Canine Nasal Mites - The Merck Veterinary Manual

Canine Nasal Mites

The canine nasal mite, Pneumonyssoides caninum , has been reported worldwide including the USA, Canada, Japan, Australia, South Africa, Italy, France, Spain, Norway, Sweden, Finland, Denmark, and Iran.

Etiology and Epidemiology:

P caninum is known as the canine nasal mite, 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 of age 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 the 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 this organism presents a zoonotic risk.

Clinical Findings:

The most common clinical signs associated with nasal mite infestation include epistaxis, sneezing, reverse sneezing, impaired scenting ability, facial pruritus, and nasal discharge, dyspnea, collapse, head shaking, and stridor. Other 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.

Diagnosis:

Differential diagnoses based on the clinical signs include many upper respiratory diseases such as rhinitis (idiopathic, secondary bacterial, or fungal), oral/nasal neoplasia, dental disease (oral nasal fistula), nasal foreign body, or laryngeal paralysis. To rule out concurrent systemic disease, a CBC, serum chemistry profile, and urinalysis should be performed. If epistaxis is present, a one-stage prothrombin time (OSPT), partial thromboplastin time (PTT), and buccal mucosal bleeding time should be considered. An alternative to the OSPT and PTT is the activated clotting time.

Imaging of the nasal chambers via nasal/dental radiographs should be considered. A laryngeal examination may also be indicated if clinical signs are suggestive of disease of the larynx. Alternative imaging modalities such as computed tomography provide excellent images of the nasal cavity and paranasal sinuses. More invasive diagnostic procedures such as rhinoscopy, nasal flushing, and nasal biopsy must be delayed until after imaging, as 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. Some authors have described flooding the nasal chambers with anesthetic gas or oxygen to encourage the mites to migrate toward the nasopharynx and the endoscope.

Nasal mite (endoscopic view)

Nasal flushing may also be beneficial in identifying P caninum . This is generally performed with the patient under general anesthesia with a cuffed endotracheal tube in place. It can be accomplished by packing the oropharynx with gauze and flushing saline through the external nares with a Foley catheter or a tight-fitting syringe and collecting 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 ascariasis 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.

Treatment:

There are currently no drugs approved for the treatment of P caninum ; however, both ivermectin (200-400 µg/kg, SC or PO) and milbemycin oxime (1 mg/kg, PO, 3 times at 10-days intervals) 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. Treatment may not completely eliminate clinical signs, however (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. Most cases are treated based on definitive diagnosis, but empirical therapy has also been performed based on a high index of suspicion.