Three species of cetacean, including a bottlenose dolphin and a long-finned pilot whale, have been found to have the classic markers of Alzheimer's disease.
Alzheimer's disease has not been found to occur naturally in other animals.
Three key brain changes associated with human Alzheimer's disease were detected by postmortem tests of 22 toothed whales.
One theory about why some whales and dolphins run aground in shallow water is supported by the fact that scientists don't know why.
Mass strandings have been linked to increasing noise in the ocean, 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.
A white-beaked dolphin, a bottlenose dolphin and a long-finned pilot whale were found to have signs of Alzheimer's.
According to the paper published in the European Journal of Neuroscience, all three individuals were old for their species and had signs of Alzheimer's. There was a build-up of glial cells, which can cause inflammation of the brain, as well as abnormal levels of theamyloid andtau.
According to Dr Mark Dagleish of the University of Glasgow, it was not possible to confirm if this damage would cause the same cognitive deficits in people. The dolphins and whales would need to be studied when they were alive to determine if they had Alzheimer's.
For the first time, it has been shown that the brain pathology in stranded odontocetes is similar to that of people with Alzheimer's disease. It is tempting to think that the brain damage in odontocetes may be related to the cognitive deficits associated with human Alzheimer's disease, but more research is needed to understand what is happening to these animals.
Unlike humans, whales and dolphins can live for a long time after they stop being reproductively active. A 2020 study suggests that deep-diving beaked whales are more susceptible to Alzheimer's-like diseases because of the low levels of oxygen in their body tissues.
A 40-year-old bottlenose dolphin has signs of Alzheimer's.
Prof Tara Spires-Jones of the University of Edinburgh, who was part of the research team, said that they were fascinated to see brain changes in aged dolphins. The question of whether pathological changes contribute to animal stranding is an important one.
The research raises more questions about Alzheimer's research in animals and humans. If these are the only animals that spontaneously develop these lesions, further study may give us some insight into what happens in the very early stages of development. Can we figure out ways to treat or prevent this?