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Aspergillosis is a frequent cause of nasal discharge in dogs, caused by a fungus called Aspergillus fumigatus. It is the second most common cause after nasal neoplasia. The disease affects mainly dogs of mesocephalic (dogs with medium length noses, e.g. Labrador Retrievers) and dolichocephalic breeds (dogs with a long nose, e.g. Collies) and most of the affected dogs are otherwise healthy young adult to middle-age. Since the infection involves the nasal cavity and frontal sinus it is therefore called sino-nasal aspergillosis (SNA).
Aspergillus fumigatus is a filamentous saprophyte and ubiquitous fungus. In humans, this organism causes severe systemic diseases in immunocompromised individuals while in dogs, systemic/disseminated aspergillosis is very rare. The reason for A. fumigatus to cause disease in only a small proportion of dogs that appear otherwise healthy is still unclear. A local immune dysfunction is suspected to be involved in the pathogenesis of canine SNA.
Aspergillosis is very difficult to avoid, however, best practices would indicate staying away from the most obvious locations of mold, such as construction sites, compost piles and grain storage. For those dogs with compromised immune systems (such as those going through chemotherapy), this is critical.
Typical symptoms are profuse mucopurulent to hemorrhagic nasal discharge, sneezing, nasal pain and ulcerations of the nostrils, and some depression and decreased appetite. The disease usually begins with a unilateral mucous to mucopurulent nasal discharge and progresses to a bilateral discharge. In very advanced cases, facial deformation, ocular discharge or even neurological symptoms like seizures may be present.
The diagnosis of SNA may be suspected based on history and clinical findings in most cases. However, in early cases, SNA cannot easily be differentiated from other nasal diseases (such as nasal neoplasia, idiopathic lymphoplasmacytic rhinitis, presence of a nasal foreign body and oro-nasal fistula secondary to a tooth abscess).
Various combinations of diagnostic tests are used to confirm the diagnosis of canine SNA. The technique of computer tomography (CT) has a good sensitivity in the diagnosis of SNA, much higher than that of radiography. However, the gold standard for diagnosing canine SNA is the direct visualisation of fungal plaques by endoscopy of the nasal cavities or the observation of fungal elements on cytology or histopathological examination of nasal/sinusal mucosal biopsy, performed during endoscopy. Rhinoscopy also allows endoscopically-guided extensive debridement that is full part of the treatment of the disease (see below). Rhinoscopy and sinusoscopy are performed under general anaesthesia using both rigid and flexible endoscopic systems and require experienced hands.
Both fungal culture and serology (determination of serum Aspergillus-specific antibody titers in the blood) are able to give false negative as well as false positive results.
Effective treatment of SNA in dogs has always been difficult and is at present still a challenge. Treatments include systemic oral therapy, topical antimycotic therapy and more invasive surgical procedures. Reported success rate, short-term and long-term outcome also vary in view of the way cure has been assessed.
Systemic oral treatments (ketoconazole, itraconazole) are non-invasive but require prolonged administration (4 to 10 weeks) because of poor to moderate efficacy. Therefore, their use is quite expensive and side effects such as hepatotoxicosis, anorexia or vomiting are commonly reported. Clinical cure is reported to be obtained in less than 50 to 70% of the patients.
Topical treatment with enilconazole or clotrimazole has been associated with greater success. Various procedures have been developed to administer medication topically, and these procedures vary in invasiveness and ease of performance. For several years, the standard treatment of canine SNA consisted in invasive topical therapy through the delivery of an enilconazole emulsion twice daily for one to two weeks via tubes surgically implanted into the nasal cavities and frontal sinus. Alternative, less invasive techniques using local infusion of clotrimazole or enilconazole topically into the nasal cavities and frontal sinus, administered under general anesthesia, through non-surgically placed catheters showed an improved efficacy. Moreover, the use of these methods eliminates the need for surgical trephination and is associated with fewer complications. Several treatment protocols have been investigated or are still under investigation in order to improve success rate, tolerance by the animal, and owner compliance. Placement of infusion catheters under endoscopic guidance with a flexible bronchoscope into the caudal part of the frontal sinus as well as extensive rhinoscopic debridement prior to infusion have been shown to be important for therapeutic success. Although the use of topical agent via non-invasive methods is well tolerated and shows a high success rate, these procedures are time-consuming and require long-lasting anaesthesia. Moreover, some dogs remain refractory to any treatment and the prognosis for these patients is poor. In these poorly responsive dogs, more invasive surgical procedures such as rhinostomy associated with topical treatments can be attempted.
After cure, about half of the patients still show mild episodic or permanent nasal signs, which are sequelae of nasal turbinate destruction by the fungus. Moreover, clinical recurrence of SNA, although not frequent, is possible.
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