Emma Hands, of Ngahere School, asks :-

When were germs first discovered?

Sandy Smith, a clinical microbiologist at Otago University's Otago School of Medical Sciences, responded.

Germ is a commonly used term for microscopic organisms (microbes) which cause disease in many living creatures, e.g. humans, other animals, plants. More common germs include (in increasing size) viruses, bacteria, protozoa and fungi.

The ability to visualise germs using some sort of microscope and to grow them in the laboratory have been major hurdles relating to our ability to recognize the role of germs in infectious diseases. The germ theory of disease was first proposed in 1530 when it was suggested that syphilis was infectious, i.e. could be passed from person to person. Bacteria were first seen under a microscope by Antoni van Leeuwenhoek in 1684, although it was not until 1839 that germs were seen in diseased tissues (yeast in oral thrush). Around this time (1849) cholera was shown to be transmitted by drinking contaminated water, and between 1877 and 1913 many of the important pathogenic (disease producing) bacteria were grown and identified.

In 1898 it was recognised that diseases could be caused by germs (microbes) that passed through filters that would remove bacteria. This was the start of the `filterable-agent' or virus era with the first virus being grown in the laboratory in the 1930s. Since then, an increasing range of viruses have been identified and associated with human disease. The list is rapidly increasing at the present time. The role and participation of germs in disease is thus relatively new with most of our present knowledge arising over the last 150 years.