Is Alzheimer’s Disease (AD) Contagious? Surprising Results

Researchers in Tübingen, Germany have discovered that certain protein plaque deposits that cause Alzheimer’s disease can be infectious not only when they are injected directly into the brain, but also when they are injected anywhere else in the body. By injecting healthy mice with the diseased gray matter, those mice develop Alzheimer’s-like symptoms within just four months time.

In 2006, a team of German scientists reported that injection of dilute extracts from human Alzheimer’s brain tissue, or from Abeta-laden mouse brain tissue, into the brains of transgenic mice (genetically modified to produce the human form of Abeta) stimulated Abeta build-up within the mouse’s brain. In this month’s issue of Science, the same team of scientists have discovered that the healthy mice can be injected into their stomachs, legs, or anywhere on the body and have the same affect on the brain.

Alzheimer’s is predicted to affect 1 in 85 people globally by 2050. Research indicates that the disease is associated with hard, neurofibrillary tangles of mis-folded protein fragments called beta-amyloid peptides (or Abeta) that form plaques between the nerve cells in the brain. Healthy brains are able to clear these useless proteins and escort them to be reabsorbed back into the body. In the case of Alzheimer’s patients, however, their brains become unable to clear away these proteins, which then build up and harden as plaques.

These plaques cause degenerative tissue damage, cell death and brain shrinkage, which cause patients to gradually lose their cognitive abilities. Although the time frame is different for each patient, eventually motor functions are lost as well, and the patient becomes unable to walk, needs a wheelchair and ultimately becomes bedridden, finally succumbing to pneumonia and dehydration. At this time, the cause and the cure for the disease are both unknown, but discovering that these proteins can act as prion-like pathogens offers so much more possibility for research.

Prions are infectious agents that are made up mostly of protein, as compared to the more complex three-part virus molecule, and fatally affect the structure of the brain in much the same way as Alzheimer’s disease. Prions cause many different diseases in mammals, but the most common are Creutzfeldt-Jakob disease (CJD) in humans and bovine spongiform encephalopathy (BSE, or “mad cow disease) in cattle. Like Alzheimers, there are no known cures for prion diseases at present.

The development of Alzheimer’s disease in otherwise healthy mice indicate that there is a previously unknown mechanism that allows infectious tissue to move around the body and pass through the barriers that protect the brain. Although they do not know how this occurs, they do know that the disease does not have to be injected directly into the brain for the disease to occur. It does, however, occur more rapidly when directly introduced into the brain than in any other part of the body.

This news does not indicate that one can “catch” Alzheimer’s disease merely by having someone with the disease brush against you or cough on you, because the disease can only be transmitted via infected brain matter entering directly into the bloodstream. And because we are not cannibals, this is highly unlikely to ever occur. What this does mean is that a new door has opened for Alzheimer’s research into the causes and onset of the AD and for the similar form of dementia, cerebral amyloid angiopathy (CAA).