Influenza Flashcards
What shift in viral DNA can be caused by mutations due to the sun’s radiation?
Antigenic shift
What are features of the influenza virus?
-From orthomyxoviridae family
-RNA virus
-3 types
>IfA (infects mammals and birds)
>IfB and IfC (infects humans only)
What are some surface proteins of the influenza virus?
> Haemagglutinin (H) - facilitates viral entry to host cell. 18 different H antigens with H1-3 in humans
Neuraminidase (N) - enables new virion to be released from host cell. 11 different N antigens
Discuss antigenic drift?
- Is the mechanism of genetic variation within the virus
- Small ongoing point mutations in genes coding for antibody binding sites
- Antigenic properties change = immune system doesn’t combat virus as well
- Causes vaccine mismatch and worsened epidemics
Discuss antigenic shift?
- Abrupt major virus change = new H/N combinations
- Enables flu strain to jump from one animal species to another
- 2 or more different viral strains combine to form new subtype
- Reassortment of virus gene segments
- Leads to PANDEMICS
What is a well known example of a pandemic that took place?
H1N1 virus in 2009/10
How is seasonal flu and pandemic flu different?
Seasonal flu
- occurs every winter
- affects 10-15%
- usually unpleasant but not life threatening
Pandemic flu
- occurs sporadically
- affects 25%+
- more serious/complications
What are the requirements for a pandemic to take place?
> human pathogenicity
‘new’ virus (antigenic shift)
efficient human-human transmission
Discuss avian influenza:
- strains
- transmissions
- fatality rate
- Many strains but few affect humans (eg H5N1, H7N9)
- Direct contact with infected birds. Occasionally close human-human contact. Not through properly cooked foods
- Fatality rate high (eg 60% H5N1)
What are clinical features of Influenza?
> Around 2-4d incubation
Fever lasting around 3d. Likely to be tired and have chills too
2 more of: cough (sore throat, rhinorrhoea), myalgia, headache, malaise
Predominantly systemic symptoms
Less commonly: nausea, vomiting, diarrhoea
WHO definition of influenza like illness?
- Fever (>38 degrees) and
- Cough
- Onset in last 10d
What is the transmission of Influenza virus?
> Airborne: person-person by large droplets (>5 microns)
>Contact: direct (person-person) or indirect (person-fomite-person)
How long does it take for influenza virus to shed?
First 4d of illness. Longer in children and immunocompromised
How long does virus survive on surfaces?
- 24-48h on non-porous surfaces
- 8-12h on porous surfaces (eg tissue)
What are high risk groups for complicated influenza?
- Neurological, hepatic, renal, pulmonary, chronic cardiac disease
- DM
- Severe immunosuppression
- > 65y
- Pregnancy (plus <2w post partum)
- Children <6m
- Morbid obesity (BMI at least 40)
What are common respiratory complications of influenza virus? What 3 organisms can present as part of complications?
- Acute bronchitis
- Secondary bacterial pneumonia (4-5d after flu start)
Microbiology
- S. pneumoniae
- S. aureus
- H. influenzae
What is an uncommon respiratory complication of influenza virus?
Primary viral pneumonia
- common in avian influenza cases
- rapid respiratory failure in 48h
- mortality >40% in 7d
What is an uncommon cardiac complication of influenza virus?
Myocarditis/pericarditis
What is an uncommon neurological complication of influenza virus?
- Transverse myelitis/GBS
- Myositis and myoglobinuria
What is encephalitis lethargica? What are clinical features
- There was a pandemic of this disease in 1918, suspected to be associated with Influenza A (serology).
- 25% mortality
- Can lead to postencephalitic
Features
- fever, headache
- external opthalmoplegia
- lethargy
- sleep reversal
Diagnosis of Influenza virus?
>Viral nose and throat swabs/VTS (pcr) >CXR (eg pneumonia) >Blood culture >Pulse oximetry - SpO2 <92% need ABG and O2 >Resp rate*** >U and E >FBC, CRP
What are the two main antiviral therapy drugs? (examples of neuraminidase inhibitors)
> Oseltamivir - oral
- common side effects: n+v, abd pain, diarrhoea
- less common side effects: headache, hallucinations, insomnia
- usually 1st line
> Zanamivir - inhaled/nebulised/IV
-rare side effect - bronchospasm
What are other antiviral therapy drugs?
- Peramivir (neuraminidase inhibitor)
- Favipiravir (viral RNA polymerase inhibitor)
What is the guidance for antiviral therapy when a woman is pregnant/breastfeeding?
> As normal for pregnancy
>Oral oseltamivir for breastfeeding
