Fungal Colonization of the Nasal Cavities of Stranded Harbor Seal Pups in the Pacific Northwest Region of the United States

Harbor seals (Phoca vitulina) are pinnipeds found in temperate and Arctic marine coastal waters in the Northern Hemisphere. Harbor seal pups are particularly susceptible to stranding due to a combination of biological, environmental, and anthropogenic factors. Infectious disease is a major contributor, often concomitant with malnutrition, and represents a leading cause of pup mortality. In this study, 29 harbor seal pups were opportunistically sampled via nasal swab collection at intake and/or release from rehabilitation, with ten seals having paired samples. Fungal culture and molecular identification were performed. Fungal nasal colonization was identified in 26% (5/19) of seals sampled at intake. Of the five seals with positive fungal culture on intake swabs, four were negative at release and one did not have a release sample collected. The fungal organisms identified were Aureobasidium melanogenum, Rhodotorula mucilaginosa, Sarocladium spp., Candida (Meyerozyma) guilliermondii, and Paradendryphiella arenariae; four of these isolates are documented causes of fungal infections in humans, often in immunocompromised patients. Intrinsic antifungal resistance was documented in two isolates of R. mucilaginosa. A significantly higher proportion of fungal positive samples were collected in May and June, although most seals were sampled in July, and zone was also significantly correlated with fungal positivity. Thus, temporal and geographic factors affect the likelihood of nasal colonization. No aspects of the physical examination served as predictors of fungal colonization. This study contributes new data regarding fungal exposure and colonization in harbor seal pups involved in strandings in the Pacific Northwest. Harbor seals may be susceptible to colonization with opportunistic fungi in the context of stress and immunosuppression.