Contains the full lesson along with a supporting toolkit, including teachers’ notes.
The Human Challenge
Since the beginning of time the human race has been threatened by disease, but it is only in relatively recent history that scientists have been able to isolate the causes of many diseases and develop the means of coping with them.
Also, in modern times, most countries have public health authorities who monitor world events and provide advance warnings of any infection that is likely to spread across countries. Such was not the case during the many outbreaks of influenzaand cholera in the 18th and 19th centuries when millions died. Neither were these services available in 1918 - 1919 when theSpanish flu resulted in millions of deaths.
The Invisible Threats
Two of the most common causes of human disease are bacteriaand viral infection.
Bacteria are unicellular living organisms about 1,000 nm (nanometres) long. This is about one eightieth the size of a human hair and cannot be seen by the naked eye. Most bacteriaare harmless and many are very beneficial. However, some can cause disease. One of the most common bacterial diseases today is tuberculosis (TB). In this lesson we will concentrate onviral infection because Irish schools and colleges have recently experienced major outbreaks of a well known viral disease called mumps.
What is a Virus?
The word virus comes from the Latin for toxic or poison. Viruses are very small, ranging from 20 to 250 nm in size. Nobody knew what a virus looked like until the invention of electron microscope in 1931. Currently, about 5,000 viruses have been identified but it is thought that most have not been discovered yet. The remarkable thing about them is that they can only reproduce inside a living cell (the host cell). When a virus invades a cell it uses the resources of the cell to produce more virus particles. Well known viral diseases are measles, mumps, flu and HIV. The study of viruses is a branch of microbiology called virology.