Photo: Bacteriophage Virus Attacking a Bacterium

Viruses are much smaller than bacteria. They are alive, but not in the same sense as bacteria.

Viruses can reproduce and multiply in numbers, but only within another living cell. They can survive for a time outside a living cell and be transferred from one place (or person) to another. However, they will not increase in number until they penetrate the cells of another living creature. Therefore, they will not multiply in the inanimate (non-living) environment, although they may survive.

Diseases caused by viruses are measles, chickenpox, hepatitis B, herpes, acquired immune deficiency syndrome (AIDS) and the common cold. Scientists have developed vaccines against many common viruses (e.g. measles, mumps and hepatitis B), which can usually prevent us from acquiring these diseases.

Most viruses are quite susceptible to drying and will die off in a matter of a few hours on dry surfaces. One exception is the hepatitis B virus, which can survive for years on a dry surface.

Current evidence shows SARS-Cov-2 or Covid-19 can also spread after infected people sneeze,
cough on, or touch surfaces, or objects, such as tables, doorknobs and handrails. Other people may become infected by touching these contaminated surfaces, then touching their eyes, noses or mouths without having cleaned their hands first. Hand hygiene is vital as it has been shown Covid-19 can live on skin for up to 9 hours.

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