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Protozoal-Related Mortalities in Endangered Hawaiian Monk Seals Neomonachus schauinslandi

September 26, 2016

This study establishes case definitions for classification of protozoal infections in Hawaiian monk seals.

Protozoal infections have been widely documented in marine mammals and may cause morbidity and mortality at levels that result in population level effects. The presence and potential impact on the recovery of endangered Hawaiian monk seals Neomonachus schauinslandi by protozoal pathogens was first identified in the carcass of a stranded adult male with disseminated toxoplasmosis and a captive monk seal with hepatitis. We report seven additional cases and two suspect cases of protozoal-related mortality in Hawaiian monk seals between 2001 and 2015, including the first record of vertical transmission in this species. This study establishes case definitions for classification of protozoal infections in Hawaiian monk seals. Histopathology and immunohistochemistry were the primary diagnostic modalities used to define cases, given that these analyses establish a direct link between disease and pathogen presence. Findings were supported by serology and molecular data when available. Toxoplasma gondii was the predominant apicomplexan parasite identified and was associated with 100 percent of mortalities (n = 8) and 50 percent of suspect cases (n = 2). Incidental identification of sarcocysts in the skeletal muscle without tissue inflammation occurred in four seals, including one co-infected with T. gondii. In 2015, two cases of toxoplasmosis were identified ante-mortem and shared similar clinical findings, including hematological abnormalities and histopathology. Protozoal-related mortalities, specifically due to toxoplasmosis, are emerging as a threat to the recovery of this endangered pinniped and other native Hawaiian taxa. By establishing case definitions, this study provides a foundation for measuring the impact of these diseases on Hawaiian monk seals. 

Barbieri MM, Kashinsky L, Rotstein DS, Colegrove KM, Haman KH, Magargal SL, Sweeny AR, Kaufman AC, Grigg ME, Littnan CL. 2016. Protozoal-related mortalities in endangered Hawaiian monk seals Neomonachus schauinslandi. Diseases of Aquatic Organisms. 121(2):85-95.  https://doi.org/10.3354/dao03047.

Last updated by Pacific Islands Fisheries Science Center on 06/01/2021

Hawaiian Monk Seal