THE bat is the known “villain” in the current Covid-19 episode. Of course, not to mention the ultimate villain, that is homo sapiens (human beings) and their appetite for exotic meat.
While everyone now knows that bats are the reservoir of SARS-CoV-2, the virus that is wreaking havoc globally, the virus seemed to have made a transit before finding its home in human. It is not snake as previously thought.
[ihc-hide-content ihc_mb_type=”show” ihc_mb_who=”2,3,5″ ihc_mb_template=”1″ ]A few scientists cracked the mystery on how the virus jumped from bats to humans. Their findings published in Nature Medicine, reports pangolins might be the intermediate hosts for this virus. It is important to understand where the virus came from and how it evolved to develop drugs against it.
Scientists studied coronavirus in Malayan pangolins (Manis javanica) seized during anti-smuggling operation in Southern China. The anteaters are the most common mammal smuggled for use as food and medicine. The Huanan seafood market is known for exotic meat. But since the market was quickly closed after outbreak of Covid-19, it became a challenge to determine the source of the virus. The scientists studied the virome composition (the viruses that found in an organism) in pangolins that they received between Aug 2017 – Jan 2018.
Samples were taken from lungs, blood, intestine and scales. The genome (genetic makeup) of the viruses were studied and it revealed that there were six types of coronaviruses in Malayan pangolins.
The novel coronavirus found in pangolins shares 85.5% to 92.4% genome sequence similarity to SARS-CoV-2. They also share similar evolutionary patterns. The spike proteins in SARS-CoV-2 also show 97.4% amino acid similarity to the coronavirus found in these pangolins. Spikes are found on the surface of the virus and are responsible for latching onto host cells to start infecting the host which leads to replication of more viruses. Amino acids are building blocks of proteins.
Diseased pangolins in Guangdong were also studied in 2019 and the findings also supported the possibility of pangolins being the most probable intermediate host of SARS-CoV-2 before reaching humans. Coronaviruses in Guangdong pangolins and SARS-CoV-2 possess identical amino acids at the five critical residues of the binding site in the spike.
The scientists concurred that more studies are needed to determine whether the similarity between coronavirus on pangolins acquired from Guangdong and SARS-CoV-2 is due to independent evolution or a process of recombination of genes. Organisms evolve independently to acquire similar traits to adapt to similar environmental conditions.
The coronavirus latches to ACE2 receptor which is found on the surfaces of hosts’ cells. The similarity of ACE2 is higher between humans and pangolins (84.8%) than those between humans and bats (80.8% – 81.4%). This is another finding that supports pangolins as the intermediate host. However, all pangolin coronaviruses lack a cleavage site that is found on SARS-CoV-2. The cleavage site is specific site on its spike that facilitate infection. This might be the reason for them to evolve and spread quickly to human for survival. Besides bats, pangolins are the only mammals documented to be infected by a SARS-CoV-2 related coronavirus to date.
But how did pangolins effectively become the intermediate host is still surprising as they are solitary animals and is a very small population. More investigations on viral diversity in this animal and how they are transmitted are needed to nail this. The outbreak of Covid-19 in Guangxi and Guangdong provinces may point to pangolins playing a big role.
These scientists suggest that many other wild mammals in Asia might carry coronaviruses and they need to be handled carefully. They also call for their sales in wet markets to be prohibited.
The scientists are from universities in China, Hong Kong and Australia.pd
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