Aspergillosis in Dogs: Nasal and Systemic Fungal Disease

Aspergillosis is a fungal infection caused by Aspergillus fumigatus, an ubiquitous environmental fungus found in soil, decaying vegetation, compost heaps, and even household dust. Unlike many fungal pathogens that are restricted to specific geographic regions, Aspergillus species are found worldwide, meaning any dog in any location can potentially be exposed. The spores are microscopic and virtually impossible to avoid — healthy dogs inhale them daily without consequence. It is only when the nasal or immune defences falter that infection takes hold.

"Aspergillosis is one of the most frustrating fungal diseases we see in dogs because the organism is everywhere. You cannot prevent exposure — the key is recognising the early signs, particularly chronic one-sided nasal discharge, before the infection causes significant damage to the nasal passages." — Dr. Sarah Chen, DVM

In dogs, aspergillosis presents in two distinctly different forms with very different prognoses. The nasal form (sinonasal aspergillosis) is by far the most common, accounting for roughly 80-90% of cases. It remains localised to the nasal cavity and frontal sinuses, gradually destroying the delicate nasal turbinate bones. The systemic or disseminated form is far rarer and far more serious — the fungus spreads via the bloodstream to distant organs including the spine, kidneys, and bone. Understanding which form your dog has is critical because the treatment approach and expected outcome differ dramatically.

While any breed can develop aspergillosis, certain dogs face a higher risk. The nasal form has a clear predilection for dolichocephalic (long-nosed) breeds — German Shepherds, Collies, Greyhounds, and Labrador Retrievers appear overrepresented in clinical studies. These breeds have larger nasal cavities with more surface area for fungal colonisation. Dogs are typically young to middle-aged at diagnosis, and there is no clear sex predisposition. Learning to recognise subtle signs of pain in your dog can help catch this infection before it progresses.

Nasal aspergillosis is the presentation veterinarians encounter most frequently, and its hallmark is chronic, unilateral nasal discharge — meaning it typically affects one nostril initially, though it can eventually involve both sides. The discharge often begins as mucoid (clear and slimy) but progresses to mucopurulent (thick, yellow-green) and frequently becomes blood-tinged or frankly haemorrhagic as the fungal plaques erode through the nasal turbinate bones and blood vessels within the nasal cavity.

The progression of nasal aspergillosis is insidious. Dogs may have intermittent sneezing and mild nasal discharge for weeks or even months before owners recognise the problem as something beyond a simple cold. As the infection advances and destroys more nasal tissue, additional symptoms appear: facial pain (dogs may paw at their nose, rub their face on furniture, or resist having their muzzle touched), depigmentation or ulceration of the nostrils (the normally black, moist nose leather becomes pale, dry, or crusted), and reduced appetite due to a diminished sense of smell. Some dogs develop a visible swelling over the bridge of the nose or forehead if the infection erodes through bone into the frontal sinuses.

What makes nasal aspergillosis diagnostically challenging is that the initial symptoms overlap significantly with other common nasal conditions in dogs — foreign bodies (such as inhaled grass awns), nasal tumours, dental disease with oronasal fistulas, and chronic rhinitis from other causes. The critical differentiating factor is duration and progression. A nasal foreign body typically causes acute, sudden-onset violent sneezing. A nasal tumour tends to affect older dogs and may cause facial deformity earlier. Aspergillosis follows a chronic, slowly progressive course in a typically younger, otherwise healthy dog. If your dog has had nasal discharge lasting more than two to three weeks despite antibiotics, aspergillosis should be high on the differential list.

Breeds most commonly affected include German Shepherds, Collies, Greyhounds, Labrador Retrievers, and other long-nosed breeds. The longer nasal passage in dolichocephalic breeds provides more mucosal surface area for Aspergillus spores to adhere to and colonise. Brachycephalic (short-nosed) breeds like Bulldogs and Pugs are rarely affected by nasal aspergillosis — their compact nasal anatomy appears to offer some protection against fungal colonisation.

Systemic or disseminated aspergillosis is a far rarer and far more devastating form of the disease. Unlike the nasal form, which remains localised, disseminated aspergillosis involves the fungus entering the bloodstream and spreading to distant organs throughout the body. This form carries a significantly worse prognosis, and despite aggressive treatment, many affected dogs do not survive long-term.

Interestingly, disseminated aspergillosis shows a striking breed predisposition for German Shepherds, with this single breed accounting for the majority of reported cases. This is thought to relate to a subtle inherited immune deficiency in some German Shepherd lines that impairs the body's ability to contain fungal infections. Other breeds can be affected, but far less commonly. Unlike the nasal form, disseminated aspergillosis does not necessarily begin in the nose — the fungus may enter through the respiratory tract but quickly becomes systemic.

The clinical signs of disseminated aspergillosis are varied and depend on which organs are involved. The spine and intervertebral discs are commonly targeted, leading to back pain, reluctance to move, and progressive hindlimb weakness or paralysis — a presentation called diskospondylitis. The kidneys may be affected, causing increased thirst, increased urination, and progressive kidney failure. Other potential sites include the eyes (causing uveitis or blindness), lymph nodes (generalised swelling), bones (causing lameness in limbs), and abdominal organs. Affected dogs are typically systemically unwell with fever, weight loss, lethargy, and muscle wasting.

The prognosis for disseminated aspergillosis is guarded to poor. Treatment requires prolonged oral antifungal therapy — typically itraconazole or voriconazole — administered for months to years. Even with treatment, many dogs relapse or succumb to organ failure. Early detection offers the best chance of a positive outcome, but the vague initial signs (lethargy, weight loss, back pain) often delay diagnosis. If your German Shepherd develops unexplained back pain, fever, or progressive weakness, disseminated aspergillosis should be considered alongside more common conditions.

Diagnosing aspergillosis requires a combination of imaging, direct visualisation, and laboratory testing. No single test is definitive on its own, and your veterinarian will typically use several complementary approaches to build a confident diagnosis. The specific diagnostic pathway depends on whether nasal or systemic disease is suspected.

For nasal aspergillosis, advanced imaging is the critical first step. CT (computed tomography) scanning of the nasal cavity and frontal sinuses is the gold standard and has largely replaced plain radiographs for this purpose. CT provides detailed cross-sectional images that can reveal the characteristic pattern of turbinate destruction — the delicate scroll-like bones within the nose become eroded and replaced by soft tissue opacity (the fungal plaques) and fluid accumulation. CT also shows whether the infection has extended into the frontal sinuses or eroded through the cribriform plate (the thin bone separating the nasal cavity from the brain), which is a critical finding that affects treatment planning. MRI may be used in some centres and is particularly valuable if intracranial extension is suspected.

Following imaging, rhinoscopy — inserting a small camera directly into the nasal cavity under general anaesthesia — allows the veterinarian to visualise the fungal plaques directly. Aspergillus plaques have a characteristic appearance: white, grey, or green-black fuzzy colonies growing on the nasal mucosa and eroded turbinate surfaces. Rhinoscopy also allows biopsy samples to be collected for histopathology (microscopic examination of tissue) and fungal culture, which confirms the species of Aspergillus involved.

Serology (antibody testing) for Aspergillus-specific antibodies is a useful screening tool. An agar gel immunodiffusion (AGID) test or ELISA can detect antibodies in the blood, with sensitivity reported around 70-90% for nasal aspergillosis. However, false negatives can occur, particularly early in the disease, so a negative serology result does not rule out aspergillosis if clinical suspicion is high. For systemic aspergillosis, serology is less reliable, and diagnosis more often relies on imaging, cytology of affected tissues, and urine antigen testing (Aspergillus galactomannan antigen). Maintaining regular veterinary check-ups ensures subtle early signs are not missed.

The treatment of nasal aspergillosis has been revolutionised by topical antifungal infusion, a technique that delivers high concentrations of antifungal medication directly into the nasal cavity and frontal sinuses. This approach achieves drug levels at the site of infection that would be impossible with oral medications alone, and it has become the standard of care with reported cure rates of 85-90% in many studies.

The procedure is performed under general anaesthesia. After CT and rhinoscopy confirm the diagnosis and map the extent of disease, the veterinarian places catheters into the nasal cavity and frontal sinuses. The most commonly used agent is clotrimazole (1% solution), which is infused through the catheters and allowed to bathe the affected tissues for approximately one hour. During this time, the dog is positioned to maximise contact between the drug and the fungal plaques. The pharynx is packed with gauze to prevent the solution from entering the airway. Some centres use enilconazole as an alternative topical agent with similar efficacy.

Many dogs require only one to three treatment sessions to achieve a cure, with treatments spaced four to six weeks apart. After each treatment, the dog is monitored for clinical improvement — reduction in nasal discharge, resolution of facial pain, and repigmentation of the nostrils. Follow-up CT and rhinoscopy may be performed to confirm that fungal plaques have been eliminated. Some dogs show improvement within days of the first treatment, while others require the full series before symptoms resolve.

Post-treatment care includes monitoring for temporary side effects such as increased nasal discharge (as dead fungal material is cleared) and mild nasal irritation. Oral antifungals are generally not used as primary treatment for nasal aspergillosis because they do not achieve adequate drug concentrations in the nasal tissues. However, in cases where topical treatment is not available or the infection has extended to areas difficult to reach with infusion, oral itraconazole or voriconazole may be used as adjunctive therapy. The overall success rate for nasal aspergillosis with appropriate treatment is excellent — the vast majority of dogs are cured, though a small percentage may experience recurrence requiring retreatment.

Knowing when to suspect aspergillosis versus other nasal diseases can save your dog weeks or months of ineffective treatment. The classic patient profile is a young to middle-aged, large-breed, long-nosed dog with chronic unilateral nasal discharge that has not responded to antibiotics. If your dog fits this description, ask your veterinarian specifically about aspergillosis testing rather than continuing empirical antibiotic courses.

Key red flags that should prompt investigation for aspergillosis include: nasal discharge lasting more than two to three weeks, discharge from one nostril that is blood-tinged or worsening over time, visible depigmentation or ulceration of the nostril margins, pain when the nose or forehead is touched, and failure to respond to one or more courses of antibiotics. While bacterial rhinitis and nasal foreign bodies are more common overall, the chronicity and progression pattern of aspergillosis is distinctive once you know what to look for.

The diagnostic workup for aspergillosis typically requires referral to a specialist or well-equipped veterinary hospital, as CT scanning and rhinoscopy are not available at all general practices. Treatment similarly requires specialist facilities for the topical antifungal infusion procedure. Be prepared for the diagnostic process to involve general anaesthesia (for CT and rhinoscopy), which carries its own small risks but is essential for accurate diagnosis and treatment planning.

For systemic aspergillosis, the situation is more complex. If your German Shepherd develops unexplained back pain, lameness, fever, or weight loss, particularly if standard treatments for more common conditions are not working, raise the possibility of disseminated aspergillosis with your veterinarian. Early detection and treatment offer the best chance, though the prognosis remains guarded. Long-term oral antifungal therapy (itraconazole or voriconazole for months to years) is the standard approach, and monitoring your dog for signs of pain throughout treatment is essential to assess response and adjust therapy as needed.