Epidemics, pandemics and plagues have played a huge role in the history of mankind, but, in this age of modern medicine, the danger posed by viruses has often been overlooked or considered a thing of the past.
Now, with the spread of the Ebola virus to the United States, the threat of an uncontrollable outbreak has many people very fearful.
A virus is a tiny infectious organism that can reproduce and even evolve and mutate, but lacks a cell structure so can only replicate inside the living cells of other organisms. If unchecked, a virus can destroy the life form it infects.
In animals and humans, a viral infection usually provokes an immune response that attacks and eliminates the virus. Vaccines can produce artificial immune responses with some viruses, but antibiotics have no effect on them.
Most viruses are endemic, meaning they are common to a population, and their rate of transmission is low. This may result from natural selection, in which those with weak immunity to the virus die out while those with a strong immunity survive, so the virus continues to exist, but spreads slowly and is no longer very deadly.
Epidemics occur when a virus suddenly spreads very rapidly. This can happen when a population in which the virus is endemic comes into contact with a population in which the virus is unknown, and so has not developed a natural immunity to it. This is what happened when the Bubonic Plague or “Black Death,” spread to Europe in the 1300s, killing a third of the population and 80 percent of the townspeople.
The plague was endemic to central Asia and Mongolia, but unknown in Europe, so the people had no natural immunity to it. Rat fleas carried the virus, and rats from central Asia were brought to Italy on merchant ships arriving from Persia (now Turkey). The Europeans had no idea how the disease was spread; flea bites were common, but the rats these people were used to did not carry the plague.
Similarly, in the 1500s, small pox was endemic in Europe but unknown in the “New World.” When the Spanish arrived in the Caribbean and Central America, they brought small pox with them. It wasn’t the military genius of Hernan Cortez that defeated the Aztecs; it was the small pox virus unknowingly carried by his soldiers.
It has been estimated that 90 percent of the native population of the New World died out due to “Old World” diseases. This unintentional de-population of the Americans was the primary reason the Europeans resorted to bringing in African slaves to work their plantations.
An epidemic is the rapid spread of a virus, but it is usually confined to a specific area. A “pandemic” occurs when the virus is everywhere. The official definition of pandemic is: “an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.”
The Great Influenza Pandemic of 1918 was one of the deadliest viral outbreaks in history, killing an estimated 50 million-100 million people worldwide. It occurred at the end of World War I, as soldiers who had been fighting around the globe returned to their home countries. The symptoms were similar to those in today’s influenza virus, but people had no natural immunity to the strains that were being transmitted.
AIDS is also considered a pandemic, because it has spread worldwide.
Not all viruses are potential mass murderers. For example, Swine Flu was first identified in Mexico in 2009, and spread rapidly from country to country, because it was a new strain of flu virus, so few people were immune to it. There were dire predictions of millions of deaths, but it proved to be relatively mild, and the pandemic was not as serious as feared.
Unfortunately, this is not the case with Ebola. The Ebola virus is extremely lethal, with death rates in the 50- to 80-percent range, but thankfully, it is not easily transmitted.
Viral infections go through three stages: an incubation period, during which one is infected but shows no symptoms of infection; a latent period, during which one is infected but not infectious; and an infectious period, during which the virus can be transmitted to others. These periods are different for each virus. What makes the AIDS virus so difficult to control is that one can be infected and infectious, meaning they can transmit it to others, before the symptoms of AIDS are apparent.
People infected with Ebola are not known to be infectious until the symptoms are apparent. Thus, people are not likely to spread Ebola unknowingly. The caveat is that the symptoms of Ebola are the same as the symptoms for the flu, so some with Ebola may think they only have the flu, and won’t seek treatment. But with as much fear of Ebola as there is right now, I suspect the situation will be the other way around: People who only have the flu may fear they have Ebola.
The Ebola virus was first identified in Zaire in 1976. Prior to the current epidemic in West Africa, there were about 20 recorded outbreaks, mostly in Central African villages, and the highest death count in an outbreak was 254 people. The main reason the virus didn’t spread to a wider area is that by the time a person becomes infectious, they are too sick to travel, so it was mostly family and caregivers to whom the virus was transmitted. The reason the death count (around 4,000) is higher in West Africa is because this outbreak is in a more densely populated area.
Ebola is very lethal, with no known antidote or vaccine, and it is highly contagious for those who come into close contact with a person in the advanced stages of infection. But this is not the formula for a pandemic: The greatest danger of a pandemic is when people are infectious before the symptoms of their infection are apparent, because then it can be unknowingly spread.
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