Coronavirus is a large family of viruses that cause illnesses ranging from the common cold to more severe infections such as pneumonia, Middle East Respiratory Syndrome and severe acute respiratory syndrome.
They belong to a family of enveloped, positive-sense, single-stranded RNA (+ssRNA) viruses.
The name “coronavirus” is derived from the Latin corona and the Greek κορώνη (korṓnē, “garland, wreath”), meaning crown or halo. This is the characteristic of the virion when seen under an electron microscope.
Coronaviridae Members of the genus Coronavirus also contribute to respiratory illness, including severe disease.
Coronaviruses cause about 1/3 of common colds and SARS
Dozens of these coronaviruses affect animals.
Until the 20th century, only two strains of human coronaviruses were known to cause disease: 229E (HCoV-229E) and OC43 (HCoV-OC43).
An outbreak of infection with SARS-associated coronavirus (SARS-CoV) showed that animal coronaviruses have the potential to cross from other species to humans, with devastating effects.
The one major epidemic to date (November 2002 through July 2003) encompassed more than 8000 cases, with mortality rates approaching 10%.
When these viruses infect epithelial cells of the enteric tract they cause diarrhea.
Strains of coronavirus
There exist seven strains of the virus that have been identified.
- Human coronavirus OC43 (HCoV-OC43)
- Human coronavirus 229E (HCoV-229E)
- Human coronavirus NL63 (HCoV-NL63)-New haven coronavirus
- Human coronavirus HKU1
- Middle East Respiratory Syndrome (MERS-CoV)-Novel coronavirus, 2012 and HCoV-EMC
- Novel coronavirus (COVID-19) Wuhan pneumonia or Wuhan coronavirus
Novel means newly discovered. It is used as a placeholder name to refer to a newly originated of discovered virus.
A novel coronavirus (nCoV) is a new strain that has not been previously identified in humans.
Out of the 7 known species of coronaviruses, only 3 are known to cause severe infections in humans:
- Severe acute respiratory disease coronavirus (SARS-CoV): emerged in 2003 in southern China from civet cats
- Middle East respiratory syndrome coronavirus (MERS-CoV): emerged in 2012 in Saudi Arabia from dromedary camels
- SARS-CoV 2: emerged in December 2019 in China possibly from bats or pangolins
Signs and symptoms
Coronaviruses cause respiratory and enteric infections in humans.
The major site for viral replication is the epithelial cells of the respiratory tract.
The common severe symptoms are;
- High fever of 100.4 degrees F or higher
- Kidney failure and death
Infected patients also present with;
- General body aches
- Mild breathing difficulties at the onset
- Dry cough after 2-7 days
- Runny nose
- Gastrointestinal disturbances
These symptoms may last for about 7 days with variations in different victims. More often there are no symptoms but the patient still sheds infectious viruses
Cough from an infected person or touching a contaminated object.
Transfer of nasal secretions ie aerosols caused by sneezes.
The viral spread is limited by the immune response of most people but this immunity is said to be short-lived.
Characteristics of coronavirus.
Coronaviruses belong to a family of enveloped, positive-sense, single-stranded RNA (+ssRNA) viruses.
The SARS-CoV 2 (Covid-19) virion has a diameter of approximately 1,250 nm , and its genome ranges from 26 to 32 kilobases. Coronavirus is the largest for an RNA virus.
SARS-Coronavirus 2 has 5 structural proteins which are:
- spike (S),
- envelope (E),
- membrane (M),
- nucleocapsid (N), and
- hemagglutinin-esterase (HE).
The neucleocapsid(N) protein holds the ribonucleicacidgenome, and the spike (S), envelope (E,) and membrane (M) proteins create the viral envelope.
The S protein, together with hemagglutin-esterase (HE), is responsible for the entry of the virion into the cell. S protein is a club-shaped surface projection, giving the virus its characteristic crown-like appearance when seenuner an electron microscopy.
The S protein in this SARS-CoV 2 binds to the host cell through an enzyme known as angiotensin-converting enzyme 2 (ACE2) and basigin (BSG). Angiotensin-converting enzyme 2 (ACE2) is expressed by epithelial cells of the intestine, kidney, blood vessels, and most abundantly in type II alveolar cells of the lungs.
This viral spike protein induces a drop in the levels of ACE2 in human cells, which might be the cause of lung damage.
Cause respiratory and enteric disease
Coronaviruses are the largest RNA virus
They have a positive single-stranded RNA genome
Nested mRNA with a common 3’ terminal
The spike protein attaches to sialic acid
M glycoprotein helps in the attachment of the nucleocapsid to the membranes of internal structures such as the Golgi Body.
Most human harbor anti-coronavirus antibodies but reinfection is common indicating that there may be many existing circulating serotypes of the virus in humans.
Major outbreaks occur every few years with a cycle that depends on the type of coronavirus involved.
Most coronavirus infections are self-limiting.
The diagnosis is made by;
Serology- Polymerase chain reaction (PCR) and Sequencing
Treatment for these infections is supportive.
Analgesics and antipyretics.
A humidifier or steamy shower can also help ease a sore and scratchy throat.
There are no vaccines or antiviral agents that are approved for the prevention or treatment of these infections but scientists are working out to create a vaccine for the virus. There are reports that the antimalarial drug chloroquine has shown some promising effects together with some antiviral medications.
Handwashing with soap and water or sanitizers
Keep hands away from the eyes
Avoid close contact with infected people
Drink a lot of fluids
Get enough rest
Severe Acute Respiratory Syndrome
Severe acute respiratory syndrome (SARS) was identified in 2002 in China but has been diagnosed in several countries, primarily in Asia.
Possible animal reservoirs include bats and civets.
Once discovered, the SARS coronavirus was rapidly sequenced: the full genome was assembled in April 2003, <6 months after the recognition of the first case.
SARS is caused by a coronavirus and is characterized by efficient human transmission but relatively low mortality. It spreads from person to person via droplets; “super-spreader” airborne events have occurred.
The potential pandemic with SARS was controlled through the identification and isolation of infected patients.
Signs and symptoms
Typically, patients present with a nonspecific illness.
The incubation period is about 6- 10 days
A 3- to 7-day prodrome characterized by;
- Sore throat,
- Headache, and
It can progress to nonproductive cough, dyspnea, and respiratory failure.
Many patients have abnormal chest radiographs.
The risk of contagion is low during the prodrome.
It is a unique form of viral pneumonia which when compared with most other viral pneumonia, SARS lacks upper respiratory symptoms, although cough and dyspnea occur in most patients.
Investigators have reported the identification of a fourth human coronavirus, HCoV-NL63.
NOV 2002: highly contagious, severe atypical pneumonia observed in China
FEB 2003: Spread to Hong Kong – a doctor who later died
Similar outbreaks occurred in different local communities
The virus was identified in March 2003 (A coronavirus)
The worldwide spread of severe acute respiratory syndrome (SARS) began as a species cross-over, most likely involving transmission of a previously unknown coronavirus of horseshoe bats to Himalayan palm civets that were subsequently captured and transported to live-animal markets in Guangzhou, China, for human consumption.
The SARS coronavirus was then transmitted to humans most likely by restaurant workers and from them to medical personnel and eventually to individuals around the world.
This spread was a consequence of human travel.
Transmission is through droplet.
Polymerase chain reaction assays are used in the detection of the coronavirus nucleic acid in the respiratory secretions and in stool samples between 4-8 days of infection.
Antigen and nucleic acid detection techniques are also used. This detects the antigens in the cells in respiratory secretions from infected persons using the ELISA test if there is a high-quality antiserum.
Isolation of these viruses in cell culture has been a difficult process though the virus was recovered from oropharyngeal specimens using Vero monkey kidney cells.
Severe Acute Respiratory Syndrome Coronavirus-2 (COVID-19)
31 Dec 2019: China reports to WHO 44 cases of pneumonia of unknown origin
07 Jan: China identifies the cause – a novel coronavirus
COVID-19 is an acronym derived from “coronavirus disease 2019.” This name was chosen to avoid stigmatizing the virus’s origins. On early February, 2020, the virus was given an official designation for the novel virus: severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
Coronavirus disease 2019 or COVID-19 is an illness that is caused by a novel coronavirus now called severe acute respiratory syndrome coronavirus. In this case, Novel stands for a new discovered virus. It was first identified amid an outbreak of respiratory illness cases in Wuhan City, Hubei Province, China and reported to the WHO on December 31, 2019.
Read also the infection cycle of SARS-CoV-2 here.
Middle East respiratory syndrome
The Middle East respiratory syndrome is caused by a novel beta coronavirus similar to the cause of severe acute respiratory syndrome (SARS) and was first recognized in 2012 in Saudi Arabia.
Human cases have been associated with direct and indirect contact with dromedary camels.
Unlike SARS, MERS exhibits inefficient human transmission but carries a high mortality rate.
As of 2015, 1180 cases had been confirmed, with 40% mortality.
MERS-CoV is a zoonotic virus (transmitted between animals and people). The virus may have emerged from bats in the Middle East.
Patients with MERS have had a history of residence or travel in the Middle East, in particular, Saudi Arabia, or contact with such patients.
The virus is probably transmitted through direct or indirect contact of mucous membranes with infectious respiratory droplets. The virus is shed in the stool, but the role of the fecal-oral transmission is unknown.
The median incubation period is 5 days (range, 2–13) with the mean age of 50 (range 9 months to 99 years) and 65% occurring among men.
Those with diabetes, kidney disease, chronic lung disease, or other immunocompromising conditions are considered to be at highest risk for severe disease.
Camels appear to be the principal reservoir.
Raw camel milk is considered a potential source.
Persons who work with camels are more likely to have antibody evidence of past infection.
Symptoms and Signs
MERS is an acute respiratory syndrome, with the most common symptoms being fever, cough, and dyspnea.
Chills and rigors are common.
Gastrointestinal symptoms may occur with diarrhea being most common, followed by nausea and abdominal pain, and may precede respiratory symptoms.
Mild and asymptomatic.
Hematologic findings include thrombocytopenia, lymphopenia, and lymphocytosis.
Moderate elevations in lactate dehydrogenase and liver enzymes.
Chest radiograph abnormalities include increased bronchovascular markings, patchy infiltrates or consolidations, interstitial changes, opacities (reticular and nodular) as well as pleural effusions and total lung opacification.
Ground-glass opacities and consolidation are most commonly seen. The findings mimic those of many other causes of pneumonia.
Highest viral loads are found in lower respiratory tract specimens, including bronchoalveolar lavage fluid, sputum, and tracheal aspirates. These samples are preferred for diagnosis.
Respiratory failure is such a common complication with most of the patients requiring intensive care and mechanical ventilation.
Patients with MERS-CoV appear to advance faster to respiratory failure than do those with SARS.
Respiratory support is essential.
There is an improved survival at 14 days with the use of ribavirin and interferon-alpha but not at 28 days.
The overall mortality rate of identified cases is about 40%.
Advanced age is associated with a poor prognosis.
Isolation and quarantine
Strict infection control measures are essential.
Practice frequent hand washing and avoid contact with those who have respiratory symptoms.
Because health care workers engaged in procedures that involve contact with respiratory droplets are at risk, isolation of high-risk patients is essential, as are simple hygienic measures.
Control measures, including quarantining in the home for high-risk exposed persons and the use of facemasks for preventing hospital-acquired infections, are important.
Camel workers including slaughterhouse and market workers, veterinarians, and racing personnel should wear facial protection and protective clothing and practice good personal hygiene, including frequent hand washing after touching animals.
Avoid direct contact with infected camels.