Previous laboratory studies showed that Abeta in Alzheimer's-ridden brain tissue, when transferred to mice or monkeys, could infect the host animal brain - even when it had been injected into their abdomens.
"So there are mechanisms to transport these protein seeds to the brain," said Collinge.
"We don't know what they are, but clearly it can happen. So that's consistent with these seeds spreading from an intramuscular injection in the children to their brains."
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Amyloid beta seeds, the team wrote, "are known, like prions, to adhere to metal surfaces and to resist... conventional hospital sterilisation."
Experts who were not part of the study underlined there was no evidence of any modern-day medical treatment, including dental surgery or blood transfusions, raising the Alzheimer's risk.
- Cautious, not concerned - For the time being, "this paper should make us cautious but not overly concerned," said Simon Lovestone of the University of Oxford.
John Hardy, of UCL, added it seemed "relatively sure" that Abeta can be transferred by injection.
"Does it have implications for... blood transfusions: probably not, but this definitely deserves systematic epidemiological investigation," he said via the Science Media Centre (SMC) in London.
"Does it suggest Alzheimer's disease is infectious through contact? Almost certainly not."
The study authors said the eight fatalities in the study did not have the full-blown features of Alzheimer's - they were missing the "tangles" caused by a different protein called Tau.
It was impossible to know whether they would have gone on to develop the disease.
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"I wouldn't want to cause alarm on this. I don't think anyone should delay or reconsider having surgery on the basis of these data at all," said Collinge.
"We've got no evidence that this is a risk to humans, but I think it would be prudent to do some research in this area going forward."
Some 30,000 people, mostly children with growth deficiency, received the hormone injections, of whom over 200 developed CJD.
The disease has a very long incubation period, and new diagnoses continue to be made.