Aspergillosis in Dogs
Overview of Canine Aspergillosis
Aspergillosis is a fungal infection caused by a species of fungus belonging to the genus Aspergillus. The nasal cavity and respiratory system are most commonly affected, although in some dogs the infection may spread throughout the body with grave consequence.
Nasal aspergillosis is a localized form involving the nose, ears and paranasal sinuses and is usually caused by the fungus Aspergillus fumigatus. Disseminated aspergillosis is characterized by signs of generalized infection and is caused by the fungus Aspergillus tereus.
Dogs with medium or long noses are more likely to get nasal aspergillosis. Short nosed breeds such as pugs, bulldogs and Pekingese are less likely. Pre-existing nasal disease and/or prolonged antibiotic therapy predisposes to nasal infection. German shepherds are at higher risk for disseminated aspergillosis compared to other breeds. Diseases or conditions that suppress the immune system such as diabetes and chemotherapy also predispose to developing disseminated disease.
Dogs of any age are susceptible to nasal aspergillosis, but 40 percent of cases are seen in dogs younger than 3, and 80 percent in dogs younger than 7 years of age.
The impact of aspergillosis varies depending on whether it is confined to the nasal cavity only, or disseminated throughout the body. Many nasal infections are treated successfully, while most disseminated infections eventually prove fatal.
What to Watch For
- Ulceration (open sores) around the nostrils
- Pain or discomfort in the facial region
- Profuse bloody and/or pus-filled nasal discharge that may alternate with periods of nasal bleeding
- Weight loss
- Muscle wasting
- Uveitis/endophthalmitis (inflammation of the structures of the eye)
- Back pain
Diagnosis of Aspergillosis in Dogs
- Complete blood count and chemistry panel
Treatment of Aspergillosis in Dogs
- Systemic antifungal drugs
- Topical antifungal drugs
- Systemic antifungal drugs
Home Care and Prevention
No specific home care recommendations are necessary for dogs with nasal aspergillosis. Dogs with disseminated aspergillosis that are being treated for paralysis must be conscientiously managed. Physical therapy and cleanliness to prevent soiling and urine scalding are very important
There are no specific preventative measures against aspergillosis. There is no vaccine.
In-depth Information on Aspergillosis in Dogs
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.
In-depth Information on Diagnosis
- Cytology and culture. Microscopic examination and culture of the nasal discharge is sometimes performed, but is often unrewarding. Fungal organisms may be missed, causing an erroneous diagnosis of a simple bacterial nasal infection. A positive fungal culture result must also be interpreted cautiously, as many normal dogs or dogs with nasal cancer will have positive cultures for Aspergillus.
- Biopsy. Examination of tissues obtained by biopsy through the nostrils is useful if fungal organisms are identified, but may lead to a misdiagnosis of nonspecific rhinitis if fungal colonies are missed.
- Serology. Several techniques have been developed to identify antibodies in the serum directed against the organism that causes nasal aspergillosis. The tests are fairly reliable, although false positives have been reported.
- Radiology. X-rays of dogs with nasal aspergillosis often show destruction of the delicate turbinate bones as well as infection involving the frontal sinuses.
- Rhinoscopy. Visualization of fungal colonies using a rhinoscope (a probe with a light and an attached camera) is an excellent diagnostic method. Biopsy of fungal plaques under direct visualization with the rhinoscope is the best method of obtaining samples for culture and definite diagnosis.
- Complete blood count and chemistry panel. These tests do not diagnose the disorder, but are performed to assess the general condition of the dog. Many dogs have an elevated white blood count. Chemistry panel abnormalities often reflect the organ system(s) affected, such as the kidneys or liver.
- Urinalysis. Identification of fungal organisms in a sterile-collected urine sample.
- Cytology. Identification of Aspergillus organisms when examining blood smears, joint fluid, lymph node aspirates, or material from an infected intervertebral disk confirms the diagnosis.
- Culture. Growing and identifying Aspergillus colonies from tissue samples is another way to confirm a diagnosis; however, it takes 5 to 7 days to grow the organism.
- Serology. Several methods are available to detect antibodies in the bloodstream directed against the Aspergillus organism. Not all dogs with disseminated aspergillosis will have detectable antibodies. False negatives may also occur if the test identifies the organism that causes nasal aspergillus (A. fumigatus) instead of the organism causing disseminated aspergillosis (A. tereus).
- Biopsy. Identification of the organism on a biopsy specimen confirms the diagnosis.
- Radiology. X-rays of the long bones often reveals areas of bone destruction.
In-depth Information on Therapy
Nasal aspergillosis is initially treated with antifungal drugs. They can be given orally, and they can be infused into the nasal cavity. Most cases are treated successfully, as evidenced by rapid resolution of nasal pain and nasal discharge, and healing of the ulcerated nostrils. Relapse is not a common problem, although bacterial infections of the nasal cavity can develop in up to 25 percent of dogs after the fungal infection is cleared. These bacterial infections usually respond well to antibiotics.
Disseminated aspergillosis has a poor prognosis, especially in dogs that are severely ill on presentation. Only two drugs have been shown to be effective in treating the disseminated disease.
Therapy for Nasal Aspergillosis in Dogs
- Oral antifungal drugs. Of the oral antifungal drugs, the newer drugs fluconazole and itraconazole have shown the best efficacy, but success rates do not exceed 60 percent or 70 percent. The drugs are expensive and must be administered for a minimum of ten weeks. Five percent of dogs given itraconazole show side effects (liver damage) and have to be treated with the other drug. The results obtained with oral therapy are not as good as that seen with topical therapy.
- Topical antifungal drugs (clotrimazole, enilconazole). Flushing enilconazole into the nasal cavity through tubes surgically implanted into the nasal cavity and frontal sinuses results in elimination of the fungus in 90 percent of affected dogs, although this is done less commonly because it is labor intensive, messy, not well tolerated by many dogs, and can be complicated if the dog removes one of the tubes. More recently, the treatment of choice is infusion of clotrimazole into the nasal cavity under anesthesia. One study reported a 94 percent cure rate for dogs treated in this fashion.
Therapy for Disseminated Aspergillosis in Dogs
- Systemic antifungal drugs. Only two drugs have been shown to be effective: amphotericin B and intraconazole. Amphotericin B seems to be more effective, but requires hospitalization; the drug is given intravenously. Newer lipid-formulations of this drug may hold more promise in the future. Amphotericin B can cause kidney damage and should not be used in dogs with pre-existing kidney problems. Oral itraconazole has shown some efficacy in a few dogs, but the dogs need to receive this drug for months or years. Some dogs that have responded to the drug relapsed and died when the medication was discontinued.
Follow-up Care for Dogs with Aspergillosis
Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your dog does not rapidly improve. Administer all prescribed medication as directed. Alert your veterinarian if you are experiencing problems treating your dog.
Return to your veterinarian for any follow up X-rays or blood tests necessary. Serum antibody levels may remain elevated for years after effective treatment, so this is not a good way to monitor the success of therapy.