CORONAVIRIDAE FAMILY

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Coronaviridae family is comprised of viruses known as coronaviruses. There are only two genera of viruses in the Coronaviridae family. Coronavirus (which contain Coronaviruses) and Torovirus (which contain Toroviruses) are the two main genera of Coronaviridae family. Both coronaviruses and toroviruses have a worldwide distribution. Viruses in this family include those that infect humans and other mammals such as pigs, mice, cattle, birds and bats. Coronaviruses are enveloped viruses that replicate in the cytoplasm of their host cell. Coronavirus are released from their host cell by a budding process through the cell membrane after completing the cycle of their replication in the affected host cell. They have a ss(+)RNA genome that measures between 26 – 32 kb.

Structurally, Coronaviruses measure between 120-160 nm in diameter. Coronaviruses have a helical nucleocapsid. Viruses in the Coronaviridae family cause respiratory infections in humans and other animals that they infect. The commonest viral member of the Coronaviridae family is used to be severe acute respiratory syndrome (SARS) Coronavirus. However, a novel strain of coronavirus known as SARS-CoV-2 (severe acute respiratory syndrome coronavirus strain 2) that causes coronavirus disease 2019 (COVID-19) have now emerged, and responsible for the 2020 pandemic of the disease that ravaged the entire universe medically and economically.

SARS Coronavirus causes a severe respiratory tract infection or lung disease that is clinically characterized by pneumonia of the lower respiratory tract system in humans. In the year 2003 for example, SARS Coronavirus caused several outbreaks of SARS infection in most parts of the world; and the epidemic was marked by several morbidity and mortality especially in hospital environments. Healthcare practitioners who had direct contact with cases or patients suffering from the SARS infection were also infected. The first outbreak of SARS actually occurred in the Chinese city of Guangzhou province in 2002 from where the world outbreak of the disease started from. Aside the lower respiratory tract of humans which SARS Coronavirus is known to colonize, the virus also attacks the gastrointestinal tract and neurological tissues of the body.

The main routes through which coronaviruses are transmitted are through aerosols, body contact and through the oral-faecal route (especially for some toroviruses that infect animals). But the main major route through which SARS coronaviruses are spread or transmitted in human population is through the respiratory tract of infected individuals especially when they cough and sneeze. Aerosols from SARS Coronavirus infected individuals are highly infectious and can serve as route through which susceptible individuals can become infected. SARS Coronavirus infection in humans has an incubation period of 2-7 days and infected individuals are highly infectious especially when they present with respiratory symptoms that characterize the disease. Common cold, malaise and fever are some of the asymptomatic symptoms of SARS; and when individuals become very symptomatic, infected individuals have myalgia, dry throat and even shortness of breath. No specific antiviral therapy exists for the treatment of SARS in humans. However, the management of the disease is mainly based on supportive therapy.

Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV) is a relative of SARS Coronavirus that affects parts of the Middle East including Saudi Arabia, Lebanon, Jordan and the Saudi Arabian peninsula. Unlike SARS Coronavirus which affects the lower respiratory tract in humans, MERS-CoV affects the upper respiratory tract in humans. However, both SARS infections and MERS-CoV infections are respiratory tract infections caused by viral pathogens. The clinical signs and symptoms of MERS-CoV infection are akin to those of SARS Coronavirus infection in humans, and they include cold or chill, fever, shortness of breath, gastroenteritis, pneumoniae and cough. MERS-CoV infection in humans is zoonotic in nature, i.e., they can be transmitted from animals to humans. However, the main reservoir and source of the infection in human population is still a subject of intensive research. There is currently no formal antiviral treatment or vaccine for MERS-CoV infection in humans. Supportive therapy which is geared towards restoring vital organ functions such as breathing in the affected individual is usually the major type of medical attention given to MERS-CoV infected individuals.

The second strain of coronavirus is SARS-CoV-2 (severe acute respiratory syndrome coronavirus strain 2) that causes COVID-19. Coronavirus disease (COVID-19) is an infectious disease caused by a newly discovered coronavirus strain known as SARS-CoV-2. Most people infected with the COVID-19 virus will experience mild to moderate respiratory illness and recover without requiring special treatment.  However, older people and those with underlying medical problems like cardiovascular disease, diabetes, chronic respiratory disease, and cancer are more likely to develop serious illness and may die from COVID-19 if proper medical care is not given. Coronavirus disease 2019 (COVID-19) is a pneumonia-like respiratory tract disease that is caused by SARS-CoV-2 as aforementioned, and the disease is usually spread via droplets that emanate from the mouth or nose when infected persons cough, talk or sneeze. SARS-COV-2 is a new strain of coronavirus that was first discovered in Wuhan, China where the first cases had their symptom onset in December, 2019.

SARS-CoV-2 is a novel strain of virus in the family or genera of viruses known as Coronaviridae or Coronaviruses. The first strain is SARS-CoV (severe acute respiratory syndrome coronavirus) – which caused SARS in the world in the early 2000, starting from China. SARS-CoV-2 is the only known strain to cause COVID-19 at the moment; and this strain of coronavirus is more infectious than SARS-CoV – owing to the rate of spread and morbidity and mortality associated with SARS-CoV-2 around the globe. COVID-19 pandemic has resulted in a global crisis with short- and long-term implications for health, the economy, and social relations. SARS-CoV-2 is a novel viral strain of coronavirus and thus the biology, pathophysiology and pathogenesis of the virus is still unraveling as scientists are now faced with finding a functional cure and vaccine for the pandemic that have ravaged the economy of the world. There is currently no cure or vaccine for COVID-19; however, there is a race and persistent search for a vaccine and possible cure for COVID-19.

Further reading

Acheson N.H (2011). Fundamentals of Molecular Virology. Second edition. John Wiley and Sons Limited, West Sussex, United Kingdom.

Brian W.J Mahy (2001). A Dictionary of Virology. Third edition. Academic Press, California, USA.

Cann A.J (2011). Principles of Molecular Virology. Fifth edition. Academic Press, San Diego, United States.

Carter J and Saunders V (2013). Virology: Principles and Applications. Second edition. Wiley-Blackwell, New Jersey, United States.

Dimmock N (2015). Introduction to Modern Virology. Seventh edition. Wiley-Blackwell, New Jersey, United States.

Kudesia G and Wreghitt T (2009). Clinical and Diagnostic Virology. Cambridge University Press, New York, USA. 

Marty A.M, Jahrling P.B and Geisbert T.W (2006). Viral hemorrhagic fevers. Clin Lab Med, 26(2):345–386.

Strauss J.H and Straus E.G (2008). Viruses and Human Diseases. 2nd edition. Elsevier Academic Press Publications, Oxford, UK.

Zuckerman A.J, Banatvala J.E, Schoub B.D, Grifiths P.D and Mortimer P (2009). Principles and Practice of Clinical Virology. Sixth edition. John Wiley and Sons Ltd Publication, UK.

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