Alzheimer’s: The heretical and hopeful role of infection – BBC News

It is more than 150 years since scientists proved that invisible germs could cause contagious illnesses such as cholera, typhoid, and tuberculosis. The role of microbes in these diseases was soon widely accepted, but "Germ Theory" has continued to surprise ever since with huge implications for many apparently unrelated areas of medicine.

It was only in the 1980s, after all, that two Australian scientists found that Helicobacter Pylori triggers stomach ulcers. Before that, doctors had blamed the condition on stress, cigarettes and booze. Contemporary scientists considered the idea to be "preposterous", yet it eventually earned the Nobel Prize for Physiology or Medicine in 2005.

The discovery that the human papillomavirus can cause cervical cancer proved to be similarly controversial, but vaccines against the infection are now saving thousands of lives. Scientists today estimate that around 12% of all human cancers are caused by viruses.

We may be witnessing a similar revolution in our understanding of Alzheimer's disease. Lifestyle and genetic factors certainly play a role in the development of the illness. But it looks increasingly possible that some common viruses and bacteria the kinds that give us cold sores and gum disease may, over the long term, trigger the death of neural tissue and a steady cognitive decline. If so, infections may be one of the leading causes of the dementia.

Like the germ theories of ulcers and cancers, this hypothesis was once considered a kind of heresy yet a string of compelling findings has sparked renewed interest in microbes' contributions to dementia. "There's a huge amount of work being done now, compared to even five years ago," says Ruth Itzhaki, an emeritus professor at the University of Manchester in the UK, who has spent three decades investigating the role of infection in Alzheimer's.

The hypothesis has inspired a clinical trial of a drug that could target the infection before it decimates the brain, radically reducing the risk of senility in old age. And there may soon be many other exciting new treatments in the pipeline.

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A new understanding of Alzheimer's disease could not come soon enough. While there are many forms of dementia, Alzheimer's causes around 60-70% of cases. Globally, that amounts to around seven million people who have been newly diagnosed every year, who desperately need new treatments to slow their decline.

The disease takes its name from the German doctor Alois Alzheimer. In 1906, he noted the build-up of plaques in the brain of a 55-year-old woman, Auguste Deter, who had been suffering from memory decline, language problems and unpredictable behaviour. We now know that these plaques are made from a protein called amyloid beta, and they are thought to be toxic to brain cells and impair the synaptic connections that are important for neural signalling. The accumulation of amyloid beta plaques may also cause tangles of another protein, tau, to build within cells, which can itself lead to neuronal death, and it appears to be accompanied by widespread inflammation in the brain, which adds to the damage.

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Alzheimer's: The heretical and hopeful role of infection - BBC News