Aspergillosis in Dogs and Cats

TL;DR. Aspergillosis is an uncommon but serious fungal infection that primarily causes chronic, painful nasal disease in dogs, and while it is highly treatable in its localized nasal form, the rare systemic form is unfortunately often fatal.

The intricate, scroll-like turbinate bones inside a dog's nasal cavity are the primary target of nasal aspergillosis.

What is it?

Aspergillosis is an opportunistic fungal infection caused by species of the mold Aspergillus, most commonly Aspergillus fumigatus. These fungal spores are ubiquitous in the environment, found commonly in soil, dust, decaying vegetation, and hay. While healthy pets inhale these spores daily without consequence, the fungus can take hold in animals with compromised local nasal defenses or systemic immune deficiencies.

In dogs, the infection most frequently manifests as localized nasal aspergillosis (also known as mycotic rhinitis). This form of the disease is characterized by the colonization and destruction of the delicate, scroll-like bony structures inside the nasal cavity called turbinates. As the fungus grows, it forms thick, felt-like mats called fungal plaques that erode the surrounding tissue and sinuses.

While nasal aspergillosis is primarily a canine disease, it is occasionally diagnosed in cats. In rare instances, the fungus can bypass the localized nasal defenses and enter the bloodstream, resulting in systemic or disseminated aspergillosis. This systemic form spreads to multiple organs, including the bones, kidneys, spleen, and central nervous system, and carries a much graver outlook.

Causes & risk factors

Inhalation of environmental Aspergillus spores is the sole cause of the infection. Because these spores are present everywhere in outdoor and indoor environments, exposure is virtually guaranteed for all domestic pets. However, the development of active disease depends heavily on host susceptibility.

Young to middle-aged dogs, particularly those with medium to long snouts (mesocephalic and dolichocephalic breeds), are most commonly affected by the nasal form. Young male dogs appear to have a higher statistical representation. In cats, nasal infection is exceptionally rare and is typically associated with pre-existing nasal trauma, severe viral infections, or localized immunosuppression.

For the systemic form of the disease, there is a strong, documented breed predisposition. German Shepherd Dogs are uniquely susceptible to disseminated aspergillosis. This susceptibility is believed to stem from an inherited immunodeficiency, specifically involving a deficiency in secretory immunoglobulin A (IgA), which impairs their mucosal and systemic defense mechanisms against fungal pathogens.

Signs to watch for

Recognizing the signs of aspergillosis early is critical to preventing extensive destruction of the nasal bones. The clinical signs vary depending on whether the infection is localized to the nose or has spread systemically.

Nasal Aspergillosis Symptoms

• Nasal discharge (Cardinal): This is the most consistent sign. The discharge may be mucoid (slimy mucus), mucopurulent (pus-filled), or hemorrhagic (bloody). It can affect one nostril (unilateral) or both (bilateral), and often fluctuates in severity.
• Sensitivity to palpation of the face (Common): Dogs with nasal aspergillosis often experience significant pain. They may pull away, whine, or show aggression when their snout or muzzle is touched.
• Depigmentation and ulceration of the external nares (Common): The chronic, corrosive nature of the discharge often causes the black or brown skin around the nostrils to lose its pigment, turning pink, raw, and ulcerated.
• Sneezing (Occasional): While sneezing occurs, it is often less prominent than the persistent discharge and pain.

Systemic Aspergillosis Symptoms (Red Flags)

If the infection spreads systemically, the signs are much more generalized and severe. These constitute a veterinary emergency:

• Progressive weight loss and muscle wasting
• Persistent fever unresponsive to antibiotics
• Lameness or spinal pain (due to fungal infection of the bones or intervertebral discs)
• Lethargy and depression
• Increased thirst and urination (if kidneys are affected)

Depigmentation and raw ulceration of the nostrils are common signs of the chronic, corrosive discharge caused by nasal aspergillosis.

How vets diagnose it

Diagnosing nasal aspergillosis is a multi-step process. Because other diseases, such as nasal tumors, foreign bodies, or other fungal infections, can mimic these signs, your vet will need to perform several diagnostic tests to confirm the diagnosis.

Another type of fungus, Penicillium, can cause signs similar to those of aspergillosis. [2]

Your vet will likely begin with nasal radiography or, ideally, a computed tomography (CT) scan. Advanced imaging is highly valuable for assessing the extent of bone destruction and identifying fluid accumulation in the sinuses. As noted in a leading veterinary internal medicine reference:

Fluid opacity within the frontal sinus can represent a site of infection or mucus accumulation from obstructed drainage. In some patients the frontal sinus is the only site of infection. [1]

Following imaging, a rhinoscopy is typically performed. This involves inserting a small, flexible camera into the nasal passages under general anesthesia. This allows the veterinarian to directly visualize the nasal cavity, look for the destruction of nasal turbinates, and identify characteristic fungal plaques, which appear as white-to-green mold-like patches on the nasal lining.

While visualizing these plaques is highly suggestive, your vet must obtain a definitive diagnosis. The gold standard for diagnosis is histopathology of a nasal mucosa biopsy. A pathologist will examine the tissue sample under a microscope to confirm that the branching fungal structures (hyphae) are actually invading the nasal tissue, rather than just sitting on the surface.

Other supportive tests include:

• Cytology: Examining a swab or smear of the nasal discharge under a microscope to look for fungal hyphae.
• Fungal culture: Growing the organism in a lab. However, because Aspergillus can be a normal inhabitant of the nasal cavity in healthy dogs, a positive culture alone does not confirm active infection.
• Serum antibody titers: A blood test that measures the immune system's response to the fungus. As noted in veterinary literature:

Positive serum antibody titers also support a diagnosis of infection. Although titers provide indirect evidence of infection, animals with Aspergillus organisms as a normal nasal inhabitant do not usually develop measurable antibodies against the organism. [3]

Rhinoscopy allows direct visualization of the characteristic white-to-green fungal plaques growing on the nasal lining.

Treatment options

Treating nasal aspergillosis requires clearing the fungal plaques from the nasal passages and sinuses. Because the fungus is protected within the nasal cavity, systemic oral medications alone are often less effective than direct, topical therapies.

First-Line Topical Therapy

The most effective treatment for localized nasal aspergillosis is a topical infusion of an imidazole antifungal drug, such as clotrimazole or enilconazole. This procedure is performed under general anesthesia.

The veterinarian will place catheters into the nasal cavity, seal the back of the throat with inflatable tubes (to prevent the drug from entering the lungs), and infuse the liquid antifungal directly into the nasal passages. The medication is left to bathe the tissues for approximately one hour before being drained. This highly concentrated exposure is very effective at killing the fungal plaques. In some cases, a second treatment is required several weeks later.

First-Line Oral Therapy

In cases where topical therapy is not tolerated, or if the infection has penetrated the thin bones separating the nasal cavity from the brain, oral antifungal therapy is utilized. Itraconazole (a triazole antifungal) is the primary oral drug of choice. Oral therapy is prolonged, typically requiring daily administration for several months, and requires regular blood monitoring to ensure liver health.

Second-Line Therapy

If first-line therapies fail or if the dog cannot tolerate them, second-line oral antifungals such as terbinafine (an allylamine antifungal) may be prescribed, often in combination with other medications.

For systemic aspergillosis, treatment is exceptionally difficult. It requires aggressive, long-term combination therapy with systemic antifungals, but the success rate is unfortunately very low.

Prognosis

The prognosis for nasal aspergillosis is fair to good, provided the infection is diagnosed before extensive bone destruction has occurred and the pet undergoes appropriate topical or oral therapy. Owners must be prepared for a prolonged treatment course, and some dogs may suffer from permanent damage to their nasal turbinates, making them more prone to secondary bacterial nasal infections for the rest of their lives.

In contrast, the prognosis for systemic aspergillosis is grave. Because the disease is typically advanced by the time it is diagnosed and is highly resistant to treatment, it is generally fatal.

Prevention

Because Aspergillus spores are a natural and unavoidable part of the outdoor environment, complete prevention of exposure is impossible. There is currently no vaccine available for aspergillosis.

For healthy pets, maintaining a strong immune system through proper nutrition, regular veterinary care, and minimizing exposure to highly dusty, moldy, or agricultural environments (such as barns or compost piles) is the best defense. For breeds known to be predisposed to the systemic form, such as German Shepherds, avoiding environments with high concentrations of decaying organic matter is highly recommended.

When to call your vet

If your pet is showing signs of chronic nasal disease, you should schedule an appointment with your veterinarian. However, you should seek immediate veterinary care if you observe any of the following red flags:

• Severe, continuous bleeding from the nose (epistaxis)
• Extreme distress, vocalization, or aggression when the face is touched
• Inability to breathe comfortably through the nose
• Sudden onset of neurological signs, such as seizures or difficulty walking
• Severe lethargy, persistent fever, or rapid weight loss

For specific breeds

As noted, the German Shepherd Dog carries a significant genetic predisposition for the systemic, disseminated form of aspergillosis. If you own a German Shepherd, it is vital to monitor them closely for vague signs of illness, such as unexplained lameness, back pain, fever, or weight loss. Early diagnostic intervention is their only chance at a successful outcome, though the disease remains highly challenging to treat in this breed.

Sources

• Internal Medicine, 5th Edition, page 271.