Explained: Why Covid-19 Is More Potent Than SARS?

Seventeen years ago, in 2003, China reported the outbreak of Severe acute respiratory syndrome (SARS). The epidemic affected 26 countries and had over 8000 cases. The SARS is caused by the same family of the virus as COVID-19 and has very similar symptoms. Yet it did not reach the same numbers as the ongoing coronavirus pandemic. What made it different?

A laboratory technician from Dr. Dangs Lab displays a coronavirus testing tube for a drive-through service during a government-imposed nationwide lockdown as a preventive measure against the COVID-19 coronavirus, in New Delhi on April 7, 2020. (Photo by Sajjad HUSSAIN / AFP)

Seventeen years ago, in 2003, China reported the outbreak of Severe acute respiratory syndrome (SARS). The epidemic affected 26 countries and had over 8000 cases. The SARS is caused by the same family of the virus as COVID-19 and has very similar symptoms. Yet it did not reach the same numbers as the ongoing coronavirus pandemic. What made it different? Coronavirus family The coronavirus comes from a family of viruses that can infect human beings and mammals such as cattle, pigs, cats, dogs, etc. There are also coronaviruses that infect animals such as cats and dogs but have no effect on humans. The current pandemic is caused by the novel coronavirus (SARS-CoV-2) which was transferred by animals to humans. The infection emerged in China’s Hubei province in 2019. So far, the virus has caused around 1,431,900 cases of infection and over 82,172 deaths (CSSE, John Hopkins data). The SARS coronavirus (SARS-CoV) was identified in 2002 and the first case of SARS infection was reported from Guangdong province of southern China. According to research, it had a similar transmission route as the novel coronavirus. The virus transferred from bats to possibly civet cats before jumping to humans. Similarly, the MERS (MERS‐CoV) is another coronavirus that was identified in Saudi Arabia in 2012. 27 countries have reported cases of MERS including Algeria, Austria, Bahrain, China, Egypt, France, Germany, etc.  Out of all the cases, 80 percent was reported from Saudi Arabia. The symptoms of infection caused by the virus are similar to variations in severity and the time of incubation of the virus. There are no drugs or vaccines available for the cure or prevention of all three infections. The answer lies in how it spreads According to the current research, what makes the novel coronavirus deadly is the way it spreads. Viruses are non-living entities almost like zombies which replicates once inside a living being. The coronavirus family has evolved to attach the human cell with its spike proteins (remember corona helmet?). Once inside they take over the cell’s mechanism. In the case of coronaviruses, travel through air droplets and attach to cells in our respiratory system. In the case of the SARS virus, it will go to the upper respiratory system and replicate quickly. This caused the infected person to show symptoms quickly, making it easier to put them in quarantine faster. But in the case of the novel coronavirus (SARS-CoV-2) the virus attaches to throat cell first. At this point, the person may not show any symptoms and without any knowledge of the condition can transmit it to others. By the time the infection manifests itself, the person has infected several people with the virus. This is despite SARS having a greater Ro (a term used to measure how contagious an infectious disease is and the average number of people who will be infected by a contagious person) which is one person can infect over 3 people while for Covis-19  it is 2-2.5. But since SARS could be contained faster, the spread was comparatively slower. This is the reason why preventive measures such as social distancing become imperative to stop the spread of novel coronavirus. This is not the first animal transmission Cases of Zoonotic diseases have been around through the ages and some of them have been responsible for large scale fatalities.

• Black Death: This is caused by the bacterium Yersinia pestis which is carried by fleas in rats. The pandemic is supposed to have caused over 60 percent reduction in medieval Europe’s population. An overhaul of sanitary infrastructure in Europe helped overcoming the disease.
• AIDS: The condition is caused by the Human immunodeficiency viruses (HIV). According to research this virus may have jumped from Chimpanzees to humans. The original reservoir for this virus may also have been bats.
• Spanish Influenza: This deadly pandemic lasted from 1918 to 1920 and had infected over 500 million people around the world. The virus causing the disease is supposed to have transferred form birds to horses and then to humans.
• Bird Flu: This is can infect both birds and humans. The most common virus causing it is H5N1 which appeared in China in 1999.

So, what is causing an increase in outbreaks? According to experts, destructive human activities such as deforestation, poaching, clearing land jungles for industrial agriculture are leading to exposure to pathogens that earlier did not have much access to humans. The loss of habitat of many wild animals is causing it to come closer to human settlements. This proximity increases the likelihood of the transmission of such viruses. Apart from this, legal and illegal wildlife trade such as what is prevalent in China is also creating a risk for species jumping pathogens that can eventually infect a human.