Marine Mammal Parasite of the Month- Answer July 2019

parasite of the month

This parasite is Otostrongylus circumlitis, one of my favorite lungworms. Their primary host is the harbor seal, but infections have also been found in grey seals and elephant seals. In infected elephant seals, Otostrongylus circumlitis can be found in the heart. Not only is this not the primary host, these worms should not be in the heart of the elephant seals, as this can be incredibly fatal.  When harbor seals or grey seals are infected, O. circumlitis primarily causes bronchitis or bronchopneumonia.

Otostrongylus circumlitis matures in the bronchioles of its host, releasing larvae into the airways that settle in the mucus lining.  This has expanded due to an increased production of mucus as a side effect of the parasitic infection. It is hypothesized that the seal coughs up the larvae into the surrounding water because of excess mucus created by the infection. Once the larvae are coughed up into the ocean, they are consumed by an intermediate host. This host is thought to be a fish and many scientists think a possible fish vector are Hippoglossoides. The seal then consumes these fish and becomes infected.



Bergeron, E., Measures, L. N., & Huot, J. (1997). Lungworm (Otostrongylus circumlitus) infections in ringed seals (Phoca hispida) from eastern Arctic Canada. Canadian Journal of Fisheries and Aquatic Sciences, 54(10), 2443–2448.
Elson-Riggins, J. G., Al-Banna, L., Platzer, E. G., & Kaloshian, I. (2001). Characterization of Otostrongylus circumlitus from Pacific harbor and northern elephant seals. The Journal of Parasitology, 87(1), 73–78.[0073:COOCFP]2.0.CO;2
Leidenberger, S., & Boström, S. (2009). Description of the lungworm Otsostrongylus circumlitus (Railliet, 1899) de Bruyn, 1933 (Metastrongyloidea: Crenosomatidae) found in the heart of harbour seals from Sweden. Journal of Nematode Morphology and Systematics, 12, 169–175.
Vercruysse, J., Salomez, A., Ulloa, A., Alvinerie, M., Osterhaus, A., & Kuiken, T. (2003). Efficacy of ivermectin and moxidectin against Otostrongylus circumlitus and Parafilaroides gymnurus in harbour seals (Phoca vitulina). The Veterinary Record, 152(5), 130–134.
Williams, K., Fessler, M. K., Gallay, M., Keroack, C., Dorit, R., & A. Williams, S. (2017). Identification of The Parasites Acanthocheilonema spirocauda and Otostrongylus circumlitus in Phoca vitulina (harbor seals) By Quantitative PCR.

Posted by Maddy G

Maddy is a summer 2019 intern at the National Marine Life Center. She is a recent graduate of Smith College.