RNA viruses

Both RNA viruses the entire genome consists only of RNA. However, it is not a single group of viruses. Their properties and propagation strategies are different.

What are RNA Viruses?

The term RNA virus is a collective term for a large number of viruses whose genetic material consists exclusively of RNA. Their propagation strategies are completely different. What all RNA viruses have in common, in addition to the RNA genome, is that they need a host organism to multiply.

Almost all plant viruses, many animal viruses and some bacteriophages are RNA viruses. Most of them have only one RNA strand. However, there are also double-stranded RNA viruses. Single-stranded RNA viruses can contain a minus-stranded RNA genome or a plus-stranded RNA genome. In some cases they also have a plus-minus strand. Minus strands are single strands of RNA that are built up in the opposite direction to translation. The reverse is true for the plus strands.

Minus strand RNA viruses contain a complementary single strand as a genome, which must first generate a plus strand for protein synthesis. For propagation, the minus strand is replicated in the plus strand. The plus strand creates a minus strand again. In the case of plus-strand RNA viruses, the single strand corresponds to the mRNA and can immediately synthesize virus protein. To multiply the virus, the complementary minus strand is first built up, which again serves as the basis for the synthesis of the next plus strand.

Retroviruses are a special form of RNA viruses. They incorporate their RNA genome into the host cell's DNA using the enzyme "reverse transcriptase". However, the ICTV (International Committee on Taxonomy of Viruses) does not count retroviruses among the RNA viruses, even though their genome consists of RNA.

Occurrence, Distribution & Properties

Viruses in general, and RNA viruses in particular, are ubiquitous. However, they cannot reproduce without a host organism and therefore infect it in several ways.

RNA viruses are the cause of such infectious diseases as influenza, rubella, polio, hepatitis E, SARS, dengue fever, Lassa fever or Ebola. The rotavirus or the norovirus is also one of the RNA viruses. The HI virus is probably the best known retrovirus.

The transmission routes of the individual viruses are very different. Influenza virus is transmitted through airborne droplets. Many intestinal viruses are passed on through smear infection. The risk of infection can be reduced here through hygienic measures. However, viral diseases that can easily be transmitted through the air, such as influenza, can lead to epidemics or even global pandemics in crowds.

Short-term vaccinations help against the current type of influenza, which can, however, change. Other diseases such as Ebola are partly present in the tropics and can be transmitted through diet with infected meat or body contact. The HIV virus is again difficult to transmit. Infection can only occur when body fluids such as blood or semen are exchanged.

Meaning & function

A virus infection always represents a health disorder of the body. This applies to both RNA and DNA viruses. Viruses of any kind cannot survive outside a host organism. So they are always dependent on a living organism for their reproduction.

Regardless of whether an infection with viruses, bacteria or fungi takes place, the body reacts with the formation of antibodies against foreign protein bodies. That is why it often happens that lifelong immunity occurs after infection with a certain pathogen. Only if the pathogen changes genetically can it repeatedly infect the same organism.

Bacteria, fungi and DNA viruses have double-stranded DNA in their genome. Mutations are relatively rare due to the double strand, since the DNA in the form of the second strand has a backup copy of the genetic code. Any errors in the replication of the DNA are usually eliminated by repair mechanisms.

This backup copy is missing in the case of RNA viruses. In addition, the host organism does not have an enzyme to repair errors in RNA replication. Mutations are constantly taking place in the RNA virus, which enable it to evade many of the body's defense mechanisms. Since the virus strains of RNA viruses are constantly changing due to mutations, it can be infected for life. A double infection with a genetically identical strain is usually not possible.

Illnesses & ailments

When infected with RNA viruses, different courses of the diseases can be expected. For the course of the disease, it plays a role whether systemically important organs are affected, which virus strain is currently active and what the general health situation of the person affected is. At the same time, it is also not insignificant how severely the infected cells are damaged.

The reaction strength of the immune system is also decisive for the course of the disease. A violent immune reaction can even worsen the situation if the body temperature rises too much and healthy cells are destroyed in addition to the diseased cells. A temperature that is too high would be a fever of over 40 ° C, which lasts for many hours. Only then are the body's own proteins affected by denaturation. Generally speaking, fever helps the body fight viruses.

Older people and young children in particular are usually at particular risk of dying from complications from influenza because their body's defenses are lower. In the Spanish flu in 1918, however, a particularly large number of young people and middle-aged people died, caused by a special type of influenza virus.

In the case of RNA viruses, due to the high mutability, there is always the risk of a particularly severe course. Furthermore, RNA viruses that are still insignificant today can mutate into highly infectious virus strains in the future. A preventive development of vaccines has so far been ruled out. The vaccine can only be developed for existing virus strains.

The particular tenacity of HI viruses is also due to their strong mutability. In the course of the HIV infection, the virus changes constantly so that it can constantly oppose the immune reaction of the organism.