Basics of Avian and Pandemic Influenza

Basics of Avian and Pandemic Influenza

The Pandemic Clock is ticking…we just don’t know what time it is.

Edgar Marcus University of Washington School of Medicine

Will pandemic flu strike again?

The “Forgotten Pandemic”

The influenza pandemic of 1918-19 killed more humanskilled more humans than any other disease in a period of similar duration in the history of the world.

Alfred W. Crosby, historian & author

Influenza pandemics in the 20th century

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

50 million deaths 1-4 million deaths

1-4 million deaths

An Influenza Ward during the 1918: “Spanish Flu”

Avian strain of influenza virus

Virus was similar to current bird flu virus

Spread around the globe in 4-6 months

Infected between 25-30% of the world population

Killed 40-100 million world-wide

Majority of deaths in persons 18 to 40 years old

Influenza pandemics are recurring events

• Influenza pandemic is NOT a one-off event.

• They are regular events that occur a few times per century.

• As long as the influenza virus continues to mutate we will continue to have influenza pandemics.

• We cannot be sure exactly when the next one will be, but experts agree it will happen eventually.

• The H5N1 Avian Influenza virus currently circulating in birds is the

No.1 candidate for causing the next pandemic.

A Pandemic WILL occur:

the question is “when and how severe will it be”?

WHO Situational Assessment as at May 2006

• Risk of Pandemic is great• The risk will persist• The evolution of the threat cannot be

predicted• The early warning systems are weak• Reduction of morb/mort impeded by

inadequate medical supplies

• Preparation is the best protection

H5N1 - The Basics

– Avian influenza H5N1 virus in poultry flocks

– Aggressive infection - quickly kills whole flocks

– Can infect humans - mainly only people living/working with poultry

– Over 200 people infected - more than half have died (mortality rate >50%!!!!)

– CannotCannot yet easily spread from person to person

H5N1 has similarities to 1918-19 virus

THE DISEASE IN HUMANS

Influenza viruses are normallynormally highly species-specifichighly species-specific, meaning that viruses that infect an individual species (humans, certain species of birds, pigs, horses, and seals), and only rarely spill over to cause infection in other species.

Of the hundreds of strains of avian influenza A viruses, only four are known to have caused human infections: H5N1, H7N3, H7N7, and H9N2. In general, human infection with these viruses has resulted in mild symptoms and very little severe illness,

with one notable exception: the highly pathogenic H5N1 virus.

H5N1--great concern for human health

First, the H5N1 virus has caused the greatest number of human deaths.

The virus has met all prerequisites for the start of a pandemic save one: an ability to spread efficiently among humans.

H5N1 - The Basics

An Influenza Virus must have three attributes to become a Pandemic Virus:

1) A novel (new) virus which humans have no

immunity

2) The virus causes significant human illness and

death

3) The virus can spread easily from person to

person x

Avian Flu H5N1 has 2 out of 3 today…

H5N1 - The Basics

An Influenza Virus must have three attributes to become a Pandemic Virus:

1) A novel (new) virus which humans have no

immunity

2) The virus causes significant human illness

and death

3) The virus can spread easily from person to

person xx

Avian Flu H5N1 has 2 out of 3 today…

禽流感在公共衛生的重要性在 20世紀時的三次重大「世界性大流行」均與其病毒來自「禽類」有關。若張三感染了「『禽』流感病毒（紅色基因）」而他的親友李四卻感染「『人』流感病毒（藍色基因）」，那重新洗牌八段藍色基因與八段紅色基因，容易產生一種『新』型病毒是原來人的抗體無法抵擋的，卻又可在人群中傳播。

禽流感病毒　　 　 人流感病毒 新型流感病

××

Genetic drift

• A change that occurs on the molecular level to effect a change in the antigenic properties of a bacteria or virus.

• Antigenic drift occurs naturally and more rapidly in certain viruses (for example HIV).

• It is antigenic drift which complicates the development of an effective HIV (AIDS) vaccine.

As the human influenza strains are continually evolving

via these mutations, the virus is able to escape from the human immune response and cause epidemics.

For this reason, manufacturers must change the composition of the influenza vaccine on an annual basis in order to ensure an accurate match is achieved with the circulating viral strains

Genetic shift

• Antigenic shift is the process by which different strains of a virus, (or different viruses), combine to form a new subtype

• having a mixture of the surface antigens of the two original strains.

Antigenic drift is the natural mutation over time of known strains of influenza (or other things, in a more general sense) which may lead to a loss of immunity, or in vaccine mismatch. Antigenic drift occurs in all types of influenza including influenza A, B and C.

Antigenic shift, however, occurs only in influenza A because it infects more than just humans. Affected species include other mammals and birds, giving influenza A the opportunity for a major reorganization of surface antigens

What is the difference between Antigenic shift and antigenic drift?

Antigenic drift is the natural mutation over time of known strains of influenza (or other things, in a more general sense) which may lead to a loss of immunity, or in vaccine mismatch. Antigenic drift occurs in all types of influenza including influenza A, B and C.

Antigenic shift, however, occurs only in influenza A because it infects more than just humans. Affected species include other mammals and birds, giving influenza A

the opportunity for a major reorganization of surface antigens.

Antigenic shift vs antigenic drift:

Infectivity period: 1 day before, 14 days after

1. Contact transmission: Direct - Kissing Indirect – Sharing

2. Mainly by “droplet” spread: Coughing, sneezing and talking Mucous membranes Virus active on hard surfaces for 48

hours 3. “Aerosol” spread:

Unusual but possible in very crowded conditions

How is Influenza Spread?

                                                                                                                                   

                                         

WHO Classification of Pandemic Phases

H5N1 Avian Flu – where is it now?

• Human infections (as at 8 May 2006):

– Turkey (12 cases, 4 deaths)– Vietnam (93 cases, 42 deaths)– Indonesia (33 cases, 25 deaths)– Cambodia (6 cases, 6 deaths)– Thailand (22 cases, 14 deaths)– China (18 cases, 12 deaths)– Iraq (2 cases, 2 deaths)– Azerbaijan (8 cases, 5 deaths)– Egypt (13 cases, 5 deaths)

Prevention and control of

Avian Flu

Annual influenza vaccination is now recommended for the following groups

• persons at high risk for influenza-related complications

• persons who live with or care for persons at high risk

• health-care workers.

Vaccines: the first line of defence

Depopulation of farms and markets

PILLARS OF THE STRATEGY

• Preparedness and

Communication

• Surveillance and Detection

• Response and Containment

Influenza A(H7N9) is one of a subgroup of influenza viruses that normally circulate among birds. Until recently, this virus had not been seen in people. However, human infections have now been detected.

The disease is of concern because most patients have been severely ill. There is no indication thus far that it can be transmitted between people, but both animal-to-human and human-to-human routes of transmission are being actively investigated.

H7N9

Courtesy of WHO Collaborating Centre for Reference and Research on Influenza, National Institute of Infectious Diseases, Japan

Dr Margaret Chan Director-General of WHO

Hong Kong Quarantines 19 People After Second Case of H7N9

Hong Kong health officials have quarantined 19 people who had contact with an 80-year-old man confirmed to have the city’s second case of H7N9 influenza, which has killed 45 people in China this year.

Bloomberg news Dec 8, 2013

Disease Outbreak News

SARS

Pandemic Influenza is different to SARS

SARS Pandemic Flu

One off unexpected event Recurring event

Difficult to catch Easy to catch

People only infectious when they are symptomatic

People are infectious before they are symptomatic

Several thousand cases, epidemic lasted several months

Potentially millions of cases, pandemic could last more than a year

Easy to contain an outbreak Almost impossible to contain an outbreak

• Many institutions are using their SARS plan as the basis for their pandemic influenza plan.

• But SARS is different to pandemic influenza:

咳嗽禮節

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