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1. SHAHRIAR SHAMIM
SHAMIM
GONO BISHWABIDYALAY
DEPARTMENT OF MICROBIOLOGY
SHAHRIAR SHAMIM
Course Title : Virology –II
SARS COV -2 virus
Definition : The coronavirus (severe acute respiratory syndrome coronavirus 2
of the genus Betacoronavirus ) that is the caugetive agent of COVID-19 .
Structure :
Coronaviruses contain a canonical set of four major structural
proteins: the spike (S), membrane (M), and envelope (E) proteins,
all of which are located in the membrane envelope, and
the nucleocapsid (N) protein, which is found in the ribonucleoprotein
core . (see figure)

2. SHAHRIAR SHAMIM
SHAMIM
Types of corona Virus : There are now 7 types of coronaviruses that
have been identified by the CDC , which includes
 Common human coronaviruses
1. 229E (Alpha coronavirus)
2. NL63 (Alpha coronavirus)
3. OC43 (Beta coronavirus)
4. HKU1 (Beta coronavirus)
 Other human coronaviruses
5. MERS-CoV (Beta coronavirus that causes Middle East
Respiratory syndrome, or MERS )
6. SARS-CoV (the Beta coronavirus that causes a severe acute
respiratory syndrome,or SARS
7. 2019 Novel coronavirus (SARS-CoV-2)
Epidemiology :
The COVID-19 epidemic expanded in early December from Wuhan,
China’s 7th most populous city, through out China and was then exported
to a growing number of countries. The first confirmed case of COVID-
19 outside China was diagnosed on 13th January 2020 in Bangkok
(Thailand) . On the 2nd of March 2020, 67 territories outside mainland
China had reported 8565 confirmed cases of COVID-19 with 132
deaths, as well as significant community transmission occurring in
several countries worldwide, including Iran and Italy and it was declared
a global pandemic by the WHO on the 11th of March 2020 . The number
of confirmed cases is constantly increasing worldwide and
after Asian and European regions, a steep increase in cases is currently
(31 March 2020) being observed in low-income countries. It is
problematic to quantify the exact size of this pandemic as it would
necessary to count all cases including not only severe and symptomatic

3. SHAHRIAR SHAMIM
SHAMIM
cases but also mild ones .Unfortunately, to date, there is not a global and
standard response to the pandemic and each country is
facing the crisis based on their own possibilities, expertise and
hypotheses. Thus, there are different criteria for testing, hospitalisation
and estimating of cases making it difficult to calculate the number of
people affected by epidemic. Based on the data we have so far, the
estimated case fatality ratio among
medically attended patients is approximately 2%, but, also in this case, a
true ratio may not be known for some time.
Pathogenesis :
After the virus enters the body, it needs a special receptor to help it enter
the cell. This receptor is called (Angiotensin Converting Enzymes - 2)
Symbolized by ACE-2. The ACE-2 is present on the surface of the
alveolar cells in the lung.
We have 3 types of alveolar cells:
1. Responsible for gas exchange.
2. It is responsible for producing "surfactant" which is a mixture of
proteins and fats that reduce the surface tension of the alveoli.
3. Dust cell, which is macrophages.
The ACE_2 is found on type 2 of these cells. Corona virus envelope
contains proteins called spikes and special (S-Spike) that help the virus
bind to ACE-2.
When the above association occurs, the genetic material of the virus
enters the cell and the cell is harnessed to produce viral proteins, thus the
virus multiplies and the cell dies.

4. SHAHRIAR SHAMIM
SHAMIM
When (type 2 alveolar cells) die, they release substances called specific
inflammatory mediators.
These substances stimulate the existing immune cells "macrophages"
and when they stimulate the macrophages.
they secrete 3 immune substances called "cytokines" which are:
1. Interleukin_1 (IL-1)
2. Interleukin_6 (IL-6)
3. Tumor Necrosis Factor (TNF-α).
These three substances, when they reach the blood stream, cause the
symptoms associated with infection with Corona virus.
Symptoms
First - at the level of lungs:
 These substances cause expansion of the blood vessels surrounding
the vesicle, as well as increased permeability of the wall of these
vessels
 Vasodilation
 Capillary permeability increased. and thus leads to "alveolar
edema", which leads to hypoxia and shortness of breath.
 The loss of surfactant leads to an increase in the surface tension of
the vesicle and consequently leads to Alveolar collapse. It also
leads to Hypoxia and shortness of breath.
 These three substances also lead to an increase in the flow of
"neutrophils" cells to the place of the viral infection as an immune

5. SHAHRIAR SHAMIM
SHAMIM
response. Neutrophils cells kill some viruses by secreting two
substances such as:
 Reactive Oxygen Species "ROS"
 Proteases.
But the above articles also destroy some of the alveolar cells
responsible for gaseous exchange and cause a condition called
consolidation that causes cough symptoms.
Second: At the CNS level:
The three substances "IL-1, IL-6, TNF" go to the "hypothalamus" and
thus increase the body temperature and cause the symptoms of "Fever".
Third:
In the case of severe "SIRS" will occur Systemic inflammatory response
syndrome. That lead to septic shock. Also "MODS" Multiple organ
dysfunction syndrome. Especially the kidney and kidney failure.
SYMPTOMS : v
HOST RANGE :
Natural hosts include humans, Himalayan palm civets (Paguma larvata),
racoon dogs (Nyctereutes procyonoides), Chinese ferret badgers
(Melogale moschata), cats, and pigs. Experimental hosts include non-
human primates, ferrets, golden hamsters, guinea pigs, mice, and rats.
MODE OF TRANSMISSION :

6. SHAHRIAR SHAMIM
SHAMIM
Person-to-person contact (direct mucous membrane contact (eyes, nose
and mouth) with infectious respiratory droplets and/or direct contact
with infected body fluids) and/or through exposure to fomites. Other
possible modes of transmission include through blood transfusions, or
by sharps injuries.
INCUBATION PERIOD:
The incubation period of SARS CoV-2 ranges from 2 to 14 day