AVIAN INFLUENZA

Influenza: A devastating disease!“Flu spreads across the world and

ages.” 412 BC: Epidemic reported by Hippocrates1580: First pandemic1781 & 1830: Epidemics Asia -> Russia1918: Spanish Flu killed 20-40M people1933: First human influenza virus isolated1957: Asian Flu1968: HongKong Flu1977: Russian Flu

Influenza:

“The World Health Organization (WHO) estimates that seasonal influenza epidemics result in 3 to 5 million cases of severe illness and lead to 250,000 to 500,000 deaths each year worldwide.”

“Influenza affects all ages.”

DOH - Technical Working Group on Influenza, Nov. 20, 2003

TEN LEADING CAUSES OF MORBIDITY (No. & Rate/100,000 Population)          PHILIPPINES, 2001

CAUSE NO. RATE 1. Diarrheas 845.526 1085.0 2. Bronchitis/Bronchiolitis 694,836 891.7 3. Pneumonias 652,585 837.4 4. Influenza 499,887 641.5 5. Hypertension 318,521 408.7 6. TB Respiratory 110,841 142.2 7. Diseases of the Heart 47,040 60.4 8. Malaria 40,543 52.0 9. Measles 24,494 31.4 10. Chickenpox 24,359 31.3 

INFLUENZA: BY AGE GROUP (No. & Rate/100,000 Population)          PHILIPPINES, 2001

020,00040,00060,00080,000

100,000120,000140,000160,000

<1 yr 1-4 yrs. 5-14 yrs. 15-49 yrs. 50-64 yrs. >65 yrs.FemaleMale

ClassificationRNARNA virusvirus

Type A Type B

Influenza virus

Type C

Influenza C virus

ORTHOMYXOVIRIDAEFamily:Family:

GenusGenus::

TypesTypes::

Specificity:Specificity:ManMan

AnimalAnimal ManMan ManMan

Kingsbury D. W., Virology, IInd edition, New York, 1990, 1076-87

Structure: segmented and enveloped viruses

Nucleocapsid:Nucleocapsid:Nucleoprotein (NP) -RNA Nucleoprotein (NP) -RNA (7 or 8 segments)(7 or 8 segments)

Matrix protein (M)Matrix protein (M)

Lipid bilayerLipid bilayer

Haemaglutinin (HA)Haemaglutinin (HA)

Neuraminidase (NA)Neuraminidase (NA)

80 to 120 nm

SurfaceSurfaceantigensantigens

InternalInternalantigensantigens

Kingsbury D. W., Virology, IInd edition, New York, 1990, 1076-87

Antigenic drift Affects Influenza A and B viruses Occurs every year or every few years

within an influenza subtype Mutations affecting RNA amino acids Does not result in new subtype Can result in significant epidemics

Antigenic shift: emergence of a "new" virus worldwide

affects only Influenza A virus major and sudden genetic

variations in HA and/or NA no immunity in population intervals between previous

pandemics - 11 to 42 years last pandemic in 1968/69

What is Bird Flu?

An infectious disease of birds ranging from mild to severe form of illness.

All birds susceptible to avian influenza,

though some species are more resistant to infection than others.

Some forms of bird flu infections can cause

illness to humans.

What causes bird flu?

Bird flu is caused by15 subtypes of influenza A virus subtype of avian influenza .

Viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses.

Host distribution of influenza A subtypes

Kilbourne E. D., Influenza, New York, plenum 1987:229-51

HA subtypesHA subtypesManSwineHorseSealTurkeyDuck

++++

++++H1H1

++

++H2H2

++++++

++H3H3

++++++H4H4

++++H5H5

++++H6H6

++++++++H7H7

++H8H8

++++H9H9

++++H10H10

NA subtypesNA subtypes++++

++++N1N1

++++

++++N2N2

++

N3N3

++++N4N4

++

++N5N5

++N6N6

++++++++N7N7

++

++++N8N8

++N9N9

+H15

To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses of subtypes H5.

A/ QUAIL/HONG KONG /G1/97 VIRUS 1997 – H5N1 – Hongkong, 18

human cases, 6 died (30% mortality)

Birds - actual source of human infection

No person –to- person transmission. This occurrence highlighted the

potential of new and lethal pathogens to emerge unexpectedly.

Avian Flu in 1997

1997 - H5N1 - Hongkong, 18 cases, 6 human deaths 1999 – H9N2 - Hongkong, I human case, mild infection 2003 – H5N1 – Hongkong – 2 human cases, 1 death H7N7 – The Netherlands, hundreds with conjunctivitis, ILI , 86 confirmed, 3 cases w/ human-to-human

transmission, 1 human death (a veterinarian) H9N2 – Hongkong – 1 human case, mild infection H5N1 - South Korea, Japan – death of chickens, no human case 2004 - H5N1 - human cases and death in Vietnam and Thailand.

Recent cases of human infection caused by avian influenza viruses (New Influenza Virus Subtypes)

How is bird flu transmitted to chickens and other birds?

Direct contact with discharges from infected birds, especially feces and respiratory secretions

Contaminated feed, water, cages equipment, vehicles and clothing

Clinically normal waterfowl and sea birds my introduce the virus into flocks

Broken contaminated eggs may infect chicks in the incubator

How is bird flu transmitted in chickens and other birds?

Birds that survive infection excrete virus for at least 10 days, orally and in feces

Highly pathogenic viruses can survive for long periods in tissues, water and the environment, especially when temperatures are low.

How is bird flu transmitted to humans?

Direct or indirect contact with infected wild ducks and chickens through infected aerosols, discharges and surfaces.

Based on present knowledge, there appears to be no risk of transmission of the H5N1 virus to humans from raw, chilled or frozen poultry foods.

Since the virus is easily inactivated by heat, one does not get bird flu from thoroughly cooked chicken meat.

No evidence of human-to- human transmission.

Why are we concerned with bird flu?

With its capacity to cause severe disease (high pathogenicity ) and epidemics, it causes severe epidemics and mass death of chickens

The poultry industry and food security feared to be greatly affected

High mortality to humans

Why are we concerned with bird flu?

Influenza A viruses have the capacity and propensity to mutate and recombine with another subtype of influenza virus in humans resulting into a totally new influenza A virus subtype.

This new subtype having the characteristic of human influenza virus of being capable to spread from one person to another.

The absence of immunity to the totally new virus through previous infection and no existing vaccines can confer protection make the human population vulnerable, leading to high number of cases and deaths worldwide (pandemic).

Hypothesis concerning pandemics occurence

Direct transfer of viruses between animals and humans

New subtypes are reassortants of human and waterfowl Influenza virus

Pig or humans - "mixing vessel" of human and avian influenza virus South China:South China: Pandemics Pandemics

starting-point?starting-point?

Wild aquatic birds HumansHumans

or or

SwineSwine

Kawaoka Y., Bean W. J., Gorman O.T., et al. In : Elsevier Science Publishers B.V. 1992: 187-91Scholtissek C, Shultz U, Ludwig S, Fitch WM. In : Elsevier Science Publishers B.V. 1992: 193-201

Human

Subtype emergence and recirculation

YearYear DesignationDesignationExtent of antigenic change inExtent of antigenic change in

indicated surface proteinindicated surface proteinSeverity ofSeverity ofpandemicpandemic

1918195719681977

"Spanish flu" H1N1"Asian flu" H2N2

"Hong Kong flu" H3N2"Russian flu" H1N1

HA/NA: major changeHA/NA: major changeHA: moderate change

recirculation

SevereSevere

ModerateMild

20th century pandemics20th century pandemics

Betts FR, Douglas RG, Mandell G.L., Douglas R. G., Bennett J.E., Principles and practice of infectious diseases, 3rd ed., 1990;39:1306-25

What are the signs of bird flu in chickens? Sudden onset, severe illness Severe depression, inappetence Drastic decline in egg production Facial edema with swollen and cyanotic combs and wattles Petechial hemorrhages on internal membrane surfaces Sudden deaths (mortality that can reach 100%) Virus isolation needed for definitive diagnosis

What are the signs and symptoms of bird flu in humans?

A (H5N1) infection very similar to other influenza viruses, most will be self-limiting

Initial symptoms are fever, malaise, myalgia, sore throat and cough.

Conjunctivitis in some patients Persistently high fever X-ray of the chest is useful in detecting early

viral pneumonia.

Complications and death due to severe pneumonia, respiratory distress syndrome and multi-organ failure.

8. Since there are so many cases of influenza, pneumonia or any other respiratory illness, when does one suspect that the patient is a case of bird flu?

If the patient has had direct or indirect contact through handling or having taken care or getting near sick chickens or other birds.

A laboratory confirmation of the bird flu infection and epidemiologic link with unusual death or epidemics of chickens will support the diagnosis of bird flu.

What is the treatment of bird flu?

One should not wait for the laboratory diagnosis of H5N1, infection before treatment is started.

Treatment for HSN, infection is essentially the same as for other influenza viruses.

Antiviral drugs for both treatment and prevention, but have some limitations.

How do we prevent bird flu? The ban on importation of live

chickens and other poultry products from countries affected with bird flu is a critical step to prevent the entry of bird flu into the country.

How do we prevent bird flu?For poultry caretakers and handlers of

chickens and other birds: Avoid contact of poultry with wild birds, in particular

waterfowl Do not import/ avoid introduction of birds of unknown

health condition into flock Control human traffic into poultries Practice proper hand washing and cleaning and

disinfection procedures in poultries Report to authorities any unusual death or illness of

chickens and other birds Report to authorities any illness among the workers in

poultry farms

How do we prevent bird flu?For consumers and the general public:

Thoroughly wash hands with soap and water before and after handling chicken meat

Clean kitchen surfaces and utensils before and after use

Cook chicken well by seeing to it that the boiling temperature is reached

Go only to places where there are no wild waterfowl

Report to authorities any unusual death or illness of chickens and other birds

Report to authorities any case of respiratory illness with history of exposure to sick or dead chickens and other birds

How do we prevent bird flu?

♦ Everyone should consider getting a vaccine for influenza. Priority should be given to those who are directly exposed to birds.

Is it safe to travel to countries affected with bird flu?

Bird flu is not transmitted from one person to another.

Individuals at risk are those who are directly or indirectly exposed to sick chickens and other fowl.

The government thereby advises travelers to countries affected with bird flu not to go to bird parks (aviaries) and poultry farms.

Summary

Avian influenza viruses can infect and have infected people through close, unprotected direct contact with infected poultry.Human infection with high path avian influenza viruses has resulted in mild to severe illness. There is no current evidence of sustained person to person transmission. However, these viruses are continuing to evolve and have the potential for genetic resentment to evolve into a virus that may be more easily transmissible among humans which can result to a pandemic .