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Nasal Mites and Associated Lesions in the Upper Respiratory Tract of California Sea Lions (Zalophus californianus)

Upper respiratory parasites are uncommon finding in marine mammals. Although it is not a common practice to open and thoroughly examine nasal turbinates at the time of routine necropsy, we found nasal passages of several California sea lions (Zalophus californianus), to contain nasal mites (order Halarachnidae) of the genera Orthohalarachne, as reported in ottarid seals. Of these, most commonly reported in California sea lions are adults and larvae of Orthohalarachne attenuata and O. diminuata. Although accompanied by mild nasal discharge, clinical observations have indicated that this infestation does not represent a serious clinical condition for the sea lions. However, histopathologic findings associated with a heavy parasitic load suggested different. Most common pathological findings include erosions of the respiratory mucosa surrounding attachment sites of the mites and accumulations of cellular debris, edema fluid and inflammatory cells (predominantly neutrophils and eosinophils) in nasal passages, nasopharynx, and larynx. In non-eroded areas, the epithelium varies from normal to atrophic, disorganized to hyperplastic. The histopathologic lesions observed suggest that sea lions could present with dyspnea due to blockage of upper respiratory passages and spread of adult mites and larvae deeper into airways and lungs. We calculated the density of mites in nasal mucosa and suggest that large scale infestations of Orthohalarachne sp. in nasopharyngeal mucosa and spread into the pharynx could significantly affect the clinical condition of the affected animal. Also, the nasal mites could lead to lower respiratory diseases, pulmonary emphysema, and transmit other pathogens, so they should be considered of significance to the health and rehabilitation efforts of diseased California sea lions. Examination of nasal turbinates should therefore be recommended on routine necropsy for marine mammals.

nasal mites; California sea lions; gross pathology

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