Hypersensitivity Pneumonitis Due to Living Environmental Pollution Caused by Masked Musangs.

Hypersensitivity pneumonitis is an allergic disease caused by various factors such as animal proteins and chemicals. The masked musang, a small animal of the Viverridae family native to East Asia, tends to infiltrate spaces like the attics of residences, causing damage through the deposition of excrement and other means. The older Japanese patient had been experiencing cough, shortness of breath, and fever for two months before presenting to our hospital. The symptoms improved upon admission to a local medical facility but deteriorated upon discharge. This cycle was repeated twice before the patient was admitted to our hospital. Based on the recurrent pattern of improvement during hospitalization and exacerbation upon returning home, along with the results of CT imaging and bronchoscopy, we suspected hypersensitivity pneumonitis. An environmental investigation at the patient's residence revealed a masked musang nest in the attic above the patient's room. After cleaning the attic, the symptoms did not recur. Consequently, we diagnosed hypersensitivity pneumonitis due to living environmental pollution caused by masked musangs. To the best of our knowledge, there have been no previous case reports of hypersensitivity pneumonitis caused by masked musangs. When wild animals invade human living environments, there is a possibility that not only infectious diseases but also immunological disorders, including allergic diseases, may appear.