Canine Nasal Mites

The canine nasal mite has most commonly been reported in dogs and has also been reported in a silver fox. There does not seem to be a breed, age, or sex predilection, although one report suggested that dogs >3 yr old were affected more often and that large-breed dogs had a higher incidence than small-breed dogs.

The mites live in the nasal passages and paranasal sinuses. The complete life cycle of P caninum is not known or understood. Transmission is thought to be via direct and indirect contact between dogs. There is no evidence to suggest that P caninum presents a zoonotic risk.

The most common clinical signs associated with nasal mite infestation include epistaxis, sneezing, reverse sneezing, impaired scenting ability, facial pruritus, nasal discharge, head shaking, and stridor. Other reported clinical signs include coughing, restlessness, and collapse. These signs are not specific for nasal mite infection and may indicate many types of upper respiratory disease.

Differential diagnoses based on the clinical signs include many upper respiratory diseases such as rhinitis (idiopathic, secondary bacterial, parasitic, or fungal), oronasal neoplasia, dental disease (oronasal fistula), nasal foreign body, or nasopharyngeal disease (foreign body or mass lesions). To exclude concurrent systemic disease, a CBC, serum chemistry profile, and urinalysis should be performed. If epistaxis is present, a one-stage prothrombin time, partial thromboplastin time, and buccal mucosal bleeding time should be considered in addition to a platelet count.

Imaging of the nasal chambers via nasal/dental radiographs should be considered. Alternative imaging modalities such as CT provide excellent images of the nasal cavity and paranasal sinuses. More invasive diagnostic procedures such as rhinoscopy, retroflex nasopharyngoscopy, nasal flushing, and nasal biopsy must be delayed until after imaging, because iatrogenic changes may be hard to distinguish from primary disease.

Rhinoscopy and nasal flushing are the most useful diagnostic tools. Flexible rhinoscopes allow observation of the nasal choanae. This area is best visualized by putting a u-bend in the rhinoscope (retroflexed view) and advancing it into the oral cavity until it can be hooked under the soft palate. Gentle traction is applied, and the endoscopist can view the nasal choanae or the caudal nasal passages as they enter the nasopharynx. Flooding the nasal chambers with anesthetic gas or oxygen to encourage the mites to migrate toward the nasopharynx and the endoscope has been described.

Nasal flushing may also help identify P caninum. This is generally performed with the dog under general anesthesia with a cuffed endotracheal tube in place. The oropharynx is packed with gauze, and saline is flushed through the external nares with a Foley catheter or a tight-fitting syringe to collect fluid from the oropharynx. Retrograde flushing can be done by placing a modified catheter behind the soft palate, occluding the nasal pharynx, and flushing with saline. This allows fluid to be collected via the external nares. In both cases, the fluid should be evaluated using an illuminated magnifying lens to look for mites.

The definitive diagnosis of nasal acariasis can be made via endoscopy or nasal flushing if the mites are identified. This does not, however, determine whether the disease is primary or secondary.

No drugs are currently approved for the treatment of P caninum; however, ivermectin (200–400 mcg/kg, SC or PO), milbemycin oxime (1 mg/kg, PO, three times at 10-day intervals), and selamectin (topical) have been suggested. The optimal treatment regimen has yet to be determined. Treatment has been reported to be effective in >85% of cases, and the prognosis is excellent. However, treatment may not completely eliminate clinical signs, particularly if infection is suspected rather than demonstrated. In these cases, it is probable that the signs are the result of a concurrent upper airway disease. Treatment is based on definitive diagnosis, but empirical therapy has also been performed based on a high index of suspicion.