Influenza

Question 1

is the influenza virus DNA or RNA?

Answer 1

RNA

Question 2

how many segments of genome are there in the influenza virus?

Answer 2

8

Question 3

what family does the influenza virus belong to?

Answer 3

orthomyxoviridae

Question 4

name the 3 groups of influenza virus?

Answer 4

A
B
C

Question 5

what do each of the groups of influenza virus infect?

Answer 5

A - mammals and birds

B+C - humans only

Question 6

name the two surface proteins on the influenza virus

Answer 6

haemagglutinin

neuraminidase

Question 7

what does haemagglutinin do? how many H antigens are there and which ones infect humans?

Answer 7

facilitates viral attachment and entry to the host cell

18

H1-3

Question 8

what does neuraminidase do? how many N antigens are there?

Answer 8

enables new virion to be released from the host cell

11

Question 9

describe antigenic drift

Answer 9

mechanism of genetic variation
occurs continually with small on-going point mutations in the genes coding for antibody binding sites. these may change the antigenic properties and eventually the immune system will not combat the virus as well.

Question 10

what does antigenic drift result in?

Answer 10

antigenic drift results in worse than normal epidemics and vaccine mismatch

Question 11

describe antigenic shift

Answer 11

results in an abrupt major change in virus, resulting in new H/N combinations. this is the genetic change that enables a flu strain to jump from one animal species to another. it causes reassortment of the virus’s gene segments

Question 12

what does antigenic shift result in?

Answer 12

pandemics

Question 13

seasonal flu vs pandemic

Answer 13

Seasonal flu occurs every winter and affects 10-15% of the population. It is usually unpleasant but not life-threatening. Pandemic flu occurs sporadically affecting > 25% of the population. It is more serious and results in more complications. For a virus to be capable of causing a pandemic it must:

1. Human pathogenicity
2. New virus (antigenic shift) – susceptible population
3. Efficient person to person transmission

Question 14

clinical features of flu

Answer 14

• Incubation period of 2-4 days (ranging from 1-7)
• Abrupt fever up to 41°C (commonly 38-40°C) which lasts 3 days (1-5 days)
• Plus 2 or more of
o Cough (sore throat, rhinorrhoea)
o Myalgia
o Headache
o Malaise
• Predominance of systemic symptoms
• Less common symptoms:
o Nausea
o Vomiting
o Diarrhoea

Question 15

what is the WHO definition of influenza like illness?

Answer 15

fever and cough with onset within the last 10 days

Question 16

if influenza like illness requires hospitalisation what will it be known as?

Answer 16

severe acute respiratory infection

Question 17

describe the transmission of flu

Answer 17

o Airborne – person -> person by large droplets > 5 microns
o Contact
§ Direct
§ Indirect (person -> fomite -> person)

Question 18

discuss viral shedding

Answer 18

o First 4 days of illness (range 1-7)

o Longer in young children and immunocompromised

Question 19

discuss virus survival

Answer 19

o 24-48 hours on non-porous surfaces

o 8-12 hours on porous surface e.g. tissue

Question 20

what are the risk factors for complicated influenza?

Answer 20

1. Neurological, hepatic, renal, pulmonary and chronic cardia disease
2. Diabetes mellitus
3. Severe immunosuppression
4. > 65
5. Pregnancy (including up to 2 weeks post-partum)
6. Children < 6 months
7. Morbid obesity BMI >40

Question 21

complications of flu: resp

Answer 21

acute bronchitis
secondary bacterial pneumonia
primary viral pneumonia

Question 22

complications of flu: cardiac

Answer 22

myocarditis

pericarditis

Question 23

complications of flu: CNS

Answer 23

transverse myelitis/Guillian Barre

Myositis and myoglobinuria

Question 24

discuss encephalitis lethargia

Answer 24

• Fever, headache
• External ophthalmoplegia
• Lethargy
• Sleep reversal
• 25% mortality
• Postencephalitic parkinsonism
• Serology +ve flu A

Question 25

diagnosis and investigations of flu

Answer 25

• Viral nose and throat swabs/VTS (molecular detection/PCR; using flocked swabs)
• CXR – pneumonitis/pneumonia/ARDS
• Blood culture
• Pulse oximetry – SpO2 <92% need ABG and oxygen
• Resp rate
• U+Es, FBC, CRP (CRP monitoring recovery of pneumonia- should halve in 4 days)

Question 26

patients with flu like symptoms and a fever for >4 days should have what and why?

Answer 26

urgent CXR looking for secondary bacterial pneumonia

Question 27

describe the CURB-65 score for assessing the severity of bacterial pneumonia

Answer 27

confusion
urea > 7mmol/l
RR > 30
BP diastolic < 60 or systolic < 90
> 65

Question 28

name two neuraminidase inhibitors that can be used for flu

Answer 28

oseltamivir (tamiflu)

zanamivir

Question 29

how soon after onset of flu symptoms should antivirals be started?

Answer 29

48 hrs or if complicated illness at any time

Question 30

adverse effects of oseltamiver

Answer 30

common - nausea, vomiting, abdo pain, diarrhoea

less common - headache, hallucinations, insomnia, rash

Question 31

adverse effects of zanamivir

Answer 31

bronchospasm

Question 32

when does an immunocompetent adult become non-infectious with flu?

Answer 32

24hrs after last flu symptoms (fever and cough)

or when anti-viral therapy is completed whichever is longer