CBM - Influenza Flashcards
Influenza
Influenza or “flu” is an upper URTI caused by a virus belonging to the Orthomyxoviridae family.
There are three serotypes - A, B and C out of which A and B are responsible for epidemics:
type A:
- causes outbreaks in most years and is the usual cause of epidemics
- is further divided into subtypes according to the two proteins on the external coat , the hemagglutinin (H1–H16) and the neuraminidase proteins (N1–N9) (3)
type B:
- less severe disease and milder outbreaks
- but in children the severity may be similar to that seen in influenza A infection
- generally responsible for regional outbreaks
type C:
- causes a milder infection that does not cause epidemics
Seasonal influenza consists at present of variable mixes of type A and B influenza viruses:
- Epidemics of influenza occur mainly in the winter months.
- Profound changes in the viral antigens result in larger outbreaks called pandemics.
- Influenza is usually a self-limiting disease but significant mortality is observed in those with chronic chest or cardiovascular disease.
Influenza
Immunology?
Influenza viruses’ type A and B contains 8 genes that code for 10 proteins which includes the surface proteins:
- haemagglutinin (HA) and
- neuraminidase (NA) (1).
So far 16 HA subtypes and 9 NA subtypes have been identified.
The following antigenic changes are considered to be the hallmark of human influenza viruses:
antigenic drift:
- there is gradual and relatively continuous change in the viral HA and NA proteins caused by point mutations in HA and NA genes during viral replication
- results in new virus strains in both type A and B viruses
- emergence of these new strains causes:
- the necessity to frequently update the influenza virus vaccine strains
- many influenza infections over a lifetime of an individual
antigenic shift:
- occurs in influenza type A viruses when either a HA protein or a combination of HA and NA proteins that have not been circulating among humans in recent years emerges
- there are three possible mechanisms by which a new influenza virus may emerge:
- through the genetic reassortment of non-human and human influenza viruses
- an influenza virus from other animals (e.g. birds or pigs) can infect a human directly without undergoing genetic reassortment; or
- a non-human virus may be passed from one type of animal (e.g. birds) through an intermediate animal host (such as a pig) to human
Antigenic shifts occur infrequently and unpredictably while antigenic drift occurs continuously.
Influenza
Flu Vaccination?
At risk individuals:
- Adults over 65 years old
- Individuals with underlying chronic health conditions (for example, chronic heart, lung, kidney, liver, neurological, and metabolic diseases, such as diabetes)
- Individuals with reduced immunity (such as after chemotherapy, or splenic dysfunction, or HIV infection)
- Pregnant women
- Morbidly obese individuals (body mass index >40)
People at risk of influenza exposure or transmitting influenza to vulnerable groups:
- Health and social care workers
- Individuals who live with or care for vulnerable people
- Influenza spreaders
- Children aged 2-<17 years (Children under 6 months are not offered the vaccine, however their care givers are offered the vaccine to prevent transmission
Swine influenza
Symptoms?
Patients with disease may present with:
- flu-like symptoms - fever{ >=38 degC ] or history of fever
- flu-like illness (two or more of the following symptoms: cough, sore throat, rhinorrhea, limb/joint pain, headache)
additionally some patients may present with vomiting and diarrhoea
- in young children typical influenza symptoms (e.g., fever and cough) may be absent. Fever and lethargy might be the presenting symptoms in infants and may not have cough or other respiratory symptoms or signs
Severe disease in children may present with:
- apnoea
- tachypnoea
- dyspnoea
- cyanosis
- dehydration
- altered mental status
- extreme irritability
Influenza
Vaccination?
- current seasonal influenza vaccines are trivalent, two subtypes of influenza A and one type B virus
- quadrivalent vaccines with an additional B virus, the first quadrivalent influenza vaccine will be available for use in the UK in 2013
- One of the influenza vaccines available in the UK are inactivated and do not contain live viruses
- majority of vaccines are administered by intramuscular injection while
- one vaccine (Intanza) is administered by the intradermal route and another (Fluenz) by nasal spray
- it is contraindicated in patients where there is known anaphylactic hypersensitivity to egg products or to a previous dose of the vaccine or any component of the vaccine
- takes 10-14 days before protective antibody levels develop.
- Vaccination is best undertaken between September and early November and immunity can be expected to last for at least the duration of winter
Influenza
Who should be given the vaccine?
Influenza vaccine should be offered (ideally before influenza viruses start to circulate) to:
- all those aged 65 years or older, to include all those aged 65 years on or before 31 March 2014 (born on or before 31 March 1949)
- all children aged two years or three years, but not four years or older on or before the 1 September 2013 (date of birth on or after 2 September 2009 and on or before 1 September 2011).
- all those aged six months or older in the clinical risk groups
