Dr. Nehal Draz
Myxo = affinity to mucin
Myxoviruses
Orthomyxo
viruses
-Smaller
-Segmented RNA genome
-Liable to Agic variation
Influenza viruses
Paramyxo
viruses
-Larger
-Single piece of RNA
- Not liable to Agic variation
- Parainfluenza
- Mumps vairus
- Measles virus
- Respiratory
syncytial virus
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Replicate in mucus membranes
Target tissue: upper & lower respiratory
tract
Cause influenza: acute respiratory disease
that may occur in epidemics or even
pandemics

-ve sense ssRNA
viruses with
segmented genome(8
pieces)
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RNA segments +
nucleoprotein form a
nucleocapsid
RNA segments+
nucleocapsid = a
nucleocapsid with
helical symmetry
I- Type Specific Ag ( core Ag):
 Three serotypes: A,B&C
according to internal
structure ptns ( nucleocapsid
& matrix). These ptns don’t
cross react
II- Strain ( subtype) specific Ag:
 Two surface glycoptns,
HA&NA are used to subtype
the virus
 Influenza strains are named
after their types of HA& NA
surface ptns e.g. H1N1
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Haemagglutinin
Binds to host cell
surface receptor
The target of
neutralizing Abs
Haemagglutinates
RBCs from various
animal species
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Neuraminidase
Cleaves neuraminic
acid to release virus
progeny from
infected cells
Degrades the
protective layer of
mucin in the
respiratory tract
Plays a min role in
immunity to influenza
Neuraminidase
Cleaves neuraminic acid to
release virus progeny from infected cells
Haemagglutinin
Binds to host cell surface receptor
I- Type A virus:
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Infects humans as well as animals
Undergoes continuous Agic variations
Many animal species have their own
influenza A virus
Pigs & birds are important animal
reservoirs playing a role in occurrence of
influenza epidemics
II- Type B virus:
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causes milder disease
Infects human only
Undergoes Agic variation but only Agic
shift
III- Type C virus:
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Of doubtful pathogenicity
Agically stable
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It is the process in which the genetic
segment encoding for envelope
glycoproteinacs (HA&NA) is replaced by
another one from a different strain
through genetic reassortment causing
replacement of the original HA or NA by
a new one
Genetic reassortment: the exchange of
genetic material between viruses inside a
host cell

This is responsible for appearance of
completely new strains to which no one is
immune & not covered by annual vaccinations
Chicken H5N1
Human H3N2
H5N2 influenza A

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Agic shift occurs only in infuenza A
because it has a wide host range, giving
influenza A the opportunity for a major
reorganization of its genome & hence its
surface Ags
Pigs are susceptible to avian, human &
swine influenza viruses and they
potentially may be infected with influenza
viruses from different species. If this
happens, it is possible for the genes of
these viruses to mix and create a new
virus
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It is spontaneous point mutation of known
strains of influenza causing minor change
of an amino acid sequence of HA or NA.
Occurs in influenza A & B
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Highly contagious disease with person to
person transmission
Three modes of transmission
Droplet
Air- Borne
Contact
Direct
Indirect
Viral NA degrades the protective mucin layer
Allowing the virus to enter the cells
Epithelial cells of
respiratory tract
Replication inside the cells
Cilia damage
Epithelial desquamation
The infection is limited to the respiratory tract….why?
There are proteases there essential for HA to be active
Despite systemic symptoms, no viremia….why?
Those symptoms are due to cytokines
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.
FEVER
Complications
•
•
pneumonia and respiratory failure
Reye,s Syndrome
Sore throat
cough
headache
50% of infected people don’t present any symptoms
But still contagious
This makes it difficult to stop the spread of the disease
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Acute encephalopathy with hepatic necrosis
in children & adolescents (2-16 yrs)
A rare complication of influenza A, B and
Varicella- Zoster infection
There is an association between salicylate
intake and subsequent development of
Reye’s Syndrome
Specimen: nasal washings, gargles, throat
swabs
1- Direct Virus Demonstration:
a) Direct Immunofluorescence: for rapid Ag
detection in nasal aspirates, not very
sensitive
b) RT-PCR: for detection of viral RNA
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2- Viral Isolation: specimens are
inoculated into emberyonated eggs or
primary monkey tissue culture
Cell culture are tested for the virus by
Haemagglutination
I-vaccines
- Inactivated
- Live attenuated
-Amantadine& Rimantadine
-Zanamavir & Osteomavir
II- chemoprophylaxis
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A new vaccine is formulated annually using
the types & strains of influenza predicted to
be the major problem for that year.
Predictions are based on world wide
monitoring of influenza
The vaccine is multivalent
1) Inactivated vaccine:
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Whole killed vaccine prepared in chick
embryo
Recommended for persons at increased risk
for influenza related complications & their
contacts
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Given by intramuscular injection
It has a short lived protective effect so
usually given in the fall, for the protection
to be high in December & January
Given every year as protection is short
lived, and also as the most effective
strains for the vaccine will change due to
shift or drift
2) Live attenuated
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Recently approved only for healthy
individuals
Prepared from temperature- sensitive
mutants that can replicate in cooler nasal
passages (33C) but not in warm lower
respiratory tract
Given by nasal spray thus could provide
mucosal, humoral & cell-mediated immunity
1)Amantadine & Rimantadipne:
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Prevent penetration & uncoating of the virus
Treat & prevent influenza A only
Given to high risk groups
2) Zanamavir & Oseltamivir (tamiflu)
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They are neuraminidase inhibitors, inhibiting
the release of virus from infected cells
This limits the infection by reducing the
spread of virus from one cell to another
For treatment not prevention
Effective against influenza A &B