by Harriet Squier

Created on: February 02, 2009

Causes of the 1918 flu epidemic

Many details of the 1918 influenza pandemic remain a mystery. We do know that it occurred worldwide, infected one third of the population, and resulted in the deaths of up to 50 million people. Many of the victims were between age 15 and 34 years; high death rates in this age range have not occurred in other influenza epidemics.

Researchers have reconstructed the viruses that caused the 1918 epidemic, and discovered that they led to infection throughout the lungs that caused inflammation and bleeding. To make matters worse, the 1918 strains of virus were especially virulent; they produced around 40,000 times more virus particles in the lungs of victims than caused by today's influenza strains. The 1918 stain appears to have originally infected birds then became adapted to infect humans and pigs.

Before and since 1918, influenza viruses typically originated in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Asia, and then were transmitted around the world. But the 1918 epidemic originated simultaneously in waves throughout Europe, Asia, and North America. Some theorize that troop and personnel movement related to World War I may have influenced the spread of the disease. Although many people of the day suspected dire plots on the parts of various political factions, where the virus was intentionally spread, none of these theories have been substantiated.

Because the world population had no immunity to this new virus, the spread of the first wave of disease was atypical, beginning in the Spring of the year and continuing for the next 6 months. This first wave was less severe than the second and third waves that began in the Fall of 1918 and continued through the winter of 1919. Why the disease increased in severity with each wave of infection is unclear.

Measures to prevent infection were rudimentary, at best. Some towns attempted to isolate themselves from the rest of the population, sometimes to good effect. Doctors recommended everything from loose clothing to gargling; most remedies made little difference. Good hand washing and covering one's mouth with coughing probably were the most effective measures to prevent infection, aside from isolation. Unlike other influenza strains, the 1918 strain did not target the very young or very. The death rates for children and the elderly were not substantially different in 1918 than in other years. Why the virus was so virulent in previously healthy young persons remains unknown.

The location of the original source of the 1918 virus is also unknown. While it seems to be an avian influenza virus, it appeared in a totally new form from any previous influenza virus. While many people today worry that a recurrence of a pandemic like that of 1918 could occur, the use of influenza and avian influenza vaccines do give us more protection than ever before in history.

Sources: Up to Date; CDC; PBS

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