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Avian Influenza Viruses and its role in inter-species Transmission

Rokshana Parvin and T.W. Vahlenkamp

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Influenza virus

Family: OrthomyxoviridaeThree main types

Type AMultiple species

Type BHumans

Type C Humans and swine

Influenza viruses causes highly contagious respiratory disease with potentially fatal outcomes.

http://www.uct.ac.za/depts/mmi/stannard/fluvirus.html

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M1 protein

helical nucleocapsid (RNA plus NP protein)

HA - hemagglutinin

polymerase complex

lipid bilayer membrane

NA - neuraminidase

Influenza virus genomeThe influenza A genome consists of eight single-stranded negative-sense RNA molecules encoded 10 proteins within viral envelope

HANAMNSNPPAPB1PB2

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Influenza virus Type A

Influenza A viruses are further classified into subtypes based on the antigenicity of their surface glycoproteins (HA & NA )

Infect multiple speciesHumansBirds (wild birds, domestic poultry)Other animals: pigs, horses, dogs, marine mammals (seals,

whales)

Hemagglutinin (HA) Neuraminidase (NA)

H1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14, H15, H16

N1, N2, N3, N4, N5, N6, N7, N8, N9

So far at least 84 serotypes (HA &NA combination) are found in resivour

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HA 1-16 NA 1-9

H5

H3, H7

H4, H7, H13

H5, H7, H9

H1 - H3H5, H7, H9

H1 - H3 H3, H7H5

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How they transmitted ??????????????

The virus is contracted through Contact with saliva, nasal secretions and feces of the wild birds.  Contaminated surfaces or materials. Contaminated water* Direct or indirect contact 

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‘FLU’

True influenza

influenza virus A or influenza virus B

Febrile respiratory disease with systemic symptoms caused by a variety of other organisms often called ‘flu’

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Influenza descriptions

Influenza name Strain Host affected Outbreak year

Seasonal Flu H3, H1 humans yearly

Spanish Flu H1N1 humans 1918

Asian Flu H2N2 humans 1957

Hong Kong Flu H3N2 humans 1968, 1970-72

bird flu H5N1 Poultry, (endemic in avian), human, & cat

1997, 2003………..

Swine flu H1N1 Humans, swine 2009

* H1N2 is currently endemic in humans and pigs

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Bird Flu: H5N1, H7N7,H9N2…

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Bird Flu

HPAIH5, H7H5N1

LPAIH9, H7H9N2

Highly pathogenic viruses result in high death rates (up to 100% mortality within 48 hours) in some poultry species

Low pathogenicity viruses also cause outbreaks in poultry but are not generally associated with severe clinical disease

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transmitted to poultry

Natural reservoir of LPAI (H9, H5, H7) virus

LPAI virus circulates in poultry with mild disease

LPAI Virus Mutates to HPAI with severe disease

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• The current outbreaks of highly pathogenic avian influenza, which began in South-East Asia in mid-2003, are the largest and most severe on record

• Never before in the history of this disease have so many countries been simultaneously affected, resulting in the loss of so many birds

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≥ 100 outbreaks

≥ 10 outbreaks≥ 1 outbreaks

Outbreaks map of HPAI H5N1 in poultry (2003 – March 2012)

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Bird flu: Why is there a risk for humans?

Role of pigs as an intermediate host

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Pandemics are different from seasonal outbreaks or “epidemics” of influenza

Seasonal outbreaks are caused by subtypes of influenza viruses that are already in existence among people

Pandemic outbreaks are caused by new subtypes or by subtypes that have never circulated among people or that have not circulated among people for a long time

Differences between Pandemics and Epidemics

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Seasonal Epidemics vs. PandemicsSeasonal Influenza

– A public health problem each year

– Usually some immunity built up from previous exposures to the same subtype

– Infants and elderly most at risk

Influenza Pandemics

– Appear in the human population rarely and unpredictably

– Human population lacks any immunity

– All age groups, including healthy young adults

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If a new subtype of influenza A virus is introduced into the human population, most people have little or no protection against the new virus, and if the virus can spread easily from person to person, a PANDEMIC (worldwide spread) may occur

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Prerequisites for pandemic influenza

A new influenza virus emerges to which the general population has little/no immunity

The new virus must be efficiently transmitted from one human to another

The new virus must be efficiently transmitted from one human to another

The new virus must be able to replicate in humans and cause disease

Ingredients for a pandemic are abundantly available

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Influenza A viruses are renowned for their rapid evolution in aberrant hosts including humans

Antigenic drift occurs when single nucleotides are replaced over time through mutations

Antigenic shift takes place when two different viruses infect the same cell and new viral particles are created with new combinations or assortments of the 8 influenza molecules

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Sick Pig with both Strands of Influenza

Antigenic shift

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1st pandemics of 21th century

Pandemic Year Influenza virus type

People infected Estimated deaths worldwide

Swine flu 2009–2010

Pandemic H1N1

> 622,482 (lab-confirmed)

14,286 (lab-confirmed; ECDC18,036 (lab-confirmed;WHO)

The pandemic that began in March 2009 was caused by an H1N1 influenza A virus that represents a quadruple reassortment of two swine strains, one human strain, and one avian strain of influenza; the largest proportion of genes came from swine influenza viruses.

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History of Reassortment Events in the Evolution of Influenza A H1N1/09

H1N1/ 09

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20th century flu pandemics

Emergency military hospital during Spanish flu pandemic (1918)

Spanish flu

20-40 m deaths

A(H1N1)

Children's ward during Asian flu pandemic (1957)

Asian flu

1-4 m deaths

A(H2N2)

Hong Kong Flu Pandemic (1968,1970-1972)

Hong Kong Flu

1-4 m deaths

A(H3N2)

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Now literature says…

Bird flu can transmitted directly from birds to humans

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Possible mechanisms for the generation of pandemic influenza viruses

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Current situation

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http://www.who.int/csr/don/2012_04_12/en/index.html

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http://www.oie.int/fileadmin/Home/eng/Animal_Health_in_the_World/docs/pdf/graph_avian_influenza/graphs_HPAI_31_03_2012.pdf

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http://www.fao.org/ag/againfo/programmes/en/empres/maps_cum_archive.html

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Next

warning ?

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THANK YOU

For your kind attention!!!!

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