Influenza Flashcards
when does influenza occur and why is it said to be related to the sun?
From the latin word ‘influentia’ – meaning influence of the stars
Seasonal influenza occurs during winter months:
Dec – Feb in the Northern Hemisphere
Jun – Aug in the Southern Hemisphere
More severe epidemics of influenza occur every 11 years; same as increased ‘sunspot activity’
what are 20th century pandemics of influenza?
1918-9 ‘Spanish Flu’ (A/H1N1)
† 20-100 million deaths
1957-8 ‘Asian Flu’ (A/H2N2)
† 1-1.5 million deaths
1968-9 ‘Hong Kong Flu’ (A/H3N2)
† 0.75-1 million deaths
2009-10 ‘Swine Flu’ (A/H1N1)
† approximately 285.000 deaths
describe the surface proteins of influenza?
what is the mechanism of 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 the mechanism of 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
how do seasonal and pandemic flu differ?
what are the requirements for a pandemic?
Human pathogenicity
‘New’ virus (antigenic shift)
- susceptible population
🗹 Efficient person-person
transmission
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
ifluenza like illness?
Fever (>38°C) and
Cough
Onset within the last 10 days
(if requires hospitalization defined as severe acute respiratory infection (SARI))
symptoms of swine flu?
how is influenza transmitted?
Airborne – person ⭢ person by large droplets >5 microns
Contact – direct (person ⭢ person)
– indirect (person ⭢ fomite ⭢ person)
virus shedding?
First 4 days of illness (range 1-7 days)
Longer in young children & immunocompromised
virus survival?
24-48 hours on non-porous surfaces
8-12 hours on porous surface e.g. tissue
what are risk factors for complicated influenza?
Neurological, hepatic, renal, pulmonary and chronic cardiac disease
Diabetes mellitus
Severe immunosuppression
Age over 65 years
Pregnancy (including up to two weeks post partum)
Children under 6 months of age
Morbid obesity (BMI ≥40)
what are common respiratory complications of influenza?
Acute Bronchitis
Secondary Bacterial Pneumonia (~20%)
Appears 4-5 days after start of ‘flu
RESPIRATORY:
Primary viral pneumonia
- appears common in human cases of avian influenza (H5N1)
- rapid respiratory failure; within 48 hours
- mortality >40%; within 7 days
CARDIAC:
Myocarditis/pericarditis
CNS:
Transverse myelitis/Guillain-Barre
Myositis & Myoglobinuria
