Influenza

Question 1

What is orthomyxoviridae?

Answer 1

8-segments of ssRNA
Influenza A B, C and D

Question 2

What are the 2 components of influenza structure? State their function as well

Answer 2

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

Question 3

How the the influenza A strains different from each other?

Answer 3

Haemagglutinin and Neuraminidase are
type-specific antigens embedded in the viral
envelope that characterise different strains
of Influenza A (eg. H1N1, H3N2,H1N2

Question 4

How does antigenic shift occur to result in a new influenza strain?

Answer 4

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.

Question 5

How does antigenic drift occur?

Answer 5

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.

Question 6

Which virus strains are regarded as normal striains?

Answer 6

H1N1 and H3N2

Question 7

Explain the pathogenesis of influenza

Answer 7

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

Question 8

What is the incubation period of flu?

Answer 8

1-3 days

Question 9

How does the influenza virus enter the tissues?

Answer 9

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.

Question 10

How long are adults infectious after catching flu?

Answer 10

Adults are infectious from 1 day before start of symptoms until day 7 of illness. Immunosuppressed
patients may shed virus for longer

Question 11

Clinical picture of influenza

Answer 11

Chills and shivering
Fever and Malaise
Myalgia and headache
Photophobia
Resp symptoms: Dry throat, runny nose, dry cough

Question 12

What are the complications of influenza?

Answer 12

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

Question 13

List CNS complications caused by influenza

Answer 13

meningitis, encephalomyelitis, polyneuritis (as result of immunopathological mechanisms, rather than viral invasion)

Question 14

Children with flu who receive aspirin can develop what?

Answer 14

Reye’s syndrome (encephalopathy + fatty
degeneration of liver)

Question 15

How is influenza diagnosed?

Answer 15

Real-time PCR on respiratory samples to detect viral RNA (highly sensitive (90
95%) and specific)
* Typing also available on some platforms

Question 16

What are the types of flu vaccines?

Answer 16

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

Question 17

How are live attenuated vaccines administered?

Answer 17

intranasally

Question 18

Who should get flu vaccines?

Answer 18

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

Question 19

Contraindications of influenza vaccine (3)

Answer 19

Severe allergy to vaccine (incl. egg allergy)
* Acute febrile illness
* Live attenuated vaccine contraindicated in immunosuppressed patients, pregnant women

Question 20

PEP to flu

Answer 20

• 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

Question 21

What is the treatment of flu?

Answer 21

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

Question 22

How long is the duration of Tx?

Answer 22

Treatment duration = 5 days (10 days in immunocompromised patients)

Question 23

Which drug cannot be used in influenza?

Answer 23

Corticosteroids are contra-indicated for use in Influenza (mortality can be increased)