For centuries, although the diseases we now know to be caused by viruses were known to healers, the triggering factor was not. The diseases were thought to be caused by a “poison.” Until the 19th century, scientists were unable to isolate and determine the crucial substances.
The discovery of viruses
Then, as part of their investigations into foot-and-mouth disease in cattle, researchers Friedrich Löffler and Paul Frosch made an interesting discovery: no matter how much they diluted the infectious fluid from the vesicles of sick animals, the disease always occurred with the same intensity. They concluded that the so-called toxin was able to reproduce itself in some form. Derived from its original classification as “poison,” this mysterious, disease-causing substance came to be known in medicine as “virus,” the Latin word for “poison” or “slime.”
1892: The first virus is identified
Viruses could not be seen under the light microscopes available in the 19th century; they obviously had to be extremely small. In 1892, Russian Dimitri Ivanovsky stunned experts by proving that viruses were much smaller than bacteria. He sent extracts from tobacco plants affected by the so-called “mosaic disease” through filters. The pores were smaller than 0.2 micrometers (a micrometer is a millionth of a meter), so bacteria were trapped inside in any case. However, with the extract cleaned of bacteria, Iwanowski was able to infect other tobacco plants. Finding: the viruses had to be smaller than 0.2 micrometers. The tobacco mosaic virus earned the dubious honor of being the first virus to be identified. In the following years, further discoveries followed in rapid succession. Among others, the pathogens of foot-and-mouth disease, yellow fever and rabies were isolated. At the beginning of the 20th century, scientists initially focused their attention on research into polio, which was spreading rapidly at the time. Thanks to the development of a vaccine, it was later contained and eventually eradicated in the 1950s. Because of the devastating effects of the Spanish flu (influenza) of 1918, intensive research was also conducted on this.
1933: Influenza viruses are identified for the first time
About 20 years later: rhinoviruses causing colds (flu-like infections) The development of the electron microscope by Ernst Ruska in 1940 ensured that viruses could now actually be seen. From around this time, groundbreaking developments were recorded in virus research as a whole, laying the foundations for modern molecular biology. These new techniques are being refined and improved daily by researchers around the world. Today, for example, the genetic information of an emerging virus type can be decoded within a very short time.
More information on viruses
We now know that viruses are particularly small infectious agents with a very simple structure that penetrate the cells of an organism in order to reproduce there with the help of the infected organism. Viruses are between ten and 400 nanometers in size. (A nanometer is one billionth of a meter). They consist of nucleic acid, which contains the genetic information of the virus, and the proteins surrounding it. They do not have their own metabolism and belong to the parasites. Viruses are divided into different groups. These do not result from the diseases they cause, but according to the three criteria:
- Type of genetic information: RNA or DNA.
- The principle of symmetry, which is followed by the structure of the hollow proteins surrounding the genetic information and
- The presence of an envelope membrane.
Sheathless viruses, which include the cold-causing rhinoviruses, have the characteristic of being very “environmentally stable”. This means that they can not be killed by drying out, for example. Frequent hand washing during the annual cold season serves only to wash away the cold viruses, but cannot destroy them. Controversy exists among scientists as to whether viruses are living organisms or organic substances. One significant characteristic that defines “living beings” is the ability to reproduce independently. Viruses, however, need host cells to reproduce. In favor of their classification as living beings is the fact that they are able to reproduce, pass on their genetic material and grow.To do this, however, they need the help of the host cell that they have infected. This provides the viruses with their mechanisms for replication and ensures that the number of viruses in the host cell increases.