Understanding Coronaviruses: From SARS to COVID-19

For nearly a decade, scientists embarked on a quest through China's towering mountains and secluded caves, ultimately discovering the source of a deadly virus in the bats of Shitou Cave. This virus, a coronavirus, triggered the Severe Acute Respiratory Syndrome (SARS) epidemic in 2003. But what exactly is a coronavirus, and how does it propagate?

What are Coronaviruses?

Coronaviruses are a family of viruses characterized by protein spikes on their surface, resembling a crown, or "corona" in Latin. There are hundreds of known coronaviruses, with seven capable of infecting humans and causing disease.

• SARS-CoV causes SARS.
• MERS-CoV causes MERS.
• SARS-CoV-2 causes COVID-19.

Four of these coronaviruses lead to common colds – mild, highly contagious infections of the nose and throat. The remaining three can infect the lungs, leading to more severe illnesses. COVID-19 exhibits characteristics of both, spreading easily while also severely impacting the lungs.

How Coronaviruses Spread

When an infected individual coughs, droplets containing the virus are expelled. These droplets can infect others upon entering their nose or mouth. Coronaviruses thrive in enclosed spaces where people are in close proximity.

• Cold weather helps preserve the virus's casing, allowing it to survive longer.
• UV exposure from sunlight can damage the virus.

While seasonal variations affect established viruses, new viruses like COVID-19 can spread rapidly due to a lack of immunity in the population.

How Coronaviruses Infect Cells

Once inside the body, the protein spikes on the virus embed into the host's cells, fusing with them. This allows the virus to hijack the cell's machinery and replicate its own genes. Coronaviruses store their genes on RNA, making them RNA viruses.

RNA vs. DNA Viruses

RNA viruses are typically smaller with fewer genes, enabling them to infect many hosts and replicate quickly. Unlike DNA viruses, RNA viruses generally lack a proofreading mechanism. This leads to more frequent mutations during replication.

• Many mutations are useless or harmful.
• Some mutations can make the virus better suited for new environments or hosts.

Epidemics often arise when viruses jump from animals to humans, as seen with Ebola, Zika, SARS, and COVID-19. Even within humans, viruses continue to mutate, creating variations or strains of the original virus.

Key Differences in Coronaviruses

Coronaviruses differ from most RNA viruses in several key aspects:

1. They are among the largest RNA viruses, possessing the most genes.
2. They have an enzyme that checks for and corrects replication errors, making them more stable with a slower mutation rate.

Implications of Slower Mutation Rate

The slower mutation rate is a promising sign for developing effective treatments. After infection, our immune systems can recognize and destroy germs more efficiently upon re-exposure. However, mutations can make a virus less recognizable, hindering our immune response and reducing the effectiveness of antiviral drugs and vaccines.

Unlike the influenza virus, which requires a new vaccine each year due to its rapid mutation rate, the slower mutation rate of coronaviruses suggests that our immune systems, drugs, and vaccines might offer longer-lasting protection.

The Future of Coronavirus Research

Despite these advantages, the duration of immunity to different coronaviruses remains unknown. Currently, there are no approved treatments or vaccines for coronaviruses. While treatments were being developed for SARS and MERS, the epidemics ended before clinical trials could be completed.

As we continue to encroach on animal habitats, the emergence of new coronaviruses is likely inevitable. However, by investing in research and understanding these viruses, we can mitigate their devastating impact and better prepare for future outbreaks.