EMERGENCY H5N1 INFLUENZA ALERT
Concern is rapidly growing about the possibility of a serious
worldwide epidemic of avian flu this season. Every so often
in a far away place where humans and farm animals live
closely together, a new type flu virus arises in a farm
animal and jumps to humans when there is close contact.
There it can merge with a human flu strain to create a
highly virulent new virus. This happened in 1997 with the
H5N1 strain of influenza. In 2001 another deadly strain
of H5N1 was seen in Hong Kong. This area of China has hundreds
of millions of chicken, ducks, and geese, and so year after
year new strains of the virus formed and then dispersed
to South Korea, Japan, Indochina and Indonesia. This summer
the virus killed thousands of wild geese and gulls in Western
China; then it began to kill people. In August the count
was 40 dead in Vietnam, 12 in Thailand, 4 in Cambodia and
1 in Indonesia. Influenza experts fear this might be the
start of a pandemic like the one that killed over 50 million
people in 1918.
The influenza virus enters the cells that
line the nose, throat and lung and quickly forces the cells
to produce hundreds of copies of itself, which “bud” from the cell surface
to infect nearby cells. If the immune system does not control
the process, it can rapidly spread throughout the body and lead
to death. Three times in the 20th century a new flu virus killed
large numbers of people: 1918 (50 – 100 million deaths),
1957 (1 million deaths) and 1970 (750,000 deaths). The new H5N1
could be another killer if it “learns” how to spread
from person to person. If it does, up to 360 million could succumb
worldwide. As of this moment the current flu vaccines are not
specific for H5N1.
One treatment that is available is Tamiflu™, an oral medication
that interferes with the “budding” process that the
virus uses to spread itself. Tamiflu™ has been available
for several years by prescription. It must be taken no later
than 48 hours after symptoms begin; if used before the virus
enters the body, it can prevent the infection from even starting.
See Dr. Kimmelman for further information about the new H5N1
Influenza and Tamiflu™ if you have more questions.
The above diagram from the New England Journal of Medicine
Volume 353:1363-1373
September
29, 2005 illustrates the way that Tamiflu™, a
neuraminidase inhibitor, works. In the upper panel (A)
a new viral particle buds from the surface of the infected
cell. It breaks its contact with the cell by using neuraminidase
to cut an attachment that keeps the virus anchored to the
cell. Tamiflu™ blocks the neuraminidase from cutting
the virus free, so it remains attached to the cell and
cannot infect neighboring cells, as shown in the lower
panel (B).
By the end of the summer birds in Russia, Kazakhstan,
Siberia and Mongolia had already been infected with H5N1.
So far, the only way humans have contracted the virus is
by contact. But new mutations in the virus could allow
it to more easily spread from person to person. In the
past this kind of spread has allowed the virus to encompass
the entire globe. The World Health Organization says the
concern over a possible avian flu pandemic is a matter
of
when, not if. Therefore, we all must have a response
plan. The U.S. has also been working on an avian flu vaccine.
Recently, researchers at the National Institute of Allergy
and Infectious Diseases announced a promising prototype
H5N1 vaccine that triggered an immune response in volunteers.
Although vaccination is the primary strategy for the prevention
of influenza, there are a number of likely scenarios for
which vaccination is inadequate and effective antiviral
agents would be of the utmost importance. During any influenza
season, antigenic drift in the virus may occur after formulation
of the current vaccine has taken place, rendering the vaccine
less protective, and outbreaks can more easily occur among
high-risk populations. In the course of a pandemic, vaccine
supplies would be inadequate, and, even worse, current
methods are too slow to halt the progress of a new strain
of influenza virus. Antiviral agents thus form an important
part of a rational approach to epidemic influenza and are
critical to societal and personal planning for a pandemic.
Links to additional information about the way that the influenza
virus behaves:
http://www7.nationalgeographic.com/ngm/0510/feature1/index.htm
http://www.who.int/mediacentre/factsheets/avian_influenza/en/
http://zhuang.harvard.edu/cellentry.html
http://www.biomedcentral.com/1523-3820/5/129
http://72.14.207.104/search?q=cache:r6vobNs37iQJ:www.biomedcentral.com/content/pdf/cto-id5221.pdf+mechanism+of+infection+of+influenza&hl=en
