An epidemic occurs when a disease spreads through a population because its members have no natural immunity to it. Since people started living in cities about 10,000 years ago, our history is one of constant war between humans and diseases. Early cities had poor food and water supplies and poor sanitation systems, so diseases were common. Cholera used to kill many people in Europe but has now almost disappeared there because of improved sanitation. Cholera epidemics still cause many deaths in underdeveloped countries.
In the 14th century an epidemic known as the “Black Death” killed 40 million people in Europe. It arrived in Europe on fleas living on rats that came with traders from China. Europeans caused many epidemics as they settled new parts of the world. Spanish explorers introduced smallpox into South America in the 16th century, killing off half the Aztec population. Measles, introduced into Fiji in the 19th century, killed off 40 percent of the population.
A pandemic is an epidemic that occurs worldwide. An influenza pandemic at the end of the First World War caused 20 million deaths. Most experts believe that another influenza pandemic is inevitable at some time in the future. Some people feared that the outbreak of SARS (Severe Acute Respiratory Syndrome) that arose in China in 2003 was that pandemic, but a major campaign to isolate infected people and those they had come into contact with was effective. By June 2003 the disease had been brought under control, although some cases were reported in 2004. During the SARS epidemic over 8,000 people were infected worldwide. Around 800 people died.
AIDS is caused by the Human Immunodeficiency Virus (HIV). It emerged in the last decades of the 20th century and has a high death rate. A lot of research has been directed toward trying to find a cure and a vaccine, but neither has yet been developed. It is estimated that AIDS will have claimed 65 million lives by 2010.
Bacteria multiply rapidly. Some double their numbers every 20 minutes. Mutations cause some of the new bacteria to be different to the older ones. Some of the new bacteria may be resistant to antibiotics that are effective against the original ones. These new bacteria thrive while the antibiotic destroys the originals. So the antibiotic actually promotes the development of bacteria that are resistant to it.
Hospitals throughout the world are now having problems with “superbugs”, bacteria that are resistant to different types of antibiotics. Resistance to one type of antibiotic is not a problem, since others can be used. But multi-resistance, in which bacteria develop resistance to most or all antibiotics, is increasing. One particularly nasty bacterium, MRSA, infects more than 100,000 people in the U.S. each year and has spread to other countries. It is now one of the greatest dangers to patients undergoing surgery.
Doctors now accept that antibiotic resistance will always be with us. We need to develop new antibiotics faster than the bacteria can develop resistance to the older ones. Viruses also mutate, which is why we need to be vaccinated each year against new types of influenza. A frightening prospect is that some countries are developing new or modified diseases that could be used in warfare or by terrorists. Since they would be new diseases, populations would have no natural immunity to them.