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Hot, cold, damp? What viruses need to survive

What viruses need to survive

Does the corona virus go down as temperatures rise? Virologist Thomas Pietschmann explains why spring really gives hope and why women have a clear advantage in the fight against the viral disease.

The hope is that everything will get better in spring. If it goes well, this new coronavirus, also known as SARS-CoV-2, behaves  like the influenza virus. Then spring with its rising temperatures would put an end to the pathogens – and the ghost would be over. The coronavirus season would have spilled over us and ebbed away just like the flu wave every year when winter comes to an end.

So much for hope. Virologists like Thomas Pietschmann, however, can not say whether SARS-CoV-2 behaves as desired “strictly speaking and honestly not yet because we do not yet know the virus.”

Pietschmann is a molecular virologist and conducts research at the Center for Experimental and Clinical Infection Research, called Twincore, in Hanover. He deals with so-called RNA viruses – the hepatitis C virus is one of them. And SARS-CoV-2 also belongs to this group.

Virus? Unknown!

“The special thing about this virus is that humans are confronted with it for the first time. From the data that we have from China, it can be concluded that the virus has only passed from animal to human once and has spread from there spread, “says Pietschmann.

In other words, unlike influenza viruses, which almost everyone has had contact with at some point, our immune system is not prepared for an attack with corona pathogens. 

In addition, the external conditions in the northern hemisphere are currently perfect for the rapid spread of viruses. First, there is the temperature. Respiratory viruses, i.e. those that spread through the respiratory tract, are particularly easy to play when it is cool. “Viruses are more stable at low temperatures. Similar to foods that have the longest shelf life in the refrigerator,” explains Pietschmann. 

Cool and dry, please!

The warmer it gets, the more difficult the conditions for many viruses. “The corona virus is surrounded by a lipid layer, ie a layer of fat,” says Pietschmann. This is not particularly heat-resistant, so that the virus breaks quickly with rising temperatures. “Other viruses, such as the norovirus, are much more stable because they mainly consist of proteins and genetic material.”

For other pathogens, the temperature also only plays a minor role. So come dengue viruses found mainly in tropical and subtropical regions. This is not so much because dengue pathogens like to be warm; rather, the hot areas are the preferred habitat of the mosquitoes that transmit the virus. “In this case, it is not the temperature that plays the main role in spreading the pathogen, but the animal that transmits the virus,” says Pietschmann.

Humidity also has a major impact on the portability of respiratory viruses. Once the pathogens have been removed from the airways with a strong sneeze, they literally hang in the air. “On cold and mostly dry winter days, the small droplets, together with the viruses, float in the air longer than in high humidity,” says Pietschmann.

In this way, the pathogens can spread rapidly. However, first of all they do it quietly and secretly. A few weeks can pass from the first contact with the pathogens to the first symptoms of the disease. The length of this so-called incubation period depends on the properties and the biology of the virus. 

Double X chromosome and estrogens

Fever, pain, and chills are typical symptoms of a viral disease and a sign that the body is fighting the invaders. How successful this fight depends not only on the age and state of health of the infected person but also on their gender. In the case of the coronavirus, too, the numbers show that women have significantly better cards than men: the mortality rate of 2.8 percent is significantly higher than that of women at 1.7 percent.

“On the one hand, there are genetic reasons for this,” says Pietschmann, “because some genes relevant to the immune system, for example, genes that are responsible for recognizing pathogens, are encoded on the X chromosome.” Because women have two X chromosomes and men only one, the female gender has the advantage here. 

The female sex hormone estrogen also helps women to defend themselves against the viral disease. “Some immunologically relevant genes also have binding sites for estrogens, where these genes are switched on. This means that these genes are also controlled by the hormones,” explains Pietschmann. 

Perhaps the corona season actually ends with the beginning of spring in the northern hemisphere. However, according to the World Health Organization (WHO), there is now a case of SARS-CoV-2 in Brazil, in the southern hemisphere. Then winter is yet to come.

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