Researchers discovered stranded dolphins with signs of Alzheimer's disease

The current study included five different species, such as Risso's dolphins, long-finned pilot whales, white-beaked dolphins, bottlenose dolphins, and harbor porpoises. Among them, all the different dolphin species had markers of Alzheimer's disease.

A most extensive study into dementia in toothed whales

"I have always been interested in answering the question: do only humans get dementia? Our findings answer this question as it shows potential dementia-associated pathology is indeed not just seen in human patients. This study is also a great example of both different research institutes, but also different branches of the Life Sciences working together," said co-author Professor Frank Gunn-Moore from the University of St Andrews.

The findings may provide a possible answer to unexplained live-stranding events in some odontocete species. Study authors confirm the results could support the ‘sick-leader’ theory, whereby an otherwise healthy pod of animals finds themselves in dangerously shallow waters after following a group leader who may have become confused or lost.

The animals were examined for the formation of amyloid-beta plaques, the accumulation of phospho-tau, and gliosis - "hallmarks" of Alzheimer's disease. The results revealed that the brains of all the aged animals studied had amyloid-beat plaques. 

Now three animals, among the 22 odontocetes studied, had amyloid-beta plaques along with other dementia-related pathologies in their brains, clearly showing that some odontocete species do develop Alzheimer-like neuropathology.

Did the animals suffer the same cognitive defects noted with the disease in humans? Too early to tell

"These are significant findings that show, for the first time, that the brain pathology in stranded odontocetes is similar to the brains of humans affected by clinical Alzheimer’s disease," said lead researcher, Dr. Mark Dagleish from the University of Glasgow. "While it is tempting at this stage to speculate that the presence of these brain lesions in odontocetes indicates that they may also suffer from the cognitive deficits associated with human Alzheimer’s disease, more research must be done to better understand what is happening to these animals."

The study, however, is no confirmation if the animals suffered the same cognitive defects noted with clinical Alzheimer's disease in humans.

"We were fascinated to see brain changes in aged dolphins similar to those in human aging and Alzheimer’s disease. Whether these pathological changes contribute to these animals' stranding is an interesting and important question for future work," said Professor Tara Spires-Jones, University of Edinburgh.

The results of the study were published in the European Journal of Neuroscience.

Study Abstract:

Alzheimer’s disease (AD) is the most common neurodegenerative disease and the primary cause of disability and dependency among elderly humans worldwide. AD is thought to be a disease unique to humans although several other animals develop some aspects of AD-like pathology. Odontocetes (toothed whales) share traits with humans that suggest they may be susceptible to AD. The brains of 22 stranded odontocetes of five different species were examined using immunohistochemistry to investigate the presence or absence of neuropathological hallmarks of AD: amyloid-beta plaques, phospho-tau accumulation and gliosis. Immunohistochemistry revealed that all aged animals accumulated amyloid plaque pathology. In three animals of three different species of odontocete, there was co-occurrence of amyloid-beta plaques, intraneuronal accumulation of hyperphosphorylated tau, neuropil threads and neuritic plaques. One animal showed well-developed neuropil threads, phospho-tau accumulation and neuritic plaques, but no amyloid plaques. Microglia and astrocytes were present as expected in all brain samples examined, but we observed differences in cell morphology and numbers between individual animals. The simultaneous occurrence of amyloid-beta plaques and hyperphosphorylated tau pathology in the brains of odontocetes shows that these three species develop AD-like neuropathology spontaneously. The significance of this pathology with respect to the health and, ultimately, death of the animals remains to be determined. However, it may contribute to the cause(s) of unexplained live-stranding in some odontocete species and supports the ‘sick-leader’ theory whereby healthy conspecifics in a pod mass strand due to high social cohesion.