Influenza Flashcards
How does influenza related to the sun?
More severe epidemics of influenza occur every 11 years; same as increased ‘sunspot activity’
The sun’s radiation may cause mutations leading to “antigenic shifts’ in viral RNA.
Theory that Vitamin D levels help to prevent viral infection
what is the structure of influenza?
- RNA virus. 8 segment genome
- Orthomyxoviridae family
- Three main groups:
- A (1933)
- B (1939)
- C (1950)
INfluenza A, B and C affect whoa dn what?
IfA infects mammals and birds, IfB & IfC only humans
what are the surface proteins of influenza and their function?
18 different H antigens (H1-3 in humans) and 11 different N antigens
Haemagglutinin (H) - facilitates viral attachment and entry to host cell
Neuraminidase (N) - enables new virion to be released from host cell
what is antigenic drift?
- Mechanism of genetic variation within the virus
- Occurs continually over time, small on-going point 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 epidemics & vaccine mismatch
what is 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 is the difference between antigenic drift and shift?
Antigenic drift - Mutations causing minute changes in the hemagglutinin and neuraminidase antigens on the surface of the Influenza virus is termed as antigenic drift
Antigenic shift - Antigenic shift refers to the gene recombination occurring when influenza viruses re-assort
How is pandemic flu different form seasonal flu?
Seasonal flu:
- Occurs every winter
- Affects 10-15 % of the population
- Usually unpleasant but not life-threatening
Pandemic flu:
- Occur sporadically
- Affects 25% + of the population
- More serious, more complications
what are the requirements for a pandemic?
Human pathogenicity
‘New’ virus (antigenic shift) - susceptible population
Efficient person-person transmission
what age has the greatest mortality?
What is avian flu?
- Many types of avian influenza - Few strains affect humans: H5N1 (since 1997), H7N9 (since 2013)
- Spreads through direct contact with infected birds, dead or alive
- Occasional transmission via close human to human contact (staff, caregivers)
- No known transmission by eating properly cooked food/eggs etc
- High case fatality rate: 60% (H5N1), 36% (H7N9)
- Current outbreaks in China (H7N9) and Egypt (H5N1)
what are the clinical features of influenza?
- Incubation period 2-4 days (range 1-7 days)
- Abrupt fever up to 41°C (commonly 38-40°C) which lasts 3 days (range 1-5 days)
- Plus 2 or more of: Cough, [sore throat, rhinorrhoea], myalgia, headache, malaise.
- Predominance of systemic symptoms
- Less common symptoms: Nausea, vomiting, diarrhoea
Influenza like illness (ILI)
WHO definition (2011); for epidemiological purpose is what?
- Fever (>38°C) and
- Cough
- Onset within the last 10 days
(if requires hospitalization defined as severe acute respiratory infection (SARI))
what are the symptoms of swine flu?
how is it transmitted?
- Airborne - person = person by large droplets >5 microns
- Contact – direct (person = person)
– indirect (person = fomite = person)