Three species of cetacean stranded off the coast of Scotland, including a bottlenose dolphin and a long-finned pilot whale, have been found to have the classic markers of Alzheimer’s disease, according to a study.
Although types of dementia have been fairly widely detected in other animals, Alzheimer’s disease has not been found to occur 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, detected three key brain changes associated with human Alzheimer’s disease in three animals.
Scientists do not know the cause of this brain degeneration but it could support one theory about why some groups or pods of whales and dolphins run aground in shallow water.
Some mass strandings have been linked to increasing anthropogenic noise in the oceans, but Alzheimer’s-like signs in the brain could support a “sick leader” theory, whereby mostly healthy cetaceans are stranded because they follow a group leader that has become confused or lost.
The researchers found signs of Alzheimer’s in three of 22 stranded odontocetes: a white-beaked dolphin, a bottlenose dolphin and a long-finned pilot whale, also a member of the dolphin family.
According to the paper published in the European Journal of Neuroscience, all three individuals were old for their species, and showed three hallmarks of Alzheimer’s in humans. Abnormal levels of the beta-amyloid protein had accumulated into plaques that disrupt neurons in the brain, another protein called tau had gathered into tangles inside the neurons, and there was a build-up of glial cells, which cause inflammation of the brain.
Pathologist and lead researcher Dr Mark Dagleish of the University of Glasgow said it was not possible to confirm whether this damage would cause the same cognitive deficits associated with Alzheimer’s in people. To determine whether the dolphins and whales had Alzheimer’s would require also studying the individual animals when they were alive.
He said: “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. While it is tempting at this stage to speculate that the presence of these brain lesions in odontocetes indicates that they may also suffer with the cognitive deficits associated with human Alzheimer’s disease, more research must be done to better understand what is happening to these animals.”
One possible reason for whales and dolphins showing Alzheimer’s-like brain lesions is that, like humans but unlike many other animals, they can live for many years after they cease being reproductively active. Another possible cause was suggested by a 2020 study which found that deep-diving beaked whales are more susceptible to Alzheimer’s-like pathologies because of the hypoxia – low levels of oxygen in their body tissues – caused by their deep-ocean foraging.
Signs of Alzheimer’s were also recently found in a single, captive 40-year-old bottlenose dolphin.
Prof Tara Spires-Jones of the University of Edinburgh, who was part of the research team, said: “We were fascinated to see brain changes in aged dolphins similar to those in human ageing and Alzheimer’s disease. Whether these pathological changes contribute to these animals’ stranding is an interesting and important question for future work.”
Dagleish said the research raised further questions for Alzheimer’s research in animals and humans. “If these are the only animals that spontaneously develop these lesions, further study may 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 of this, can we work out ways to treat or prevent it?”
