UNRESERVED Exclusive: An Expert's Opinion on What Exactly is A Coronavirus
Wuhan, December 2019
One person goes to hospital withfever, headache, slight cough, muscle aches.
Another person comes in with similar symptoms.
Then another, then another…
A chest X-ray is not normal, test results are negative for influenza or other viruses.
Persons infected become a group; these groups become a cluster, then even more clusters are formed, all suggesting the presence of a previously unidentified microbial agent requiring urgent medical interventions.
This is how a mysterious outbreak begins.
The present outbreak of respiratory infections is the third “spillover” of an animal coronavirus to humans resulting in an epidemic, within a span of only two decades.
On February 2020, the World Health Organization (WHO) declared this outbreak a “Public Health International Emergency” caused by a novel coronavirus. The previous nomenclature of 2019-nCoV has now been replaced with its official name “SARS-CoV-2”, while COVID-19 is the name of the disease or illness the virus causes.
Novel outbreaks from any microbe should always be a matter of public health concern. The risks from these outbreaks depend on the characteristics of the microbe, the host it infects and the setting where the infection occurs. This is known as the epidemic triangle. In emerging microbial outbreaks, the interplay between these three factors is complex, requiring a refined understanding and close monitoring of the outbreak to produce the best possible plans and precautions, without needless panic.
Microbes are micro-organisms which are found in most living materials and play a major role in maintaining the Earth’s ecosystem. Micro-organisms are characterised by their cellular composition, structure and means of reproduction and are categorised into several types, including bacteria and virus.
They display a variety of complex relationships with other micro-organisms and larger forms of life that serve as host for them. In fact, our bodies are host to millions of these microbes, but most of them do not cause disease and indeed, many are beneficial.
Occasionally, however, pathogenic microbes can cause illnesses. Pathogens differ from normal non-pathogenic microbes in that they cause damage to the host. Pathogens invade and colonise novel sites, antagonise the host’s immune response, facilitating the spread of the infection. As a result, disease occurs when signs and symptoms of an illness appear.
Animals also play host to pathogens. In the past 50 years, a host of infectious diseases has spread rapidly, after making the evolutionary jump from animals to humans, resulting in a type of disease called a zoonosis. Zoonotic transmissions are common and cause many different types of illnesses in people and animals, ranging from mild to serious. Dengue, for example, is a mosquito-borne disease endemic in many countries in Southeast Asia. However, the emergence of novel zoonotic infectious diseases such as HIV/AIDS in the 1980s, the avian and swine flu pandemics in the 2000s, and the Ebola epidemic of 2014 have exposed the extent of human vulnerability to new zoonotic health threats.
But what exactly is a coronavirus?
Coronaviruses are so named because they look like halos (known as coronas, Latin for “crown”) when viewed under the electron microscope. The first coronavirus was isolated in 1937 while human coronaviruses were first identified in the mid-1960s. There are seven coronavirus strains that can infect humans and while the term coronavirus was initially unfamiliar to many, most of us have encountered milder forms of such viruses. The 229E, NL63, OC43, and HKU1 strains, are known as the “common” human coronavirus, and until recently, rarely caused any disease more serious than a common cold.
Coronaviruses also utilise animals as their primary hosts including camels, cats and bats. Since its discovery, related coronaviruses have been found to infect cattle, pigs, horses, turkeys, cats, dogs, rats and mice. Rarely, animal coronaviruses can evolve to infect other people via a process known as a spillover.
This occurs when the virus mutates (giving the virus new powers and abilities) while increased contact between animals and humans facilitates the jump from animals to humans, becoming a new (novel) human coronavirus. This was the case for SARS-CoV, MERS-CoV and now, the newly-crowned SARS-CoV2.
Long known to cause upper respiratory infections, coronaviruses were not known to significantly cause pneumonia (the infection of one or both lungs), that is, until the SARS (SARS-CoV) outbreak in 2002. This outbreak is believed to have started when a coronavirus jumped from civet cats to humans. Coronaviruses’ propensity for such jumps was underlined in 2012, when another virus (MERS-CoV) was transmitted from camels to humans, causing MERS.
In December 2019, a cluster of acute respiratory illnesses, then referred to as “novel coronavirus-infected pneumonia” occurred in Wuhan, Hubei Province, China. On 3 January 2020, a novel coronavirus, SARS-CoV2, was confirmed as the cause of the infection. Similar to SARS-CoV and MERS-CoV, bats were the original host for SARS-CoV2. A genetic analysis early in the outbreak of COVID-19 in China revealed that the virus was similar to, but distinct from, SARS-CoV. While the first animal-human transmission of SARS-CoV2 is still being investigated, current evidence suggests that the outbreak may have begun at the Huanan Seafood Wholesale Market in Wuhan, where wild animals were sold illegally. The virus likely had an intermediate host, just as SARS-CoV and MERS-CoV had crossed from civet cats and camels to infect humans.
