16 - Influenza Flashcards
What type of microorganism is influenza and what system does it affect?
Viral infection of respiratory tract that is highly infectious and spreads rapidly. Mainly occurs over 8 to 10 week period over winter
What is the structure of the influeza virus?
- Orthomyxovirus that is spherical, enveloped and negative ssRNA.
- 3 RNA polymerases with high error rates
- Two surface antigens: N and H
What are the antigens of the influenza virus?
- Haemagglutin (H): binds to cells of infected person
- Neuraminidase (N): releases virus from host cell
What are the differences between the three types of influenza?
What are the differences between influenza B and A on the host?
How does the influenza virus replicate?
What are the different modes of transmission of influenza?
VIA RESPIRATORY ROUTE
- Small particel aerosols suspended in air for hours and inhaled
- Droplets will fall to ground within 3m of infected person and are passed on by direct contact
- Droplets could land on suface and remain infectioius
Why does not everyone who is infected with virus particles of influenza get sick?
How does the influenza virus enter cells?
Attaches to hemagluttin
How does the influenza virus leave cells once it has replicated?
Neuraminidase cleaves where the galactose is attached to sialic acid to release the virus
What are some complications and symptoms of influenza?
- Incubation 1-5 days
- Fever, chills, headache, muscle and joint pain, fatigue, cough, sore throat
- Complications: viral pneumonia, secondary bacterial pneumonia, CNS syndrome, Reye syndrome
If someone presented to your GP with symptoms of influenza, who should you be more cautious with?
Those at high risk of complications
- Children under six months
- Older people over 65
- Underlying health conditions e.g immunosuppression
- Pregnant women up to 2 weeks post partum
- Morbid obesity BMI>40
What happens if you have influenza whilst pregnant?
High risk for:
- Perinatal mortality
- Prematurity
- Smaller neonatal size and birth weight
How do you diagnose influenza?
- Usually diagnose from symptoms and clinical assessment
- Nasopharyngeal swab with rapid influenza diagnostic tests (antigen detection). Takes 15 minutes and can detect type A and B. Would only really do in hospitals
What are the treatments for influenza?
- Prevention: vaccinations and supportive treatment
2. Antivirals: rimantadine and amantadine that inhibit viral upcoating and uptake through M2 protein Influenza A
3. Neuraminidase inhibitors: Tamiflu (Oseltamivir) and Zanamivir (Relenza) that prevent release of virus and cause aggregation of virus Influenza A and B
What are the vaccines for influenza?
- Formalin inactivated vaccine (quad and trivalent) by injection for A and B
- Live attentuated, cold adapted vaccine (quad) by nasal spray for A and B
Why is there lots of genetic changes in influenza?
- Constantly replicating
- High error rate of RNA polymerases and lack of proofreading
What is antigenic drift?
Minor antigenic changes (due to natural mutations) that occur gradually overtime. They cause seasonal epidemics.
No change in viral subtype
Explained by random mutations in viral RNA.
What is antigenic shift?
- Major changes in genes of virus that occur suddenly when two or more different strains combine in one host cell
- Cause widespread epidemics and pandemics as no previous immunity
- Random gene segments get assembled into one and there is a change in subtype but only happens every 10-20 years
Which influenza virus does antigenic shift occur in and explain the mechanism?
- Type A
- In environments where pigs, birds and humans are in close contact the pig can be infected with multiple viruses at once
- Reassortment occurs in the pig so mRNA encoded H and N are in random combinations and new virus can now affect pigs, birds and humans as contains strains from them all
What are the consequences of antigenic shift and why?
Epidemics and Pandemics as no exposure and protection to the new subtype
How does flu kill the host?
- Immune system overreacts and T cells attack and destroy tissue the virus is replicating in
- Chance for opportunistic secondary infection
Who is recommended to have the flu jab?
- Pregnant women
- 6 months to 5 year olds
- Over 65s
- Chronic medical conditions
- Healthcare workers
What is the animal reservoir for influenza?
- Type A
- Poultry
- Horses
- Pigs
- Humans
Briefly describe the difference in antigenic shift and drift regarding influenza?
- Shift: novel H and N acquisition by virus
- Drift: yearly accumulations of mutations in H and N
How does the WHO determine which flu vaccine to use each year?
Monitor the epidemiology worldwide and can predict based on Australia what flu strains will be prevalent next winter
