Comparison of three methods for the diagnosis of otoacariasis due to Otodectes cynotis in dogs and cats.

Background: The diagnosis of otoacariasis due to Otodectes cynotis is based on the visualization of the parasite, either directly by otoscopy or indirectly after microscopic examination of cerumen collected by several methods.

Objectives: To compare the sensitivity of three techniques: conventional handheld otoscopy, Volkmann's curette sampling and cotton-tipped swabbing.

Animals: Five dogs and 12 cats (30 naturally infested ears).

Methods And Materials: For each case, following otoscopy, the order of examinations (swab or curette) was chosen randomly and the samples were observed on a slide mixed with lactophenol and covered with a coverslip. Parasite detection was noted as positive or negative and parasitic stages were counted separately.

Results: The diagnostic sensitivity of otoscopy alone was 67% (positive in 20 of 30 cases), using the curette sampling it was 93% (28/30) and 57% (17/30) for the swabbing. The curette technique had a significantly higher sensitivity than classic ear-swabbing (P = 0.001) or otoscopy alone (P = 0.02). Combining otoscopy and the curette, we obtained a sensitivity of 100% compared to 86% when otoscopy and swabbing were combined. Moreover, the parasite count in the curette samples (average 25 ± 30 SD) was significantly higher than the swab samples (4.5 ± 11) (P < 0.001).

Conclusions And Clinical Importance: When suspecting O. cynotis infestation, otoscopic examination should be performed. To confirm the nature of the parasites observed or whenever this examination result is negative, doubtful or cannot be performed, the curettage sampling method for microscopic cerumen examination is recommended.