pus, nasal pain, ulceration surrounding the nostrils, and nosebleed. Cancer of the nasal cavity can have very similar signs, and careful diagnostics are important so that the proper diagnosis can be made. Most cases of nasal aspergillosis can be successfully treated. Relapses are possible, but are uncommon.
Most cases of disseminated aspergillosis have occurred in German shepherd
dogs aged 2 to 8 years. Aspergillus tereus
is the most common species of organism responsible, although other species of Aspergillus have been isolated occasionally. It is thought that the fungus enters through the respiratory tract and goes to the lungs, then travels through the bloodstream where it spreads throughout the body. Infection often takes hold in the intervertebral discs of the spine, the eyes or the kidneys. Other organs, muscles or bones may be affected.
Disease tends to develop over several months, but most dogs are terminally ill when veterinary care is finally sought. The most consistent features of the disease are back pain progressing to partial or complete paralysis, or lameness of a limb with pronounced swelling and a discharging tract. A sudden onset of paralysis may result if an infected intervertebral disc ruptures and injures the spinal cord, or if the spine becomes unstable and dislocates. Other nonspecific findings include anorexia, weight loss, muscle wasting, fever, weakness, lethargy, vomiting, inflammation of the eye and lymph node enlargement. Severely ill dogs have a poor prognosis. Most dogs die from the disease although a few have been treated successfully.