Influenza Flashcards
Describe the structure and the various types of influenza virus
- RNA virus with 8 segment genome
- 3 types: A, B & C
- A infects mammals and birds, B & C only humans
What are the two important surface proteins on the surface of influenza virus? Function of each?
- Haemagglutinin (H) - facilitates viral attachment and entry to host cell
- Neuraminidase (N) - enables new virion to be released from host cell
- H/N variations in name. eg. H1N1
What is antigenic shift?
Where two or more different strains of a virus, or strains of two or more different viruses combine to create a new subtype with different surface antigens
- Can make vaccines and immunity ineffective due to antigenic changes
What is antigenic drift?
Mutations within the viral genome that may cause changes in the antigenic properties of the virus
What is the classical presentation of influenza viruses?
- Incubation period 2-4 days
- Abrupt fever (up to 48 celsius) for 1-5 days
- 2 or more of: cough, sore throat, rhinorrhoea, myalgia, headache, malaise
- Less common: diarrhoea, vomiting, nausea
What are 2 big examples of influenza viruses that have caused pandemics?
- Avian flu
- Swine flu
Which groups are at risk of developing complicated influenza?
- Established neuro, hepatic, pulm., renal & cardiac disease
- Diabetes mellitus
- Immunosuppressed patients
- 65 + yrs old
- Pregnancy (including up to 2 weeks post partum)
- < 6 months old
- Morbid obesity (BMI > 40)
What are some common respiratory complications occurring after contracting the flu?
- Acute bronchitis
- Secondary bacterial pneumonia (usually appears 4-5 days after start of flu - affects about 20%)
What are some less common complications of influenza infection?
- Primary viral pneumonia (aggressive, rapid resp. failure within 48hrs, mortality 40% at 7 days)
- Myocarditis / pericarditis
- Transverse myelitis / Guillian Barre
- Myositis / Myoglobulinuria
What is encephalitis lethargica? Symptoms?
- Atypical form of encephalitis
- Fever
- External ophthalmoplegia (progressive inability to move eyes & eyebrows)
- Lethargy
- Sleep reversal (become nocturnal)
What is the prognosis like for encephalitis lethargica? Post-infective complications for survivors? What would you expect to see on serology?
- 25% mortality
- Postencephalitic Parkinsonism
- Serology: positive influenza A
What are some investigations for suspected influenza infection?
- Viral nose and throat swabs (PCR)
- CXR
- Blood culture
- Pulse oximetry (determine if O2 support needed)
- FBC, U&E, CRP
If a patient has had “flu like symptoms and a fever for more than 4 days” what investigation you ordering?? What diagnosis you thinking? Test to assess severity?
- CXR
- Secondary bacterial pneumonia
- CURB65 score
Management of influenza infection? Examples?
- Antiviral therapy: NEURAMINIDASE INHIBITORS
First Line - OSELTAMIVIR (TAMIFLU) - Oral
Second Line - ZANAMIVIR (RELENZA) – Inhaled & or I.V.
What are some other antivirals used for influenza infection?
- Peramivir (Alpivab®): Neuroaminidase inhibitor
- Favipiravir (Avigan®): Viral RNA polymerase inhibitor
- Baloxavir Marboxil (Xofluza®): Endonuclease inhibitor
