History, Classification and Origins of Coronaviruses

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History

It looks like that the earliest reports of a coronavirus infection in animals took place in the late 1920s, when an acute respiratory infection of domesticated chickens emerged in North America. The virus responsible that caused the infection was isolated in 1933 and was then known as infectious bronchitis virus, IBV. New researchers cultivated the virus for the first time in 1937 and the specimen was known as the Beaudette strain. In the late 1940s, two more animal coronaviruses, JHM that causes brain disease in mice, and mouse hepatitis virus, MHV were discovered. At the time it was still not evidence that these three different viruses were related.

Human coronaviruses were discovered in the 1960s using two different methods in the United Kingdom and the United States. Scientists working at the Common Cold Unit of the British Medical Council Research collected a unique common cold virus denominated B814 in 1961. The virus could not be cultivated using standard techniques as those used for rhinoviruses, adenoviruses, and other known common cold viruses.

In 1965, the British scientists successfully cultivated the novel virus by serially passing it through organ culture of human embryonic trachea. The isolated virus when inoculated intranasally into volunteers caused a cold and was inactivated by ether which pointed to the presence of a lipid envelope. Scientists at the University of Chicago isolated a novel cold from medical students in 1962, they isolated and grew the virus in kidney tissue culture, denominating it 229E. The novel virus caused a cold in volunteers and, like B814, was inactivated by ether.

Scientists at St. Thomas Hospital in London, collaborating with those from the Medical Council Research in 1967 compared the structures of IBV, B814 and 229E using electron microscopy. The three viruses were shown to be morphologically related by their general shape and distinctive club-like spikes

A research group at the National Institute of Health the same year was able to isolate another member of this new group of viruses using organ culture and entitled one of the samples OC43, OC is for organ culture. Like B814, 229E, and IBV, the novel cold virus OC43 had distinctive club-like spikes when observed with the electron microscope.

The IBV-like novel cold viruses were soon shown to be also morphologically related to the mouse hepatitis virus. This new group of viruses were named coronaviruses after their distinctive morphological appearance. Other human coronaviruses have since been identified, including SARS-Covid in 2003, HCoV-NL63 in 2003, HCoV-HKU-1 in 2004, MERS-Co-V in 2013, and SARS-CoV-2 in 2019. There have also been many animal coronaviruses identified since the 1960s.

Classification

Coronaviruses belongs to the family of Coronaviridae, subfamily Orthocoronavirinae, order Nidovirales, and realm Riboviria. They are divided into the four genera: Alpha-coronavirusBeta-coronavirusGamma-coronavirus, and Delta-coronavirus. Alfa-coronaviruses and Beta-coronaviruses infect mammals, while Gamma-coronaviruses and Delta-coronaviruses primarily infect birds.

The genus alfa-coronavirus includes the Human coronavirus 229E and Human coronavirus NL63 among other animal coronaviruses

To the beta-coronavirus belong, the Human coronavirus HKU1, and OC43, MERS, SARS-CoV, and SARS-CoV-2 among other animal coronaviruses.

Delta and gamma genus includes only animal coronaviruses, (As of Wikipedia literature).

CDC Classification of Coronaviruses types

Alpha-coronavirus– 229E, Alpha-coronavirus– NL63

Beta-coronavirus– OC43, Beta-coronavirus– HKUI

-These are not to related to the variants of SARS-CoV-2, but to the genera of the coronaviruses family, variants are due to mutations of the same virus and are designed with same Greek alphabetical letters-

Origin

The most recent common ancestor of all coronaviruses is estimated to have existed as 8000 BCE, some models place the common ancestor even as far back as 55 million years or more, suggesting long term coevolution with bat and avian species. Bats and birds, as warm-blooded flying vertebrates, are an ideal natural reservoir for the coronavirus gene pool.

It seems that bats were the reservoir for alpha-and beta-coronavirus, and birds the reservoir for gamma and delta-coronaviruses. The large number and global range of bat and avian species that host viruses have facilitated massive evolution and dissemination of coronaviruses.

Many human coronaviruses have their origin in bats. MERS-CoV emerged in humans from bats through the intermediate host of camels. MERS-Cov, although related to several bat coronavirus species, appears to have diverged from these several centuries ago. The most closely related bat coronavirus and SARS-CoV diverged in 1986. The ancestors of SARS-CoV first infected leaf-nose bats of the genus Hipposideridae; subsequently, they spread to horseshoe bats in the species Rhinolophidae, then to Asian Palm civets, and finally to humans.

Unlike other beta-coronaviruses, bovine coronavirus of the species Beta-coronavirus-1 is thought to have originated in rodents and not in bats. In the 1790s, equine coronavirus diverged from the bovine coronavirus after a cross-species jump. Later in the 1890s, human coronavirus OC43 diverged from bovine coronavirus after another cross-species spillover event. It is speculated that the flu pandemic of 1980 may have been caused by this spillover event, and not by the influenza virus, because of the related timing, neurological symptoms, and unknown causative agent of the pandemic.

Besides causing respiratory infections, human coronavirus OC43 is also suspected of playing a role in neurological diseases. In the 1950s, the human coronavirus OC43 began to diverge into its present genotypes. Phylogenetically, mouse hepatitis virus, murine coronavirus, which infects the mouse’s liver and central nervous system is related to human coronavirus OC43 and bovine coronavirus. Human coronavirus HKU1, like the above-mentioned viruses, also has its origins in rodents.

Infection in Humans

Coronaviruses vary significantly in risk factor, they can cause colds with major symptoms, such as fever, and a sore throat from swollen adenoids, they can cause pneumonia, either direct viral pneumonia or secondary bacterial pneumonia, and bronchitis, either direct viral bronchitis or secondary bacterial bronchitis. The human coronavirus discovered in 2003, SARSCoV, which causes severe acute respiratory syndrome, SARS, has a unique pathogenesis because it causes both upper and lower respiratory tract infection.

Six species of human coronaviruses are known, with one species subdivided into two different strains, making seven strains of human coronaviruses in total.

Four human coronaviruses produce symptoms that are generally mild, even though it is argued they might have been more aggressive in the past:

  1. Human coronavirus (HCoV-OC43), β-CoV
  2. Human coronavirus HKU1 (HCoV-HKU1), β-CoV
  3. Human coronavirus 229E (HCoV-229E), α-CoV
  4. Human coronavirus NL63 (HCoV-NL63), α-CoV

Three human coronaviruses produce potentially severe symptoms:

  1. Severe acute respiratory syndrome (SARS-CoV), β-CoV (identified in 2003)
  2. Middle East respiratory syndrome related coronavirus (MERS-CoV), β-CoV (identified in 2012)
  3. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), β-CoV (identified in 2019)

These cause the diseases commonly known as SARS, MERS, and COVID-19 respectively.

Common cold

Although the common cold is usually caused by rhinoviruses in about 15% of cases the cause is a coronavirus. The human coronaviruses HCoV-OC43, HCoV-HKU1, HCoV-229E, and HCoV-NL63 continually circulate in the human population in adults and children worldwide and produce the generally mild symptoms of the common cold. The four mild coronaviruses have a seasonal incidence occurring in the winter months in temperate climates. There is no preponderance in any season in tropical climates.

Severe Acute Respiratory Syndrome, SARS

In 2003, following the outbreak of severe acute respiratory syndrome, SARS was developing in Asia, and secondary cases elsewhere in the world, the World Health Organization, WHO, released a statement where was tested that a novel coronavirus identified by several laboratories was the causative agent for SARS. The virus was officially named the SARS coronavirus, SARS-CoV.

Middle East Respiratory Syndrome, MERS

In September 2012, a new type of coronavirus was identified and officially called Middle East respiratory syndrome coronavirus, MERS-CoV. The WHO issued a global alert soon after, and update in September 2012 that the virus did not seem to pass easily from person to person. However, in May 2013, a case of human-to-human transmission in France was confirmed by the French Ministry of Social Affairs and Health. In addition, cases of human-to-human transmission were reported by the Ministry of Health in Tunisia. Despite this, it appears the virus had trouble spreading from human to human, as most individuals who are infected do not transmit the virus. 

After the Dutch Erasmus Medical Center sequenced the virus, the virus was given a new name, Human Coronavirus—Erasmus Medical Centre, HCoV-EMC. The final name for the virus is Middle East respiratory syndrome coronavirus, MERS-CoV. The only U.S. cases, both survived, were recorded in May 2014.

In May 2015, an outbreak of MERS-CoV occurred in the Republic of Korea, when a man who had traveled to the Middle East, visited four hospitals in the Seoul area to treat his illness. This caused one of the largest outbreaks of MERS-CoV outside the Middle East. 

Coronavirus Disease 2019, COVID-19

In December 2019, a pneumonia outbreak was reported in Wuhan, China on December 31, 2019, the outbreak was traced to a novel strain of coronavirus, which was given the name 2019-nCoV by the WHO later renamed SARS-CoV-2 by the International Committee on Taxonomy of Viruses.

The Wuhan strain has been identified as a new strain of β-coronavirus from group 2B with approximately 70% genetic similarity to the SARS-CoV. The virus has a 96% similarity to a bat coronavirus, so it is widely suspected to originate from bats as well, new variants due to mutations have been identified since the begin.

Observation

-The 70% of genetic similarity to SARS-CoV, justifies for myself the reason of cross reactivity from previous infections with other types of coronaviruses, like those responsible of common cold, for example, and why some people were infected in more serious and dramatic way while others in a mild way, or not at all, or did not get sick despite of not being vaccinated; all of this to account to the distinction of the population in secretor and non-secretor, blood group influence and methylation status-

Sources:

Coronaviruses: Wikipedia

Coronaviruses Types: CDC

Picture by: shreddfigure.com

Thanks for Reading

Mariarosaria M.

https://wordpress.com/refer-a-friend/j2wxElXCm903EzWZ2pRG/

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