EDWARD-BENGIE L. MAGSOMBOL, MD
FPCP, FPCC, DASNC
Associate Professor, Department of Microbiology
Fatima College of Medicine
A 22-year old man suddenly experienced
headache, myalgia, malaise, dry cough, and
fever. He basically felt “lousy”. After a couple
of days, he had a sore throat, his cough had
worsened, and he started to feel nauseated
and vomited. Several of his family members
had experienced similar symptoms during the
previous two weeks.
Characteristics:
•
•
•
•
Influenza A, B and C the only members
Enveloped virion; inactivated by detergents
Segmented negative-sense RNA genome
with eight nucleocapsid segments
Genetic instability responsible for annual
epidemics (mutation:drift) and periodic
pandemics (reassortment: shift)
Structure & Replication:
•
Envelope with two group-specific glycoproteins:
1. Hemagglutinin (HA)
 Functions:
a. Viral attachment protein – bind to sialic
acid on epithelial cell surface
receptors
b. Promotes fusion of the envelope to the
cell membrane
c. Hemagglutinates human, chicken and
guinea pig rbc
d. Elicits protective neutralizing antibody
response
Structure & Replication:
•
Envelope with two group-specific glycoproteins:
2. Neuraminidase (NA)
 With enzyme activity
 Cleaves the sialic acid on glycoproteins,
including the cell receptor  prevents
clumping & facilitates release of virus
from infected cells
 Target for two antiviral drugs: zanamivir
(Relenza) and oseltamivir (Tamiflu)
Structure & Replication:
•
Type-specific proteins: used to differentiate
among influenza A, B, and C viruses
1. Matrix protein (M1)
 Viral structural protein
 Interacts with nucleocapsid & envelope
 promotes assembly
2. Membrane protein (M2)
 Forms membrane channel
 Facilitates uncoating & HA production
 Target for amantadine
3. Nucleocapsid proteins (NP)
Structure & Replication:
•
Transcribes and replicates its genome in the
target cell nucleus
•
Assembles and buds from the plasma
membrane
Pathogenesis & Immunity:
•
Virus first targets & kills mucus-secreting, ciliated,
and other epithelial cells  loss of primary
defense system
•
Cleavage of sialic acid residues of mucus by NA 
provide access to tissues
•
Preferential release of the virus at the apical
surface of epithelial cells and into the lungs 
promote cell-to-cell spread & transmission to other
hosts
Pathogenesis & Immunity:
•
Spread to lower respiratory tract  shedding of
bronchial or alveolar epithelium
•
Promotes bacterial adhesion to the epithelial cells
 pneumonia
•
Histologic: inflammatory response of mucosal
membrane (primarily monocytes & lymphocytes)
with submucosal edema
Pathogenesis & Immunity:
•
Systemic symptoms due to the interferon and
lymphokine response to the virus
•
Local symptoms due to epithelial cell damage
•
Interferon & CMI responses (NK & T cell)
important for immune resolution and
immunopathogenesis  classic symptoms
associated with interferon induction
•
Antibody important for future protection against
infection
Major contributors to pathogenesis
Immune response
Antibody
T-cell
response
Less frequent outcomes
Future protection
Interferon
induction
Aerosol
inoculation
of virus
Pneumonia
Replication
in resp. tract
Desquamation
of mucussecreting and
ciliated cells
Secondary bacterial pneumonia
Primary viral pneumonia
CNS/muscle involvement
Influenza
syndrome
Why is influenza difficult to
control even when there is
vaccination available?
Antigenic Changes:
1. Antigenic drift
• Minor change
• Mutation of the HA and NA genes
• Occurs every 2 to 3 years
• Cause local outbreaks of influenza A & B
2. Antigenic shift
• Major change
• Result from re-assortment of genomes
among different strains, including animal
strains
• Associated with pandemics
• Occurs only with influenza A
Chicken
influenza
virus
Human
influenza
virus
Lung cell
Re-assortment of RNA
genome segments
New strain of influenza
virus
How is the virus
transmitted?
•
Virus is spread by inhalation of aerosol
droplets expelled during talking, breathing,
and coughing.
•
Virus likes cool, less humid atmosphere
•
Virus is extensively spread by school
children.
Who is at risk?
Seronegative people.
Adults: classic “flu” syndrome
Children: asymptomatic to severe respiratory
tract infection
High-risk Groups:
 Elderly
 Immunocompromised people
 People with underlying cardiac or
respiratory problems (including people
with asthma and smokers)
What are the clinical
syndromes associated with
the virus? What are the
possible complications?
Diseases Associated with Influenza Virus Infections
Disorder
Acute infection in adults
Symptoms
Rapid onset of fever, malaise, myalgia,
sore throat, and non-productive cough
Acute infection in children Acute disease similar to that in adults
but with higher fever, gastrointestinal
tract symptoms (abdominal pain,
vomiting), otitis media, myositis, and
more frequent croup
Complications
Primary viral pneumonia
Secondary bacterial pneumonia
Myositis & cardiac involvement
Neurologic syndromes:
Guillain-Barre syndrome
Encephalopathy
Encephalitis
Reye’s syndrome
How would the
diagnosis of influenza
be confirmed?
Laboratory Diagnosis of Influenza Virus Infection
Test
Cell culture
Hemadsorption to
infected cells
Hemagglutination
Hemagglutination inhibition
Antibody inhibition of
hemadsorption
Immunofluorescence,
ELISA
Serology: HI, headsorption inhibition, ELISA,
immunofluorescence,
complement fixation
Detects
Presence of virus, limited cytopathologic
effects
Presence of HA protein on cell surface
Presence of virus in secretions
Type and strain of influenza virus or
specificity of antibody
Identification of influenza type and strain
Influenza virus antigens in respiratory
secretions or tissue culture
Seroepidemiology
Which antiviral drugs are
effective for the treatment of
influenza virus infection? What
are the targets & mechanisms of
action of these drugs?
Amantadine, Rimantadine
• Target: M2 protein  inhibit an uncoating
step
• Do not affect influenza B or C virus
Zanamivir (Relenza) & Oseltamivir (Tamiflu)
• Target: neuraminidase  prevent release of
virus from infected cells
• Inhibit both influenza A and B
• Effective for prophylaxis and for treatment
during the first 24 to 48 hours after the
onset of influenza A illness
What is the best way to
control the virus?
The best way to control the virus is through
IMMUNIZATION!
•
Killed vaccine representing the “strains of the
year”
o Killed (formalin-inactivated) whole-virus
vaccine
o Detergent-treated virion preparations and
HA- and NA-containing detergent extracts
of virus
•
Vaccination routinely recommended for the
elderly and people with chronic pulmonary or
heart disease.
Properties of Orthomyxoviruses and Paramyxoviruses
Property
Orthomyxoviruses
Paramyxoviruses
Viruses
Influenza A, B, and C
Measles, mumps, RSV, and
parainfluenza viruses
Genome
Segmented (8 pieces) ssRNA Non-segmented ssRNA of
of negative polarity
negative polarity
Virion RNA
polymerase
Yes
Yes
Capsid
Helical
Helical
Envelope
Yes
Yes
Size
Smaller (110 nm)
Larger (150 nm)
Surface spikes
HA and NA on different
spikes
Hemagglutinin &
neuraminidase on same
spikes
Giant cell
formation
No
Yes
Members of the Family Paramyxoviridae
Genus
Human pathogens
Morbillivirus
Paramyxovirus
Measles virus
Parainfluenza viruses 1 to 4
Mumps virus
Respiratory syncytial virus
Nipah virus (1998, Malaysia and
Singapore)
Hendra virus (1994, Australia)
Pneumovirus
Members of the Family Paramyxoviridae
Unique Features of the Paramyxoviridae
•
•
•
Large virion with helical nucleocapsid
Negative RNA genome
Envelope containing viral attachment protein (HN,
paramyxovirus and mumps virus; H, measles
virus, and G, RSV) and a fusion protein (F)
o
o
o
•
•
•
HN with hemagglutinin & neuraminidase activity
H with hemagglutinin activity
G without hemagglutinin or neuraminidase acvitity
Replicates in cytoplasm
Penetrate the cell by fusion with and exit by
budding from the plasma membrane
Induce cell-to-cell fusion  multinucleated giant
cells
Envelope Spikes of Paramyxoviruses
Virus
Hemagglutinin Neuraminidase
Fusion
protein1
Measles virus
+
-
+
Mumps virus2
+
+
+
Respiratory
syncytial virus
-
-
+
Parainfluenza
virus2
+
+
+
1The
measles and mumps fusion proteins are also hemolysins.
2In mumps and parainfluenza viruses, the hemagglutinin and
neuraminidase are on the same spike and the fusion protein is on a
different spike.
An 18-year old college freshman
complained of a cough, runny nose, and
conjunctivitis. The physician in the
campus health center noticed small
white lesions inside the patient’s mouth.
The next day, a confluent red rash
covered his face and neck.
•
•
•
How is the disease
transmitted?
What clinical characteristics
of this case were diagnostic
for measles?
When was the patient
contagious?
Transmission:
• Inhalation of large-droplet aerosols
Disease Mechanisms:
• Infect epithelial cells of respiratory tract
• Spread systemically in lymphocytes and
by viremia
• Replicate in cells of conjunctivae,
respiratory tract, lymphatic system,
blood vessels, and CNS
• Characteristic rash caused by immune T
cells targeted to measles-infected
endothelial cells lining small blood
vessels
Mechanisms of spread and pathogenesis of measles
Inoculation of
respiratory tract
RASH
Recovery
(lifelong
immunity)
Local replication
in respiratory
tract
Virus-infected
cell + immune
T cells
Post-infectious
encephalitis
(immunopathological;
etiology)
Lymphatic
spread
Conjunctivae
Respiratory tract
Urinary tract
Small blood vessels
Lymphatic system
CNS
Subacute sclerosing
panencephalitis
(defective measles
virus infection of CNS)
Viremia
Wide
dissemination
No resolution of acute
infection due to
defective CMI
(frequently fatal
outcome)
•
Incubation period: 7 to 13 days
•
Prodrome: high fever + 3C’s + P  most infectious
•
Koplik’s spots after 2 days of illness  last 24 to
48 hours
•
Appearance of exanthem within 12 to 24 hours of
the appearance of Koplik’s spots
•
Rashes undergo brawny desquamation
Clinical Consequences of Measles Virus Infection
Disorder
Symptoms
Measles
Characteristic maculopapular rash, cough,
conjunctivitis, coryza, photophobia,
Koplik’s spots
Complications: otitis media, croup,
bronchopneumonia, and encephalitis
Atypical measles
Rash (most prominent in distal areas);
possible vesicles, petechiae, purpura, or
urticaria
SSPE
CNS manifestations (e.g. Personality,
behavior, and memory changes; myoclonic
jerks; spasticity; and blindness)
How can the
infection be
prevented?
Post-exposure: Immune serum globulin given
within six days of exposure
Pre-exposure:
1. Live, attenuated vaccine
2. MMR
• Composition:
a. Measles – Schwartz or Moraten substrains of
Edmonton B strain
b. Mumps – Jeryl Lynn strain
c. Rubella – RA/27-3 strain
•
•
Schedule: at 15-24 months and at 4-6 years
Efficacy: 95% lifelong immunization with a
single dose
A 13-month-old child had a runny nose,
mild cough, and low-grade fever for several
days. The cough got worse and sounded
like “barking.” The child made a wheezing
sound when agitated. The child appeared
well except for the cough. A lateral
radiograph of the neck showed a subglottic narrowing.
What is the specific and
common name for these
symptoms?
What other agents would cause
a similar clinical presentation
(differential diagnosis)?
What is the most common
cause?
How was the virus
transmitted?
Answer: Droplet inhalation
Parainfluenza Viruses
Characteristics:
•
Four serotypes
•
Infection limited to upper respiratory tract
 Upper respiratory tract disease most
common, but significant disease can occur
with lower respiratory tract infection
•
Not systemic and do not cause viremia
•
Infection induces protective immunity of short
duration
Parainfluenza Viruses
Four serologic types
•
Types 1, 2, and 3
 Second only to RSV as important causes of
severe lower respiratory tract infection in
infants and young children
 Cause respiratory tract syndromes ranging
from a mild cold-like URTI to bronchiolitis to
pneumonia
 Especially associated with croup
•
Type 4
 Mild upper respiratory tract infection in
children and adults
Parainfluenza Viruses
•
Clinical:
•
Main cause of croup in children < 5 y/o
•
Characterized by harsh cough (“seal bark
cough” and hoarseness  due to subglottal
swelling
•
Other clinical conditions: common cold,
pharyngitis, otitis media, bronchitis, and
pneumonia
Respiratory Syncytial Virus
•
Most important cause of pneumonia and
bronchiolitis in infants
•
Fusion protein causes formation of
multinucleated giant cells  syncytia
•
Humans and chimpanzees are the natural
hosts
•
Two serotypes – subgroup A and B
Respiratory Syncytial Virus
•
MOT:
1. Respiratory droplets
2. Direct contact of contaminated hands with the
nose or mouth
•
Infection in infants more severe and usually
involves lower respiratory tract than in older
children and adults
•
No viremia occurs
Respiratory Syncytial Virus
•
Severe disease in infants with
immunopathogenic mechanism
o
Maternal antibody passed to infant  react with
the virus  form immune complexes  damage
respiratory tract cells
•
Most individuals with multiple infections  indicate
incomplete immunity
•
IgA respiratory antibody reduces the frequency of
infection as a person ages
Respiratory Syncytial Virus
•
Clinical:
1. Bronchiolitis
2. Pneumonia
3. Otitis media in young children
4. Croup
5. Upper respiratory tract infection similar to
common cold in older children and adults
Respiratory Syncytial Virus
•
Treatment:
 Aerosolized ribavirin (Virazole) for
severely ill hospitalized infants
 Combination ribavirin + hyperimmune
globulin may be more effective
A 7 year-old boy developed fever, body
malaise, and loss of appetite. This was
followed by tender swelling around the
right mandibular area, with increase in
the pain everytime he drinks calamansi
juice. The condition spontaneously
resolved after one week.
Mumps Virus
•
Two types of envelope spikes:
1. With both hemagglutinin and neuraminidase
activities
2. With cell-fusing and hemolytic activities
•
Only one serotype
•
Neutralizing antibodies directed against the
hemagglutinin
•
Humans are natural hosts
Mumps Virus
•
MOT: respiratory droplets
•
Infects both upper and lower respiratory
tracts  spread through blood  parotid
glands, testes, ovaries, pancreas, and in
some cases, meninges
•
Occurs only once  subsequent cases may
be caused by parainfluenza viruses,
bacteria, and by duct stones
Mumps Virus
Mumps Virus
Mumps Virus
•
Complications:
1. Orchitis in post-pubertal males  may lead to
sterility if bilateral
2. Meningitis – usually benign, self-limited, and
without sequelae
Mumps Virus
•
Prevention:
Live, attenuated vaccine given subcutaneously to
children at 15 months of age (MMR)
Immune globulin not useful for preventing or
mitigating mumps orchitis.