This unit is about diseases that pass from person to person and infect many people right across the world. Pandemics cause the deaths of millions of people. Each death is a tragedy for the person whose life is brought to an early end and who misses out on the good things that life has to offer. It is also a huge blow for their loved ones; their family and friends who will lose someone dear to them and whose lives will be affected by their loss. As fellow human beings we share and feel the pain of others. Out of concern for all humanity we must try to understand the scientific causes of pandemics and find ways to reduce their prevalence and the suffering they cause.


Infection: An infection occurs when germs (bacteria, viruses or parasites) invade the body and start to multiply causing disease.

Epidemic: When an infection spreads from person to person causing disease through a whole community.

Pandemic: When an epidemic spreads from country to country, across a continent or worldwide.

Immune: If a person is immune to a disease, they have antibodies from a previous infection which protect them from getting it again. Immunity can wear off after a time. (eg. Immunity to malaria lasts only a year.)

Susceptible: When a person has no immunity to a disease, they are said to be susceptible, which means they are likely to become ill from it if they become infected.

Major Pandemics

COVID-19 (Started December 2019)– Started in Wuhan in China. Caused by a virus. It is thought the virus came from bats, passed into chickens that ate the bat droppings and then to humans from eating poorly cooked chicken. Once it got into the human population the virus spread quickly from person to person, in droplets in coughs and sneezes.

The virus, which caused the Covid-19 disease, lives for up to 3 days outside the body. So, if a person touches a surface with the virus on it, then touches their mouth or eyes the virus can get into the body and start an infection in them. It is a problem because it is a new virus that all people are susceptible to. The disease spread rapidly across the world, through infected people travelling between countries, and by March 2020 over a half a million people had caught the disease and 30,000 had died through respiratory failure.

To slow the spread of the disease people have used:

Hand washing with soap – the soap kills the virus so long as it is in contact with the virus for 20 seconds.

Social distancing – keeping at least 2 metres from other people reduces the spread of the disease, as this is how far droplets from coughs can travel.

HIV/AIDS (Started 1967) – This disease has killed 36 million people. It started in D.R. Congo in 1976. Today up to 35 million people live with the disease – keeping alive with drugs called antiretrovirals.

FLU PANDEMIC (1918-1920) – A new strain of influenza spread across the world between 1918 and 1920. 500 million people were infected and up to 50 million people died.

THE BLACK DEATH/Bubonic Plague (1346-1353) – This plague killed an estimated 200 million people across Europe, Africa and Asia. At that time, there was no science, and people did not understand the cause of the disease or how to control it. Many believed the Black Death was sent by God to punish the sins of the people, or they blamed people from a different religion to themselves.

In modern times, science tells us that the disease must have been caused by either a bacterium or a virus. For many years people believed it was caused by a bacterium spread by rat fleas carried by ships from country to country. Today, because it spread so quickly from person to person, some scientists think Black Death is more likely to have been caused by a virus like Covid-19.

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