Why Does COVID-19 Primarily Affect Humans?

When discussing the reasons for why the SARS-CoV-2 virus primarily affects humans, it is often mistakenly believed that COVID-19 only infects them. However, this belief is not entirely accurate. In reality, the virus can infect a variety of animals, including bats, pangolins, minks, dogs, cats, and even deer. The reason for its preference for human infection lies in the specificity of its receptor, the ACE-2 receptor. This article will delve into the intricacies of this receptor and explain why the virus is highly optimized for infecting humans.

The ACE-2 Receptor and Its Role in Infection

The SARS-CoV-2 virus primarily gains entry into cells through the ACE-2 receptor. These receptors are widely present in the nasal and oral mucous membranes, the lining of the gut, the lung airways, and blood vessels. While it has been documented that the virus can infect many animals other than humans, such as cats, small and large dogs, and even tigers, it is particularly optimized for human cells due to the specific affinity between the SARS-CoV-2 spike protein and the ACE-2 receptor in humans.

The Spike Protein and Its Furin Cleavage Site

The SARS-CoV-2 spike protein is designed to maximize its affinity for the human ACE-2 receptor. This affinity involves a protease called furin, which is common in humans. Furin cleavage in the spike protein is crucial for the virus to infect human cells effectively. On the other hand, although the virus can infect other mammals such as bats, it is not nearly as efficient due to the differences in their ACE-2 receptors. This is why the SARS-CoV-2 virus is so specific to humans and why it can spread rapidly among them.

Other Infected Animals and Their Receptors

While it is clear that not all animals are susceptible to the SARS-CoV-2 virus, recent studies have shown that the virus can infect a range of other species. For example, cats, minks, and even some big cats like tigers have been observed to be infected. This suggests that while the virus has a higher affinity for the human ACE-2 receptor, it can still infect similar receptors in other animals, albeit with varying degrees of efficacy.

Conclusion

In summary, while the SARS-CoV-2 virus does not only affect humans, it is particularly well-suited for infecting human cells due to the high affinity of the ACE-2 receptor in humans for the virus's spike protein. The specifics of this receptor and the presence of the furin cleavage site make the virus highly optimized for infecting humans, even though it can infect other animals. Continued research will help us better understand the full extent of the virus's reach and the specificities of its interaction with various ACE-2 receptors.

References:

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