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…
Swine origin of Influenza virus.
- It was through contact with infected pigs
- And through contact with a person with “swine flu”
- Human to human spread of “swine flu” through coughing and sneezing.
What is a Pandemic?
-An epidemic or outbreak of disease that spreads across a large, multinational area.
Pandemic Influenza?
- An influenza epidemic so large it essentially involves the entire world
- Requires a “novel” influenza subtype that is unfamiliar to humans
- Requires the ability to spread well from person to person
Phases of a Pandemic
Phases 1-3 [Predominantly animal infections: few human infections]
Phase 4 [Sustainednhuman-human transmission]
Phases 5-6/pandemic [Widespread human infection]
Post peak [Possibility of recurrent events]
Post pandemic [Disease activity at seasonal levels]
Interpandemic period
Phase 1:
Phase 2: Slide 30 read aloud from phone
Pandemic alert period
Phase 3:
Phase 4:
Phase 5:
Pandemic period
Phase 6: Pandemic increased and sustained transmission in the general population.
What are the responses to a Pandemic?
- Surveillance [Active and Passive]
- Clinical (Case Definition)
- Laboratory - Control
- Individual
- Institutional: Hospitals and Schools
- Public: decreasing contact
- Travel
- Antivirals
- Vaccine
Passive Surveillance
- Passive surveillance methods (in which symptomatic individuals report illness)
Active Surveillance
Active Surveillance
- Screening of temperatures at airports (random surveillance)
- Identification of suspected cases presenting to health care facilities (syndromic surveillance)
- Sentinel surveillance (sentinel sites)
- ->Laboratory confirmation
- Based on CASE DEFINITION
Case definition (Clinical)
Clinical Case definition is based on whether the case of swine influenza A is asuspected or confirmed case.
A suspected case of swine Influenza A
A suspected case of swine influenza A (H1N1) virus infection is defined as a person with acute febrile respiratory illness with onset:
- within 7 days of close contact with a person who is a confirmed case of swine influenza A (H1N1) virus infection, or
- within 7 days of travel to a community where there are one or more confirmed swine influenza A(H1N1) cases, or
- resides in a community where there are one or more confirmed swine influenza cases
A confirmed case o swine influenza A
A confirmed case of swine influenza A (H1N1) virus infection is defined as a person with an acute febrile respiratory illness with laboratory-confirmed swine influenza A (H1N1) virus
Laboratory Diagnosis
- Isolation and culture (Eggs)
- Immunofluoresence
- Real time PCR – mainstay of diagnosis
- Rapid Tests (Point of care testing)
Influenza Preparedness
Impact of pandemic influenza outbreaks on individuals and societies can be reduced by being well prepared.
A comprehensive plan that has been tested and refined through conducting exercises, engaging society should be activated.
National plans should be flexible to respond to outbreaks of various intensities.
Communication will be one of the most challenging tasks during an outbreak and it should be planned well in advance.
Public Health Response to Control of Pandemic
General Measures:
- Individual level
- Institutional level: Hospitals and Schools
- Decreasing contact at the public level
- Travel
- Public education
Specific measures:
- Antivirals for prophylaxis or therapy (may not have enough)
- Vaccines (delay of 4-6 months possible)
Individual measures
-Covering the nose and mouth with a tissue when coughing or sneezing
- Dispose of the tissue in the trash after use.
- Handwashing with soap and water especially after coughing or sneezing.
- Cleaning hands with alcohol-based hand cleaners
- Avoiding close contact with sick people
- Avoiding touching eyes, nose, or mouth with unwashed hands.
- If sick with influenza, stay home from work or school and limit contact with others to keep from infecting them.
Institutional measure: School closures
- Preemptive school closures - delay the spread of disease
- Once schools reopen - the disease will be transmitted and spread
- Impact of school closures – loss of teaching time, the economic impact on caregivers
Institutional measures: Healthcare setting
- Single-patient room with the door kept closed
- Negative pressure room with HEPA (High-Efficiency Particulate Air) filter
- The ill person should wear a surgical mask when outside, the patient room
- Frequent hand washing
- Cups and other utensils used by ill person should be washed with soap and water before use by others
- Routine cleaning and disinfection strategies
- Disposable non-sterile gloves, gowns, and eye protection (e.g. goggles)
- Disposable N95 mask for personnel - aerosol-generating activities (e.g. collection of clinical specimens, endotracheal intubation, nebulizer)
Ways to decrease contact.
- Isolation
- Quarantine
- Social-distancing
Isolation:
sequestration of symptomatic patients either in the home or hospital so that they will not infect others
Quarantine:
Defined as the separation from circulation in the community of asymptomatic persons that may have been exposed to infection]: Can be
Compulsory or Voluntary
Social-Distancing:
range of non-quarantine measures that might serve to reduce contact between persons, such as, the closing of schools or prohibiting large gatherings
Travel measure
- Travel Advisories
- Border closures/Travel restrictions
- Screened for fever at airports, train stations, and roadside checkpoints
- Airport closures
