Avian and Pandemic Influenza

Kathy Harriman

Minnesota Department of Health

Infectious Disease Prevention and Control Division

Acute Disease Epidemiology Section

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

What is influenza?

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

Migratory water birds

Domestic birds

Where does influenza A virus come from?

Humansand other animals

Human influenza A viruses start as avian (bird) influenza viruses

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 20th Century

1920 1940 1960 1980 2000

H1N1 H2N2 H3N2

1918 “Spanish Flu” 1957 “Asian Flu” 1968 “Hong Kong Flu”

20-40 million deaths 1 million deaths 1 million deaths

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/H5N1) 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

MDHhttp://www.mdhflu.com

CDChttp://www.cdc.gov/flu/avian/ index.htm

HHShttp://www.pandemicflu.gov/http://www.hhs.gov/pandemicflu/ plan/

WHOhttp://www.who.int/csr/disease/ avian_influenza/en/index.html

Please call the Minnesota Department

of Health at: 651-201-5414 or

1-877-676-5414

Questions?