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The current Covid-19 pandemic and its virus Sars-Cov-2 can be dangerous, especially for vulnerable groups like the elders. But however, I have seen studies that this virus become less dangerous in the future, when human population has built some immunity against it.

There are many other viruses still present and most of them produce only harmless diseases like the cold. But were some of such viruses really dangerous in the past and cause only mild symptoms on infected persons in present day (due to immunity)? Perhaps thousands of years they caused a bad epidemic?

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  • $\begingroup$ The variant which caused the Spanish flu is still circulating today. $\endgroup$ – user438383 Apr 30 at 16:37
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There are a few viruses which are around for a long time and have caused recurring episodes of disease. Most of these where not pandemic, which is probably more of a problem for modern times due to fast travel/exchange of people and are also a problem of "modern" cities where many people come together in a limited space.

Among theses viruses are:

  • Measles: This virus is around since at least 400 BC, profiting from the first big cities. (see reference 1 and 2 for more details)

  • Polio: This virus has been described already in ancient Egypt, although major outbreaks didn't happen before the early 20th century. There is a nice article in Wikipedia about it, see reference 3.

  • Smallpox: These are only not threat anymore because mankind successfully eradicated them. They have been described first around 1500BC in India, later also in China and Egypt. See reference 4 and 5.

Not viruses but also pathogens which caused historic epidemics: Typhoid fever, Cholera and the Yersinia Pestis (also known as The Plague or the Black Death).

References:

  1. The history of measles: from a 1912 genome to an antique origin
  2. Measles may have emerged when large cities rose, 1500 years earlier than thought
  3. History of Polio
  4. Emergence and reemergence of smallpox: the need for development of a new generation smallpox vaccine
  5. History of Smallpox
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  • $\begingroup$ Lovely answer, but what is the "Pest"? Did you possibly mean Yersinia pestis (the Black Death aka. the Plague and apparently also as the Pestilence)? $\endgroup$ – tyersome Apr 30 at 17:12
  • $\begingroup$ @tyersome Yes, you are right. I edited my answer. $\endgroup$ – Chris Apr 30 at 18:55
  • $\begingroup$ Great answer. I'd add that we can't definitively identify many historical illnesses, even those in well recorded history because medicine, diagnostics and even language has changed, so things that were recorded as an illness a few hundred years ago might have been ascribed to "humors", but we now know as a virus. There's also different diseases being lumped together into one name or vice versa. Also, there are lots of unknowns - what caused "dancing mania"? Could it have been an illness? $\endgroup$ – bob1 May 1 at 10:01
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The 1890 "Russian Flu" pandemic is now believed to have been caused by one of the common cold Coronaviruses, HCoV-OC43. At the time of historical pandemics, there was no way to identify the infectious agent, though. So connecting the pandemic to the virus is based on descriptions of symptoms, and patterns of which demographic groups were most affected; as well as genetic analysis to estimate when the virus jumped from animals to humans.

Accounting for expected mutation rates and working backwards, they calculated that the jump into humans occurred around 1890.

That date isn't the only thing linking OC43 with Russian flu. Many patients of that pandemic had pronounced symptoms affecting their central nervous system. Today, although mostly associated with mild colds, OC43 is also known to infect nervous tissue.

It's likely that all of the common cold Coronaviruses caused pandemics when they first started infecting humans. For the others, that happened much longer ago than OC43, so the historical record is less detailed, and there is more uncertainty in the genetic analysis.

In fact, it's possible that many or even all of the viruses that currently circulate among humans without problems were much less benign when they first emerged. Another example is the outbreak of severe symptoms from Zika infections in the Americas when the virus arrived there, after circulating in humans for (at least) decades in Africa with only mild symptoms:

In the outbreaks reported up to 2013, most of the infected patients were asymptomatic and only 20% of them had mild symptoms such as fever, arthralgia, maculopapular rash, and conjunctivitis.

So it's suspected that many "harmless" viruses were worse when they first emerged into humans, but with the tools that are currently available, there is no way to establish definitively whether any particular virus caused major pathogenic outbreaks in the past.

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