It is a respiratory disease caused by severe acute respiratory syndrome corona virus2.The term "coronavirus" actually refers to a family of viruses that causes many different types of diseases, including the common cold. Corona means "crown" in Latin,coronaviruses are named for the crown-like spikes on their surface.Covid 19 was characterized as a pandemic on march 11,2020. The first case of covid 19 was traced in wuhan, China in late 2019, with an outbreak developing in December.
Coronaviruses(CoV )are a family of enveloped,positive -sense, single stranded RNA(++RNA) viruses. They tend to cause mild upper respiratory disease in humans .Of the seven known species of CoV only 3 are known to cause severe infections in humans.SARS-CoV2 emerged in December 2019 in china possibly from bats or pangolins.
The SARS-CoV 2 virion is 1,250 nm in diameter, and its genome ranges from 26 to 32 kilobases, the largest for an RNA virus. It has 4 structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N). N protein forms a complex with RNA and aids in the viral assembly after its replication.
S, E, and M proteins create the viral envelope.
S protein, is a club-shaped surface projection, giving the virus its characteristic crown-like appearance on electron microscopy. It’s responsible for viral entry into the human cell.
SARS-CoV 2 attaches to the host cell by binding its S proteins to the receptor protein, angiotensin-converting enzyme 2 (ACE2). ACE2 is expressed by epithelial cells of the intestine, kidney, blood vesselsand most abundantly in type II alveolar cells of the lungs. The virus induces a drop of ACE2 in human cells, possibly inducing lung damage.
The human enzyme transmembrane protease, serine 2 (TMPRSS2) is also used by the virus for S protein priming and to aid in membrane fusion.
CoV are zoonotic or transmitted to humans through animals. It is hypothesized that horseshoe bats are the natural reservoir of SARS-CoV 2 since its genome is 97% identical to that of a bat coronavirus. The intermediate host is still unknown.Once in humans, the virus is transmitted mainly via inhalation of aerosol droplets from coughing, sneezing, or talking of symptomatic individuals. In the air, larger droplets tend to drop towards the ground within 1 m (3 ft), while smaller droplets can travel as an aerosol cloud over 2 m (6 ft) and remain viable in the air for up to 3 hours under certain conditions. Other forms of transmission include, direct transmission through hand-to-face contact from infected surface.The reproductive number or the number of secondary infections generated from 1 infected individual, is 2 to 2.5, higher than for influenza (0.9-2.1). COVID-19 is highly contagious due to the following aspects:
Asymptomatic individuals are also infectious, albeit to a slightly lesser degree, posing a real challenge for contagion prevention,production of high viral loads,efficient and prolonged shedding of virions from the upper respiratory tract (URT).Median duration of viral RNA shedding from URT is 20 days,viral life-span depends on the type of surface, temperature, and humidity levels.
CLINICAL PRESENTATION :The incubation period for COVID-19 ranges from 2–14 days, with an average of 5 days. 80% of infections are mild or asymptomatic.15% are severe infections (requiring oxygen therapy).
5% are critical infections (requiring ventilation) Asymptomatic cases:Can transmit the virus.Represent>50% of all infections,may not develop any noticeable symptoms.
Anosmia, hyposmia, and dysgeusia have been reported in many laboratory-confirmed cases of patients that were otherwise asymptomatic.
It has not been clearly determined how long asymptomatic individuals remain contagious after initial infection.
Mild cases:Dry cough and moderate fever.
Common flu-like symptoms, including fatigue, malaise, runny nose, nasal congestion, and sore throat
Recovery time: 2 weeks
Severe cases and complications:Median time from onset of symptoms to the onset of critical care/ICU transfer: 8-9 days Patients develop dyspnea, high fever, chest pain, hemoptysis, respiratory crackles, and progressive respiratory failure .Recovery time: 3-6 weeks
Refractory cases: Nearly 50% of COVID-19 patients did not achieve clinical and radiological remission within 10 days of hospitalization. Patients with male sex, older age, anorexia, and no/low fever at the time of admission have a higher risk of presenting a refractory progression.
Polymerase chain reaction (PCR) is currently the only test being used to confirm cases of COVID-19 infection and should be performed as soon as possible once a person under investigation (PUI) is identified. The specimens used for testing include:
Sputum,bronchial and tracheal secretions or bronchoalveolar lavage (for patients receiving invasive mechanical ventilation).
Inflammatory markers: ↑ Lactate dehydrogenase and ferritin
Ground-glass opacities (GGO)
Crazy paving appearance (GGOs + inter-/intralobular septal thickening).
Inflammatory markers: ↑ IL-6 and C-reactive protein in severe cases.
↑ procalcitonin in bacterial coinfection with pneumonia and/or sepsis
Chest X-ray and CT: severe infections may also present :
Pleural thickening and effusion
Air bronchograms and atelectasis
Solid white consolidation
Remdesivir: Have in-vitro activity against SARS-CoV and MERS-CoV by incorporating into nascent viral RNA chains and producing pre-mature termination.
Chloroquine and hydroxychloroquine, widely-used antimalarial drugs, are reported to block viral entry by inhibiting virus/cell fusion.
The combined use of hydroxychloroquine and azithromycin, a macrolide antibiotic, was reported to reduce the detection of SARS-CoV-2 RNA in upper respiratory tract specimens. Caution is advised when administering these drugs in patients with chronic medical conditions as both are associated with QT prolongation and may lead to life-threatening arrhythmia or sudden death.
Lopinavir-ritonavir: a combined protease inhibitor usually used for HIV infection, was reported as having in vitro inhibitory activity against SARS-CoV. However, no benefit was observed in hospitalized adult covid 19 patients.
Tocilizumab is an anti-IL-6 receptor agent used for rheumatoid arthritis. It is currently being investigated in patients with severe COVID-19 presenting with high IL-6 levels.
Camostatmesilate (CM): a TMPRSS2 inhibitor, is reported to block viral entry by inhibiting S protein priming.
There is no FDA-approved vaccine yet available to prevent COVID-19,so the only way to protect ourselves is prevention.
Author: Ms. Neha Shirse
Dental Undergraduate Student
NSVK Sri Venkateshwara Dental College & Hospital, Bengaluru, Karnataka, India