Infections Caused by COVID-19 Causing Virus Family—Coronaviridae
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Electron microscope image of Novel Coronavirus SARS-CoV-2. (NIH Image Gallery / Flickr)
Infections with coronavirus are more common than we know. Now in news for the COVID-19, coronaviruses are associated with the common cold and other respiratory disorders. These viruses with positive-stranded RNA as their genetic material constitute the taxonomic family Coronaviridae. This family includes subfamilies of viruses that infect mammals, birds and fishes. Coronaviruses infect the epithelial lining of the respiratory tract, resulting in respiratory distress.
Warm-blooded birds like bats serve as definitive hosts of the virus. Severe Acute Respiratory Syndrome (SARS) is one such example wherein bats acted as hosts for the virus SARS-CoV, and COVID-19, caused by the virus SARS-CoV-2, is also likely to have been originated in bats.
Other animals that act as hosts and vectors for coronaviruses include cattle, raccoons, swine, horses, camels etc. The virus is then transmitted to humans through cross-species transmission. Middle Eastern Respiratory Syndrome (MERS) is an example of cross-species transmission of the virus from camels to humans. Coronaviruses thus are classified as zoonotic viruses.
Diseases due to coronaviruses
While birds and animal coronaviruses are responsible for causing epidemical diseases MERS, SARS and the ongoing COVID-19, human coronaviruses—that is viruses that use humans as reservoirs or vectors—are responsible for the common cold and other respiratory diseases, often asymptomatic infections.
Human coronavirus belongs to the genus Alphacoronavirus of subfamily Coronavirinae, Coronaviridae. 30% of mild respiratory tract infections are caused by human coronaviruses. Seasonal outbreaks of Common cold, Influenza-like illness, Croup, Bronchiolitis and Pneumonia are triggered by this family of virus.
Common cold and Influenza-like illness affect the upper respiratory tract and Croup, Bronchiolitis and Pneumonia are infections of the lower respiratory tract.
Symptoms of the infections
These viral infections begin as the virus replicates in the epithelial cells of the nasopharynx, this results in the destruction of epithelial cells lining the tract—ciliated cells and evokes immune responses such as rhinorrhoea (runny nose), pharyngitis, cough, headache and, and mild fever within 2-5 days of infections. These are the symptoms often associated with most of the coronavirus infections.
Illustration of the respiratory epithelium. The highlighted box shows the epithelial lining. (Medical gallery of Blausen Medical 2014)
Further, different infectious diseases are characterised by similar symptoms. For example, a person infected with SARS complains of dry cough, fever above 100 F, malaise, chills and diarrhoea. 30% of patients are disturbed with severe respiratory disturbance—intestinal pneumonia. COVID-19 is also present with these symptoms. Patients with MERS showcased similar indications.
As stated above Common cold is a syndrome of the upper respiratory tract with symptoms like nasal blockage, runny nose, sneezing, cough and sore throat. Sometimes, headaches and body aches that develop after 1-3 days of infection.
Influenza-like illness is a spectrum of upper respiratory tract infections; fever equal or greater than 100 F, cough and sore throat are uncomplicated indications of infection. Malaise, body aches, loss of appetite and nausea are observed 1-4 days after infection and other respiratory signs and symptoms occur on the 5th-7th day of infection.
Bronchiolitis is a common acute viral lower tract infection, the symptoms include rhinorrhoea, cough, tachypnea(rapid breathing), wheezing and increased respiratory efforts in 3-7 days.
Pneumonia is characterized by its high morbidity and mortality rates in children and adults over the age of 75. It is caused due to either direct inhalation of viral load or contiguous spread of the upper respiratory tract. In the latter case, the symptoms include fever, cough and shortness of breath. Common to both are non-respiratory symptoms like fatigue, sweats, headache, nausea and myalgia.
While most of these diseases often affect the adults too, Croup is a childhood disease with distinctive barky cough, inhalation stridor (noisy breathing/wheezing), hoarse voice, respiratory distress with upper airway obstruction at night. As the child grows older, he is often healed off the illness.
Precautions to be observed
As these diseases mainly affect the airway and lungs, and are contagious, maintaining distance with those affected helps to keep infections at bay as these infections are transmitted through aerosols.
• Disinfection of surfaces and objects is really important to avoid chances of surface transmission of the virus.
• Wash hands regularly and maintain personal hygiene.
• Avoid eating raw and uncooked meat, and contact with live animals.
For more information visit the WHO official website.
References:
-Virus Taxonomy: Ninth Report of Internation Committee on Taxonomy of Viruses
-Viruses: From Understanding to Investigations by Susan Payne
-Elsevier’s Integrated Review Immunology and Microbiology (Second Edition)
-Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases
Enjoyed this article? Also, check out “Coronavirus and Other Deadly Outbreaks of the Past“.
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