The influence of influenza

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The potential long-term consequences of viral infections is not a popular topic for a research blog in the middle of a pandemic (and yes, we are still in the middle of it!), but there is a recent Parkinson’s-related report that is worth discussing.

Researchers have recently looked at medical records dating back several decades and noticed something interesting about influenza infections: They are associated with diagnoses of Parkinson’s more than 10 years after infection.

NOTE: The data does not indicate a causal link, just an association.

In today’s post, we will discuss what influenza is, how it has previously been associated with PD, what the new report found, and we will speculate on potential mechanisms by which viral infections could be playing a role in Parkinson’s.

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1918 Spanish flu. Source: Chronicle

Between January 1918 and December 1920, there were two outbreaks of an influenza virus during an event that became known as the 1918 flu pandemic.

Approximately 500 million people across the globe were infected by the H1N1 influenza virus, and this resulted in 50 to 100 million deaths (approximately 3-5% of the world’s population). Given that it occurred during World War 1, censors limited the media coverage of the pandemic in many countries in order to maintain morale.

The Spanish media were not censored, however, and this is why the 1918 pandemic is often referred to as the ‘Spanish flu’.

At the same time that H1N1 was causing havoc, a Romanian born neurologist named Constantin von Economo reported a number of cases involving unusual symptoms. The collection of symptoms was eventually given a name: encephalitis lethargica (EL).

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Constantin von Economo. Source: Wikipedia

This disease left victims in a statue-like condition, speechless and motionless. By 1926, EL had spread around the world, with nearly five million people being affected.

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An individual with encephalitis lethargica. Source: Baillement

Was influenza causing EL?

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