MEDICAL: DISEASES: INFLUENZA: Dynasty: Influenza Virus in 1918 and Today

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MEDICAL: DISEASES: INFLUENZA: Dynasty: Influenza Virus in 1918 and Today

David P. Dillard


Dynasty: Influenza Virus in 1918 and Today

Date: Tue, 30 Jun 2009 09:16:26 -0400
From: "NIH OLIB (NIH/OD)" <[hidden email]>
To: [hidden email]
Subject:  Dynasty: Influenza Virus in 1918 and Today

U.S. Department of Health and Human Services

National Institute of Allergy and Infectious Diseases (NIAID)

Embargoed for Release: Monday, June 29, 2009, 5:00 p.m. EDT


Anne A. Oplinger


e-mail: [hidden email]


The influenza virus that wreaked worldwide havoc in 1918-1919 founded a
viral dynasty that persists to this day, according to scientists from the
National Institute of Allergy and Infectious Diseases (NIAID), part of the
National Institutes of Health. In an article published online on June 29
by the New England Journal of Medicine, authors Anthony S. Fauci, M.D.,
Jeffery K. Taubenberger, M.D., Ph.D., and David M. Morens, M.D., argue
that we have lived in an influenza pandemic era since 1918, and they
describe how the novel 2009 H1N1 virus now circling the globe is yet
another manifestation of this enduring viral family.

"The 1918-1919 influenza pandemic was a defining event in the history of
public health," says NIAID Director Dr. Fauci. "The legacy of that
pandemic lives on in many ways, including the fact that the descendents of
the 1918 virus have continued to circulate for nine decades."

Influenza viruses have eight genes, two of which code for virus surface
proteins-hemagglutinin (H) and neuraminidase (N)-that allow the virus to
enter a host cell and spread from cell to cell. There are 16 H subtypes
and 9 N subtypes, and, therefore, 144 possible HN combinations. However,
only three (H1N1, H2N2 and H3N2) have ever been found in influenza viruses
that are fully adapted to infect humans. Other combinations, such as avian
influenza H5N1, occasionally infect people, but they are bird viruses, not
human viruses.

"The eight influenza genes can be thought of as players on a team: certain
combinations of players may arise through chance and endow the virus with
new abilities, such as the ability to infect a new type of host," says Dr.
Morens, Senior Advisor to the NIAID Director. That is likely what happened
to spark the 1918 pandemic, he adds. Scientists have shown that the
founding virus was an avian-like virus. The virus had a novel set of eight
genes and-through still-unknown mechanisms-gained the ability to infect
people and spread readily from person to person.

Not only did the 1918 H1N1 virus set off an explosive pandemic in which
tens of millions died, during the pandemic the virus was transmitted from
humans to pigs, where-as it does in people-it continues to evolve to this
day. "Ever since 1918, this tenacious virus has drawn on a bag of
evolutionary tricks to survive in one form or another...and to spawn a
host of novel progeny viruses with novel gene constellations, through the
periodic importation or exportation of viral genes," write the NIAID

"All human-adapted influenza A viruses of today-both seasonal variations
and those that caused more dramatic pandemics-are descendents, direct or
indirect, of that founding virus," notes Dr. Taubenberger, Senior
Investigator in NIAID's Laboratory of Infectious Diseases. "Thus we can be
said to be living in a pandemic era that began in 1918."

How exactly do new influenza gene teams make the leap from aquatic birds
to a new host, such as people or other mammals? What factors determine
whether infection in a new host yields a dead-end infection or sustained,
human-to-human transmission, as happened in 1918? Research on such topics
is intense, but at this time definitive answers remain elusive, notes Dr.

It is known that the human immune system mounts a defense against the
influenza virus's H and N proteins, primarily in the form of antibodies.
But as population-wide immunity to any new variant of flu arises, the
virus reacts by changing in large and small ways that make it more
difficult for antibodies to recognize it. For nearly a century, then, the
immune system has been engaged in a complicated pas de deux with the 1918
influenza virus and its progeny, say the NIAID authors. The partners in
this dance are linked in an endless effort to take the lead from the

While the dynasty founded by the virus of 1918 shows little evidence of
being overthrown, the NIAID authors note that there may be some cause for
optimism. When viewed through a long lens of many decades, it does appear
that successive pandemics and outbreaks caused by later generations of the
1918 influenza dynasty are decreasing in severity, notes Dr. Morens. This
is due in part to advances in medicine and public health measures, he
says, but this trend also may reflect viral evolutionary pathways that
favor increases in the virus's ability to spread from host to host,
combined with decreases in its tendency to kill those hosts.

"Although we must be prepared to deal with the possibility of a new and
clinically severe influenza pandemic caused by an entirely new virus, we
must also understand in greater depth, and continue to explore, the
determinants and dynamics of the pandemic era in which we live," conclude
the authors.

(See a diagram of the genetic relationships among human and swine
influenza viruses at


For more information on influenza visit <> for
one-stop access to U.S. Government information on avian and pandemic flu.
Also, see NIAID's flu portal


and the CDC's Seasonal Flu page at


NIAID conducts and supports research -- at NIH, throughout the United
States, and worldwide -- to study the causes of infectious and
immune-mediated diseases, and to develop better means of preventing,
diagnosing and treating these illnesses. News releases, fact sheets and
other NIAID-related materials are available on the NIAID Web site at


The National Institutes of Health (NIH)-The Nation's Medical Research
Agency-includes 27 Institutes and Centers and is a component of the U. S.
Department of Health and Human Services. It is the primary federal agency
for conducting and supporting basic, clinical and translational medical
research, and it investigates the causes, treatments and cures for both
common and rare diseases. For more information about NIH and its programs,




DM Morens et al.
The persistent legacy of the 1918 influenza virus
New England Journal of Medicine
DOI: 10.1056/NEJMp0904819 (2009)


This NIH News Release is available online at:


Also of Possible Interest:

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The Pandemic Flu Guide

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Bushell, R. & Sheldon, P. (eds),
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