Aspergillosis in Dogs
Dr. Arnold Plotnick
Diagnosis In-depth 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.
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.
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.
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.