Canine Fungal Rhinitis

Introduction

In the UK, the primary cause of fungal rhinitis is Aspergillus fumigatus. In other parts of the world different fungi have been identified including other strains of Aspergillus, Penicillium and Scedosporium. The underlying pathology is of a destructive rhinitis. A fumigatus is ubiquitous in the environment, although the heaviest concentrations are in specific situations such as damp or badly stored hay/straw or composting grass clippings. It is still unclear why some dogs appear to develop an active infection with the development of large numbers of hyphae and fungal colonies, whilst the majority of dogs simply harbor some spores as normal inhalants.

Certainly some predisposing factors have been implicated in a small proportion of cases, such as trauma, septicemia, or other intercurrent disease (including nasal neoplasia). Severe immunocompromise, one of the main factors for human aspergillosis in the Western world, has not been substantiated in the dog, or indeed the cat. The evidence of impaired cellular immunity in canine aspergillosis may be due to the effect of the fungus rather than pre-existing in the animal.

The first description of this condition dates from 1905, and aspergillosis is now well recognized as a cause of chronic nasal discharge in the dog. However, it does require to be differentiated from a number of other conditions before satisfactory management can be instigated. On the basis of rhinoscopic and diagnostic imaging findings, the infection is well established by the time of diagnosis in the majority of cases. This is probably due to the fact that the nasal discharge – the major presenting sign – has been either licked from the external nares or drawn caudally to the nasopharynx and swallowed for some time before the animal is presented to the veterinarian.

Key Points

• Nasal fungal infections cause destructive rhinitis in dogs but the predisposing factors which allow infection to establish are unclear
• Clinical signs can mimic other conditions but a careful work-up should allow a definitive diagnosis
• The most common presenting sign is chronic nasal discharge`
• The most successful method of treatment is still debatable; untreated infection can be fatal