Seasonal flu may be a direct descendant of the 1918 ‘Spanish flu’


Seasonal flu virus may be a direct descendant of the 1918 ‘Spanish flu’ that caused a global pandemic and killed up to 100 million people, study finds

  • Seasonal human flu virus ‘possibly descended from 1918 Spanish flu strain’
  • Based on analysis of samples collected in Europe during the 1918 pandemic
  • Berlin researchers have revealed more details about the biology of the H1N1 flu virus
  • Detection of mutations in the virus that may have helped it adapt better to human hosts

The seasonal human flu virus may have originated from the 1918 Spanish flu strain, new research suggests.

The findings are based on an analysis of samples taken in Europe during the 1918 pandemic, which was the deadliest respiratory pandemic of the 20th century and killed between 50 and 100 million people.

Researchers have detected mutations in the composition of the H1N1 virus – or swine flu – that may have helped it adapt better to human hosts.

Seasonal human flu virus may have originated from 1918 Spanish flu strain, new research suggests

Researchers have detected mutations in the composition of the H1N1 – or swine flu – virus that may have helped it adapt better to human hosts

Researchers have detected mutations in the composition of the H1N1 – or swine flu – virus that may have helped it adapt better to human hosts

HOW THE SPANISH FLU EMERGED

Experts believe the Spanish flu virus emerged shortly before 1918, when a human H1 virus, which they believe had already been circulating in the human population since around 1900, scavenged genetic material from a flu virus. avian.

The human influenza A virus generally has higher mortality rates in infants and the elderly, but the pandemic virus has caused many deaths in people aged 20 to 40, mainly from secondary bacterial infections. , especially pneumonia.

Experts believe this is because many young adults born between around 1880 and 1900 were exposed as children to a population-circulating H3N8 virus, which had very different surface proteins than the H1N1 virus. .

In contrast, most individuals born before or after 1880-1900 would have had better protection because they were more likely to have been exposed to a variant of the virus more similar to the 1918 virus.

The international team from the Robert Koch Institute, University of Leuven, Charité Berlin and many others have revealed more details about the biology of H1N1, as well as evidence of its spread between continents.

Sébastien Calvignac-Spencer and his colleagues analyzed 13 lung samples from different individuals kept in the historical archives of museums in Germany and Austria, collected between 1901 and 1931.

This included six samples collected in 1918 and 1919.

The researchers believe the genetic differences between the samples are consistent with a combination of local transmission and long-distance dispersal events.

They compared the genomes from before and after the peak of the pandemic, indicating that there is a variation in a specific gene associated with resistance to antiviral responses and which could have allowed the virus to adapt to the virus. ‘male.

The authors also performed molecular clock modeling, which allows estimation of evolutionary timescales, and suggest that all of the genomic segments of seasonal H1N1 flu may be directly derived from the original 1918 pandemic strain.

According to the researchers, this contradicts other hypotheses about the emergence of seasonal influenza.

Dr Calvignac-Spencer said: “Our findings in brief show that there has been genomic variation during this pandemic.

“And when we interpret it, we detect a clear signal for frequent transcontinental dispersal.”

The findings are based on an analysis of samples (pictured) collected in Europe during the 1918 pandemic, which was the deadliest respiratory pandemic of the 20th century and killed between 50 and 100 million people.

The findings are based on an analysis of samples (pictured) collected in Europe during the 1918 pandemic, which was the deadliest respiratory pandemic of the 20th century and killed between 50 and 100 million people.

Nurses are pictured caring for victims of the Spanish flu in 1918 in Massachusetts as the virus spread around the world

Nurses are pictured caring for victims of the Spanish flu in 1918 in Massachusetts as the virus spread around the world

Members of the Red Cross Motor Corps are pictured wearing masks as they transport a patient on a stretcher to their ambulance in Missouri in October 1918

Members of the Red Cross Motor Corps are pictured wearing masks as they transport a patient on a stretcher to their ambulance in Missouri in October 1918

“We also show that there is no evidence of lineage replacement between waves – as we see today with Sars-CoV-2 variants replacing each other.

“And another thing that we discovered with the sequences and the new statistical models is that the seasonal flu virus that continued to circulate after the pandemic may well have directly evolved from the pandemic virus entirely.”

The results are published in Nature Communications.

WHAT IS THE SPANISH FLU?

The 1918 flu pandemic was exceptionally deadly and the first of two involving the H1N1 flu virus.

It has infected 500 million people worldwide, more than a third of the world’s population, including people in remote Pacific and Arctic islands.

It resulted in the death of approximately three to five percent of the world’s population, making it one of the deadliest natural disasters in human history.

The Spanish Flu killed an estimated three to five percent of the world's population, making it one of the deadliest natural disasters in human history.  This image shows soldiers at Fort Riley, Kansas, sick with the virus

The Spanish Flu killed an estimated three to five percent of the world’s population, making it one of the deadliest natural disasters in human history. This image shows soldiers at Fort Riley, Kansas, sick with the virus

Within months it had killed three times as many people as World War I and did so faster than any other disease in recorded history.

Most influenza epidemics disproportionately kill juvenile, elderly, or already debilitated patients. In contrast, the 1918 pandemic primarily killed previously healthy young adults.

To maintain morale, wartime censors downplayed early reports of illness and death in Germany, Britain, France, and the United States. However, newspapers were free to report the effects of the outbreak in Spain.

This created a false impression that Spain was particularly hard hit, giving the pandemic the nickname Spanish flu.

The close quarters and massive troop movements of World War I accelerated the pandemic and likely both increased transmission and increased mutation, the researchers say.

The true global death rate from the pandemic is not known, but an estimated 10-20% of those infected have died. This would lead to a death toll of between 50 and 100 million people.

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