Transcript Structure of the H5N1 Avian Virus

Bird Flu
Disease Categories
• Sporadic occurrences: Limited in scope.
Affect a few individuals in a small area.
• Epidemics: More widespread. Affect large
areas.
• Pandemics: Occurs worldwide. The 1918
super flu killed 40 million people.
• Endemic: Caused by an infectious agent that is
always present in a population.
– Hantavirus –endemic in rats in western US.
Viruses
• Viruses require a host
• Viruses are essentially packets of genetic
information; RNA or DNA.
• Viruses can be latent.
• Viruses are specific for different cell types.
– Polio virus infects nerve cells
– HIV infects immune T cells
– Hepatitis B infects liver cells
• Essentially, Viruses are composed of:
– Envelope
– Caspid (capsule that holds genetic material)
– Genetic Material, RNA or DNA
• RNA=Retrovirus
• 1. Binding--this requires specialized envelope proteins. These
proteins make viruses specific for different cells.
• 2. Penetration--viral particles enter the cell, the caspid is
removed and genetic material enters the nucleus.
• 3. Replication--the virus uses the host replication machinery to
make many copies of itself.
•
• 4. Viral protein production--the virus uses the host’s
translation machinery -copies of the viral proteins - capsid and
new envelope proteins. Envelope proteins move to the plasma
membrane thanks to protein secretion performed by the host.
• 5. Assembly--genetic material is packaged into the new
caspids.
• 6 Budding--the caspids move to the cell membrane, get
wrapped in their envelope proteins and move on to infect a
neighboring cell.
How a virus changes
• Antigenic drift: Mutations cause a
gradual change in caspid spikes
– Antibody gradually becomes less
effective
• Antigenic shift: An abrupt , major
change occurs in the antigen of the
spike.
– Because the virus acquires one or more
new genome segments.
– This is how pandemic strains of flu
occur
What is Avian Influenza
• Is an infection caused • Bird flu is very
by avian (bird)
contagious among
influenza viruses.
birds.
• These flu viruses
• Can make
occur naturally among
domesticated birds
birds.
like chickens, ducks,
and turkeys very sick
• Birds carry the
and kill them.
viruses in their
intestines, but usually
do not get sick.
How is it Transmitted ?
•
•
•
•
From Bird to Bird
Domesticated birds may
become infected with avian
influenza virus through direct
contact with infected waterfowl
or other infected poultry, or
through contact with surfaces
(dirt, or cages) or materials
(water, or feed) that have been
contaminated with virus.
Infected birds shed virus in their
saliva, nasal secretions, and
feces
People, vehicles and other
inanimate objects can spread
the virus from one farm to
another.
• From Bird to Human
•
•
•
Two main ways
Directly from birds or from avian
virus-contaminated environments
to people
Through an intermediate host,
such as a pig
Structure of the H5N1 Avian Virus
• Influenza viruses have eight
separate RNA gene segments. PB2,
PB1, PA, HA, NP, NA, M, and NS
• HA, NA, and M specify the
structure of proteins that are most
medically relevant as targets for
antiviral drugs and antibodies.
• HA and NA make the spikes in the
protein coat surface which helps
the virus attach to a host cell
Structure of the H5N1 Avian Virus
• The influenza virus RNA
polymerase is a multifunctional
complex composed of the three
viral proteins PB1, PB2 and PA,
• Together with the viral
nucleoprotein NP, these form the
minimum complement required for
viral mRNA synthesis and
replication.
Structure of the H5N1 Avian Virus
• HA codes for hemagglutinin
which is an antigenic
glycoprotein found on the
surface of the influenza viruses
and is responsible for binding
the virus to the cell that is being
infected.
• forms spikes at the surface of flu
viruses that function to attach
viruses to cells
Structure of the H5N1 Avian Virus
• NA codes for neuraminidase
which is an antigenic
glycoprotein enzyme found on
the surface of the influenza
viruses.
• It helps the release of progeny
viruses from infected cells.
Structure of the H5N1 Avian Virus
• The segmented genome allows
viruses from different species to
mix and create new influenza A
virus if viruses from two
different species infect the
same person or animal.
• Resulting new virus might then be
able to infect humans and spread
from person to person, but it
would have surface proteins not
previously seen in influenza
viruses that infect humans.
The Influenza Pandemic of 1918
• Killed more people than world war one
– Within 6 months 1/5 of the world was infected
– Most deadly to those aged 20 to 40.
• "Spanish Flu"
• In the USA: infected 28% of the population
– An estimated 675,000 Americans died of
influenza during the pandemic (10 times the
number KIA)
– An estimated further 43,000 U.S. servicemen
mobilized for WWI died of influenza
The Influenza Pandemic of 1918
The 1918 flu overwhelmed the
body's natural defenses, that
the usual cause of death in
influenza patients---a
secondary infection of lethal
pneumonia---oftentimes never
had a chance to establish
itself.
Instead, the virus caused an
uncontrollable hemorrhaging
that filled the lungs, and
patients would drown in their
own body fluids
Trends in Infectious Disease Mortality in the
United States During the 20th Century
Armstrong, GL. JAMA. 1999 Jan 6;281(1):61-6.
What About
today?
Pandemic Influenza
Outbreak of Avian Influenza A (H5N1) in Asia
What about today?
• W.H.O.
• More advanced medical practices
• Better isolation techniques
• Better Medical and genetic knowledge
• Global communications
What is the risk?
• The risk is generally
low.
• However, during an outbreak of bird flu among
poultry (domesticated chicken, ducks, and
turkeys), there is a possible risk to people who
have contact with infected birds or surfaces that
have been contaminated with excretions from
infected birds.
• The current outbreak of avian influenza among
poultry in Asia is an example of a bird flu
outbreak that has caused human infections and
death.
What is being done to prevent an
Avian Flu Pandemic?
• CDC is working with the Association of Public
Health Laboratories on training workshops for
state laboratories on the use of special
laboratory (molecular) techniques to identify H5
viruses.
• Starting a $5.5 million initiative to improve
influenza surveillance in Asia.
• Performing laboratory testing of H5N1 viruses.
• Working with other agencies such as the
Department of Defense and the Veterans
Administration on antiviral stockpile issues.
What you need to Take Home
from This?
• The current risk to Americans from the
H5N1 bird flu outbreak in Asia is very low.
• The CDC is working on ways to prevent
and cure the U.S in the event a pandemic
occurs.
• Don’t play with domesticated birds in the
wild 