This document discusses orthomyxoviruses, which include influenza viruses A, B, and C. It provides details on their structure, including being linear, segmented RNA viruses with negative-sense and enveloped. It also describes the influenza virus life cycle, pathogenesis in humans, clinical symptoms of influenza infection, and methods for prevention and control including inactivated viral vaccines and live attenuated influenza vaccines.

2. ORTHOMYXOVIRUSES
• Linear
• 8 segmented(7 in influenza C) RNA
• Negative sense, single stranded RNA
• Replication take place in cytoplasm
• Helical
• Enveloped
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3. ORTHOMYXOVIRUSES
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4. Group V: (-)sense RNA Viruses
Family
(Subfamily)
Genus Type Species Hosts
Orthomyxoviridae Influenza A virus Influenza A virus Vertebrates
Influenza B virus Influenza B virus Vertebrates
Influenza C virus Influenza C virus Vertebrates
Isavirus Infectious
salmon anemia
virus
Vertebrates
Thogotovirus Thogoto virus Vertebrates
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5. Pathogenesis & Pathology
• Spreads from person to person by airborne droplets, or
contaminated hands and surfaces.
• Viral NA lowers the viscosity of the mucous film in the resp T,
exposing the cellular surface receptors and promoting the
spread of virus-containing fluid to lower resp T. Within short
time, many resp cells are infected and eventually killed.
• Interferon is effective against influenza virus and attributes to
host recovery.
• Influenza infections cause cellular destruction and
desquamation of superficial mucosa of the respiratory tract but
do not affect the basal layer of epithelium. Viral damage in the
epith lowers its resistance to secondary bacterial invaders esp
staphylococci, streptococci and Haemophilus influenzae.
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6. Clinical findings
• Uncomplicated Influenza : Abrupt symptoms include
chills, headache, dry cough, muscular aches. These
may be induced by influenza A or B. In contrast,
influenza C causes a common cold illness, Coryza.
• Pneumonia : complications occur only in the elderly
and debilitated. Influenza infection enhances the
susceptibility of patients to bacterial superinfection,
due to loss of ciliary clearance, dysfunction of
phagocytic cells.
• Reye’s Syndrome : an acute encephalopathy of
children and adolescents (2-16yrs)
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7. Prevention & Control by Vaccines
• A) Inactivated Viral Vaccines:
• Parenteral use;usually contain 1 or 2 type A and a type B
viruses, isolated from previous winter’s outbreaks.
• Strains are grown in embryonated eggs and the virus is
harvested from egg allantoic fluid.
• Vaccines are either whole virus (WV), subvirion (SV), or
surface Ag (SAg) preparations. WV=contains intact, inactivated
virus; SV=purified virus disrupted with detergents; SAg
contains purified HA and NA glycoproteins.
• Sometimes called “flu shot” or “flu jab”.
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8. Prevention & Control by Vaccines
• B) Live Attenuated Influenza Vaccine
• Contains live but attenuated (weakened) vaccine. It is sprayed
into nostril.
• For both types of vaccines, it will take up to 2 weeks to
develop protection after vaccination.
• The synthetic drugs amantadine and rimantadine
hydrochloride effectively prevent infection and illness caused
by type A, but not by type B, viruses. The drugs interfere with
virus uncoating and transport by blocking the transmembrane
M2 ion channel (see fig of replication).
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