Transcript Viral Infection

Viral Infections of the Respiratory
System
Clinical manifestations
 Common cold (rhinitis)
 Pharyngitis
 Tonsilitis
 Sinusitis & otitis media
 Croup (acute laryngotracheobronchitis)
 Acute bronchitis
 Acute bronchiolitis
 Viral pneumonia
 Influenza (Flu)
The common respiratory viruses
Name of the virus
Family
Disease
1- Influenza virus
Orthomyxoviridae
URT & LRT infection
2- Parainfluenza virus
Paramyxoviridae
URT & LRT infection
3- Respiratory syncytial virus Paramyxoviridae
LRT infection
4- Rhinovirus
Picornaviridae
URT infection
5- Coronavirous
Coronaviridae
URT infection
6- Adenovirus
Adenoviridae
URT and eye infections
7- Human metapneumovirus
Paramyxoviridae
LRT infection
 Upper respiratory tract infection includes
rhinitis (common cold), tonsillitis, pharyngitis
 Lower respiratory tract infection includes
croup, bronchitis, bronchiolitis, pneumonia
ORTHOMYXOVIRIDAE
 Orthomyxoviruses are spherical, enveloped viruses containing a
segmented, negative strand RNA genome
 Viruses in this family infect humans, horses, and pigs, and are the cause
of influenza
 Orthomyxoviruses are divided into three types:
 Influenzae A, B, and C
 Only influenza virus types A and B are of medical importance
 Type A influenza viruses differ from type B viruses in that they have
an animal reservoir and are divided into subtypes
 Influenza virus C is not a significant human pathogen
Structure
 Influenza virions are spherical, enveloped, pleomorphic particles
 Two types of spikes project from the surface
 One is composed of H protein and the second of N protein
 Both the H and N influenza proteins are integral membrane proteins
 The M (matrix) proteins underlie the viral lipid membrane
 The RNA genome, located in a helical nucleocapsid, is composed of eight
distinct segments of RNA
 Each of which encodes one or more viral proteins
 Each nucleocapsid segment contains not only the viral RNA but also four
proteins
Influenza Virus
 Orthomxoviridae family
 They are helical, enveloped, single stranded RNA genome
 They are enclosed in a lipid envelop and a layer of glycoprotein
spikes
 known as haemagglutinin (HA) and neuraminidase (NA), which
are major antigenic determinants
 They are divided into different genera on the basis of the
nucleoprotein antigen
 Genera A, B, C
 Pathogenesis
 The virus infects the epithelial cells of the nose, throat, bronchi
and occasionally the lungs
Clinical Significance
 Influenza spread by respiratory droplets and is an infection solely of the
respiratory tract
 There is rarely viremia or spread to other organ systems
 Influenza has an acute onset, with symptoms including a nonproductive cough
and chills, followed by high fever, muscle aches, and extreme drowsiness
 Runny nose is unusual, differentiating influenza virus infection from the
common cold
 The disease runs its course in 4 to 5 days, after which recovery is gradual
 The most serious problems, such as development of pneumonia or bacterial
pneumonia
Influenza Virus
Electron micrograph.
Electron micrograph.
Influenza viral proteins
 Haemagglutinin (H)
 Attachment to the cell surface receptors
 Antibodies to the HA is responsible for immunity
 16 haemagglutinin antigenic type, H1 – H16
 Human associated H antigenic type are H1, H2, H3
 Neuraminidase (N)
 Responsible for release of the progeny viral particles from the
infected cell
 9 neuraminidase antigenic type, N1 – N9
 Human associated N antigenic type are N1, N2
Summary of the ecology of influenza viruses
 Prevention
 Influenza vaccine: Two types of vaccines available
1- The flu shot vaccine: Inactivated (killed vaccine)
 Given to people older than 6-months, including healthy people and those
with chronic medical conditions
2- The nasal spray flue vaccine: Live attenuated vaccine
 Approved for use in healthy people between 5-49 years of age
 Both vaccines contain two strains of the current circulating
influenza A and B viruses
 Vaccine should be given in October or November
 before the influenza season begins
Role of H AND N Proteins
 H = Hemagglutinin and N = Neuraminidase
 Hemagglutinin allows the virus to bind to host cells
 Neuraminidase helps the virus to release itself from the highjacked cells
in which it has reproduced
 Influenza A Virus Constantly Changes
 Antigenic drift


Small changes in H or N proteins that occur from year to year
Population is partially immune, but may be re-infected over time
(periodic epidemics)
 Antigenic shift


Acquisition of new H or N protein, possibly from an animal virus
Population is not immune, everyone is susceptible (pandemics)
Influenza A Virus
 Influenza A virus only is further classified into subtypes
based upon HA and NA antigens
 16 HA subtypes and 9 NA subtypes are now recognized
circulating in birds, humans, swine and horses
 The most famous subtypes are:
 A (H1N1): circulating in humans causing swine flu
 A (H5N1): circulating in birds causing avian flu
Clinical picture
• Fever
• Headache
• Myalgia
• Cough
• Rhinitis
• Ocular Symptoms
Incubation period: 1 to 2 days
 Transmission: droplet infection or hand-to-hand contact
 Diagnosis:
 1- Isolation of the virus from nose, throat swab
 2- Tissue culture
 3- Provisional - clinical picture + outbreak
Avian flu
 Viral etiology: Avian influenza type A virus (H5N1)
 Family: orthomyxovirus
 Epidemiology
 Wild birds are the natural reservoir for the virus
 They shed the virus in saliva, nasal secretion and feces
• All domestic poultry are susceptible to infection
• They become infected, when they eat food contaminated with secretion
from infected bird
• Avian influenza viruses do not usually infect human
• High risk group includes those who working in poultry farms and those
who are in close contact with poultry
 Symptoms in human
 Ranges from typical flu to severe acute respiratory disease
 Diarrhea, abdominal pain and bleeding from the nose have been
reported
 Treatment
 Should be initiated within 48 hours
 Lab diagnosis
 PCR, detection of the viral RNA in throat swap
Parainfluenza Virus

Family: Paramyxoviridae

Structural features
 Enveloped virus with - ssRNA genome, with 5 serotypes

Transmission
 Inhalation of infectious aerosol droplets mainly in winter

Clinical syndrome
a. Croup (or laryngotracheobronchitis)
b. Fever, harsh cough, difficult inspiration can lead to airway obstruction
need hospitalization to do tracheostomy
c. Bronchiolitis and Pneumonia
Lab diagnosis
Direct detection immunofluorescence
Treatment and prevention
Supportive treatment, No specific treatment or vaccine available
Respiratory Syncytial Virus (RSV)
 Family: Paramyxoviridae
 Structural features: Enveloped virus with - ssRNA genome
 Transmission: Inhalation of infectious aerosols mainly in winter
 Clinical syndromes:
a. Bronchiolitis
a. Life-threatening disease in infant especially under 6 month of life
with respiratory distress and cyanosis can be fatal and can lead to
chronic lung disease in later life
b. Pneumonia
a. can also be fatal in infant
 Lab diagnosis
 Isolated of virus by cell culture
 Direct detection of the Ag by direct I.F.

Treatment and prevention


Ribavirin administered by inhalation for infants with severe cases
Vaccine

No vaccine available, but passive immunization immunoglobulin can
be given for infected premature infants
Rhinovirus
 Family: Picornaviridae
 Structural features: Non-enveloped virus with + ssRNA genome,
more than 100 serotypes available
 Transmission: Inhalation of infectious aerosol droplets
 Clinical symptoms: The 1st cause of common cold. The main
symptoms of common cold are sneezing, clear watery, nasal discharge
with mild sore throat, and cough
 Lab diagnosis: Direct detection of the Ag by direct I.F.
 Treatment and prevention: Usually self-limiting disease, no specific
treatment, and no vaccine available
Coronavirus
 Family: Coronaviridae
• Structural features: They are large helical, enveloped, single stranded RNA
viruses
 Transmission: Inhalation of infectious aerosol droplets
 Clinical symptoms: The 2nd cause of common cold. The human coronaviruses
(CoVs) are responsible for about 30% of mild upper respiratory tract illness
(common cold)
• Severe Acute Respiratory Syndrome (SARS)
• Newly emerged SARS-CoV causes severe acute respiratory syndrome (SARS)
that has been reported in Asia, North America, and Europe
 In winter of 2002, a new respiratory disease known as (SARS) emerged in
China
 A new mutation of coronavirus MERS-CoV, with probably an animal reservoir,
and cause atypical pneumonia with difficulty in breathing
 Treatment and prevention: No specific treatment or vaccine available, yet
SARS Disease
 Severe acute respiratory syndrome (SARS)
 viral respiratory disease
 zoonotic origin
 caused by the SARS coronavirus (SARS-CoV)
 Incubation period: 2 - 10 days
 Transmission: droplet infection or contact to contaminated skin or fomites
 Clinical Picture
 Fever, chills, headache, myalgia and malaise
 Respiratory symptoms often begin 3-7 days after symptom onset and peak in the
second week
 Laboratory Diagnosis

Serological Testing



Molecular Testing


IFA: Indirect fluorescent antibody
ELISA: Enzyme-linked immunosorbent assays
RT-PCR: Reverse transcriptase-PCR
Culture: SARS-CoV (Vero E6 cell)
Adenovirus
 Family: Adenoviridae
 Structural features: Non-enveloped virus with ds-DNA genome
 Pathogenesis: Adenovirus infects epithelial cell lining respiratory
tract, conjunctiva, urinary tract, gastrointestinal tract and genital
tract.
 Clinical syndrome
1. Phrayngitis and tonsilitis
2. Pharyngioconjunctivitis
3. Keratoconjunctivitis
4. Pneumonia: in preschool children
5. Gastroenteritis
6. Acute hemorrhagic cystitis
7. Cervicitis and urethritis

Treatment and prevention: No specific treatment or vaccine