Influenza Flashcards
Orthomyxovirus
Enveloped
Spherical
Contains segmented negative strand RNA genome
Surface antigens:
Haemagglutinin
Neuraminidase
Haemagglutinin
Binds to host cells
Neuroaminidase
Release the virus from host cells surface
Influenza A natural hosts
Animals and humans
Influenza B natural host
Humans
Influenza C natural host
Humans
Pigs
Influenza A spread
Antigenic drift
And antigenic shift
Large pandemics
Replication of orthomyxovirus
- Negative SsRNA invades host cell and transcribed to mRNA and coverted to positive SsRNA
- Positive ssRNA replicates and RNA dependent RNA polymerase is used from the infected virus to translate to viral proteins
- Using viral proteins and negative ssRNA nucleocapsids are assembled
Viral entry
- Virion binds to NANA residues on the host receptors cell via haemagglutinin antigens
- Receptor mediated endocytosis in upper respiratory cells
- Endocytic vescile formed
- Virion released from vesicle into cytoplasm a neurominidase cleaves glycoprotein from haemagglutinin
Antigenic shift
New subtype
Pandemics
Rapid
Transmission
Respiratory route
- small particle aerosols
- large particle aerosols
- indirect contact - particles land on surface
Barriers to entry
Upper respiratory mucous - trap virus particles
Cilia
Immunoglobulins in the lung - IgA
Macrophages and natural killer T cells
How does influenza leave cells
Neuraminidase cleavage sites therefore cleaved at sialic acid
Symptoms
Fever, headache
Sore throat, cough, nasal congestion
Nausea and vomiting and diarrhoea
Myalgia, fatigue
Incubation
1 - 5 days
Who is at risk for more serious complications
Children under 6 Older people Underlying health issues Pregnant women Morbid obesity
Treatment
Influenza A
- Antivirals - rimantadine
Influenza A and B
- Neuraminidase inhibitors - oseltamivir
Vaccine
Formalin inactivated vaccine
- quadrivalent or trivalent
Or
Live attenuated cold adapted vaccine - nasal spray (used in children)
Why is antigenic drift seen in influenza
Life cycle of 6 hours RNA Polymerase error rate is high Lack of proof reading Genetic variation and resistance Seen in H and N proteins
Antigenic shift
Only seen in influenza A
Surface antigens hemagglutinin and neuraminidase from different species
When 2 or more strains combine
