A virus is a tiny disease-causing agent. Viruses are not cells and are also smaller. They carry a programme inside them, similar to a computer. Viruses do not change outside a living body. They can only do that in the cell of an animal or a plant. Scientists therefore disagree about whether viruses belong to living organisms or not.
Viruses cannot move on their own. Under favourable circumstances, they can float in the air, enclosed in tiny water droplets. Then they belong to the aerosols. Mostly, however, they live in a moist place, for example on our mucous membranes. They are found, for example, in the mouth, nose and intestines.
There they penetrate the cells. Once they are inside, they wake up. They use all the possibilities that the cell actually needs for itself and multiply. If there are a lot of viruses, the cell usually dies, which releases the viruses again. Now, sooner or later, they stick to new cells and the whole thing starts all over again.
Some viruses cause colds or flu. When you cough or sneeze, some of the viruses are thrown out of your nose or mouth along with fine droplets of mucus. If someone else then breathes in these mucus droplets with the viruses, they also stick to the mucous membrane of that person. You can also get the viruses on your hands and bring them there when you touch your nose. You can also pass them on when you shake hands or leave them on a door handle, for example. From there, the next person takes them with them. The coronavirus is also transmitted in these ways.
Other viruses spread through food and even through contact with other people's blood. The HI virus, known by the abbreviation HIV, is one of these. It can also be transmitted during sex, because there are also many mucous membranes in the sexual organs.
Viruses can trigger very different diseases. These include coughs, colds and diarrhoea. The treatment of the disease is completely different. It depends on which type of virus someone is ill with. However, the medicines known so far mainly combat complaints such as headaches or fever. There is no actual medication against viruses. For bacteria, on the other hand, there are antibiotics. However, they are not effective against viruses.