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
what antiviral drugs can be used to treat influenza?
- OSELTAMIVIR (TAMIFLU): oral administration, dose: over 13 years - 75mg every 12 hours for 5 days. 1st line.
- ZANAMIVIR (RELENZA): inhaled & or IV, dose: over 2 years - 10mg inhaled daily for up to 10 days. 2nd line.
OSELTAMIVIR (TAMIFLU) side effects
common:
- nausea
- vomiting
- abdominal pain
- diarrhoea
ZANAMIVIR (RELENZA) side effects
rare: occasional bronchospasm
when does an individual with influenza become non-infectious?
immunocompetent adults:
- 24hrs after last flu symptoms (fever and cough)
- or when anti-viral therapy is completed
immunocompromised adults and young children: consider each case separately
how is the seasonal flu vaccine administered?
single 0.5ml intramuscular injection
why is the seasonal flu vaccine contraindicated in those with egg allergy?
grown in chick embryos
