Abstract

The purpose of this presentation is to describe the clinical neurologic disease, histopathology findings, and probable role that thiamin deficiency played in the mortality of three dolphins housed at Dolphinaris Arizona in Scottsdale, AZ. Three dolphins died in a matter of eight months between May 2018 and January 2019. All animals were fed a daily diet consisting of capelin (60–80%) and herring (20–40%), occasional squid and vitamin supplementation of Mazuri® Vita-Zu® Marine Mammal Lutein Tablets. Clinical signs included depression, ataxia, blindness, muscle fasciculations, tremors, diminished reflexes, and erratic swimming and breathing patterns. In the first dolphin to die, death was due to respiratory compromise secondary to aspiration pneumonia. Mild non-specific cerebral edema was also noted histologically, though at the time of death, thiamine deficiency was not initially suspected. In the second dolphin, histopathology revealed very severe, unilateral polioencephalomalacia with marked loss of cerebral grey matter highly consistent with thiamine deficiency. In the third dolphin, significant post-mortem findings were limited to cerebral edema with occasional neuronal necrosis. Extensive diagnostics ruled out infectious agents and toxins. On re-evaluation of the first dolphin death following the subsequent mortalities, the cerebral edema noted may have been an early indication of thiamine deficiency. Liver thiamine concentrations were not performed. Serum thiamine levels were markedly low in one dolphin with no clinical signs.

Thiamine (vitamin B1) is an essential vitamin required for carbohydrate metabolism, brain function, and peripheral nerve myelination.¹ Thiamine is obtained from the diet. Body stores are limited, and deficiencies can develop quickly. The total thiamine pool in the average adult human is about 30 mg.^2–3 Normal thiamin levels for cetaceans have not been established, nor their sensitivity to low levels, but deficiencies in marine mammals have been reported many times.^4–6 Several species, such as cats, require higher amounts of thiamin than other domestic species.⁷ Thiamine deficiency can be caused by several factors including poor dietary intake, reduced gastrointestinal absorption, concurrent infections or disease, compromised immune system, excessive loss, thiaminase activity in dietary fish and decomposition of thiamin by bacteria in the GI tract.

A case study of this magnitude can raise many questions. After assessment of the health, environment, and pathology records, as well as having several formal evaluations by various marine mammal experts, a clearer picture emerged. Although some of the conclusions might be difficult to definitively prove, pathologic findings indicate the primary underlying factor leading to two, possibly three, individual mortalities, were due to neurologic complications secondary to thiamine deficiency. Thiamine levels were only tested once while these individuals were living in Arizona and deemed low. Testing the four remaining dolphins at numerous time points after being moved to St. Thomas, follow up treatment, and wild counterpart thiamin levels, it is clear, that most, if not all animals, were low and even deficient in thiamine. In summary, the neurologic signs and pathologic evidence of PEM matched much of what is observed with thiamine deficiency.⁸

Acknowledgements

The authors wish to acknowledge Dawn Stokka DVM, previous Staff Veterinarian at Dolphinaris Arizona, Erica Palmer, Veterinary Technician, Coral World Ocean Park, Robert L Kellar, Curator, Coral World Ocean Park, Christian Schaffer, General Manager, Dolphinaris Arizona, Jay Sweeney, the Dolphin Quest staff and the dedicated, caring training staff at Dolphinaris Arizona and Coral World Ocean Park. The team effort and dedication at both of these facilities is a true reflection of the amazing people involved. We would also like to thank the following experts who so graciously assisted in formal evaluations, clinical case studies, environmental studies and water quality assessments, Skip Young, and Drs.Tom Reidarson, Micheal Renner, Marina Ivancic, Mike Kinsel, Judy St. Ledger, Jim Wellehan, and Daniel Vanderhart.

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