Coronavirus: The pandemic-causing COVID-19 virus and how it infected 500,000 people
Within three months of first appearing in Wuhan, China, more than 500,000 people have now been infected with COVID-19 worldwide.
While this virus is new, the corona family of viruses has been studied within the human population since 1965.
This family of viruses are named corona because of the protein spikes protruding from the main body of the virus and their appearance under a microscope.
These spikes are used to gain entry to a cell by binding to human proteins in the lungs.
Tom Wileman, director of the biomedical research centre and professor of molecular virology at the University of East Anglia said: "It is thought that the precursor of COVID-19 was carried by bats or pangolins. The spike protein mutated to make a spike that that binds very strongly to a human protein. This allows the virus to get into human cells. The protein is called ACE and is found in the lungs and this is why it is a respiratory infection.
He added: "The big problem with Covid-19 is efficient transmission from human to human."
Once inside a cell, the virus turns the cell into a production factory which replicates the virus many times over before releasing those copies to infect other cells.
Coronaviruses are responsible for life threatening outbreaks SARS (2003), MERS (2012) and COVID-19, but there are also four varieties known to regularly infect humans which are responsible for mild symptoms resembling common colds.
All coronaviruses are zoonotic, meaning that they have been introduced into the human population by jumping from another species.
Bats are known reservoirs of several families of viruses, with SARS thought to have been passed from bats to civet cats, then to humans with MERS passed from bats to camels, before humans.
Markets filled with live animals stored in close proximity, as found in China, offer the perfect conditions for viruses to jump species.
The immediate aftermath of this transition is when viruses are at their most deadly, as they can then mutate and evolve over many years to become less deadly.
The reason this evolution takes place is that viruses are not spread most effectively when they are deadly.
Killing a host is not a desirable outcome for the virus, as this limits the opportunity for it to be transmitted to multiple new hosts.
Therefore, mutations which diminish the deadliness of a virus are the ones that stick, from an evolutionary perspective.
This is why a virus does not usually cause any noticeable symptoms when present within the animal from which the virus jumps into humans.
The virus has been present within the animal's population for years and has evolved to be carried by it, without harming it.
One widespread fear is that COVID-19 may mutate into something worse, but coronaviruses are comparatively slow to mutate.
Professor Wileman said: "The smaller RNA (genome) viruses use rapid mutation to avoid antibodies. Viruses that do not mutate rapidly (like coronaviruses) make proteins to stop the antibodies being made in the first place."
Influenza viruses are among those that rapidly mutate and are inaccurate in replicating their RNA genome.
These mutations are why you can catch flu more than once.
The virus mutates frequently as it replicates and when it has mutated sufficiently, your immune system will no longer recognise it.
Coronaviruses have a larger genome which is carefully replicated, leading to less mutations.
Theoretically, this makes is highly unlikely that someone would ever catch COVID-19 twice, but the novel nature of the virus means that this cannot yet be confirmed as absolutely certain.
The virus is, however, highly effective at transmitting between new hosts and this strength has created the pandemic we now face.
Despite that concern, the news is not all bad, as the virus has a weakness in having only a thin fatty envelope protecting it.
This is why hand washing with soap is so effective, as it doesn't simply wash the virus away, it breaks down this protective layer and kills the virus.
High transmission figures are clearly a concern, but mortality and transmission rates also directly impact one another, as high mortality rates drive down transmission.
This was seen in the SARS virus with its 14% mortality rate, which was largely contained within Asia.
The majority of MERS virus cases, which were fatal in 34.4% of cases remained confined to Saudi Arabia.
The mortality rate for COVID-19, which has become a global pandemic, is hard to pinpoint with many countries currently not testing those with mild symptoms.
However, China has 77,338 cases classified as concluded, with 4.4% of those infected having died.
With regular testing and by far the highest number of concluded cases of any nation, this figure represents a reasonable estimate.
It should be noted however, that some mild cases in China may have not been tested, meaning the true mortality figure could well be lower.
For more on the coronavirus, read here.
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