|Year : 2020 | Volume
| Issue : 3 | Page : 234-238
History and Origin of Coronaviruses
Department of Cardiology, AIIMS, New Delhi, India
|Date of Submission||14-May-2020|
|Date of Decision||14-Aug-2020|
|Date of Acceptance||26-Sep-2020|
|Date of Web Publication||23-Dec-2020|
Dr. Pooja Bhardwaj
Department of Cardiology, AIIMS, New Delhi
Source of Support: None, Conflict of Interest: None
Objective: The coronavirus disease 2019 (COVID-19) also known as COVID-19 or severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a viral infection caused by severe acute respiratory syndrome coronavirus 2, emerged first in Wuhan, China, and spread all over the world. The World Health Organization on January 30, 2020, officially declared the COVID-19 epidemic as a public health emergency of international concern. There is speculation as to the origin of the infection and the objective of this narrative review is to scan the available literature to create a cohesive review. Methodology: This review article is based on a literature search of PubMed, Google, and Google Scholar using the keywords “ Corona virus,” “COVID-19,” “COVID” “Origins,” “Review,” and “classification.” Articles providing new information were selected. Results: The coronavirus which has caused a pandemic has a genomic structure which closely resembles that of a bat coronavirus. The region that binds angiotensin-converting enzyme 2 (ACE2), i.e., the region of the spike proteins, resembles a coronavirus found in the pangolin (a scaly anteater found in the Chinese market and used in Chinese medicine). It is possible that the coronavirus was existing initially in its natural hosts, the bat, or pangolin. It is likely that the spike proteins mutated to bind to molecules similar to the human ACE2 protein therefore allowing it to infect humans. Another possibility is that it jumped species from bat to human and then became capable of causing pathogenic disease. The mutations in the receptor-binding domain portion of the spike protein and its distinct backbone, rules out laboratory manipulation as a potential origin for SARS-CoV-2. It is not certain if the necessary mutations for causing the pandemic occurred before or after SARS-CoV-2 made the jump to humans. Conclusions: The current corona pandemic is due to the SARS-CoV-2 and there is evidence that it has spread to humans from bats. Pangolins, civet cats may be reservoirs for the virus, but as of now, there is no evidence of a laboratory origin of the virus. It is not clear whether the virus jumped species recently or was preexisting in humans and became pathogenic because of a recent mutation.
Keywords: Bats, coronavirus, origin of coronavirus, pangolin, SARS-CoV-2, wet market China
|How to cite this article:|
Bhardwaj P. History and Origin of Coronaviruses. J Pract Cardiovasc Sci 2020;6:234-8
| Introduction|| |
Coronaviruses are RNA viruses that are found in both mammals and birds. In humans, they cause respiratory tract infections. On electron microscopy, they have club-shaped spikes that project from their surface, which creates an image like a solar corona. In 1968, the word coronavirus was used to designate the new family of viruses by a group of virologists in the journal nature.,
In the 1930s, coronavirus was first described when an acute respiratory infection of domesticated chicken was found to be caused by the infectious bronchitis virus (IBV). It was described as a new respiratory infection of chicken in North Dakota by Arthur Schalk and Hawn in 1931.. It was in 1937 that Fred Beaudette and Charles Hudson successfully isolated and cultivated the IBV that caused the disease in 1930.
Later, in the 1940s, mouse hepatitis virus and transmissible gastroenteritis virus, the two other types of animal coronaviruses, were isolated. In 1960, the human coronaviruses were discovered and first imaged at the St. Thomas Hospital, London, by a Scottish Virologist June Alminda.
| Methodology|| |
In this narrative review, we are tracing the origin of the current corona epidemic by searching published literature using the keywords “Corona”, “Covid”, “Covid-19”, “Origin”, “molecular epidemiology”, “zoonosis”, “bats”, and “Review” in the search engines Google, Google Scholar, and PubMed. The initial 176 articles, blogs, webinars, and websites were screened to search for relevant information, and only articles providing the first reports of the origin of the virus or giving a critical commentary based on available literature were selected.
| Results|| |
We discuss very briefly the characteristics and types of coronavirus, history of the pathogenesis of the coronaviruses, and then the origin of the current corona pandemic.
Characteristics and types of coronavirus
Coronavirus are enveloped viruses with a single-stranded RNA as nucleic material. They are spherical with bulbous surface projections with a diameter of around 125 nanometers (0.125 microns, an N95 mask blocks 95% of 0.1–0.3 micron NaCl particles). Six species of human coronavirus are known, with one species subdivided into two different strains, making seven strains of human coronavirus altogether.,,
Four human coronaviruses produce symptoms that are generally mild:
- Human coronavirus OC43 (HCoV-OC43), β-CoV
- Human coronavirus HKU1 (HCoV-HKU1), β-CoV
- Human coronavirus 229E (HCoV-229E), α-CoV
- Human coronavirus NL63 (HCoV-NL63), α-CoV.
Three human coronaviruses produce symptoms that are potentially severe:
- Middle East respiratory syndrome-related coronavirus (MERS-CoV), β-CoV
- Severe acute respiratory syndrome coronavirus (SARS-CoV), β-CoV
- Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), β-CoV.
Of these 4 kinds of coronavirus subgroups, gamma and delta coronaviruses infect birds and beta coronaviruses infect mammals. α-CoV HCoV-229E and HCoV-NL63, β-CoV HCoVHKU1, and HCoV-OC43 are having low pathogenicity and cause mild respiratory symptoms such as the common cold. β-CoV like SARS-CoV and MERS-CoV cause severe respiratory infection and are fatal to human beings.
The timelines of the discovery of these viruses were [Table 1]:,,,,
- 2003-SARS-CoV (severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1)
- 2004-HCoV-NL63 is a species of coronavirus that was identified in late 2004 in a 7-month-old child with bronchiolitis in the Netherlands)
- 2005-HKU1 (first discovered in January 2005 in two patients in Hong Kong)
- 2012-MERS-CoV MERS-CoV infects humans, bats, and camels
The coronavirus pathogenesis
The very first case of coronavirus was reported as early as in 1960. According to a Canadian study in 2001, nearly 500 people were infected and had flu-like symptoms. Of them, 17–18 cases were reported and confirmed to have coronavirus strain. Till 2002, coronavirus was not proved as fatal.
In 2003, people of Gaungdong, China, started having symptoms of pneumonia due to the viruses, leading to acute respiratory distress syndrome and death, which was then reported as SARS-CoV. There were different proofs and reports of spread of this virus in the United States, America, Hong Kong, Singapore, Thailand, Vietnam, and Taiwan. It was reported that 8000 people were infected and 766 deceased.
In 2012, in Saudi Arabia, people were diagnosed with SARS-like symptoms and later it was named as Middle East respiratory syndrome coronavirus (MERS-CoV). More than 2428 people were infected and 838 died because of this virus.
In 2019, December, the Wuhan city of China was attacked by the coronavirus again, which killed more than 18,000 people and infected over 70,000 individuals in the first 50 days of the epidemic. It was reported that possibly the spread was related to the Seafood Market.
The authorities in China then informed the World Health Organization (WHO) about increased pneumonia cases of unknown etiology. The WHO on January 30, 2020, officially declared the COVID-19 epidemic as a public health emergency of international concern. It was investigated and then found that this virus belongs to the beta coronavirus group.
Origin and evolution of coronavirus
At the beginning of SARS 2003, the patients diagnosed with the disease were found to have animal contact before they were infected with the virus. Once virologists got to know about the causative agent of SARS, SARS-CoV, or anti-SARS-CoV, antibodies were found in the masked palm civets and the people who were handling the animals in the marketplace.,, However, later, after thorough investigations on the farmed and wild palm civets, it was found that they were just the intermediate host, and the strains of SARS CoV found in them were transmitted to them by other animals.
In 2005, a novel coronavirus related to humans was discovered and named as SARS-CoV-related or SARS-like coronavirus, in horseshoe bats. With this discovery, it was reported that civets might only the intermediate host and bats were the natural host.,
Coronavirus disease 2019 (COVID-19) or SARS-CoV-2 was first identified in December 2019 in Wuhan, China, and the first case can be traced back to 17 November, 2019. The WHO declared the COVID-19 outbreak a public health emergency of international concern on 30 January 2020 and a pandemic on 11 March 2020. By 31 May 2020, more than 6.05 million cases had been reported around the world.
The origin of the outbreak was initially linked to the Huanan Seafood Wholesale Market. There were also initial reports from China that the coronavirus was found in the animal section of the market (Wuhan report). The first patient apparently did not have exposure to the market. Fourteen of the first 41 patients also were not exposed to this market. Hence, it is possible that the virus was already around, but was somehow amplified in this market.,
Sixty-six percent of the 41 patients had had exposure to the seafood market (where different types of snakes, marmots, poultry, and bats and other animals were sold illegally) and it was presumed that the infection had come from the animals sold in the market. The index case, however, had not had exposure to the market. Furthermore, the virus was not identified in any of the animals sold in the seafood market. This suggests that there was a significant human-to-human transmission.
The genetic structure of the virus revealed clues that it could have at some point been transmitted from animals, though how and when it occurred is not clear.
Genome sequences obtained from five patients shared 79.6% sequences identical to SARS-CoV and 96% similarity to a bat coronavirus bat coronavirus (BatCoV RaTG13), which was previously detected in Rhinolophus affinis from the Yunnan province in China. It was also shown that the virus used angiotensin converting enzyme 2 (ACE2) like SARS-CoV for cell entry. The small amount of genetic dissimilarity between the 2019-nCoV and RaTG13 suggests that the latter did not provide the exact variant that caused the outbreak in humans, but it does support the theory that Covid-19 could have come from bats.
In support of this, an older study had also found the coronavirus evidence in bats and civets (which are sold in the seafood markets in China).
All these data suggest that the virus is likely to have an origin in the bat. There may or may not have been an intermediate host like the pangolin. Subsequently, it is likely that there has been human to human transmission [Figure 1].
|Figure 1: Spread of coronavirus. SARS-CoV-2: Severe acute respiratory syndrome coronavirus 2.|
Click here to view
There has been speculation that the virus is a lab construct.
Six receptor-binding domains (RBDs) in the spike protein have been shown to be critical for binding to ACE2 receptors (necessary for virus entry into the host cells). Structural and biochemical studies suggest that while COVID-19 binds human ACE2 with high affinity, computational analyses reveal that the interaction is not ideal. On the other hand, the RBD sequence in SARS-CoV is optimal for receptor binding. Therefore, the binding of the SARS-CoV-2 spike protein to human ACE2 is most likely the result of natural selection and evidence that SARS-CoV-2 is not the product of manipulation.
Studies have looked at the viruses found in bats and pangolins in great detail to assess if they were the immediate hosts from which the infection jumped to humans. As discussed earlier, RaTG13, from a Rhinolophus affinis bat, is 96% identical to SARS-CoV-2, but its spike diverges in the RBD, which suggests that it may not bind efficiently to human ACE2. Pangolin coronaviruses exhibit strong similarity to SARS-CoV-2 in the RBD, suggesting that the SARS-CoV-2 spike protein optimized for binding to human-like ACE2 could, be because of natural selection.
A feature of SARS-CoV-2 is a polybasic cleavage site at the junction of the two subunits of the spike. This has a role in determining viral infectivity and host range. Neither the bat betacoronaviruses nor the pangolin betacoronaviruses sampled thus far have polybasic cleavage sites, suggesting that these could not be the direct origins of the pandemic.
What could also be possible is that a precursor of SARS-CoV-2 may jumped into humans, acquiring the genomic features as described above during the undetected human-to-human transmission. Once acquired, these adaptations would enable the pandemic to take off.
| Conclusions|| |
After the first description of the coronavirus in the 1930s, there have been multiple outbreaks. This is the latest outbreak on the scale of a pandemic. There are 7 coronaviruses and the current virus is SARS-CoV-2, β-CoV. The origin was initially linked to the Huanan Seafood Market, but subsequent reports suggest that there was significant human-to-human exposure and the market might not have been the sole source. Evidence of the coronavirus in the pangolin (an anteater) and the civet cat suggests that there might be alternate reservoirs from which the virus could have jumped to humans also. Significant differences in the structure of the virus especially in the RBD suggest that it is unlikely that the virus is a laboratory construction, escaped from a Chinese lab.
Future studies will take into account potential routes of transmission and subclinical infections, in addition to the adaptation, evolution, and virus spread among humans and possible intermediate animals and reservoirs.
Detailed understanding of how an animal virus jumped species boundaries to infect humans, so productively will help in the prevention of future zoonotic events.
For example, if SARS-CoV-2 preadapted in other animal species, there is the risk of future re-emergence events. In contrast, if the adaptive process occurred in humans, even if repeated zoonotic transfers occur, they are unlikely to take off without the same series of mutations. Answers to some of these basic questions that would provide a framework for which more specific and detailed public health measures can be implemented.
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Conflicts of interest
There are no conflicts of interest.
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