influenza

Question 1

RNA virus

Answer 1

8 segment genome
-mutate more quickly
3 main groups: A, B, C
IfA infects mammals and birds, IfB & IfC only humans

Question 2

surface proteins

Answer 2

haemagglutinin
-facilitates viral attachment and entry to host cell
neuraminidase
-enables new virion to be released from host cell

Question 3

antigenic drift

Answer 3

mechanism of genetic variation within virus
small on going point mutations in genes coding for antibody binding sites occur continually
-change antigenic properties and eventually immune system cannot combat
causes worse than normal epidemics and vaccine mismatch

Question 4

antigenic shift

Answer 4

abrupt major change in virus- resulting in new haemagglutinin and neuraminidase combinations

• enables flu strain to jump from one species to another
• process which two or more different strain of virus combine to form a new subtype (reassortment of virus gene segments)
• new antigenic properties, population at risk is unprotected and cause pandemic

Question 5

seasonal flu

Answer 5

occurs winter
affects o 10-15 % of the population
o Usually unpleasant but not life-threatening

Question 6

pandemic flu

Answer 6

o Occur sporadically (about 3 times each century)
o Affects ~25% of the population
o More serious, more complications

Question 7

avian flu

Answer 7

• Spread through direct contact with infected birds, dead or alive.
o No known transmission by eating properly cooked food/eggs etc.

Question 8

clinical features

Answer 8

• Clinical features:
o Incubation period 2-4 days (range 1-7 days)
o Abrupt fever up to 41°C (commonly 38-40°C) which lasts 3 days (range 1-5 days)
♣ Plus 2 or more of: cough, sore throat, rhinorrhoea, myalgia, headache, malaise.
o Predominance of systemic symptoms
o Less common symptoms: Nausea, vomiting, diarrhoea

high risk-
Chronic respiratory disease
other chronic disease
diabetes mellitus
immunosuppression -corticosteroid, transplant
-pregnancy
-obesity >40

Question 9

complications

Answer 9

o	Respiratory:	
♣	Acute Bronchitis
♣	Secondary Bacterial Pneumonia (~20%)
Appears 4-5 days after start of ‘flu
uncommon:
primary viral pneumonia
myocarditis
transverse myelitis
myositis

Question 10

investigation and diagnosis

Answer 10

o Viral nose and throat swabs (Flocked swabs)
o Chest X-ray – pneumonitis/pneumonia/ARDS
o Blood culture
o Pulse oximetry – SpO2 <92% need ABG and oxygen
o Respiratory rate
o U & E’s, Creatinine & FBC
o CRP – monitoring recovery of pneumonia - should halve in 4 days
♣ Tends to be low in influenza
-secondary bacterial pneumonia

Question 11

treatment

Answer 11

o antiviral therapy ASAP and within 48hours of symptom onset.
o Should always be given in complicated illness, no matter how long after onset of illness.

Question 12

Oseltamivir (tamiflu)

Answer 12

neuraminidase inhibitor
• Common – Nausea, vomiting, abdominal pain, diarrhoea
• Less Common – Headache, hallucinations, insomnia and rash
Cautions: Renal dosing needed

Question 13

zanamivir (relenza)

Answer 13

neuraminidase inhibitor

• dry powder inhaler
• bronchospasm

Question 14

in pregnancy

Answer 14

use only if benefits outweighes risk

Question 15

vaccination

Answer 15

o Prepared each year using viruses considered most likely to be circulating in the forthcoming winter
o Contraindicated in those with egg allergy
o Chemically inactivated and purified
o Vaccines are trivalent – containing 2 type A & 1 type B subtype viruses
Single 0.5 ml intramuscular injection