Otitis Media in Pinnipeds

Otitis media is the inflammation of the middle ear resulting in infection (Otitis Media, 2020). Otitis media is usually an extension of otitis externa through a rupture tympanic membrane (Mooris, 2004). Otitis media or middle ear disease is understudied in pinnipeds. However, otitis media in humans and domestic dogs/cats is thoroughly researched. While information on middle ear infections in other species is relevant, pinnipeds’ middle ear has a slightly different function compared to their fully aquatic and fully terrestrial counterparts. For example, human hearing decreases approximately 30dB when fully submerged underwater but this is not the case in pinnipeds (Kastak & Schusterman, 1998). One notable difference between pinnipeds and terrestrial mammals is that pinnipeds have a larger and denser middle ear bone (Kastak & Schusterman, 1998). Studies have also found that pinniped pathology shows that seals sustain otitis media more than cetaceans (Ketten, 2002). This is the case because pinnipeds have lower peak sensitivity frequencies and therefore are susceptible to an acoustic threshold shift (Ketten, 2002). The function of the middle ear in pinnipeds is highly debated in the scientific community (Ketten, 1998). Kastak’s (1998) research points to the middle ear functioning as a variable transformer for hearing underwater. While Stanford (2003) claims the middle ear in hooded seals have dual function.

Hooded seals have the ability to dive up to 100m in depths (Stenfors et al., 2003). Extreme pressure conditions can be ruled out as a cause of ear rupture because seals have the ability to adjust their middle-ear volume by filling cavernous tissue with blood and simultaneously maintain constant pressure (Stenfors et al., 2003). Although water pressure is not a cause of otitis media, underwater explosions have been known to result in otitis media. In two research studies, otitis media is classified as a moderate blast injury resulting in partial hearing loss (Ketten, 1998; Ketten, 1995). Moderate auditory impairments are often attributed to underwater explosion blasts, extreme intensity shifts or trauma from explosions (Ketten, 1995). Middle ear bone fractures caused by these blasts usually coincide with ear rupture resulting in otitis media (Ketten, 1995).

There needs to be more scientific research on the causes of otitis media in pinnipeds. The only published articles that cover causes of otitis media in pinnipeds talk about blast injuries. Although non-human impacts are known to cause middle ear disease in terrestrial animals. In human children acute otitis media is often the result of a bacterial infection (Levy et al., 2019). Then in cats it is hypothesized that viral upper respiratory infections in early life can initiate otitis media (Gotthelf, 2004). Research should be conducted to see if known causes of otitis media in other species also result in middle ear disease in pinnipeds.

References

Gotthelf, L. N. (2004). Diagnosis and treatment of otitis media in dogs and cats. Veterinary Clinics: Small Animal Practice, 34(2), 469-487.

Kastak, D., & Schusterman, R. J. (1998). Low-frequency amphibious hearing in pinnipeds: Methods, measurements, noise, and ecology. The Journal of the Acoustical Society of America, 103(4), 2216-2228.

Ketten, D. R. (1995). Estimates of blast injury and acoustic trauma zones for marine mammals from underwater explosions. Sensory systems of aquatic mammals, 391-407.

Ketten, D. R. (1998). Marine mammal auditory systems: a summary of audiometric and anatomical data and its implications for underwater acoustic impacts.

Ketten, D. R. (2002). Ocean noise as a stressor of marine mammals. In Invited paper, Florida Marine Mammal Health Conference, Gainesville, Fla.

Levy, C., Varon, E., Ouldali, N., Wollner, A., Thollot, F., Corrard, F., … & Cohen, R. (2019). Bacterial causes of otitis media with spontaneous perforation of the tympanic membrane in the era of 13 valent pneumococcal conjugate vaccine. PloS one, 14(2), e0211712.

Morris D. O. (2004). Medical therapy of otitis externa and otitis media. The Veterinary clinics of North America. Small animal practice, 34(2), 541–viii. https://doi.org/10.1016/j.cvsm.2003.10.009

Otitis Media (Middle Ear Infection). Stanford Children’s Health. (2020.). Retrieved July 28, 2020, from www.stanfordchildrens.org/en/topic/default?id=otitis-media-middle-ear-infection-90-P02057

Stenfors, L. E., Bye, H. M., & Tikkakoski, T. (2003). Shrapnell’s membrane in a mammal exposed to extreme pressure variations: morphological and radiological observations in the hooded seal. The Journal of Laryngology & Otology, 117(10), 756-762.

Research review paper written by summer intern, Jordan R. Jordan is a student at North Carolina State University studying Zoology and Marine Science.