Epidemics
In North America and Asia most people will think of the flu when they hear the word pandemic, while Europeans tend to think of the Black Death, which is a common name for the bubonic plague of the Middle Ages. A pandemic is an epidemic with a global spread. For examples of a contemporary pandemic, rather than Avian Influenza, people should think of HIV/AIDS. In a very short period of time HIV/AIDS has killed as many people as the bubonic plague did during the second half of the 14th century. What is remarkable is that we know what HIV/AIDS is and how it can be handled. Today’s hysteric reactions to the Bird Flu, which has killed not 40 million but less than 200 people, is a good example of the media exerting a bad influence on a public that is not educated about fundamentals of natural science.
Most people have probably not considered that pandemics and plagues are natural hazards. Usually a virus or bacterium constitutes the potential disaster. Bacteria and viruses are very small organisms, but like all living things they are dependent on their natural environment. In the case of the Black Death the necessary environment for effective spread is a population of not just humans but also rats and rat fleas. The plague bacteria Yersinia pestis live in the blood of the black rat, but also the blood of the rat flea Xenopsylla cheopsis. The plague bacteria will eventually kill both the rat and the flea, but not before they have given birth to several generations of infected offspring.
When a plague rat dies the fleas leave its body. If they do not find a new warm-blooded animal to feed from, the fleas will die within a few weeks. Other animals that were bitten by the plague flea—in the beginning this included humans—did not become sick, because their immune system could kill the bacteria that the flea carried. So the plague was limited to rats and rat fleas and did not spread outside of a certain area.
It wasn’t until the plague bacteria mutated so they could survive in human blood that we saw the first epidemic of bubonic plague, a few hundred years B.C. The first serious epidemic took place in the 4th century, when Rome was struck hard. A large population density was one of the most important factors in the spread of the plague. In the 14th century population density in Europe and Asia was great enough for the first pandemic, the Black Death.
Today the bubonic plague does not concern people, although plague-infected rats and fleas still remain in a few restricted parts of the world. We have the knowledge of how the disease should be handled, although it took us several hundred years to gain this knowledge. The Ebola virus was a source of fear during a few years, but it turned out that the virus was so lethal that it killed faster than it could spread.
The spread of bacteria and viruses are dependent on the ecological demands of its host animal. Rats, for instance, have a tendency to stay in one place as long as there is food. Not even prolonged periods of drought will cause them to leave. However, if drought is followed by heavy rainfall, rats will move quickly. Earthquakes and volcanic activity will also cause migration.
The fastest way for a virus to spread is through the air. In large volcanic eruptions organisms follow dust particles in the air currents around the globe. Needless to say fast travel can be achieved by aircraft as well. Airline companies are aware of the risk and are prepared to stop infectious diseases from spreading and avoiding that local epidemics become pandemics. But the risk of pandemics highlights the importance of our comprehensive approach and our database TRITON for all kinds of natural hazards.