Canine sinonasal aspergillosis is a fungal infection of the nasal cavity and frontal sinuses caused by the Aspergillus fungus, a mold widespread in the environment. Although dogs commonly inhale the fungal spores, infection only occurs in a small number, suggesting a predisposition in some animals. The disease is characterized by a persistent infection that can cause significant damage to the delicate structures within the nose.
This condition affects the upper respiratory tract and is localized, meaning it does not spread throughout the body in healthy dogs. The fungus colonizes the mucous membranes lining the nasal passages and sinuses, leading to a chronic and destructive inflammatory response.
Causes and Clinical Signs
Dogs become infected by inhaling microscopic fungal spores from substances like soil, dust, and decaying vegetation. While any dog can inhale these spores, a healthy immune system usually clears them without issue. The development of sinonasal aspergillosis is often linked to a local defect in the immune system’s ability to manage the fungus within the nasal cavity.
Certain breeds are more susceptible, particularly dogs with long noses (dolichocephalic) and medium-length noses (mesaticephalic), such as Collies and German Shepherds. This predisposition may be due to the larger surface area within their nasal passages, which can trap more spores. Young to middle-aged dogs are most commonly affected.
The clinical signs of sinonasal aspergillosis are persistent and can worsen over time. One of the most common indicators is a chronic nasal discharge, affecting one or both nostrils, that can range from clear mucus to thick with pus or blood. As the infection progresses, nosebleeds can become more frequent.
Affected dogs often show discomfort through facial pain, pawing at the nose, and loud sneezing. Other visible signs include the loss of pigment or sores on the nostrils and, in some cases, a foul odor from the nose.
Veterinary Diagnostic Process
A definitive diagnosis is necessary because its symptoms overlap with other conditions like nasal tumors, foreign bodies, or severe dental disease. While a diagnosis begins with a physical exam, specialized procedures are required to confirm the fungus and assess the extent of the damage.
Imaging is a component of the diagnostic workup. While standard X-rays can offer some information, Computed Tomography (CT) scans are the superior method. CT scans provide detailed images of the nasal passages and sinuses, allowing veterinarians to visualize fungal plaques and the extent of bone erosion, a common feature of this disease.
The most definitive diagnostic step is rhinoscopy, which involves inserting a small camera into the dog’s nasal passages under general anesthesia. Rhinoscopy allows the veterinarian to directly see the fungal colonies, which often appear as whitish-gray, plaque-like mats. During this procedure, the veterinarian can collect tissue samples (biopsies) and fungal swabs for laboratory analysis.
These collected samples are submitted for analysis. Fungal culture can identify the Aspergillus organism, while histopathology, the microscopic examination of biopsy tissue, confirms the invasive nature of the infection.
Treatment Protocols
Treatment aims to eliminate the fungal infection at its source, most commonly through a procedure under general anesthesia. The protocol involves infusing a topical antifungal medication directly into the nasal and sinus cavities. This method delivers a high concentration of the drug to the fungus with minimal systemic exposure.
Before the antifungal agent is administered, the veterinarian will often perform a debridement of the fungal plaques. Using instruments guided by an endoscope, the visible fungal material is removed from the nasal passages. This step reduces the fungal burden and allows the medication to penetrate the underlying tissues more effectively before the cavities are flushed.
Following debridement, a topical antifungal agent like clotrimazole is infused into the nasal and frontal sinuses. The dog is positioned to ensure the liquid medication coats all surfaces where the fungus might be present. The medication is left in place for about an hour for maximum contact time before being drained.
Systemic oral antifungal medications may be used with topical therapy. This is often reserved for cases where the infection is severe, has recurred, or is suspected to have eroded through bone into surrounding tissues. Oral medication is administered for several months and requires careful veterinary monitoring.
Prognosis and Management
The prognosis is favorable when the infection is confined to the nasal cavity and treated with topical antifungal therapy. A single topical treatment is often successful, and many dogs experience a full recovery with a significant reduction in clinical signs within a few weeks.
Recurrence of the infection is possible, and some dogs may require a second round of topical therapy if signs return. The prognosis becomes more guarded if the infection has spread beyond the nasal passages into the brain or the bones of the skull, although this is a less common complication.
Long-term management involves monitoring for any return of symptoms, such as nasal discharge or sneezing. Follow-up examinations with a veterinarian are needed to ensure the infection has not returned. Sinonasal aspergillosis is not contagious, and the risk of transmission from an infected dog to humans or other animals is minimal.