The maddening viruses

The viruses are so tiny (that they cannot even be seen under a light microscope) and cause such great trouble (diseases and even deadly epidemics). They are very interesting, and not at all certain that they are living creatures

Written by: Zvi Atzmon, Young Galileo

Viruses are tiny parasites that take up residence in living cells, multiply in them, damage them and may even cause their death, thus causing disease. There are viruses that harm all groups of living beings: humans, animals, plants, fungi and even bacteria! Viruses that attack bacteria are called bacteriophages (a word that means "bacteria eaters").

how small are they

The viruses are so tiny that most of them cannot be seen with a normal microscope (light microscope), but only with an electron microscope. Before the development of the electron microscope, scientists hypothesized that there are tiny factors that are responsible for the outbreak of infectious diseases even though they cannot be seen under a light microscope. They came to this conclusion because solutions that were produced from diseased creatures infected healthy creatures and caused them disease, even though no bacteria could be seen in them under the microscope. When these solutions were passed through filters with very narrow holes, which prevent the passage of bacteria, they caused infection with the disease.

Since the viruses pass through extremely tiny pores, some speculated that it was a liquid substance that acts as a poison, and therefore called them viruses (virus in Latin - poison). Later it was proven that they are composed of nucleic acid and proteins, and with the invention of the electron microscope they were able to see them. In Hebrew they are called viruses because many of them can cause epidemics, such as the flu epidemic.

What are they made of?

A virus is made of genetic material wrapped in a capsule made of proteins, and some viruses also have a membrane that covers them. The hereditary material determines the properties of the virus - its size, in which cells it can reproduce and from which proteins its box is built.

In all living things the hereditary material is the nucleic acid DNA (DNA), but in many viruses the nucleic acid used as hereditary material is RNA. Since RNA is less stable than DNA "A, RNA viruses are more likely to undergo mutations (changes in the hereditary material) and change their properties. Thus, new strains are created with high frequency, and therefore it is more difficult to vaccinate against them. This is why new vaccine components are often produced against the flu, according to the new strains of the virus.

Are they living things?

Unlike all living things, viruses do not have a metabolism: they do not eat (like humans and animals), do not absorb food (like bacteria and fungi), do not photosynthesize (like plants), do not breathe and do not excrete. Hence the viruses are not really living things; You can say that they are on the border between living and inanimate. However, they have an excellent reproduction capacity: relatively few viruses that we inhale can reproduce at an enormous speed in our bodies and cause us to catch a cold, for example.

How can bodies that are not really living things reproduce? They penetrate the cells and take over the cell mechanisms in such a way that the cell begins to produce the components of the virus. Since viruses have no metabolism, it is very difficult to find drugs that only harm them, such as antibiotic drugs that are used to fight bacteria.

DNA viruses utilize the mechanisms of the host cell to replicate their DNA for reproduction. RNA viruses cannot do this, because cells do not have a mechanism for replicating RNA, but only a mechanism for building RNA based on DNA. If so, how do these viruses reproduce? Most of them use a special enzyme that the host cell produces according to an instruction included in the virus's RNA; It is an enzyme that replicates RNA.

How are viruses transmitted?

Viruses are transmitted through the air - in droplets of mucus that are carried in the air, which originate from the cough or sneeze of a sick person (this is how, for example, flu viruses, colds and measles are transmitted); In food and drink - the source is secretions and sewage (this is how the polio viruses, some of the jaundice viruses, and other viruses pass); by insect bites, such as female mosquitoes (this is how West Nile fever viruses are transmitted); or in direct contact between a sick person and a healthy person (this is how AIDS viruses are transmitted, for example). Another way is from the blood of a sick person to the blood of a healthy person, for example through a blood transfusion that has not been properly tested or following the use of syringe needles and surgical instruments that are not sterile.

There are viruses that usually cause relatively minor illnesses, but if they reach the fetus in the womb, they may cause severe damage and disability. Such are, for example, the rubella viruses and also the recently published Zika viruses, which are feared to seriously damage the development of the fetal brain.

The most effective way to deal with the spread of viral diseases is to prevent them with an appropriate vaccine.

Did you know?

Rabies viruses affect many species of mammals, not just dogs and humans. In contrast, the smallpox and polio viruses can only reproduce in humans. Therefore, if we succeed in vaccinating all the people on earth against these diseases, we can eradicate them once and for all. This is what happened with smallpox: this terrible disease - which probably killed more people than any other disease in history - was completely eradicated from the earth thanks to the vaccine. A great effort was made to eradicate polio as well, but still the success is not complete.

The article was published in the Galileo Young Monthly for curious children. For a gift digital sheet Click