Aspergillosis in Dogs

What is aspergillosis?

Aspergillosis is an infection caused by the Aspergillus fungus. This fungus grows on dead leaves, stored grain, compost piles, and other decaying vegetation. The Aspergillus species includes more than 180 types of molds that occur widely in indoor and outdoor environments. Aspergillus is commonly found as a lacy mold that grows on foods.

Although most Aspergillus molds are harmless, a few can cause serious illnesses in people and in dogs with weakened immune systems, underlying lung disease, or asthma. The most common species of Aspergillus that cause problems in dogs are Aspergillus fumigatus and Aspergillus terreus, although several other species can also cause illness.

How do dogs get aspergillosis?

Aspergillus is an opportunistic pathogen and usually affects animals whose immune systems are suppressed or compromised. Aspergillus fungi shed microscopic spores that float in the air and are easily inhaled. Fortunately, dogs have several protective mechanisms built into their bodies that help prevent infection.

In the nose, the nasal sinuses trap debris, as does the mucus layer that lines the nasal passages. A dog can also sneeze to expel inhaled debris and foreign bodies. In the remainder of the respiratory tract, the mucus lining of the passages traps debris that enters the airways, and tiny hair-like cilia constantly move to “sweep” the mucus and trapped debris up and out of the airways. A healthy immune system provides active protection of the entire body, preventing invasion and fighting infections within the body.

If Aspergillus spores, called conidia, are inhaled and manage to evade or bypass these protective respiratory mechanisms, the spores can begin to grow, which makes them more difficult for the body to remove. Some strains of the fungus are more likely to cause disease than others, and a dog may simply be exposed to so many spores that its defenses are overwhelmed.

Aspergillosis begins when susceptible dogs inhale mold spores. In some dogs, the spores trigger an allergic reaction. In others, the spores cause an infection. Most infections are localized in the nose (nasal aspergillosis), but some dogs develop mild to serious lung infections as well. The deadliest form of aspergillosis, called systemic or disseminated aspergillosis, occurs when the infection spreads beyond the lungs to other organs. Even when discovered and treated early, systemic aspergillosis is often fatal.

What are the clinical signs of aspergillosis?

The different forms of aspergillosis affect dogs in different ways.

Nasal aspergillosis

Nasal aspergillosis is divided into two forms. Sino-nasal aspergillosis (SNA) is the more common form in dogs. SNA destroys the delicate bones of the sinuses, causing an accumulation of mucous and fungus commonly referred to as a “fungal ball” or aspergilloma. Signs include:

• Chronic nasal discharge that has a strong odor, lasts for weeks to months, typically involves only one nostril, and does not respond to antibiotics or other common therapies
• Nosebleeds that occur intermittently
• Rough, inflamed, and ulcerated nostril edges (the tissue breaks open and bleeds due to the discharge, which irritates the skin)
• Sneezing and pawing at the nose or face

Sino-orbital aspergillosis (SOA) is less common in dogs. SOA causes a reactive fungal mass to develop behind the eye, resulting in exophthalmos (a bulging eye). Signs include:

• Squinting
• Development of ulcerations of the cornea
• Eye abnormalities and possibly neurological abnormalities that appear over time, depending on the extent of swelling
• Facial swellings and enlargement of the lymph nodes under the chin

While any dog can develop nasal aspergillosis, affected dogs often have long noses (e.g., collies, greyhounds, dachshunds). Recent studies show that retrievers and rottweilers have the highest incidence of aspergillosis infection, but it is possible that these affected dogs lived in areas with high levels of pathogenic (disease-causing) Aspergillus.

Systemic aspergillosis

In systemic or disseminated aspergillosis, the fungus enters the body through the respiratory tract and travels to other organs via the bloodstream, creating a more serious generalized or systemic fungal infection. According to some studies, German shepherds may be predisposed to systemic aspergillosis.

The clinical signs of systemic aspergillosis depend on the location where the fungus settles in the body. Common sites of infection in dogs include the bones and the intervertebral discs of the spine. Signs include:

• Lameness, weakness, and incoordination if the bones or spinal discs are infected
• Development of draining tracts in the areas of infection (holes in the skin with pus or bloody discharge)
• Fever
• Weight loss
• Appetite loss
• Uveitis (deep inflammation of the eye)

Most dogs with systemic aspergillosis do not have nasal symptoms. Unfortunately, most dogs are terminally ill by the time they exhibit clinical signs.

How is aspergillosis treated?

Fungal infections generally require extended treatment and many of the drugs traditionally used to treat aspergillosis have toxic side effects. Advances in techniques and medications have improved the success of nasal aspergillosis treatment, but systemic aspergillosis is still challenging to treat.

Treatment of nasal aspergillosis

Treatment involves direct topical antifungal treatment or oral antifungal treatment or a combination of both. There are several methods of topical treatment, but all require general anesthesia and removal of any fungal plaques through rhinoscopy before applying the topical medication (e.g., clotrimazole). In some cases, trephination (creating holes in the face to enter the sinuses) may be required.

This treatment is highly effective, but often requires multiple treatments. In most cases, the nasal discharge will resolve within two to four weeks. If there is still evidence of continuing infection one month after the treatment, as determined by another endoscopic examination, another treatment should be performed.

If there is evidence that the infection has eroded through the bones of the nasal sinuses and has entered the brain, treatment with oral antifungal medication, such as itraconazole (Itrafungol®, Sporanox®), fluconazole (Diflucan®), or terbinafine (Lamisil®) is required. Several months of therapy are needed and a 60% to 70% success rate has been reported.

Treatment of systemic aspergillosis

Treatment of systemic or disseminated aspergillosis in dogs is very difficult. Antifungal treatments are available, although they can be expensive. Long-term treatment (for months to years) is often required. Drugs such as itraconazole have proven successful in some cases. Systemic aspergillosis in humans has been treated with terbinafine and posaconazole (Noxafil®). The effectiveness of other antifungal drugs used in human medicine is less clear.

What is the prognosis?

The prognosis is generally good for cases with localized nasal aspergillosis. The prognosis for systemic aspergillosis is guarded (uncertain) to poor, especially if there is evidence of sinus destruction.

Can I get aspergillosis from my dog?

Birds are the most common source of infection in humans. While you can contract aspergillosis from your dog, it is less likely if you practice good personal hygiene, especially handwashing, and avoid handling any discharges. If your dog has been diagnosed with aspergillosis, ask your physician for advice.