influenza

Question 1

influenza virus characteristics

Answer 1

RNA virus
8 segment genome
orthomyxovirdae family

Question 2

what are 3 main groups of influenza virus and who/what can they infect

Answer 2

A
B
C

A infects mammals and birds
B and C only humans

Question 3

surface proteins of influenza virus

Answer 3

haemagglutinin (H)

• 18 different H antigens
• facilitates viral attachment and entry to host cell

neuraminidase (N)

• 11 different N antigens
• enables new virion to be released from host cell

Question 4

what is antigenic drift

Answer 4

mechanism of genetic variation within virus

occurs continually over time, small on-going point mutations in genes, coding for antibody binding sites

may change antigenic properties and eventually immune system will not combat virus as well

Question 5

what can antigenic drift cause

Answer 5

worse than normal epidemic

vaccine mismatch

Question 6

what is antigenic shift

Answer 6

abrupt major change in virus, resulting in new H/N combinations

genetic change than enables flu strain to jump from one animal species to another

2 or more different strains combine to form new subtype

Question 7

what can antigenic shift cause

Answer 7

with new antigenic properties the at risk population is unprotected
can lead to pandemics

Question 8

pandemic requirments

Answer 8

human pathogenicity
new virus - antigenic shift
efficient person-person transmission

Question 9

how is avian flu spread

Answer 9

direct contact with infected birds, dead or alive

occasional transmission via close human to human contact

Question 10

incubation period influenza

Answer 10

2-4 days (range 1-7)

Question 11

presentation of influenza

Answer 11

abrupt fever for ~3 days

plus 2+ of: 
cough
sore throat/rhinorrhoea
myalgia
headahce
malaise

Question 12

influenza like illness

Answer 12

fever (>38) and cough

onset within last 10days

Question 13

transmission of influenza

Answer 13

airborne: person–>person by large droplets
contact: direct (person-person) or indirect (person-fomite-person)

Question 14

when does influenza virus shedding occur

Answer 14

first 4 days of illness (range 1-7days)

**longer in young kids and immunocompromised

Question 15

influenza virus survival times

Answer 15

24-48hrs non-porous surface

8-12hrs on porous surface e.g. tissue

Question 16

risk factors for complicated influenza

Answer 16

neurological, hepatic, pulmonary, cardiac disease
DM
immunosuppresion
>65yrs
pregnancy (incl 2wks post-partum) 
children <6mo 
morbid obesity (BMI 40+)

Question 17

common complications

Answer 17

acute bronchitis

secondary bacterial pneumonia

Question 18

less common complications: respiratory

Answer 18

primary viral pneumonia

rapid respiratory failure (within 48hrs)

Question 19

less common complications: cardiac

Answer 19

myocarditis/pericarditis

Question 20

less common complications: CNS

Answer 20

transverse myelitis/Guillain-Barre

myositis + myoglobulinuria

Question 21

diagnosis and investigations

Answer 21

viral nose and throat swabs (PCR)
CXR
blood culture
pulse oximetry
resp rate
U&Es, FBC, CRP

Question 22

when does an individual become non-infectious

Answer 22

immunocompetent adult: 24hrs after last flu symptoms (fever, cough) or when anti-viral therapy completed –> whichever longest

immunocompromised adults and young kids: consider each case seperately