Transcript 5- viral infection (1)x

Viral Infections of
the Respiratory
System
Respiratory infections caused by viruses:
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Common cold (rhinitis).
Sinusitis & otitis media.
Pharyngitis & tonsillitis.
Croup (acute laryngotracheobronchitis).
Acute bronchitis & acute bronchiolitis.
Viral pneumonia.
Common respiratory viruses
Name of the virus
Rhinoviruses
Human metapneumovirus
Adenoviruses
Influenza viruses
Parainfluenza viruses
Respiratory syncytial virus
Coronaviruses
Disease
URT infection
LRT infection
URT and eye infections
URT & LRT infection
URT & LRT infection
URT & LRT infection
URT & LRT infection
 URTI: common cold, tonsillitis, pharyngitis.
 LRTI: croup, bronchitis, bronchiolitis,
pneumonia.
Some viruses cause pneumonia as
part of a multisystem syndrome, e.g.
Measles, Varicella-zoster virus,
Epstein - Barr virus, Cytomegalo
virus (CMV) and Herpes simplex
virus.
Rhinoviruses
The most common cause of common cold.
• Family: Picornaviridae.
• Structural features: Non-enveloped Ss
RNA viruses. more than 100 serotypes.
• Transmission:
-Inhalation of infectious aerosol droplet
-Contaminated fingers or fomites.
• Treatment and prevention:
self-limiting, no specific treatment & no
vaccine available.
Adenovirus
 Family: Adenoviridae > 50 serotypes.
 Virology: Non-enveloped, Ds DNA virus.
 Pathogenesis: Adenoviruses infect the epithelial
cells of respiratory tract, conjunctiva, urogenital
tract & GIT.
 Clinical syndromes:
 Pharyngitis and tonsillitis.
 Epidemic pharyngioconjunctivitis (pink eye).
 Pneumonia.
 Gastroenteritis (diarrhoea & vomiting)
 Acute hemorrhagic cystitis & urethritis.
 No specific treatment or vaccine.
Parainfluenza Virus
 Family: Paramyxoviridae.
 Structural features: Enveloped viruses with
Ss RNA genome. There are 4 types (1-4)
 Transmission: Inhalation of infected droplets.
 Clinical syndrome:
• Croup (or laryngotracheobronchitis). Fever,
harsh cough, difficult inspiration.
• Bronchiolitis (cough, fever & wheeze ≤ 2
years).
• Pneumonia.
 No specific treatment or vaccine.
Respiratory Syncytial Virus (RSV)
 Family: Paramyxoviridae.
 Virology: Enveloped, Ss RNA virus.
 Transmission: Inhalation of infectious
aerosols mainly in winter.
 Clinical syndromes:
• Bronchiolitis.
• Pneumonia.
These conditions can be fatal in neonates,
prematures and in infants with congenital
defects or who are immunodeficient.
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Treatment: Inhaled ribavirin for infants
with severe cases.
 Vaccine:
 No vaccine available.
 Specific immunoglobulin can be given
for high risk infants.
Influenza Viruses
Influenza Virus
 Family: Orthomyxoviridae
 Genome: Enveloped Ss RNA with 8 Segments.
 The envelop contains two glycoproteins:
 Haemagglutinin (HA)
 Neuraminidase (NA)
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Three Types (Genera):
• Type A: infects Man, and animals (birds, pigs).
Causes epidemics and pandemics.
• Type B, C: infects Man only.
 Influenza viruses are highly susceptible to
mutations and reassortment within the infected
Haemagglutinin (HA):
 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. H5, H7, H9.
Neuraminidase (NA):
 Responsible for release of the viruses from the
infected cell.
 9 neuraminidase antigenic type, N1 – N9
 Human associated N antigenic type are N1, N2.
N7.
Genetic variability
Antigenic drift: accumulated mutations lead
to chemical changes in HA or NA antigens.
Partial protective immunity in population.
 Antigenic shift: Genetic re-assortment
between two viruses results in production of a
new virus with different NA-HA
combinations.
› Usually in Influenza A virus and lead to
pandemics because there is no previous
population immunity.
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 Before
1968; H2N2 (Asian flu ; human; killed 1.5
million).
 Since 1968; H3N2 (Hong Kong flu; Avian; killed
1 million),
 2004- 2009; H5N1 (Hong Kong, Avian); 718
cases and 413 deaths. Rarely spread between
humans.
 In the last years:
› H1N1 (Swine flu; Animal-Human) (five genes
from swine, two from avian, one from human).
12,000 deaths.
› H7N9 (avian, China)no human to human spread
Transmission:
 Respiratory droplets, aerosols and fomites.
 Some subtypes can be transmitted from animals
to human e.g. H1N1, H5N1.
Pathogenesis:
 Tropism: viral hemagglutinin (H) bind to sialic
acid containing glycoproteins on columnar cells
of the throat, bronchi and lungs.
• Certain subtypes (H5N1, H1N1) bind to lower
cells at a higher rate (sever pneumonia).
 Up-take of virus into endocytic vesicle.
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Uncoating and release of the viral genome
segments into the cytoplasm.
Replication of viral RNA in the nucleus &
release from the cell by the NA.
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Tissue Damage:
 Infected columnar cells produce interferon-α;
monocytic and lymphocytic attraction.
 Massive inflammation with edema formation.
 In sever cases (e.g. H1N1): hemorrhagic and
necrotizing bronchitis and tracheobronchitis
and later: bronchopneumonia & alveolar
damage with extensive fibrosis can happen.
Symptoms: starts as URTI then LRT:
 Fever, dry cough, muscle pain, and
generalized pain.
 In sever cases: bleeding from mouth and
throat with symptoms of acute respiratory
distress syndrome (ARDS).
Prognosis:
 Seasonal influenza is usually a self-limiting
disease but epidemic and pandemic influenza
are severe and may be fatal.
Diagnosis:
 Usually clinical.
 Specimens: nasopharyngeal swabs, throat
swabs or other respiratory secretions.
 Laboratory diagnosis:
o Direct detection of viral antigens by
rapid test, direct immunofluorescent or
ELISA.
o Detection of viral RNA by PCR.
Treatment and Prophylaxis:
Anti-viral drugs:
• Amantadine and rimantadine inhibit viral
uncoating process.
• Zanamivir, oseltamivir and peramivir are NA
inhibitors.
Vaccines:
• Inactivated vaccine: injectable.
• Live attenuated vaccine: nasal spray.
o Both vaccines contain B virus and two
strains of influenza A virus; It should be
given annually for high risk group.
Coronaviruses
Greek word; crown because of the crown like
appearance of the viral surface projections.
Virology:
• Family: Coronaviridae (Co-Vs).
• Helical, enveloped, Ss RNA viruses.
• They infect humans and animals and due
to their high mutation rate they can cross
species.
 Transmission:
inhalation of respiratory
aerosols.
 Clinical manifestations:
› Upper respiratory infection: 10-30% of
common cold cases.
› Lower respiratory infection: by the new
viruses known as SARS-CoV; and MERSCoV.
 Immunity is short lived and reinfection can
happen within few months.
 Sever Acute
Respiratory Syndrome (SARSCoV): jumped from bats to civet cats and then to
human after mutation.
 The virus became able to spread between human
in 2003 and caused a large outbreak in china
which spread world wide with high mortality. (29
countries, 8273 cases, 775 deaths)
 Super spreader: one patient with SARS can
transmit the disease to > 10 persons.
 Interact with lungs-cellular receptor (angiotensinconverting enzyme 2).
 Symptoms: fever, dry cough, myalgia, diarrhea
followed by tachypnea and respiratory distress.
Middle East Respiratory Syndrome
Coronavirus (MERS-CoV)
 Was first identified in Saudi Arabia in 2012
then other cases were discovered inside &
outside the Arabian Peninsula.
 Symptoms: fever, cough, and shortness of
breath, diarrhoea. Severe illness can cause
respiratory failure & requires mechanical
ventilation.
 Mortality rate ≈ 27%.
 Camels may be the source of infection.
 Tell 2nd
February 2015 there were 971
laboratory-confirmed cases of MERSCoV reported to WHO, including at least
356 deaths.
 No specific treatment or vaccine is
available for coronaviruses.