Scientists have long been aware that a protein called amyloid plays an integral role in the development of Alzheimer's disease.
There are many theories as to how and why it affects the brain. A recent study suggested it may begin in one area of the brain and then multiply and spread to multiple regions.
However, latest research by scientists at the University of Pennsylvania has dismissed this possibility.
It has been theorised that if this contagion theory were true, Alzheimer's could potentially be passed between humans through infected blood or tissue transplants.
That is a characteristic of the proteins involved in Creutzfeldt-Jakob disease, but the team's research indicates this is not the case with amyloid.
Dr John Trojanowski, who led the study, said: "Our findings argue there is no evidence in this large cohort of human to human transmission. The likelihood of a transplant conveying the disease would be very low."
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