Abstract
Cryptococcus gattii is an important infectious disease in the northeastern Pacific. The condition has been associated with significant mortality in harbor porpoise (Phocoena phocoena), Dall's porpoise (Phocoenoides dalli) and Pacific white sided dolphins (Lagenorhynchus obliquidens). As with humans and terrestrial wildlife, the primary route of exposure is through inhalation. The lack of a cribriform plate in cetaceans prevents direct inoculation and invasion into the central nervous system and neurologic disease is likely more common in humans than marine mammals.
An approximately 3 year-old, 41 kg, male sub-adult live stranded Pacific harbor porpoise (P. phocoena) presented to the Vancouver Aquarium Marine Mammal Rescue Centre (MMR) in late July of 2012 with poor body condition, moderate lethargy, marked weakness, and inability to swim. Physical examination revealed moderate dehydration, mucopurulent discharge from the blowhole, blepharospasm OU and multiple superficial to deep necrotizing cutaneous wounds along the dorsum, flank, and ventrum including lacerations and abrasions. Clinical pathology detected elevated liver enzymes and mild inflammation. Fecal parasitology identified Nasitrema sp. and Stenurus sp. ova and larvae. Prime differentials for the clinical signs included peri-stranding trauma, septicemia, verminous pneumonia and malnutrition. Therapy consisted of antibiotics, corticosteroids, benzodiazepines, antiemetics, bronchodilators, fenbendazole, praziquantel, rehydration and wound care.
Approximately 30 days after admission to MMR, marked inflammation was noted on CBC and serum chemistry results and yeast was found associated with skin wounds as well as in gastric samples. Itraconazole therapy was initiated. Inflammation resolved over the next 16 days and the porpoise continued to improve. However, on the 58th day after admission, the porpoise began to slowly deteriorate showing increased vomiting, weakness and decreased mobility. The animal developed marked scoliosis, head pressing and erratic head movements. Radiographs, sonography, and gastroscopy revealed no significant lesions.
The animal was sedated with midazolam and high-field (1.5T) whole-body magnetic resonance imaging (MR) was performed on Day 71. MR revealed patchy, coalescing, solid intra-axial brain lesions in the basal ganglia (caudate nucleus, putamen) and thalamus that were hyperintense on T2w and FLAIR sequences. Due to ongoing deterioration and poor prognosis, the porpoise was euthanized. Histopathology confirmed meningoencephalitis with intralesional yeast morphologically consistent with Cryptococcus sp. Efforts to recover the organism were unsuccessful.
To the authors' knowledge, this is among the first clinical presentations of a primarily neurologic form of cryptococcosis in a cetacean. It is the first antemortem detection of imaging findings consistent with central nervous system cryptococcosis. These findings highlight the need for more rapid diagnosis to provide better case management for stranded cetaceans.
Acknowledgements
A great many people helped to take care of Theo during his stay at the Vancouver Aquarium's Marine Mammal Rescue Centre. The authors would like to thank Chelsea DeColle, Gwyneth Nordstrom, Shanie Fradette, Kate Cooper, Taryn Roberts, Sion Cahoon and over 80 volunteers and interns for their invaluable efforts in this and every other case brought to The Centre.
* Presenting author