Alzheimer's disease is the most common type of dementia and research suggests it has been passed between humans in a rare medical error.
It found five people in the UK developed the illness as the side effects of medical treatment given between 1959 and 1995.
The illness passing between people was found to happen as a result of a treatment given to some Britons and there is no evidence it could happen day to day.
Researchers found those affected received human growth hormone from the pituitary glands of the corpses of deceased donors.
Britons appear to have developed the illness passed from corpses
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This appears to have led them to develop early-onset Alzheimer’s due to contaminated hormones.
More than 1,800 children were given the hormone in the UK between 1959 and 1995 before it was withdrawn.
This was given commonly to increase the height of the children, but it was withdrawn as evidence showed it could cause the degenerative brain disease CJD.
Researchers at the University College London Hospital (UCLH) found it also appeared to trigger cases of Alzheimer's in some patients, including one as young as 38 years old.
Testing ruled out that the affected patients got this as an inherited form of the illness.
Instead, it is likely people acquired the amyloid-beta protein that can cause Alzheimer's through the human growth hormone injections.
Director of the UCL Institute of Prion Diseases and a consultant neurologist at UCLH and lead author of the research Professor John Collinge said: “We are not suggesting for a moment you can catch Alzheimer’s disease. You can’t catch it by being a carer or living with a husband or wife with the disease.
“The patients we have described were given a specific and long-discontinued medical treatment which involved injecting patients with material now known to have been contaminated with disease-related proteins.
“However, the recognition of transmission in these rare situations should lead us to review measures to prevent accidental transmission via other medical or surgical procedures, in order to prevent such cases occurring in future.
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Alzhiemer's disease is the most common form of dementia
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"There is no suggestion whatsoever that Alzheimer's disease can be transmitted between individuals during activities of daily life or routine medical care."
No other cases have been reported of Alzheimer's disease being passed through medical surgeries or procedures and Britons should not be put off getting treatment, experts warn.
Co-author from the Institute of Neurology and the chief medical officer at Alzheimer's Research UK Co-author Professor Jonathan Schot said: "There is no risk that the disease can be spread between individuals or in routine medical care.
"These findings do, however, provide potentially valuable insights into disease mechanisms, and pave the way for further research which we hope will further our understanding of the causes of more typical, late onset Alzheimer's disease."
Group leader at the UK Dementia Research Institute at UCL Prof Bart De Strooper said: "No one should reconsider or forego any medical procedure, especially for blood transfusion or neurosurgery which saves many lives worldwide every year.
"However, it is always important that we continue to review and scrutinise evidence where public health is concerned."
