Influenza Virus Influenza: Highly infectious viral illness Virus was first isolated in 1933 Single-stranded RNA virus Orthomyxoviridae family 3 types: A, B, C Subtypes of type A determined by hemagglutinin (H) and neuraminidase (N)
Swine Influenza Type A Subtype H1N1Type A - moderate to severe illness - all age groups, potential for epidemic - humans and other animalType B - milder disease - primarily affects children - humans onlyType C - rarely reported in humans - no epidemics
Antigenic Drift Gradual change in the virus with mutations and substitutions in the amino acid chain of the surface proteins (neuraminidase and haemagglutinin). A new strain can trigger a new epidemic usually prevail for 2-5 years before next antigenic drift.
Antigenic Shift A type A influenza virus with a completely novel haemagglutinin or neuraminidase formation moves into the human species from other host species The primary source is birds, with recombination in swine or humans.
Pandemic influenza The fact is, that flu is one of the most formidable infections confronting humankind. The virus mutates constantly as it circulates among birds, pigs and humans. So each new flu season brings new challenges First pandemic known in 15th century In pandemic response and planning, prediction of the future is not possible. Thought is to hope for best, but plan for worst
Recent Pandemics 1889-1890 – first recorded pandemic 1918 ―Spanish‖ flu- 20-40 million deaths 1957 ―Asian‖ flu- 1 million deaths 1968 ―Hong Kong‖ flu- 1 million deaths 1976 ―Swine‖ flu – unreported deaths
Influenza Pathogenesis Respiratory transmission of virus Replication in respiratory epithelium with subsequent destruction of cells Viremia rarely documented Viral shedding in respiratory secretions for 5-10 days
Symptoms of influenza include: – Fever – Cough – Headache – Myalgia – Fatigue and weakness – Chest discomfort – Nausea, diarrhea with swine flu
Risk factors for complications: Age > 65 years Residence of nursing homes and other chronic care facilities Chronic cardiac or pulmonary disorders Chronic conditions such as diabetes Long term ASA therapy Immunosuppression
Diagnosis Symptoms of cough and fever has a 30%– 40 % predictive power. Symptoms with surveillance (flu in community) has a 70% - 80% predictive power.
Current Pandemic Influenza Phase (as of June 15, 2009): Phase 6
World Health Organization Pandemic Influenza Phases (2009)Pandemic Influenza Phase Characterization of Phase Public Health Goals Ensure rapid characterization of the Human infection(s) with a new subtype, but no human- new virus subtype and early detection, Phase 3 to-human spread, or at most rare instances of spread notification and response to additional to a close contact cases Contain the new virus within limited foci Small cluster(s) with limited human-to-human or delay spread to gain time to Phase 4 transmission but spread is highly localized, suggesting implement preparedness measures, that the virus is not well adapted to human including vaccine development Larger cluster(s) but human-to-human spread still Maximize efforts to contain or delay localized, suggesting that the virus is becoming spread, to possibly avert a pandemic, Phase 5 increasingly better adapted to humans, but may not yet and to gain time to implement pandemic be fully transmissible (substantial pandemic risk) response measures Pandemic increased and sustained transmission in Phase 6 Minimize the impact of the pandemic general population
How does novel H1N1 Influenza spread? This virus is thought to spread the same way seasonal flu spreads • Primarily through respiratory droplets • Coughing • Sneezing • Touching respiratory droplets on yourself, another person, or an object, then touching mucus membranes (e.g., mouth, nose, eyes) without washing hands
Persons at High Risk Persons at increased risk of severe illness from influenza include: people older than 65 years, children younger than five years, pregnant women, and people of any age with certain chronic medical conditions, like diabetes, asthma, immune-suppression, or chronic lung disease. See Interim Recommendations for Facemask and Respirator Use to Reduce Novel Influenza A (H1N1) Virus Transmission Information on care of certain groups at increased risk of severe illness from influenza can be found at the following links. Pregnant Women and Novel Influenza A (H1N1) Considerations for Clinicians H1N1 Flu and Patients With Cardiovascular Disease (Heart Disease and Stroke) Interim Guidance—HIV-Infected Adults and Adolescents: Considerations for Clinicians Regarding Novel Influenza A (H1N1) Virus
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