Abstract

A 1.5-year-old male California sea lion (Zalophus californianus) stranded on October 2, 2020 in Dana Point Marina, California in poor body condition (BCS 2/5; 24.7 kg; snout length 114.5 cm) and was brought to the Pacific Marine Mammal Center for treatment. On intake physical exam, findings included a cough with intermittent episodes of open mouth breathing, lungs clear in all fields, and mild bilateral white nasal discharge. During examination, the patient developed mild generalized muscle tremors and, when released from restraint, ran into the wall. Palpebral reflexes were intact, pupils were miotic bilaterally, and although the patient was able to track objects, menace reflexes were weak, and vision was decreased. Muscle tremors subsided after two minutes.

Intake bloodwork showed mild electrolyte abnormalities (hyponatremia, mild hypocalcemia, and mild hypokalemia), mild hyperproteinemia and an unremarkable complete blood cell count (CBC). Patient was started on doxycycline (6 mg/kg PO BID), subcutaneous fluid (normal saline), and nutritional support. The patient was found dead three days following intake.

Significant findings on necropsy included thickened and opaque meninges that were tightly adhered to the skull and surface of the brain, indicative of meningitis. The brain was diffusely soft and friable with a swollen optic chiasm. The gastric mucosa was dark grey to black, lungs were mildly congested, and kidneys were mildly swollen and red with variably distinct corticomedullary junctions. A bacterial culture of brain yielded Klebsiella pneumoniae (2+), Enterococcus faecalis (1+), Enterococcus faecium (few) and no anaerobic growth. Fungal culture was not submitted at time of necropsy.

The main histologic finding and cause of clinical signs was severe granulomatous meningitis with myriad fungal yeasts, consistent with a Cryptococcus species, which was confirmed via molecular analysis. The route of entry of fungal infection was likely inhalation, as few yeasts were found focally in the lung, though substantial pneumonia was not appreciated in examined sections. Minimal granulomatous inflammation in the kidneys likely represented early fungal dissemination, though organisms were not seen. Lymph nodes ranged from reactive to depleted and corresponded to chronic inflammatory disease. Other histologic findings were associated with inanition, including pancreatic atrophy and cholestasis.

Cryptococcus sp. are encapsulated yeasts found in avian excrement-contaminated soil (C. neoformans) and decaying trees (C. gattii). Aerosolized basidiospores can be inhaled, resulting in respiratory and central nervous system infections in humans, domestic animals, and terrestrial wildlife, particularly in immunocompromised individuals.¹ Cryptococcosis has been reported in marine mammals from Western Australia,² Hawaii,³ South Africa,⁴ British Columbia, Washington, and California,^5,6 There have been three published reports in pinnipeds species (two harbor seals in British Columbia, one harbor seal in Washington and one sea lion in California).^7,8 Outbreaks have been linked to anthropogenic environmental disturbances, as construction and deforestation can aerosolize spores, resulting in increased inhalation and infection. This is the first report of Cryptococcus infection in a marine mammal in southern California and warrants continued monitoring in this region.

Acknowledgements

The authors wish to thank the staff and volunteers at Pacific Marine Mammal Center as well as University of Illinois Zoo Pathology Program for their contributions to this study and continued efforts to improve marine mammal rehabilitation and conservation. Rescue and rehabilitation activities were conducted under a stranding agreement with NOAA.

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