Avian and Pandemic Influenza Kathy Harriman Minnesota Department

Avian and Pandemic Influenza Kathy Harriman Minnesota Department of Health Infectious Disease Prevention and Control Division Acute Disease Epidemiology Section

What is influenza? § An acute respiratory illness resulting from infection with an influenza virus § Highly infectious and can spread rapidly from person to person § Some strains cause more severe illness than others

Types of influenza viruses § Influenza viruses are divided into three main types: influenza A, B, and C § A viruses – infect birds and other animals, as well as humans § A viruses – source of seasonal influenza epidemics and all pandemics § B and C viruses – infect humans only and do not cause pandemics

Where does influenza A virus come from? Human influenza A viruses start as avian (bird) influenza viruses Migratory water birds Domestic birds Humans and other animals

Influenza symptoms § Sudden onset § Fever, headache, muscle aches, severe weakness § Respiratory symptoms, e. g. , cough, sore throat, difficulty breathing

How influenza spreads § Spreads easily from person to person through coughing and sneezing § Transmitted by: – inhaling respiratory aerosols containing the virus, produced when infected person talks, coughs, or sneezes – touching an infected person or an item contaminated with the virus and then touching your eyes, nose, or mouth

Courtesy of CDC

Seasonal influenza: minor changes - antigenic drift § Occurs among influenza A viruses resulting in emergence of new variants of prevailing strains every year § New variants result in seasonal influenza each winter § Some years are worse than others – partly related to degree of ‘drift’

What is an influenza pandemic? § Influenza pandemics are worldwide epidemics of a newly emerged strain of influenza § Few, if any, people have any immunity to the new virus § This allows the new virus to spread widely, easily, and to cause more serious illness

What causes a pandemic? § Pandemics occur when a new avian influenza strain acquires the ability infect people and to spread easily person to person § This can occur in two ways: – Reassortment (an exchange of seasonal and avian influenza genes in a person or pig infected with both strains) – Mutation (an avian strain becomes more transmissible through adaptive mutation of the virus during human avian influenza infection)

Pandemic influenza: major changes - antigenic shift § Major changes occur in the surface antigens of influenza A viruses by mutation or reassortment § Changes are more significant than those associated with antigenic drift § Changes lead to the emergence of potentially pandemic strains by creating a virus that is markedly different from recently circulating strains so that almost all people have no pre-existing immunity

Seasonal vs. pandemic influenza § Pandemic influenza is not just a “bad flu, ” it is a wholly new threat to humans § A severe pandemic would cause social disruption unlike anything most persons now alive have ever experienced § Compared to seasonal influenzas, pandemic influenzas infect more people, cause more severe illness, and cause more deaths § Seasonal influenza viruses most often cause severe disease in the very young, the very old, and those with chronic illnesses, but pandemic influenza strains can infect and kill young, healthy people § The highest mortality rate in the 1918 -19 pandemic was in people aged 20 -40 years

History of influenza § 412 BC - first mentioned by Hippocrates § 1580 - first pandemic described § 1580 -1900 - 28 pandemics

Pandemic influenza in the 20 th Century 1918 “Spanish Flu” 1957 “Asian Flu” 1968 “Hong Kong Flu” 20 -40 million deaths 1 million deaths H 2 N 2 H 3 N 2 H 1 N 1 1920 1940 1960 1980 2000

1918 Pandemic Highest mortality in people 20 -40 years of age - 675, 000 Americans died of influenza - 43, 000 U. S. soldiers died of influenza

Lessons from past pandemics § Occur unpredictably, not always in winter § Great variations in mortality, severity of illness, and pattern of illness or age most severely affected § Rapid surge in number of cases over brief period of time, often measured in weeks § Tend to occur in waves of 6 - 8 weeks, subsequent waves may be more or less severe Key lesson – unpredictability

Why is there concern about an influenza pandemic now? § A highly pathogenic avian influenza strain (A/H 5 N 1) emerged in Hong Kong in 1997, reemerged in birds and humans in 2003, and is now circulating widely in birds in many countries § Since 2003, this strain has spread from birds to humans and as of August 23, 2006 has infected 241 people (141 deaths) in 10 countries § This strain has also been documented (rarely, so far) to spread from person to person § Reassortment or mutation could allow this strain to become easily transmissible between humans – there is no way to know if or when this will happen

Would the next pandemic be severe? § We just don’t know § However, past pandemics provide clues as to how humans may be affected by a new influenza virus and how societies would react to a pandemic § Information from past pandemics is used in economic and disease models to predict the impact of future pandemics

What could happen during an influenza pandemic? § In the United States, up to 1. 9 million people could die, up to 9. 9 million could be hospitalized, and up to 90 million could become ill § Intense pressure on healthcare § Disruption to many aspects of daily life

Emergency hospital, Camp Funston, Kansas 1918 Courtesy of National Museum of Health and Medicine

Pandemic waves Past experience teaches us that following the emergence of a new pandemic virus: § More than one wave of influenza is likely § Waves typically last 6 -8 weeks § Gaps between the waves may be weeks or months § A subsequent wave can be worse than the first

What can be done to slow the spread of a pandemic? § Vaccine: – not expected to be available until later in a pandemic § Antivirals: – likely to be insufficient quantities, effectiveness unclear § Disease containment measures: – may be the only measures available in the early stages of a pandemic – may be helpful in slowing the spread of a pandemic, allowing more time for vaccine production

Vaccine § Because the virus will be new, there will be no vaccine ready to protect against pandemic influenza at the start of a pandemic § Specific vaccine cannot be made until the virus strain has been identified and will take at least 4 -6 months to produce

Antiviral drugs § Likely to be the only major medical countermeasure available early in a pandemic § Uncertainty about effectiveness for treatment or prevention § U. S. goal is to stockpile enough antiviral drugs to treat 25% of the U. S. population Reproduced with permission from Roche Products Ltd. Tamiflu ®

Disease containment measures § Isolation: restriction of movement/separation of ill infected persons with a contagious disease § Quarantine: restriction of movement/separation of well persons presumed exposed to a contagious disease § Self-shielding: self-imposed exclusion from infected persons or those who may be infected § Social distancing: reducing interactions between people to reduce the risk of disease transmission § Snow days: days on which offices, schools, transportation systems are closed or cancelled, as if there were a major snowstorm

Other methods to reduce transmission § Hand hygiene (cleaning hands with soap and water or an alcohol-based hand rub) § Respiratory hygiene, e. g. , “Cover your cough” § Cleaning and disinfection of contaminated objects, surfaces § Physical barriers (e. g. , glass or plastic “windows” to protect front desk workers) § Use of personal protective equipment (PPE) in some settings (e. g. , healthcare) such as gowns, gloves, eye, and respiratory protection

Employees of Stewart & Holmes Wholesale Drug Co. Seattle, 1918 Courtesy of Grace Loudon Mc Adam

Summary § The currently circulating avian influenza strain may or may not cause a pandemic § Global surveillance is essential; international cooperation is critical § Planning for a possible pandemic is occurring nationally and internationally § National, state, local, and individual preparedness are all important

Additional avian and pandemic influenza information § MDH http: //www. mdhflu. com § CDC http: //www. cdc. gov/flu/avian/ index. htm § HHS http: //www. pandemicflu. gov/ http: //www. hhs. gov/pandemicflu/ plan/ § WHO http: //www. who. int/csr/disease/ avian_influenza/en/index. html

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