Multi-Phase Muscle Breakdown in California Sea Lions
- Infectious disease
Abstract
A myositis syndrome has been recognized for more than a decade in California sea lions (CSLs; Zalophus californianus) but a detailed description of the lesions and potential causes of this condition is lacking. The tissues of 136 stranded CSLs with rhabdomyositis were examined. Rhabdomyositis was considered incidental in 67% (91/136) of the CSLs, and a factor contributing to the animal stranding (significant rhabdomyositis) in 33% (45/136). Of the 91 cases with incidental rhabdomyositis, lesions consisted of a few small foci of lymphohistiocytic inflammation. Of the 45 cases with significant rhabdomyositis, 28 (62%) also presented with major comorbidities such as leptospirosis (2 animals) and domoic acid toxicosis (6 animals), whereas 17 (38%) had severe polyphasic rhabdomyositis as the only major disease process associated with mortality. In these animals, most striated muscles had multiple white streaks and diffuse atrophy. Microscopically, there was myofiber necrosis surrounded by lymphocytes and histiocytes admixed with areas of myofiber regeneration, and/or moderate to severe rhabdomyocyte atrophy usually adjacent to intact Sarcocystis neurona cysts. At the interface of affected and normal muscle, occasional T lymphocytes infiltrated the sarcoplasm of intact myocytes, and occasional myofibers expressed MHCII proteins in the sarcoplasm. S. neurona antibody titers and cyst burden were higher in animals with significant polymyositis antibody titers of (26125 ± 2164, 4.5 ± 1.2 cysts per section) and active myonecrosis than animals with incidental rhabdomyositis antibody titers of (7612 ± 1042, 1.7 ± 0.82 cysts per section). The presented findings suggest that S. neurona infection and immune-mediated mechanisms could be associated with significant polyphasic rhabdomyositis in CSLs.
Mauricio Seguel, Kathleen M. Colegrove, Cara Field, Sophie Whoriskey, Tenaya Norris, and Pádraig Duignan. Polyphasic Rhabdomyositis in California Sea Lions (Zalophus Californianus): Pathology and Potential Causes. Veterinary Pathology 1-11
Cara Field
Pádraig Duignan
Sophie Whoriskey
Meet The Experts
{"image":"\/People\/Portrait\/cara-field.jpg","alt":"Cara Field","title":"Cara Field","text":"Director, Conservation Medicine","link_url":"https:\/\/www.marinemammalcenter.org\/person\/cara-field","link_text":"Read Bio"}
{"image":"\/People\/Portrait\/cropped-images\/Padraig Duignan-0-56-635-496-1601760621.jpg","alt":"Padraig Duignan","title":"P\u00e1draig Duignan","text":"Director of Pathology","link_url":"https:\/\/www.marinemammalcenter.org\/person\/padraig-duignan","link_text":"Read Bio"}
{"image":"\/People\/Portrait\/cropped-images\/sophie-whoriskey-by-bill-hunnewell-c-the-marine-mammal-center-0-0-2008-1489-1601938777.jpg","alt":"Sophie Whoriskey","title":"Sophie Whoriskey","text":"Associate Director, Hawai\u2019i Conservation Medicine","link_url":"https:\/\/www.marinemammalcenter.org\/person\/sophie-whoriskey","link_text":"Read Bio"}
Related Publications
{"image":"\/Animals\/Wild\/Other species\/nz-sea-lion-shutterstock.jpg","alt":"New Zealand sea lion","title":"Causes of Death in Two Populations of New Zealand Sea Lions","link_url":"https:\/\/www.marinemammalcenter.org\/publications\/causes-of-death-in-two-populations-of-new-zealand-sea-lions","label":"Research Paper"}
{"image":"\/Animals\/Patients\/California sea lions\/csl-by-bill-hunnewell-c-the-marine-mammal-center-6.jpg","alt":"California sea lions","title":"Zoonotic Bacteria Persistence and Susceptibility","link_url":"https:\/\/www.marinemammalcenter.org\/publications\/zoonotic-bacteria-persistence-and-susceptibility","label":"Research Paper"}
{"image":"\/Animals\/Patients\/California sea lions\/cropped-images\/csl-photo-by-bill-hunnewell-c-the-marine-mammal-center-1-0-0-2358-1722-1600891644.jpg","alt":"California sea lions","title":"Emerging Viruses in Marine Mammals","link_url":"https:\/\/www.marinemammalcenter.org\/publications\/emerging-viruses-in-marine-mammals","label":"Research Paper"}
{"image":"\/Animals\/Wild\/Other species\/nz-sea-lion-shutterstock.jpg","alt":"New Zealand sea lion","title":"Tuberculosis in New Zealand Seals, Sea Lions and Dolphins","link_url":"https:\/\/www.marinemammalcenter.org\/publications\/tuberculosis-in-new-zealand-seals-sea-lions-and-dolphins","label":"Research Paper"}
Recent News
{"image":"\/People\/Action\/Response\/cropped-images\/mbo-crew-es-rope-rescue-photo-by-lesley-simms-c-the-marine-mammal-center-2-0-0-1270-992-1749571082.jpg","alt":"MBO crew carrying a crate up a cliff","title":"The Marine Mammal Center reports high levels of marine mammal disturbance in Central and Northern California for third year in a row","link_url":"https:\/\/www.marinemammalcenter.org\/news\/the-marine-mammal-center-reports-high-levels-of-marine-mammal-disturbance-in-central-and-northern-california-for-third-year-in-a-row","label":"Press Release","date":"2025-06-10 02:00:00"}
The Marine Mammal Center reports high levels of marine mammal disturbance in Central and Northern California for third year in a row
June 10, 2025
Read More{"image":"\/Animals\/Wild\/Elephant seal\/cropped-images\/elephant-seal-mom-and-pup-photo-c-brian-simuro-156-0-1270-992-1748974858.jpeg","alt":"Northern elephant seal and pup","title":"The New York Times: Racing to Save California\u2019s Elephant Seals From Bird Flu","link_url":"https:\/\/www.marinemammalcenter.org\/news\/the-new-york-times-racing-to-save-californias-elephant-seals-from-bird-flu","label":"In the News","date":"2025-06-03 02:00:00"}
The New York Times: Racing to Save California’s Elephant Seals From Bird Flu
June 3, 2025
Read More{"image":"\/Animals\/Wild\/Gray whale\/cropped-images\/a-dead-gray-whalesf-bay40225photo-c-the-marine-mammal-center-53-0-1270-992-1748642560.jpg","alt":"a dead gray whale in the water with birds flying above","title":"NBC News: Six dead gray whales found in San Francisco Bay area in the last week","link_url":"https:\/\/www.marinemammalcenter.org\/news\/nbc-news-six-dead-gray-whales-found-in-san-francisco-bay-area-in-the-last-week","label":"In the News","date":"2025-05-29 02:00:00"}
NBC News: Six dead gray whales found in San Francisco Bay area in the last week
May 29, 2025
Read More{"image":"\/Animals\/Patients\/Elephant seals\/cropped-images\/es-hoffman47927-photo-by-bill-hunnewell-c-the-marine-mammal-center-124-0-1270-992-1748384535.jpg","alt":"An An elephant seal\u2019s face with long black whiskers and wide eyes emerges from the water. ","title":"Adaptations of the Deep: Seal Whiskers and Eyes","link_url":"https:\/\/www.marinemammalcenter.org\/news\/adaptations-of-the-deep-seal-whiskers-and-eyes","label":"Patient Update","date":"2025-05-28 02:00:00"}
