They are small, numerous and cannot be seen with the naked eye: viruses. But what is that exactly? How many of them are there? And what are the differences to bacteria?
They are everywhere where there is life. Viruses are the most primitive organisms on our planet – if you count them as living beings at all. Many cause serious illnesses and sometimes endanger entire societies. We have only known of their existence for a good 100 years. The word virus is of Latin origin and means “slime” or “poison”.
Why are viruses difficult to fight?
It is fundamentally controversial among researchers whether viruses are living organisms at all or just infectious structures. In contrast to bacteria and other microorganisms, they have no metabolism. Most viruses are much smaller than bacteria – some are only several nanometers (millionths of a millimeter) long. They often consist only of a protein shell and the genetic material packed in it, which contains the genetic information for its construction. To reproduce, the virus infiltrates its genome into cells of living organisms and uses their tools to produce new viruses. Because viruses have so few of their own points of attack, it is also harder than bacteria to fight them with medication.
How many viruses are there?
Viruses are extremely common on Earth, even outside of living things: to quantify their occurrence in the sea alone, microbiologists cited a number with more than 30 zeros. Bound to dust or salt particles from the ocean, billions of them enter the earth’s atmosphere, trickle down from there with precipitation, and are distributed across the planet, as Canadian researchers reported.
Can viruses continue to develop?
Whether rabies, hepatitis, measles or AIDS – viruses are the trigger for many diseases. Their high versatility is problematic. A virus can drastically change its properties “in a single step” and trigger a pandemic, according to the Max Planck Society. The human immune system can sometimes do little. Between 1918 and 1920, an estimated 20 million people fell victim to the Spanish flu.
Can you become resistant to viruses?
Vaccinations prevent some viruses, such as measles. In the case of the flu, the vaccines have to be adapted again and again to the variants that are likely to circulate later. Many viruses remain infectious for a long time even outside of human, animal or plant cells. After all, once an infection has survived, we usually develop a so-called immune memory, which at least temporarily prevents renewed infection with the same pathogen.
Are all viruses harmful?
No, not all viruses are harmful: For example, the food industry uses so-called phages against bacteria in food. In various gene therapies, viruses are used as transport vehicles to inject intact genetic material into cells.
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