Influenza H5N1
By Steven Yi
Contents
Overview
2. History
3. Attachment
4. Entry
5. Replication
6. Lytic Cycle
7. Diagnosis
8. Treatment
1.
Overview
Influenza, or, more commonly, the flu, is an
infectious disease caused by single-stranded
RNA viruses from the family Orthomyxoviridae.
H5N1 is a particularly pathogenic strain adapted
to avian populations. Over 60% of confirmed
victims of avian flu have died, but there only
seems to be limited human-to-human
communication of the disease. If this strain were
to become communicable between humans, a
severe pandemic would be likely.
History
In 1997, H5N1 first materialized as an extremely lethal strain of
avian flu; a disease that had hitherto only produced minor
sickness. The disease that materialized was capable of rapidly
killing poultry and required the culling of millions of animals to
contain the spread of the disease. Hong Kong culled its entire
domestic population.
Since then, hundreds of outbreaks were reported in Asia. One of
the things that make this strain of avian flu so dangerous is its
capacity to mutate. Huge amounts of money have been spent by
the US and other countries in anticipation of H5N1 mutating into
a form capable of spreading from human to human. Without
adequate preparation, such an outbreak could potentially take out
a significant portion of the human population.
Attachment and Entry
Influenza viruses bind to sialic acids on the
surfaces of epithelial cells, such as those
found in the nose, throat, and lungs, and red
blood cells via antibodies called hemaglutinin.
The cell then engulfs the virus through
endocytosis. The virus then injects its vRNA,
RNA polymerase, and accessory proteins into
the host cell’s cytoplasm. These materials are
then transported to the nucleus of the cell.
Replication + Lytic Cycle
RNA polymerase transcribes negative- sense vRNA into positivesense (translatable into proteins) vRNA. The vRNA then either
remains in the nucleus or is transported into the cytoplasm, where it
is translated into viral proteins. These are then either secreted by
the Golgi body to the cell surface, or transported back into the
nucleus to be combined with negative-sense vRNA and assembled
into new viruses.
Meanwhile, other proteins assist in degrading host mRNA or
inhibiting the translation of host mRNA. Nucleotides from the former
for vRNA synthesis.
New viruses do not exit the cell by lysing the membrane; instead,
they bud off the host cell, taking with them a portion of the plasma
membrane. The host cell is now dead.
Symptoms
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Fever
Cough
Aches
Sneezing
General discomfort
Problems breathing
Pneumonia
Sore throat
Conjunctivitis
Treatment
There are currently no effective treatments for
H5N1. Mainly, drugs such as Tamiflu are used
that act as asneuraminidase inhibitors that
prevent the virus from adhering to the cell
membrane.
The constant and rapid evolution of H5N1
renders vaccines and largely ineffective. Only
good hygiene and safe, cautious practices can
hope to limit the spread of an H5N1 outbreak,
should one occur in the near future.