influenza Flashcards
influenza virus characteristics
RNA virus
8 segment genome
orthomyxovirdae family
what are 3 main groups of influenza virus and who/what can they infect
A
B
C
A infects mammals and birds
B and C only humans
surface proteins of influenza virus
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
what is antigenic drift
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
what can antigenic drift cause
worse than normal epidemic
vaccine mismatch
what is antigenic shift
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
what can antigenic shift cause
with new antigenic properties the at risk population is unprotected
can lead to pandemics
pandemic requirments
human pathogenicity
new virus - antigenic shift
efficient person-person transmission
how is avian flu spread
direct contact with infected birds, dead or alive
occasional transmission via close human to human contact
incubation period influenza
2-4 days (range 1-7)
presentation of influenza
abrupt fever for ~3 days
plus 2+ of: cough sore throat/rhinorrhoea myalgia headahce malaise
influenza like illness
fever (>38) and cough
onset within last 10days
transmission of influenza
airborne: person–>person by large droplets
contact: direct (person-person) or indirect (person-fomite-person)
when does influenza virus shedding occur
first 4 days of illness (range 1-7days)
**longer in young kids and immunocompromised
influenza virus survival times
24-48hrs non-porous surface
8-12hrs on porous surface e.g. tissue
risk factors for complicated influenza
neurological, hepatic, pulmonary, cardiac disease DM immunosuppresion >65yrs pregnancy (incl 2wks post-partum) children <6mo morbid obesity (BMI 40+)
common complications
acute bronchitis
secondary bacterial pneumonia
less common complications: respiratory
primary viral pneumonia
rapid respiratory failure (within 48hrs)
less common complications: cardiac
myocarditis/pericarditis
less common complications: CNS
transverse myelitis/Guillain-Barre
myositis + myoglobulinuria
diagnosis and investigations
viral nose and throat swabs (PCR) CXR blood culture pulse oximetry resp rate U&Es, FBC, CRP
when does an individual become non-infectious
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
