Wherever people have lived together in large numbers,
diseases have spread. As ships travelled around the
world, diseases like bubonic plague, flu, and cholera
spread from country to country. In the past, treatment
was often ineffective as people did not understand the
true causes of these diseases. We now know that they
are caused by microscopic bacteria and viruses.DISEASE
◀ BUBONIC PLAGUE
In the 1340s, bubonic
plague killed around half the
population of Europe, and
millions more in Asia and
Africa. People believed that
they could catch the plague
by breathing bad air. The true
cause was bacteria, passed on
by flea bites.246
Some doctors wore
bird-like masks stuffed
with herbs believed to
ward off the plagueCHOLERA
▲These bones in the Paris catacombs are
from victims of cholera, a disease that
originated in India and was brought to
Europe by merchant ships in 1829. It is
caused by drinking water polluted with
sewage, which carries the cholera
bacteria. Victims die a painful death,
after hours of vomiting and diarrhoea.FLU PANDEMIC ▶
A widespread outbreak
of disease is called a
pandemic. The worst
case in history took
place in 1918–20, when a
deadly strain of flu
spread around the globe,
killing 50–100 million
people. Face masks were
widely worn, for it was
correctly understood that
flu is spread by coughs
and sneezes.SMALLPOX ▲
Smallpox was a disease that could scar,
blind, and even kill its victims. Like flu or
the common cold, it was caused by a virus,
a minute agent that can only grow or
reproduce inside the cells of living things.
Smallpox is one disease that has been
wiped out by modern medicine.Smallpox caused
painful raised blisters,
which left scars behind
after they healed246_247_Disease.indd 246 03/01/19 12:11 PM