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)
what is virus shedding?
viral shedding occurs when a virus replicates inside your body and is released into the environment. at that point, it may be contagious
what is the virus shedding of this infection?
• First 4 days of illness (range 1-7 days)
Longer in young children & immunocompromised
what is the virus survival?
- 24-48 hours on non-porous surfaces
- 8-12 hours on porous surface e.g. tissue
high risk groups:
What are some risk factors for complicated influenza?
a. Neurological, hepatic, renal, pulmonary and chronic cardiac disease
b. Diabetes mellitus
c. Severe immunosuppression
d. Age over 65 years
e. Pregnancy (including up to two weeks post partum)
f. Children under 6 months of age
g. Morbid obesity (BMI ≥40)
what are some common respiratory complications?
- Acute Bronchitis
- Secondary Bacterial Pneumonia (~20%) - Appears 4-5 days after start of ‘flu
What are some Less Common respiratory Complications?
• Primary viral pneumonia
- appears common in human cases of avian influenza (H5N1)
- rapid respiratory failure; within 48 hours
- mortality >40%; within 7 days
what are some less common cardiac complications?
Myocarditis/pericarditis
What are some less common CNS complications?
- Transverse myelitis/Guillain-Barre
- Myositis & Myoglobinuria
influenza is a ____________ disorder
multi-system
what is the diagnosis and investigations required?
- Viral nose and throat swabs/VTS (Molecular detection /PCR; using flocked swabs)
- Chest X-ray – pneumonitis/pneumonia/ARDS
- Blood culture
- Pulse oximetry – SpO2 <92% need ABG and oxygen
- Respiratory rate !
- U & E’s, FBC, CRP (CRP monitoring recovery of pneumonia - should halve in 4 days)
what is secondary bacterial pneumonia and what needs to be done?
- Patients with ‘flu symptoms and a fever for > 4days – should have an urgent CXR
- Severity assessment – use C(U)RB-65 score
- Confusion
- Urea >7mmol/l
- Respiratory rate >30mm
- Blood Pressure (diastolic <60 or systolic <90)
- >65 years of age
• C(U)RB score: Risk of death in the next 30 days (0=0.6%, 1=3.2%, 2=13%, 3=17%, 4=41.5%, 5=57%)
should you use antiviral therapy?
Use ASAP and within 48hours of symptom onset!
what antiviral treatments are there avalible?
OSELTAMIVIR (TAMIFLU) - Oral
Dose : Over 13 years – 75mg every 12 hours for 5 days
Adverse Effects:
Common – Nausea, vomiting, abdominal pain, diarrhoea
Less Common – Headache, hallucinations, insomnia and rash
Cautions: Renal dosing needed
ZANAMIVIR (RELENZA) – Inhaled & or I.V.
Available only as a dry powder inhaler
Dose: Over 12 years – 10mg inhaled daily for up to 10 days
Adverse Effects: Rare – occasional bronchospasm
what are some other antiviral therapies?
•Peramivir (Alpivab®)
–Neuroaminidase inhibitor
–Licensed in USA and approved by European Medicines Agency (EMA) 1st May 2018 !
–Intravenous infusion, for uncomplicated influenza
• Favipiravir (Avigan®, Toyama Chemicals Ltd)
–Viral RNA polymerase inhibitor
–Licenced in Japan for ‘re-emerging influenza viruses’
–Oral medication
• Baloxavir Marboxil (Xofluza®, Roche)
–Endonuclease inhibitor
–One single dose
•(Amantadine & Rimantadine not used due to resistance)
what are the current guidelines for antiviral therapy in pregnancy?
Antivirals have been recommended…due to the adverse outcomes …in this group
Oseltamivir remains first line option…
Recent studies (2014) suggests there is no evidence of harm of either oseltamivir or zanamivir
FDA pregnancy category C: No malformation, maternal toxicity or embryotoxcity were observed in animal studies. No data available in humans.
Antiviral therapy and breastfeeding
- Only tiny amounts of Oseltamivir in milk
- Current guidance is – Oral Oseltamivir
When does an individual become non-infectious?
IMMUNOCOMPETENT ADULTS
- 24hrs after last flu symptoms (fever & cough)
- Or when anti-viral therapy completed, Which ever is longer
IMMUNOCOMPROMISED ADULTS & YOUNG CHILDREN
•Consider each case separately
what protection is required for healthcare staff?
- Surgical face mask
- Plastic apron
- Gloves
Wash hands after any examination
what is the vaccine prepared and given? (seasonal flu vaccine)
- Prepared each year using viruses considered most likely to be circulating in the forthcoming winter
- Grown in chick embryos (therefore C.I. in those with egg allergy)
- Chemically inactivated and purified, trivalent vaccines - Containing 2 type A & 1 type B subtype viruses
- Single 0.5 ml intramuscular injection
- Only adverse effect in large placebo controlled trials is sore arm
why should healthcare workers have the vaccine?
- To protect themselves and their families
- To reduce the risk to ‘at risk’ patients
- To reduce absence from work during influenza ‘surge’ activity
