Scientists made the discovery after triggering persistent inflammation in unborn mice.
A single infection during late pregnancy was enough to induce long-term neurological changes and memory problems in old age.
Mice developed boosted levels of immune system signalling molecules linked to inflammation.
If the immune system challenge was repeated in adulthood, the effect was strongly amplified, resulting in changes similar to those seen in Alzheimer’s patients.
Mice genetically modified to produce a human version of the Alzheimer’s- associated brain protein amyloid-beta showed the most striking reaction.
“It seems likely that chronic inflammation due to infection could be an early event in the development of Alzheimer’s disease,” said study leader Dr Irene Knuesel, from the University of Zurich.
The research is published in the Journal of Neuro-inflammation.
If the findings can be shown to apply to humans, it would suggest a role for anti-inflammatory drugs in treating Alzheimer’s.
Dr Marie Janson of Alzheimer’s Research UK said trials with anti-inflammatory drugs have not yet shown conclusive benefits in treating the disease.