Massive Health Record Review Links Viral Illnesses to Brain Disease

Colored scanning electron micrograph (SEM) of influenza (flu) viruses (blue) budding from a ruptured epithelial cell.

In this false-color scanning electron microscope image, influenza virus particles (blue) are ready to break free from a ruptured epithelial cell (red).Credit: Lennart Nilsson, Boehringer Ingelheim International GmbH, TT/SPL

An analysis of about 450,000 electronic medical records found a link between infections with influenza and other common viruses and an elevated risk of developing a neurodegenerative condition such as Alzheimer’s or Parkinson’s disease later in life. But the researchers caution that the data shows only one possible connection, and that it is not yet clear how or if the infections trigger the onset of the disease.

The analysis, published in Neuron on January 191, found at least 22 links between viral infections and neurodegenerative diseases. Some of the viral exposures were associated with an increased risk of brain disease up to 15 years after infection.

“It’s surprising how widespread these associations seem to be, both because of the number of viruses and the number of neurodegenerative diseases involved,” says Matthew Miller, a viral immunologist at McMaster University in Hamilton, Canada.

mining health records

This is not the first time that viruses have been linked to neurodegenerative diseases. Infection with a type of herpes virus has been associated with the development of Alzheimer’s disease2, for example. And a landmark study published in Science3 last year found the strongest evidence yet that the Epstein-Barr virus is linked to multiple sclerosis. But many of these earlier studies looked at just one virus and one specific brain disease.

To understand whether viruses are linked to brain diseases more broadly, Kristin Levine, a biomedical data scientist with the Center for Alzheimer’s-Related Dementias at the US National Institutes of Health in Bethesda, Maryland, and colleagues they analyzed hundreds of thousands of medical records to look for instances. in which a person had a registered viral infection and brain disease.

First, the team looked at the records of about 35,000 people with brain diseases and about 310,000 people without them, drawn from FinnGen, a large Finnish database of health information. The team found 45 significant links between infections and brain diseases, then compared them to more than 100,000 records in another database, the UK Biobank. After this analysis, they were left with 22 significant matches.

One of the strongest associations was between viral encephalitis, a rare inflammation of the brain that can be caused by multiple types of viruses, and Alzheimer’s. People with encephalitis were about 31 times more likely to develop Alzheimer’s in the future than people without encephalitis. Most of the other associations were more modest: People who had a bout of flu that led to pneumonia were four times more likely to develop Alzheimer’s than people who didn’t develop flu with pneumonia. There were no matches to suggest a protective link between viral infection and brain disease.

“I am very excited that they are expanding this research beyond what other studies have looked at,” says Kristen Funk, a neuroimmunologist at the University of North Carolina, Charlotte, who studies the link between herpes viruses and Alzheimer’s.

Data gaps

Kjetil Bjornevik, an epidemiologist at the Harvard TH Chan School of Public Health in Boston, Massachusetts, and author of the Epstein-Barr paper in Science, applauds Levine and his colleagues for drawing more attention to the role of viral infections in brain disease. But he cautions that his approach to using medical records “could be problematic” because they only looked at infections that were serious enough to warrant a trip to a health professional. Factoring in milder infections could weaken the associations, she says.

The data also comes almost exclusively from people of European descent, which means the findings might not be applicable to the global population at large, Funk says. Also, he adds, outside of Europe, “certain viruses are more prevalent,” such as Zika or West Nile virus, so the analysis might have missed the links between those pathogens and brain disease. Levine acknowledges the limitations of the analysis; the team worked with the data that was available, she says.

These limitations also underscore the difficulty of unraveling whether a viral infection leads to a neurodegenerative disease or whether the disease makes a person more susceptible to infection, Bjornevik says. To complicate matters further, the authors found that the longer the time between infection and diagnosis of brain disease, the weaker the link. The body is known to start changing years before symptoms of brain disease develop and a diagnosis is made,4 so it’s hard to pinpoint the cause, he adds. Another plausible theory is that these viral infections could be accelerating molecular changes in the body that were already underway, says Cornelia van Duijn, a genetic epidemiologist at the University of Oxford, UK.

If future studies add more weight to the connection between viral infection and brain disease, it could offer health officials a tangible way to slow the onset of neurodegenerative diseases. Vaccines exist for many of these viruses, says van Dujin. Because multiple types of dementia are diagnosed late in life, close to the average life expectancy, if doctors could postpone the onset of the disease for even a couple of years, that could mean many people would never develop the disease, he adds. .

“It’s not very clear that the infections are causing brain disease,” she says. But viral infections are not pretty, and if there is any link to brain disease, “I think we owe it to people to prevent it.”

Source: news.google.com