 These days we're all talking about viruses. The coronavirus has changed our lives in so many ways. But what exactly is a virus and what can we do about it? Viruses cause many kinds of illness. Common colds, coughs and sneezes are often caused by viruses so it is very likely that you have had one at some time. There are viruses that affect plants, bacteria and animals. The first virus ever discovered in 1892 infected tobacco plants. Bacteria phages are viruses that only attack bacteria and some viruses cross from one animal to another like the coronavirus that probably started in bats. Viruses are tiny, really really tiny. They're too small to see even with a microscope. A human cell is pretty small, you can't see it with the naked eye but you can fit tens of thousands of viruses in a single human cell. Viruses are made of genetic material inside a protein shell. They multiply by putting their genes into the cells of another organism. Some viruses like the coronavirus have an envelope of fat. That's good news because soap breaks up fat and destroys the virus. The spikes on a virus are proteins. The spikes stick to proteins on the cells of other organisms like you. After attaching the virus passes its genes into the cell. The cell is turned into a sort of zombie. The zombie cells are forced to make new viruses instead of doing their proper job. Eventually there are so many virus particles in the cell it bursts and the virus spreads through the bloodstream. Viruses are quite simple. The coronavirus for example only has about 30 genes compared to 20,000 in a person but because of the damage they do to our cells and the speed they multiply viruses cause many diseases from flu to measles and now COVID-19 the disease caused by the new coronavirus. To study viruses scientists need to grow them but that's not easy because viruses need the cells of another organism to multiply. Remember the zombie cells that make new viruses? That means that viruses usually have to be grown in animals if we want to make vaccines. Fertilized chicken eggs are one of the main ways we can safely grow viruses. To understand how a new virus works we often have to study it in a fully grown animal. The mouse is the animal that is most often used to study viruses including the coronavirus. Animal studies have helped us find vaccines for many viruses. The first polio vaccine was available in 1955, smallpox was eradicated by vaccination in 1979 and a vaccine for Ebola virus was developed in 2019. Thanks to a huge international effort and careful animal research we have every reason to hope that a vaccine for coronavirus will come along soon. To find out more about the fight against disease and how scientists use animals visit our website at www.understandinganimalresearch.org.uk