Influenza Flashcards
Structure of influenza virus
- Spherical, enveloped viruses containing a segmented, negative strand RNA genome
- 2 surface antigens - haemagglutinin + neuraminidase
What type of virus is influenza?
Orthomyxoviridae
What do the haemagglutinin (H) surface antigens on influenza virus do?
Binds to cells of infected person
What do the neuraminidase (N) surface antigens on influenza virus do?
Release virus from the host cell surface
Types of influenza
Influenza A,B + C
Who does influenza A effect?
Humans
Birds
Swine - pigs
Who does influenza B effect?
Only humans
Who does influenza C effect?
Humans
Swine - pigs
What is the mildest form of influenza?
Influenza C
Clinical manifestations of influenza C
Mild disease
No seasonality
Clinical manifestations of influenza B
Severe disease
Often in older adults or people at higher risk
Clinical presentation of influenza A
Could cause large pandemics
Significant mortality in young persons
Transmission of influenza virus
Respiratory
e.g. coughing, sneezing, inhaling
- small article aerosols in air
- direct contact with larger particles or droplets
- indirect contact of viral particles on surfaces
What are barriers to entry via respiratory route
- Respiratory epithelial cells - thick glycocalyx + tracheobronchial mucus
- Ciliated respiratory epithelial cells - sweep mucus up respiratory tract
- Macrophages, natural killer cells, secretory IgA - immunological defences in lungs
How does the influenza virus enter cells?
1- H antigen allows virus to bind to NANA residues
2- invagination of membrane
3- formation of endocytosis vesicle
4- release of virion (virus particle) into cytoplasm
Entry via receptor mediated endocytosis
Symptoms of influenza
Fever
Headache
Dry cough
Nasal congestion
Muscle ache
Nausea + vomiting - in children
Complications of influenza
Meningitis
Pneumonia
Sinusitis/bronchitis/pharyngitis
Maternal complications
Croup - more common in children
Otitis media - more common in children
Incubation period of influenza virus
1-5 days
Who do most serious complications from influenza occur in?
Children under 6 months
> 65 years old
Underlying health conditions
Pregnant women (+ 2 weeks post partum)
Morbid obesity BMI>40
Recovery time for influenza
2-7 days
Treatments for influenza
- antivirals rimantadine + amantadine - inhibit viral uncoating after uptake
- neuraminidase inhibitors oseltamivir + zanamivir - inhibit val release from infected cell + cause aggression of viral particles influenza A+B
What drugs can be used to treat influenza?
rimantadine + amantadine
oseltamivir + zanamivir
Outline the vaccinations for influenza as prevention methods
Vaccinations
- formalin-inactivated (not live) vaccine (quadrivalent/trivalent) by injection
- live attenuated cold adapted vaccine (quadrivalent) by nasal spray (for children)
What vaccine is given to children for influenza?
Live, attenuated, cold adapted vaccine (quadrivalent) by nasal spray
What vaccine is given to adults for influenza?
Formalin-inactivated vaccine (quadrivalent/trivalent) by infection
Not live
Why are there different strains of influenza virus?
Viral RNA polymerase have a high error rate
What is antigenic drift?
Minor changes (natural mutations) in the gene of flu viruses that occur gradually over time»_space; seasonal epidemics
What is antigenic drift due to?
Random mutations in viral RNA
Single or few amino acid substitutions in H + N proteins
What is antigenic shift?
Minor changes in genes of flu viruses that occur suddenly when two or more different strains combine
Result in a new subtype»_space; casues widespread epidemics/pandemics
What is antigenic shift due to?
Reassortment of different RNA segments from each species in a new capsid»_space; new subtype made
Consequences of antigenic shift
New subtype of virus made
Can cause epidemic/pandemic as immune system will have no defence against new strain
Where does a secondary infection after influenza commonly occur?
In lungs
What is influenza?
A acute viral infection of respiratory tract
Influenza A
Effects animals + humans
Undergoes antigenic drift + shift
Responsible for pandemics
Influenza B
Only effects humans
Undergoes antigenic drift
Mainly affects older adults
Influenza C
Affects humans + pigs
Undergoes antigenic drift
Produces mild disease
Diagnosis of influenza
From symptoms and clinical assessment
There are rapid antigen tests + PCR
What is a cold adapted vaccine?
Virus can grow in nose + throat but not in lower respiratory tract where temp is higher
