Influenza Flashcards
What are we focusing on when it comes to Influenza?
- Virology and classification
- Antigenic drift and antigenic shift
- Pathogenesis
- Clinical manifestations and complications
- Treatment
- Vaccines
- Avian Influenza
- Pandemic Influenza
- Public Health measures
The virology of Influenza
-Orthomyxoviridae
It is an Enveloped RNA virus
-Segmented Genome
Its Surface antigens are:
H1-15 (Haemaglutinin)
N1- 9 (Neuraminidase)
Classification of Influenza
There are 3 major types: A, B, C (according to proteins)
Type C - relatively stable
Type B - some variability
Type A - most variable, greatest human disease concern, responsible for pandemics
How do new influenza strains arise?
The surface antigens H and N are evolving:
- [^= increasing] virulence
- They Evade immune system-altered tropism and host range
The arising of new strains occurs via 2 mechanisms :
- Antigenic drift
- Antigenic shift
What is the Antigenic drift in Influenza?
- The virus is circulating through the human population.
- And over time, one or a few point mutations occur in H (Hemaglutinin surface protein) .
-Resulting in amino acid change(s) in H protein.
The immune system no longer fully recognizes the protein.
The variant virus can now re-infect
This is believed to be the mechanism responsible for annual (seasonal) epidemics
What is the Antigenic Shift in Influenza?
- It is the Re-assortment of gene segments between different influenza viruses
- Often a novel H gene
This is the postulated mechanism for the evolution of pandemics
Shift vs Drift
- The drift occurs over a number of years but the shift occurs in a space of one year.
- The drift is gradual but the shift is relatively abrupt in terms of the change in relatedness of the antigenic proteins.
Influenza Symptoms
- Fever
- Chills
- Coughing
- Muscle aches and pains
- Headaches
- Tiredness and weakness
- Runny, stuffy nose
- Sneezing
- Gastrointestinal Symptoms
The difference in the symptoms of flu and the cold.
In children, gastrointestinal symptoms (nausea, vomiting, diarrhea) may be present. Gastrointestinal symptoms are uncommon in adults.
- In flu, the fever is common, and in a common cold no fever.
- Rare chills in cold while common in flu
- Coughing most common in flu
- rare headache in cold
- Sometimes no sneezing in flu and GIT symptoms are unusual in the common cold .
Treatment of Flu
-The Antiviral treatment for influenza must be started within 48 hours (or less) of onset of symptoms for maximum effectiveness.
- Oseltamivir (Tamiflu)
=Is effective against influenza A and B, it is the recommended drug of choice for both prophylaxis and treatment in an influenza outbreak - Zanimivir (Relenza)
=Is effective against influenza A and B, it is used when the predominant circulating [flu] strain is resistant to Tamiflu.
Influenza Vaccine
- The influenza viruses selected for inclusion in the seasonal flu vaccines are updated each year, why? :
1. because of antigenic variation.
2. because immunity wanes with time. - Based on which influenza virus strains are identified and how they are spreading
- 130 national influenza centers in 101 countries conduct year-round surveillance for influenza and study influenza disease trends - send influenza viruses to WHO
Seasonal Influenza Vaccine
-Trivalent vaccine - each component selected to protect against one of the three main groups of influenza viruses circulating in humans.
-E.g. 2011 Influenza Vaccine:
A/California/7/2009 (H1N1)–like virus
A/Perth/16/2009 (H3N2)–like virus
B/Brisbane/60/2008–like virus
The H1N1 virus in the 2010-2011 seasonal influenza vaccine is the same vaccine virus as was used in the 2009 H1N1 vaccine
The same vaccine used in both hemispheres
The World Health Organization Influenza Nomenclature.
A/California/7/2009 (H1N1)
A- Influenza type California- Geographical Source 2009 - Year of isolation 7- Isolate number H1- Hemagglutinin subtype N1- Neuraminidase subtype
How do we make inactivated vaccines?
We start with a live virus, Detergents are used to chemically inactivate the virus.
Now the virus is inactive then it goes through purification-ultra-centrifugation.
It is then put in subunit vaccine
Human-Animal interface
Primary risk factor for human infection appears to be direct or indirect exposure to infected live or dead animals or contaminated environments.
-The Influenza viruses circulating in animals pose threats to human health.
> Humans can become ill when infected with viruses from animal sources, such as
- avian influenza virus subtypes: H5N1 and H9N2 and
- swine influenza virus subtypes: H1N1 and H3N2.
Avian Influenza in Humans
H5N1 Influenza Started in Hong Kong, 1997 The Outbreak was in poultry Humans: -18 confirmed cases, 6 deaths -1st case 3-year-old boy died in May 1997 -Remaining cases: Nov-Dec 1997 -Age range 1-60 years (mean age 17)
BUT, Human to human transmission is inefficient
- There is limited potential for pandemic spread (unless the virus acquires increased transmissibility)
- It Remains localized to areas where close contact between poultry and humans exists
- Avian influenza continues to evolve…
