When An Epidemic Becomes a Pandemic

By Medical Discovery News

July 7, 2012

For at least thousands of years, people have suffered flu epidemics and pandemics.  In 412 B.C., Hippocrates described what was likely an influenza epidemic in Ancient Greece. The term influenza comes from 15th century Italy, when people believed stars influenced the illness because it always came in cycles. Soon after, in 1580, the first clear account of a flu pandemic was written. From that point on, records show flu pandemics have been recurring every one to three decades somewhere in the world.

So what is the difference between an epidemic and pandemic? Flu epidemics occur every year because each year the virus comes back just slightly different. In a flu pandemic, a much larger geographic area is affected, sometimes worldwide, when a new strain of the virus infects people for the first time and everyone is susceptible.

The World Health Organization has defined three phases of pandemics. The first, or earliest, is called the Inter-Pandemic period. During this time, no new influenza viruses are detected in humans, but new flu viruses could be circulating in animal populations.

The next level is the Pandemic Alert period. Here, the flu virus is infecting humans but is either incapable or has limited ability for human-to-human transmission. The last is the Pandemic period where there’s widespread and rapid transmission in human populations.

The potential for a flu virus to be capable of causing pandemics lays in its ability to infect many different species including horses, pigs, and birds. As various strains of the flu virus spread from species to species, multiple viruses can infect the same animal, allowing the viruses to exchange genetic information and create a new virus. Once it can infect and efficiently transmit between humans, a pandemic starts.

The annual flu epidemic sickens 20 percent of America’s population and kills 40,000 people, creating a $10 billion loss in productivity and medical costs. Imagine the cost of a pandemic.  The largest recorded was the 1918 Spanish flu pandemic, which killed 675,000 people in America and 20 to 40 million people worldwide.

Today, health officials worry about avian flu (H5N1) and whether, or more likely when, this flu strain will start a new pandemic. The H5N1 virus was first recognized in Hong Kong in 1997.  Since then it has spread extensively throughout Asia and can now be found in the Middle East, Africa, and Europe. The virus is in the Pandemic Alert period with no means yet for extensive human-to-human transmission. As of spring 2012, approximately 600 people have been diagnosed with H5N1 and the mortality rate is an alarming 60 percent.

In order to understand how this virus may attain efficient transmission between people, American and Dutch scientists created a transmissible H5N1 in the lab. The controversial study could help other scientists create a vaccine for when an avian flu pandemic occurs. But others fear this research could provide a “blueprint” for terrorists to create a potential biological weapon.

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