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A Flu or Two! - Page 2

© Debbie St. Germain

Influenza Type B and Type A can both undergo an antigenic drift, but only the Type A flu virus can go through an abrupt change in the surface proteins. This is called an antigenic shift. This happens when two different viruses come together in the same host cell and exchange information. Antigenic shift can also occur when a virus that was unable to produce an infection in people previously makes a leap from another host animal. This can cause what are called pandemics, worldwide epidemics. This is possible because no one has an immunity to this new virus and, with worldwide travel, the flu can spread easily to other parts of the world.

During this past century, there have been three major pandemics. The most widely known and the most devastating to human life was the flu of 1918-1919, commonly called the Spanish Flu. It is estimated that over 500,000 deaths occurred in the United States and more than 20 million worldwide. Spanish flu got its name, because people thought the flu was carried to the United States by Spanish traders. Scientists have now confirmed that the flu of 1918 originated from pigs.

The Spanish flu is a good example of an antigenic shift. Pigs can become infected with both the human and the avian (bird) strains of flu. If a bird infected a pig with one type of influenza and a person infected those same pigs with another type, the two viruses might infect the same cell within the pig. The mixing of the genes would result in an entirely new flu virus. This could become a threat, since the human body has no defense against the bird virus that was able to sneak in. For example, the 1957 Asian flu contained five human and three bird genes. People living in farming communities in southern China have higher chance of flus caused by antigenic shift. The close proximity of the farmers, birds and pigs increases the chances of a shift in the virus.

Scientists are learning more about influenza and how it spreads by examining the remains of people who had died from previous pandemics. By studying the viruses that are found in frozen bodies, scientists can learn more about the course of antigenic shifts and, in the future, develop a vaccine if a similar outbreak occurs.

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