Can we survive without human contact?
How long viruses can survive
Flu, cold, diarrhea - no one is armed against typical viral diseases like these. The small pathogens can often pull us out of circulation for weeks. Viruses are not even living beings of their own because they have no metabolism. Rather: "Viruses are nothing more than genetic information that is packaged in a protein shell," explains Monika Redlberger-Fritz, virologist at the Medical University of Vienna.
Viruses therefore always need a host cell in order to reproduce. This is used to reproduce itself, after which it is destroyed in many cases. The result: Depending on which part of the body the host cell is located in, different symptoms such as runny nose or diarrhea occur.
How fast viruses spread depends on several factors. One comes closest to the answer if one takes a closer look at the transmission path - direct contact, air or blood. "Viruses that are transmitted via aerosols or smear infections can spread much faster than viruses that are passed on through blood contact - because this is not always there," says Heribert Stoiber, virologist at the Virology Section at the Medical University of Innsbruck.
Slow virus infection
Viruses rarely hide in the body and only start to spread years later. This occurs when the host cell does not die, but instead passes the virus on to the daughter cell. "You always need an initial infection, but you don't necessarily notice it due to the lack of symptoms," explains Stoiber.
This so-called slow virus infection can occur with measles, for example: When infected, the measles virus withdraws into the brain cells, remains hidden for years and starts to replicate from there - which leads to complications. The process is similar with the HPV virus (human papillomavirus), which takes many years before it can cause cervical cancer. A typical example of what is known as latent infection is herpes simplex: The small cold sores caused by HSV come and go at irregular intervals because the virus stays in the body.
From hours to weeks
There is also no general answer to how long viruses survive on the surface. One thing is certain: not for very long, because they need a host cell to be viable. The structure of the virus is decisive. "There are so-called enveloped and non-enveloped viruses," explains Stoiber. In this case, envelope means that the viruses have an additional lipid layer on the outside. Those viruses that are not enveloped by this layer of fat - that is, they are virtually not enveloped - are more resistant to environmental influences.
The temperature also plays a role. "In general, there is a rule of thumb that says: the colder it is, the longer viruses can remain infectious on the surface," explains virologist Redlberger-Fritz. This is probably also the reason why flu and colds are more easily transmitted in winter. Conversely, this means: the higher the temperatures, the less likely it is that viruses will survive. Knowledge of the heat sensitivity of viruses is used when working in the laboratory, where viruses can be stored for research purposes at minus 70 or 80 degrees Celsius for decades in order to keep them functional.
How long can coronaviruses survive?
How long coronaviruses can survive cannot be answered across the board either. Researchers from the Institute for Hygiene and Environmental Medicine at the University Medical Center Greifswald and scientists from the Department of Medical Virology at the Ruhr University Bochum found in a study that individual representatives of the coronavirus can stay on surfaces and remain infectious for up to nine days. How long the new Sars-CoV-2 coronavirus will remain on surfaces is currently unclear. If you cough or sneeze into your hand and then touch a door handle or touch your phone and pass it on, the virus can theoretically be transmitted in this way, according to the Austrian Agency for Health and Food Safety (Ages).
The Austrian Ministry of Health refers to the current state of research, according to which it is assumed that Sars-CoV-2 can survive on inanimate surfaces such as metal, glass or plastic for up to nine days. However, the pure "detectability of a pathogen is not necessarily relevant from an epidemiological point of view, rather the achievement of the minimum infection dose necessary for an infection is decisive. This is still unclear for SARS-CoV-2."
Often only symptoms can be treated
The lifespan of viruses also depends on the type of virus and the transmission route. In the case of respiratory viruses, i.e. viruses which can be transmitted by contact or droplet infection and often affect the respiratory tract, the lifespan is in the range of a few hours. There are no exact figures. On the other hand, noroviruses that cause gastrointestinal complaints can survive for longer periods of time. On certain surfaces for several days or weeks, for example on carpets.
Because there is no precise information about the survival time of viruses, it is important to protect yourself as well as possible, experts advise. Because: Once the virus has been caught, treatment is difficult. This is because viruses do not have their own metabolism and drugs always damage the body's cells.
Therefore, often only the symptoms are treated and waited until the immune system itself destroys the pathogen. For a few viral infections such as hepatitis B and hepatitis C, HIV or herpes simplex, there are now antiviral drugs, so-called antivirals. These take targeted action against viruses. Resistance to these preparations has so far only occurred to a relatively low extent.
Properly protect against viruses
How do you protect yourself against viruses? Virologists still advocate adequate hygiene such as frequent and thorough hand washing, for example after using the toilet. The reason for this is that gastroenteritis viruses last a very long time and even small amounts are sufficient for an infection.
You can protect yourself against viruses that are transmitted via droplet infection with mouth masks. Viruses that can be transmitted through sexual contact can be prevented with condoms and antiretroviral drugs. "Vaccinations prevent many viruses in the environment", says Stoiber and at the same time points out the increasing "vaccination fatigue" in Austria. This is the only way to avoid diseases such as measles or hepatitis B infections. (Maria Kapeller, August 29, 2017)
Article update on February 27th, 2020 with the information about the coronaviruses
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