What Is Nasal Aspergillosis?
Fungal infections are a frequent cause of nasal disease in dogs and cats. Canine nasal aspergillosis is a relatively common inflammatory disease of the nasal passages.
What Is A Aspergillus?
Aspergillus species are filamentous fungi that are ubiquitous under appropriate environmental conditions and not typically infectious. However, some species, namely:
- Aspergillus fumigatus
- Aspergillus niger
- Aspergillus nidulans
- Aspergillus flavus
can invade nasal cavities of animals with impaired immune system function.
The infection is associated with the production of bacterial toxins that cause destruction and erosion of tissues. Colonization and invasion of the nasal mucosa by A. fumigatus results in destruction and necrosis of the nasal turbinates, often accompanied by frontal sinus osteomyelitis. The cribriform plate, palatine bones, and orbits are sometimes involved.
Signs & Symptoms
Pain, loss of appetite, sneezing, and copious mucoid to hemorrhagic nasal discharge and crusting are common clinical signs. Life-threatening nose bleeding can occur due to erosion of the nasal blood vessels.
In chronic cases, depigmentation, and ulceration of the nares and masticatory muscle atrophy result. Central nervous system involvement (encephalitis, meningitis) precipitating seizures can result after the erosion of the cribriform plate. Nasal infection is most likely to occur in dogs that are 3 years old or younger.
Although the condition is not life-threatening, it often results in severe clinical signs, such as extensive foul-smelling nasal discharge, chronic sneezing, frequent pawing and rubbing at the face, and nosebleeds. Profuse pus-filled discharge that is not responsive to antimicrobial medications and ulcerations of the external nares are seen in dogs with established infection.
The most common species isolated from canine nasal cavities is Aspergillus fumigatus. This fungal pathogen of humans and animals is associated with a wide spectrum of diseases, ranging from benign colonization of the lung, to allergies, to life-threatening diseases, including invasive pulmonary aspergillosis and allergic broncho-pulmonary aspergillosis.
A. fumigatus grows abundantly in rotten vegetation, wood chips, compost, sewage, moldy hay, and soil. The fungus produces many small spores which can be inhaled. Some Aspergillus species found in moldy feed produce aflatoxins, poisonous compounds that can cause serious injury to the liver if ingested.
Diagnosis is difficult to make. Radiographs of the head, rhinoscopy, serologic tests and laboratory culture of the organism from nasal swabs or flushes may all be necessary to reach a firm diagnosis. CAT scan of the nasal passages is a crucial component of the evaluation.
Rhinoscopy is important for both the diagnosis and the therapy for nasal aspergillosis as it is the only technique that allows direct visualization of fungal colonies. Rhinoscopic findings may reveal erosions and fluffy patches of fungal growth. However, the absence of rhinoscopic findings does not rule out fungal infection.
Today, medical management of aspergillosis with clotrimazole infusion into the nasal cavity is the preferred method of treatment. A surgical approach is usually indicated only if all other methods have failed.
The prognosis for recovery from nasal aspergillosis is about 90% in patients treated with clotrimazole infusion. About 15 – 20% of patients require a second treatment. If left untreated, the infection will progress and can, in advanced cases, infect the brain.
The use of topical clotrimazole through noninvasive techniques has increased the success of treatment and decreased the morbidity and duration of hospitalization. There is no vaccine currently available to prevent aspergillosis in companion animals.
Disseminated aspergillosis has been most commonly reported in the German Shepherd Dog between 2 and 8 years of age. It is most commonly diagnosed in terminally ill dogs and cats and typically involves multiple organ systems with no history of nasal or pulmonary involvement.
Aspergillus terreus, A. deflectus, A. flavipes, and rarely A. fumigatus have been reported in cases where the species has been identified. The infection is believed to occur after inhalation of small spores that spread via the blood.
The inhaled pathogens produce highly infective aleuriospores that invade blood vessels. Genetic predisposition and impaired immunity (impaired IgA production or regulation) has been identified in some affected German Shepherd Dogs.3
Systemic aspergillosis in dogs may cause discospondylitis, osteomyelitis, lymphadenopathy, nephritis, splenitis, and meningoencephalitis. Successful treatment of the disseminated form of the disease is not common. Aggressive treatment with systemic antifungals is indicated and the most successful regimen involves itraconazole a drug similar to ketoconazole, fluconazole.
- Michael Schaer – Clinical Medicine of the Dog and Cat
- Mordecai Siegal – UC Davis Book of Dogs
- Stephen J. Ettinger, Edward C. Feldman – Textbook of Veterinary Internal Medicine
- Walker et al. – A Novel Case Of Canine Disseminated Aspergillosis Following Mating