Lecture 7: Influenza Flashcards
classification of influenza virus
- RNA virus. 8 segment genome
- orthomyxoviridae family
- three main groups: A (1933), B (1939), C (1950)
- IfA infects mammals and birds, IfB and IfC only humans.
what surface proteins are present on influenza and what is their function?
- Haemagglutinin (H): facilitates viral attachment and entry to host cell. 18 different H antigens (H1-3 in humans)
- Neuraminidase (N): enables new virion to be released from host cell. 11 different N antigens.
describe antigenic drift
- a mechanism of genetic variation within the virus.
- occurs continually over time, small on-going mutations in the genes coding for antibody binding-sites.
- may change the antigenic properties and eventually the immune system will not combat the virus as well > causes worse than normal epidemic and vaccine mismatch.
describe antigenic shift
- abrupt major change in the virus, resulting in new H/N combinations.
- the genetic change that enables a flu strain to jump from one animal species to another.
- the process by which two or more different strains of a virus combine to form a new subtype, resulting in new H/N combinations.
- reassortment of the virus’ gene segments.
- with new antigenic properties the population at risk is unprotected and this can lead to pandemics.
what are the requirements for a pandemic to occur?
- human pathogenicity
- ‘new’ virus (antigenic shift) - susceptible population
- efficient person-person transmission
how is a pandemic flu different from a seasonal flu?
seasonal flu:
- occurs every winter
- affects 10-15% of the population
- usually unpleasant but not life-threatening
pandemic flu:
- occurs sporadically
- affects 25%+ of the population
- more serious, more complications
features of the avian flu
classification, spread, fatality etc.
- many types, few strains affect humans: H5N1, H7N9
- spreads through direct contact with infected birds, dead or alive.
- occasional transmission via close human to human contact (staff, caregivers)
- high case fatality rate: 60% H5N1, 36% H7N9
what are the clinical features of influenza?
- incubation period 2-4 days (range 1-7 days)
- abrupt fever up to 41C (commonly 38-40C) which lasts 3 days (range 1-5)
- plus 2 more of: cough, [sore throat, rhinorrhoea], myalgia, headache, malaise
- predominance of systemic symptoms
- less common symptoms: nausea, vomiting and diarrhoea
what is the WHO definition of an Influenza like illness (ILI)?
- fever (> 38C) and
- cough
- onset within the last 10 days
- (if requires hospitalisation defined as severe acute respiratory infection SARI)
what is the survival time of influenza on i. non-porous surfaces and ii. porous surface?
i. 24-48 hours on non-porous
ii. 8-12 hours on porous surface e.g. tissue
how is influenza transmitted?
- airborne > person > person by large droplets > 5microns
- contact: direct and indirect (person > fomite > person)
what are the high risk groups for complicated influenza?
- neurological, hepatic, renal, pulmonary and chronic cardiac disease
- diabetes mellitus
- severe immunosuppression
- age > 65
- pregnancy (including up to 2 weeks post-partum)
- children < 6 months
- morbid obesity BMI >/= 40
what are the common complications of influenza?
- acute bronchitis
- secondary bacterial pneumonia (20%) > appears 4-5 days after start of flu
influenza diagnostic investigations
- viral nose and throat swabs/VTS (molecular detection/PCR; using flocked swabs)
- CXR - pneumonitis/pneumonia/ARDS
- blood culture
- pulse oximetry- SpO2 < 92% need ABG and oxygen
- RR
- U&Es, FBC, CRP
what are the less common complications of influenza
respiratory:
- primary viral pneumonia
cardiac:
- myocarditis/pericarditis
CNS:
- transverse myelitis/Guillain-Barre
- Myositis and Myoglobinuria
