In February of 2017, the National Aquarium reported the sudden loss of its eldest Atlantic bottlenose dolphin, Nani.
The matriarch of the Aquarium’s dolphin colony, Nani was estimated to be 45 years of age at the time of her death. Hours before her death, Nani began to exhibit unusual behaviors, including loss of appetite, an abnormal swimming pattern, and reduced interaction with the other animals. Unfortunately, Nani’s condition quickly declined and she became unresponsive to supportive care.
We now know that an acute stroke-like event led to Nani’s clinical signs and ultimate death. The following is a summary of the findings from the necropsy (animal autopsy) produced by our consulting pathologists at Johns Hopkins University School of Medicine:
- The major finding and ultimate cause of death was an acute (rapid onset) hemorrhage (bleeding) and edema (swelling) in the brain.
- The most severely affected area was in the left frontal lobe of the brain.
- The extent and severity of the changes in the brain can be correlated with Nani’s sudden presentation of neurologic signs and rapid clinical decline.
- Other findings were consistent with Nani’s history of iron storage disease, which was considered well-managed at the time of death by both Aquarium staff and the Hopkins team of experts that examined her.
- There were no signs of active infection or significant inflammation in any organs at the time of death.
Summary of Consultations with Johns Hopkins Experts in Veterinary Pathobiology
- Spontaneous brain hemorrhage is the second highest cause of stroke in humans.
- The most common cause of hemorrhagic stroke in humans is hypertension (high blood pressure). No evidence of cardiovascular disease was found at necropsy. In dolphins, it is currently not known if hypertension exists or what role it would play in the health of the animal.
- Another common cause of stroke in humans is a vascular disorder known as ‘amyloid angiopathy’. The results of a special assessment by Hopkins experts on Nani’s brain tissue were negative for this condition.
- Given her history of iron storage disease, Nani’s brain tissue was also tested for iron accumulation with negative results. This indicates that Nani did not have iron accumulation in the brain associated with iron storage disease and confirms that the bleeding event was recent (less than 48 hours prior to her death).
- There was no evidence of less common causes of spontaneous brain hemorrhage such as brain tumors, brain infection, or bleeding disorders.
Summary of Consultations with Colleague Marine Mammal Veterinary Pathologists
- Similar cases of unexplained, stroke-like events in marine mammals, especially older animals, have been noted and observed by other experts in the field.
- Nani did have a small tumor in her adrenal medulla, the part of the body that secretes adrenaline and related hormones. In other species, these tumors are sometimes “active” and capable of secreting excessive amounts of adrenal hormones. This can cause transient hypertension. These tumors are commonly observed in older dolphins, both in the wild and in human care. It is currently unknown whether the tumors produce excess adrenaline in dolphins.
- In wild dolphins, the most likely causes for brain hemorrhage are infections (parasitic or fungal) and trauma. In Nani’s case, there is no evidence to support a link to either infection or trauma.