Influenza Flashcards
What is orthomyxoviridae?
8-segments of ssRNA
Influenza A B, C and D
What are the 2 components of influenza structure? State their function as well
Haemagglutinin (H): 500 H spikes/viral
particle- Fuses viral envelope to host cell plasma
membrane to initiate infection
Neuraminidase (N) : 100 N spikes/viral
particle- Releases virus from host cell surface
How the the influenza A strains different from each other?
Haemagglutinin and Neuraminidase are
type-specific antigens embedded in the viral
envelope that characterise different strains
of Influenza A (eg. H1N1, H3N2,H1N2
How does antigenic shift occur to result in a new influenza strain?
Re-assortment/recombinationof segmented RNA can occur during viral replication and result in a
progeny virus (with novel H and N antigens) when 2 Influenza virus strains infect the same host cell
simultaneously.
* 2 different Influenza A strains (eg. H3N8 from ducks) and H2N2 for example can re-assort and result in a
new Influenza A strain (H3N2)
* This is called Antigenic shift = Sudden major change in the antigenicity of the H and N antigens. This
results in spread of the” new” strain to immune (to previous circulating strains) patients and can cause
pandemics. Only seen with Influenza A. Changes in H or N antigens may also increase pathogenicity and
/or transmissibility of the virus.
How does antigenic drift occur?
Small mutations in H and N antigens that occur constantly. Seen with Influenza A and B.
When these antigenic changes enable the virus to multiply in individuals with immunity to preceding
strains, this new subtype can re-infect the community and cause an epidemic. Main reason for annual
adjustment of vaccines.
Which virus strains are regarded as normal striains?
H1N1 and H3N2
Explain the pathogenesis of influenza
Highly infectious
* Droplet transmission
* Predilection for colder months (in tropics all year)– people gathering inside with limited air space and
possibly decreased host resistance to infection
What is the incubation period of flu?
1-3 days
How does the influenza virus enter the tissues?
Virus attaches to sialic acid receptors on respiratory epithelial cells via H glycoprotein
* Initial symptoms as result of direct viral damage as well as inflammatory response.
How long are adults infectious after catching flu?
Adults are infectious from 1 day before start of symptoms until day 7 of illness. Immunosuppressed
patients may shed virus for longer
Clinical picture of influenza
Chills and shivering
Fever and Malaise
Myalgia and headache
Photophobia
Resp symptoms: Dry throat, runny nose, dry cough
What are the complications of influenza?
Damage to respiratory epithelium predisposes to secondary bacterial infections
* Secondary bacterial infections include pneumonia, sinusitis and otitis media-Staphylococcus aureus, Streptococcus pneumonia, Haemophilus influenzae
-Primary viral pneumonia (hemorrhagic)
-Myositis, rhabdomyolysis-Myocarditis, pericarditis
List CNS complications caused by influenza
meningitis, encephalomyelitis, polyneuritis (as result of immunopathological mechanisms, rather than viral invasion)
Children with flu who receive aspirin can develop what?
Reye’s syndrome (encephalopathy + fatty
degeneration of liver)
How is influenza diagnosed?
Real-time PCR on respiratory samples to detect viral RNA (highly sensitive (90
95%) and specific)
* Typing also available on some platforms
What are the types of flu vaccines?
Trivalent and quadrivalent
Inactivated (split or subunit)or live attenuated (cold- adapted)
* Parenteral injection or intranasal (live attenuated vaccines)
* Cell culture based vs. egg grown
How are live attenuated vaccines administered?
intranasally
Who should get flu vaccines?
prioritize essential workers and people at higher risk of influenza and COVID-19
complications:
less than 6 months
* Age 6 months to 5 years
* Age ≥50 years
* Chronic conditions (excl. HPT)
Immunosuppressed
Pregnant
Contraindications of influenza vaccine (3)
Severe allergy to vaccine (incl. egg allergy)
* Acute febrile illness
* Live attenuated vaccine contraindicated in immunosuppressed patients, pregnant women
PEP to flu
- Not recommended in view of widespread Oseltamivir resistance.
- If PEP (Post-exposure prophylaxis) absolutely necessary (eg. severely
immunocompromised patients) – treatment doses of Oseltamivir (Tamiflu®)
recommended
What is the treatment of flu?
Amantadine and Rimantadine (adamantanes) – previously used for Influenza A
* M2 ion channel blockers that affect intracellular viral uncoating
* Now, Neuraminidase inhibitors (Oseltamivir and Zanamivir) favoured
* Active against both Influenza A and Influenza B
How long is the duration of Tx?
Treatment duration = 5 days (10 days in immunocompromised patients)
Which drug cannot be used in influenza?
Corticosteroids are contra-indicated for use in Influenza (mortality can be increased)
