Which of the following is a cause of otitis externa in dogs?

• A. Moisture in the ear canal
• B. Fungi
• C. Ectoparasites
• D. All of the above

Answer: (D)

Otitis externa in dogs is commonly multifactorial; the ear canal environment, microbes, and parasites all interact to cause inflammation. Moisture in the ear canal creates a warm, damp environment that promotes microbial overgrowth and can macerate the skin, weakening its defenses. Fungi, especially Malassezia species, are frequent contributors and thrive when the canal environment is disrupted, leading to itching, discharge, and inflammation. Ectoparasites such as ear mites irritate the canal lining, causing scratching and trauma that predispose to secondary infections and worsen inflammation. Because any one of these factors can initiate or amplify otitis externa and they often occur together, the best answer is all of the above.