10 - Influenza Flashcards
What family is the Influenza Virus from?
Orthomyxoviridae Family:
RNA Virus with an 8 Segment Genome
How many, and what are, main groups of Influenza Virus are there?
3:
1. IfA (Mammals and Birds)
2. IfB (Humans)
3. IfC (Humans)
What is the definition of Antigenic Drift?
A Mechanism of genetic variation (within the Virus) which occurs continually over time
By what method does Antigenic Drift occur?
- Small, on-going, point mutations in the genes coding for the antibody-binding sites
- May also change the antigenic properties
What is the advantage of Antigenic Drift?
- Eventually the immune system will not combat the virus as well
Note - it causes worse than normal epidemics and vaccine mismatch
What is the definition of Antigenic Shift?
The process by which 2+ different strains of a Virus combine to for am new sub-type, resulting in new H/N combinations, and reassortment of the Virus’ gene segments
What does Antigenic Shift allow for?
The flu strain can jump from one animal species to another
What can an Antigenic Shift lead to?
With new antigenic properties, the population at risk is unprotected, this can lead to Pandemics
E.g. An Avian Host and a Human Host both transmit into a Swine Host, and a New Reassorted Virus Subtype is formed
What is the difference between Seasonal Flu, and Pandemic Flu?
Seasonal Flu:
1. Occurs every winter
2. Affects 10-15% of the population
3. Usually unpleasant but not life threatenting
Pandemic Flu:
1. Occurs sporadically
2. Affects >25% of the population
3. More serious, more complications
What are the requirements for an infection to be “Pandemic”?
- Human Pathogenicity
- “New” Virus (due to the antigenic shift)
- Efficient Person - Person transmission
What are the 2 Surface proteins on Influenza?
- Haemagglutinin (H)
- Neuraminidase (N)
What is the function of the Haemagglutinin (H) Antigen?
Facilitates Viral Attachment and Entry to the Host Cell
How many different Haemagglutinin (H) Antigens are there?
18 (H1-3 in humans)
What is the function of the Neuraminidase (N) Antigen?
Enables the new Virion to be released from the Host Cell
How many different Neuraminidase (N) Antigens are there?
11
What are the strains of Avian Flu which affect humans?
- H5N1
- H7N9
How does Avian Flu spread to Humans?
Through direct contact with infected birds, dead or alive
Note - there is no known transmission by eating properly cooked food/eggs
What are the fatality rates of the Avian Flu which can affect humans?
- H5N1 - 60%
- H7N9 - 36%
What is the incubation period of Avian Flu?
2 - 4 days (range is 1 - 7 days)
What are the clinical features of Avian Flu?
Abrupt Fever (up to 41 degrees) which lasts for 3 days
Plus 2 or more of:
1. Cough
2. Sore Throat
3. Rhinorrhoea
4. Myalgia
5. Headache
6. Malaise
Note - there is a predominance of systemic symptoms and nausea, vomiting and diarrhoea are less common
What are the clinical features of Swine Flu?
- Abrupt Fever (above 38 degrees) which lasts for 3 days
- Sudden Cough
- Tiredness / Chills
- Headache / Sore Throat / Runny Nose / Sneezing
- Diarrhoea or Upset Stomach / Loss of Appetite
- Aching Muscles / Limb or Joint Pain
How is Swine Flu transmitted?
- Airborne: Person to Person by large droplets
- Direct Contact: Person to Person
- Indirect Contact: Person to Fomite to Person)
How long does the Virus Survive for:
1. In the host?
2. On a Porous Surface?
3. On a Non-porous Surface?
- Around 4 Days - longer in children and immunocompromised patients
- 8-12 hours
- 24-48 hours
Which groups of people are at high risk of developing Flu?
- Chronic Respiratory Disease (especially those on continuous Oral Steroids)
- Chronic Heart / Renal / Liver / Neurological Disease
- Diabetes Mellitus
- Immunosuppression
- Morbid Obesity
- Pregnancy - especially the last trimester
What are common Respiratory problems, associated with the Flu?
- Acute Bronchitis
- Secondary Bacterial Pneumonia
What are some un-common problems, associated with the Flu?
- Primary Viral Pneumonia
- Myocarditis / Pericarditis
- Transverse Myelitis / Guillian-Barre
- Myositis and Myoglobinuria
How is the Flu diagnosed / investigated?
- Clinical Diagnosis (for normal Flu)
- Viral Nose / Throat Swabs
- Chest X-Ray
- Blood Culture
- Pulse Oximetry
- Respiratory Rate
- U&E’s, Creatinine and FBC
- CRP
In relation to Secondary Bacterial Pneumonia (a common problem associated with Flu), what is the score used to assess Pneumonia?
CURB65:
C - Confusion
U - Urea (> 7mmol/L)
R - Respiratory Rate (> 30 breaths per minute)
B - Blood Pressure (Diastolic < 60, Systolic < 90)
65 - >65 years of age
What is the common Antiviral Therapy associated with Influenza?
- Oseltamvir
- Zanamivir (dry powder inhaler)
What is the treatment of an uncomplicated case of Influenza, in a previously healthy person?
- No treatment (ideal and most common course)
- Oseltamvir (If the physician feels the patient is at serious risk of developing complications)
What is the treatment of an uncomplicated case of Influenza, in an at risk (but not severely immunosuppressed) person?
- No treatment (ideal and most common course)
- Oseltamvir (If the physician feels the patient is at serious risk of developing complications)
What is the treatment of an uncomplicated case of Influenza, in an at risk (severely immunosuppressed) person?
- Oseltamvir PO and Clinical follow up within 48 hours
- Zanamivir within 36 hours of onset
Note - Zanamivir is added to those with higher risk of resistant strains
What is the treatment of an complicated case of Influenza, in a person who is not severely immunosuppressed?
1st Line - Oseltamvir PO / NG
2nd Line - Zanamivir Inh / Neb / I.V.
What is the treatment of an complicated case of Influenza, in a person who is severely immunosuppressed?
1st Line - Oseltamvir PO / NG
2nd Line - Zanamivir Inh / Neb / I.V.
What are some other, less common Antiviral Therapies, associated with Influenza?
- Peramivir
- Favipiravir
How long does it take an immunocompetent adult to become non-infectious?
- 24 hours after the last flu symptom
- When antiviral therapy is complete
What PPE is required when the Flu is suspected / proven?
- Surgical Face Mask
- Plastic Apron
- Gloves
- Hand Washing after any examination
What do Seasonal Flu Vaccines contain?
They are a Trivalent:
1. Contains 2 type A subtype virus
2. Contains 1 type B subtype virus
Why do healthcare workers have vaccinations?
- To protect themselves and their families
- To reduce the risk to “at risk” patents
- To reduce absence from work during influenza “surge” activity
