The Spanish flu killed somewhere between 20-50 million people. It is cited as the worst epidemic in recorded world history, killing more people than World War I. One of the most terrifying aspects of this virus was that it targeted healthy people age 20-40 which is highly unusual. Most deadly pandemic outbreaks affect those in the population with under developed or weak immune systems, the very young and the very old. Although rare, some victims died within hours or days after appearance of symptoms. Most people died within 7-10 days. Many died from a secondary infection of bacterial pneumonia. As the cells of respiratory tract were destroyed by the virus, it allowed bacterial infections to run rampant.
The unusual nature of this influenza virus is attributed to a surface protein, hemagglutinin (HA) which resembled avian influenza HA receptors. These receptors help the virus gain entry into their host cell. As humans have no prior exposure to an avian influenza strain, they have very little immunity, thus if it gains entry into human cells, it can be very deadly. Fortunately, avian HA receptors are not adapted to bind to human cells and usually do not cause illness in humans. It was previously theorized that the avian influenza strain must pass into an intermediately host, such as a pig, recombine, then be passed to humans. This is no longer the predominant theory after the H5N1 influenza outbreak in Hong Kong in 1997. This strain passed directly from birds to humans without an intermediate host. H5N1 is highly pathogenic with an 60- 80% mortality rate. That being said, the strain is still not adapted to humans and fortunately does not transmit from person to person. All of the infected individuals were in contact with infected poultry. This strain reemerged in 2003 and 2004 in China, spreading from Asia to Europe to Africa.
What made the Spanish flu so deadly was high person-to-person transmission. Another influenza pandemic could occur if an avian flu strain mutated to cause infection in humans combined with high transmission between people. We would have little to no immunity against the virus. With the high rates of travel and commerce around the world, a local outbreak would quickly transform into a pandemic with little time for preparation.
It is important to note influenza viruses are RNA viruses and possess rather “sloppy” replication. There are eight RNA segments. When two different strains of influenza infect the same organism, these RNA molecules can combine to form a novel strain. This is called antigenic shift and it occurs rapidly. Influenza also undergoes antigenic drift, where one strain of the virus mutates within itself. This gradual evolution is very common, but occurs much more slowly, thus the name drift.
Dr. Robert Webster, a renowned virologist warns us “All the genes of all influenza viruses in the world are being maintained in aquatic birds, and periodically they transmit to other species. . . The 1918 viruses are still being maintained in the bird reservoir. So even though these viruses are very ancient, they still have the capacity to evolve, to acquire new genes, new hosts. The potential is still there for the catastrophe of 1918 to happen again.”
Most scientists agree it’s not IF a pandemic will occur, it’s WHEN. Based on this information, do you think influenza will be the next pandemic or do you think it may be another virus?