Photograph: Mike Hill/Getty Images
Three cetacean species stranded off the Scottish coast, including a bottlenose dolphin and pilot whale, have classic markers of Alzheimer’s disease, according to one study.
Although types of dementia have been detected quite widely in other animals, Alzheimer’s disease has not been found naturally in species other than humans.
But researchers from the University of Glasgow, the universities of St Andrews and Edinburgh and the Moredun Research Institute in Scotland were surprised to find that postmortem tests of 22 toothed whales, or odontocetes, revealed three key brain changes associated with the disease. of human Alzheimer’s in three animals. .
Scientists don’t know the cause of this brain degeneration, but it could support a theory as to why some groups or pods of whales and dolphins become stranded in shallow water.
Some mass strandings have been linked to increased anthropogenic noise in the oceans, but Alzheimer’s-like signs in the brain could support a “sick leader” theory, according to which mostly healthy cetaceans are stranded because they follow a group leader who got confused or lost.
Researchers found signs of Alzheimer’s disease in three of the 22 stranded toothed whales: a white-beaked dolphin, a bottlenose dolphin and a long-finned pilot whale, also a member of the dolphin family.
According to the article published in the European Journal of Neuroscience, all three individuals were old for their species and displayed three hallmarks of Alzheimer’s in humans. Abnormal levels of the protein amyloid beta had built up in plaques that shut down neurons in the brain, another protein called tau had gathered in tangles within the neurons, and there was a buildup of glial cells, which cause inflammation of the brain.
Pathologist and lead researcher Dr Mark Dagleish of the University of Glasgow said it could not be confirmed whether this damage would cause the same cognitive deficits associated with Alzheimer’s in people. To determine whether dolphins and whales have Alzheimer’s would also need to study individual animals when they were alive.
He said: ‘These are significant results showing, for the first time, that brain pathology in blocked odontocetes is similar to the brains of humans with clinical Alzheimer’s disease. 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 is needed to better understand what is happening to these animals.”
One possible reason why whales and dolphins exhibit Alzheimer’s-like brain lesions is that, like humans but unlike many other animals, they can live for many years after they cease to be reproductively active. Another possible cause was suggested by a 2020 study that found that deep-diving beaked whales are more susceptible to Alzheimer’s-like conditions due to hypoxia – low oxygen levels in their body tissues – caused by their foraging in the deep ocean.
Signs of Alzheimer’s have also recently been found in a captive 40-year-old bottlenose dolphin.
Professor Tara Spiers-Jones of the University of Edinburgh, who was part of the research team, said: ‘We were fascinated to see brain changes in elderly dolphins similar to those of human aging and Alzheimer’s disease. If these changes pathological factors contribute to the stranding of these animals is an interesting and important question for future work.”
Dagleish said the research has raised additional questions for Alzheimer’s research in animals and humans. “If these are the only animals that spontaneously develop these lesions, further studies could give us some sort of help and insight into what happens in the very early stages of the development of these lesions. If we can determine the likely triggers for this, can we work out ways to treat or prevent it?