Around the world schools and offices are being closed, events are cancelled and hospitals are getting worried of being overloaded

This may seem like a movie, but it is all very real

This is the evolution of Coronaviruses

Coronaviruses are a group of related viruses that cause diseases in mammals and birds including pigs, camels, chickens, cows, cats, horses and humans

Most coronaviruses seem to originate from bats

But why bats?

Bats can fly, live in packed colonies and have a strong immune system

Their immune system could drive viruses to replicate faster

So, when the virus jumps to mammals or humans with a weaker immune system it can easily cause severe illness or even death

Sometimes coronaviruses can jump to other animal species or humans

The new coronavirus, SARS-CoV-2, that causes the disease called COVID-19, is thought to have originated from bats that may have infected pangolins before infecting humans

Previously, in 2012, another coronavirus causing MERS has jumped from bats to dromedaries before infecting humans

And similarly in 2002 the SARS coronavirus used civet cats as an intermediate host before infecting humans

A lot is still uncertain about these viruses and their origin

Viruses are so small that even with normal microscopes we can't see them

This makes them a kind of invisible threat

And their ability to mutate rapidly is also why it is very difficult to make a vaccine

It may take more than a year before there is a vaccine for COVID-19

A corona pandemic that most people haven't heard about is PED, Porcine Epidemic Diarrhea

The PED virus didn't infect humans, but killed approximately 7 million of pigs in the United States within one year

This is notable since pigs already live in a kind of lock-down, housed in different pens and with limited travel and strict hygiene to prevent transmission between farms

Still, the PED virus spread across the US

This was because the virus was extremely contagious and could survive up to 28 days on equipment and surfaces

By contrast, we may consider ourselves lucky, in a way, that the COVID-19 virus can probably only survive outside humans for up to three days

It is also surprising that the mortality rate of PED decreases with age

While the mortality rate for COVID-19 increases with age

In total there are 7 strains of human coronaviruses

Generally they produce mild symptoms of the common cold

However, three viruses can cause severe diseases

These are SARS, MERS and COVID-19

SARS and COVID-19 originated in China, and MERS was first discovered in Saudi Arabia

All of these diseases are similar in many ways

The transmission is mostly from person-to-person by a droplet spread when someone coughs or sneezes

Most infected people first get a high fever

Other symptoms for COVID-19 are dry cough, tiredness as well as some less common symptoms

Some people for all of these diseases develop a more serious illness featuring pneumonia

Pneumonia is an infection in the lungs

The air sacs may fill with fluid or pus, causing cough, fever, chills and difficulty breathing

The SARS outbreak mostly affected Asia and resulted in 8,000 cases in 2002 and 2003

MERS mostly affected the Middle East and resulted in 2,500 cases in 2012 until now

MERS is still active although currently there isn't an outbreak

The pandemic of COVID-19 already affected most of the world with more than 540,000 cases as of march the 27th

The mortality rates are very different

SARS has a mortality rate of 10%, MERS as high as 34% and COVID-19 between 3 and 4%

This resulted in 774 deaths for SARS, 866 death for MERS and more than 24,000 deaths for COVID-19 so far

COVID-19 is easily the scariest of the three and we've no idea where it will end

One thing we do know is that everyone must contribute to control how much the virus will spread

Step 1, Hygiene: wash your hands frequently with soap, cough in your elbow and avoid touching your face

Step 2, Social distancing: keep distance, stay home as much as possible and avoid crowded places especially if you've any symptoms

This way we make sure our healthcare systems have enough capacity to help all the sick people and less people will die

The only way we can overcome this pandemic is by working together globally