Crescentic Hair Shaft Defects and Piedra‐Like Lesions With Follicular Invasion in Northern Elephant Seals ( Mirounga angustirostris )

BACKGROUND: Historically, dermatological disease is a common cause for rescue of northern elephant seals (NES) in California, yet its aetiology and pathogenesis remain poorly understood. OBJECTIVES: To provide the first formal histological and ultrastructural description of two hair shaft lesions in NES: crescentic hair shaft defects (CHSD) and fungal (piedra)-like lesions (PLL). ANIMALS: Forty-one animals from The Marine Mammal Center and 10 animals from San Nicolas Island were examined, 38 with skin lesions and 13 without. MATERIALS AND METHODS: Age, sex, comorbidities, cause-of-death, gross skin lesions and evidence of northern elephant seal skin disease (NESSD) were recorded. Histologically, we examined each case for CHSD, PLL, suppurative luminal folliculitis (SLF), furunculosis, bacteria and fungal elements within CHSD, and fungal elements within follicular lesions. Grocott-Gomori methenamine silver, Gram and Fontana-Masson's stains were performed on 17, 11 and 8 cases, respectively. RESULTS: NESSD, CHSD, PLL, SLF and furunculosis were noted in 10 of 38 (26%), 23 of 38 (61%), 23 of 38 (61%), 20 of 38 (53%) and 6 of 38 (16%) animals with skin lesions, respectively. Within CHSD lesions, bacteria were identified in 13 animals and fungi in seven. CHSD and PLL frequently co-occurred, limited to NES over 7.5 months old and often associated with SLF, and were observed exclusively in animals with dermatological disease and present in most cases of NESSD, suggesting a pathological association. Panfungal PCR from 10 animals identified several fungi, including Cladosporium spp., a reported cause of white piedra in humans. CONCLUSIONS AND CLINICAL RELEVANCE: Although the aetiology of CHSD remains unclear, we suggest that fungal and/or bacterial colonisation of the hair shaft may contribute.