​As per a study published in the Nature journal, rare medical accidents can lead to the transmission of Alzheimer's from one human to another. The study means that in people who received human growth hormone from the pituitary glands of deceased donors the risk of developing Alzheimer's is likely because the hormones were contaminated. “We’re not suggesting for a moment you can catch Alzheimer’s disease. This is not transmissible in the sense of a viral or bacterial infection. It’s only when people have been accidentally inoculated, essentially, with human tissue or extracts of human tissue containing these seeds, which is thankfully a very rare and unusual circumstance," Prof John Collinge, co-author of the study and director of the MRC Prion Unit told the Guardian.​