Corona Viruses

7/28/2019 Corona Viruses

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CORONAVIRUSES

Genus Coronavirus

CoV&

Genus Torovirus


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Coronaviridae


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CORONAVIRUSESThe genome

- SS linearnon segmented+ve senseRNA

- the largestamong RNAviruses.


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The family coronaviridae iscomposed of two genera:

Genus Coronaviruses

Genus Torovirus: widespread in horses & cattle

associated with gastroenteritis.


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Genus Coronavirus First isolated in chicken in 1937

First human corona virus wasisolated in 1965

They cause prevalent disease inhumans and domestic animals (cats,dogs, birds)


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Structure:

Coronaviruses are large envelopedvirions 80 to 160 nm,

Helical nucleocapsids.


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A Crown-like Appearance

when viewed by EM

On the surface of the envelop areclub shaped projections that resemble

asolar corona


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Genus Coronavirusesare difficult to

isolate in cell culture

So infections with this virus are

rarely diagnosed in clinical practice

Genus Coronaviruses


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Tropism To Epithelial

Cells

Respiratory tract

GI in infants


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Relationship to human

infections- Based on serologic studies,coronaviruses cause respiratory tract

infections and pneumonia in humans.

- Electron microscopy links

coronaviruses to gastroenteritis ininfants children and adults ( tropismto epithelial cells)


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Genetic variation &

evolution of new strainsa high frequency of:

deletion mutations

high frequency of recombination duringreplication which is unusual for an RNAvirus with unsegmented genome


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The three major

antigenic groups of CoV Group I contains canine, feline, porcine

coronaviruses and a human corona virus

HCoV 229E the prototype of the group

Group II contains bovine, porcine, rat andmouse CoV and the other human strainwhich is OC43

Group III no human strains only Turkey

and Avian CoV


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Evolution of SARS 2002

A novel human corona virus named

SARS associated corona virusrepresents a new fourth antigenicgroup intermediate between groups

I & III


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A NOVEL FOURTHANTIGENIC GROUP

SARS

Evolution of SARS

gp III

SARS CoV

gp II

(OC43)

gp I (229E)

NO HUMANstrains


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Clinical picture & epidemiology

Upper respiratory infections, similar to coldscaused by rhinoviruses, but with a longerincubation period (average three days).

15-30% of respiratory illness in adults during wintermonths but lower respiratory infections were rare.

Antibodies appear early in childhood and are found in

90% in adults


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CLINICAL PICTURE &

EPIDEMIOLOGY

CORONAVIRUSES may be associated

with gastroenteritis which occursyear-round.

Confirmation of the etiology of thisrelationship is needed.


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Laboratory Diagnosis Direct Detection

Isolation

Serology


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Laboratory Diagnosis of

1. coronavirusesDIRECT DETECTION: Antigen detection in cells of respiratory

secretions by IF or ELISA

NA detection in respiratory secretions by RT-PCR

ISOLATION: CoV are difficult to grow in CC.

Reliable isolation of the virus is accomplishedusing human embryonic tracheal organ cultures.

These methods are not routinely available.


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Detection of Corona virus byImmunofluorescent Technique


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Serology:

Serologic tests are not routinely available.

Practical means to confirm coronavirus

infection using paired sera to detect risingor stationary high antibody level by:

- PASSIVE HAEMAGGLUTINATION

TEST- ELISA


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Laboratory diagnosis ofGastroenteritis caused by

toroviruses

BASED ON DIRECT DETECTION ONLY:

Ag detection

NA detection


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SARS


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SEVERE ACUTE RESPIRATORYSYNDROME

SARS

Mystery pneumonia late 2002 in

southern China

Resulting in progressive respiratory

failure


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SEVERE ACUTE

RESPIRATORY SYNDROME

Animal strain from a cat like

mammal in Southern China

Person to person spread by closecontact through respiratorydroplets


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STRUCTURE&

CHARACTERISTICS Similar to coronaviruses

EXCEPT:

Grown easily on tissue culture cellsresulting in cytopathic effect

Has tropism to LRT


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SARS

First coronavirus that causessevere LRT disease in humans


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Clinical picture IP: 6 days

First epidemic 10% MR fromprogressive respiratory failure


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Laboratory Diagnosis Direct Detection: NA detection

Isolationof the virus using Veromonkey cells resulting in CPE.Confirmation by RT-PCR

Serology: 4 fold or greater rise inantibody response by ELISA or IF


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Treatment No successful treatment

No vaccine


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YET STOPPING THESPREAD OF INFECTION

WAS POSSIBLETHROUGH

EFFECTIVE CONTROLMEASURES


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Control Measures1. Isolation of patients

2. Quarantine of those exposed

3. Use of barrier Precautions:1. gloves2. gowns

&3. respirators by health workers

4. Hand Hygiene


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Co- evolution

&pathogenicity


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Majority of corona virusescauseasymptomatic infection in their natural

hosts

reflecting

CO- EVOLUTIONof

HOST AND PATHOGEN


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WHY SARS INFCTION

IN HUMANS IS FulminantThis is attributed to

SARS jumped from animals tohuman

i.e. A non natural host isinfected


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OTHER CAUSES OF

FULMINANT INFECTION

The natural host is infected by an

unusual route

The infection is caused by a more

virulent virus variant


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EVIDENCE OF THE EFFECT

OF CO-EVOLUTION

Milder cases of SARS Coronavirus

infections in South China

SARS coronavirus cause milderinfections in populations previouslyaffected by outbreaks


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NOTE!!!

Co-evolution takes yearsto develop


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Always remember


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CHANGE IN PATHOGENICITY

IS ATTRIBUTED TO A non natural host is infected

The natural host is infected by anunusual route

The infection is caused by a morevirulent virus variant

4 families of 1ry Respiratory


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4 families of 1ry Respiratory

1.NA

Name

DNA RNA viruses

Adeno Rhino Orthomyxo Corona2.Envelope Not Enveloped Not Enveloped Enveloped Enveloped

3.Structur

e

70-90 nm

ds-DNAnon segmentedicosahedral

,20-30nm

Ss +vesenseNon segmented

Icosahedralsymmetry

80-120 nm

ss ve Sensesegmented RNAHelical symmetry

80 to 160 nm

ss+ve RNAnon segmentedHelical symmetry

4.Antigenic

structure

six groups (A to F)

49 types


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4 families of 1ry Respiratory viruses

DNA RNA viruses

Adeno Rhino Orthomyxo Corona7. Isolation Human cells

are requiredCells ofprimate origin,

Human diploidfibroblast cells

Primary tissueculture MK

humanembryonictracheal organcultures

SARS Veromonkey cells

8.Treatment No antiviraldrug

No antiviral Treatment No successfultreatment

9. ImportantfeatureLatencyoncogenicpotential inanimals

Corona Viruses

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