influenza Flashcards
types of influenza viruses
influenza A
Influenza B
what type is avian influenza
H5N1 type A
What is H1N1
swine
current who alert for H5N1
is pandemic alert
attributes of pandemic influenza
- new strains
- virulent: severe disease
- transmits efficiently from human to human
what is the influenza virus called
orthomyxoviridae
what is influenza A
avian reservoir: aquatic birds are the source but then can also be found in humans and pigs
what is antigenically unstable mean
it means you can get antigen drift and shift which can lead to mutation and new variants
- gives rise to the annual outbreaks/epidemics of seasonal flu but then gives rise to pandemic every 10-40 years when bigger change
what is antigenetic drift
small changes in antigens affecting H and N antigens due to point mutations
what is antigenetic shift
is a major change resulting in new H and N so more likely to become pandemic due to lower immunity.
- when 2 or more viruses infect and their genes are mixed
- pandemic potential
where is influenza B reservoir found and what type of antigenically unstable does it show
no animal reservoir found in humans only
exhibit antigenetic drift so may give rise to epidemics
where is influenza c found and how severe is it
no animanl reservoir only humans soo may exhibit antigenetic drift giving rise to only mild,sporadic resp illness
how are influenza viruses defined
o The type o The host of origin o Geographic origin o Strain number o Year of isolation o H and N designation (for type A only H3N2 A hong kong/ 03/68
how is the influenza flu vaccine made up
H antigen variability results in epidemic so
-seasonal vaccine contains 2 influenza A strains and one or two influenza B strains
biological features of influenza a virus
ss negative RNA
replicates in nuclues
what are the 2 matrix proteins on influenza
o M1 forms a shell around nucleic material
o M2 forms an ion channel in envelope
what are the 2 main influenza A surface antigens
H=Haemagglutinin
N=Neuraminidase
how does haemagglutinin work
- usually the one that the immune system targets so changes this molecule to allow the virus to avoid detection which results in epidemics
- attaches to resp sialic acid receptors and mediates fusion of virus to cell
- avian strains recognise the a2,3 bonds on receptors whilst human recognise a2,6
how many subtypes of neuramindiase
n1-n9
how does neuraminidase work
allows the newly created viruses to exit a cell and spread the infection
-ie facilitates budding during egress from host cells by cleaving the glycosidic linkages to sialic acid on virion and host cell surfaces
what caused all the pandemics in the 20th centrury
avian influenza a
incubation of influenza
1-4 days
how is it spread
- airborne droplets
- contaminated hands
how do H and N antigen increase the viruses virulence
- H antigen mediates infection of the respiratory epithelium, progeny virus infects adjacent epithelium
- N antigen: reduces mucous viscosity and promotes spread to lower resp ract
what is the cytokine storm
severe influenza A virus strains are thought to trigger a dysregulated immune response resulting in a cytokine storm that leads to severe symptoms eg multi-organ failure
uncomplicated signs of influenza a flu
-chills headache dry cough fever muscular aches malaise anorexia last 5-10 days
complication of influenza a virus
- pneumonia
- usually elderly
- superinfection
- bacterial agents - Reye’s syndrome
- other organs eg gi symptoms
- multi-organ failure
what is reye’s syndrome
- usually young patients with acute encephalopathy
- cause presumed linked to salicylates
how does swine influenza normally present
normally mild disease except 2009 outbreak
immune antibody response to influenza
- specific to subtype
- long lived
- neutralising antibodies against H antigens confer resistance to infection although re-infection with the same virus can occur
- antibodies against the N antigens reduce disease severity and transmission
cell mediated immunity to influenza
- mediated by cytotoxic T lymphocytes that lyse virus infected cells
- CTLs are usually key players to eradicating and curtailing virus infections
lab dx of influenza
- sputum and throat swabs, bal
- blood samples
- antigen detection
- PCR most sensitive
how does influenza a multiply
multiplies in birds gut and is then excreted in faeces contaminating environment
how many of the H/ N subtypes are in humans and how many are in birds
humans=H5N1 Only H5N1, H7N3, H7N7, H7N9 and H9N2 avian influenza A virus strains have so far caused human infections birds= all h and n subtypes
criteria for classification influenza
- Fever >38 and lower resp tract symptoms or CXR findings of consolidation or ARDS
OR - Other severe/ life threatening illness suggestive infectious
- Additionally
o Exposure 7 days prior to symptoms with a poultry or wild bird
o Close contact with another human with unexplained resp illness
what is swine flu made up of
birds prigs and human flu
what can swH1N1 be treated with
neuraminidase inhibitors
antiviral therapy M2 envelope protein inhibitors 2
Amantadine and rimantadine
• Resistance is widespread-not used
what are the neuraminidase inhibitors
zanamivir and oseltamivir
effective if given with 48 hours from onset of symptoms
