2009 H1N1 Influenza A Virus
2009 H1N1 Influenza A Virus
Soon after the emergence of the H1N1 virus in April 2009, ARS scientists at
the National Animal Disease Center in Ames, Iowa, began research using virus
samples provided by the Centers for Disease Control and Prevention (CDC). The
first step was to evaluate whether current U.S H1N1 swine influenza vaccines
can protect pigs from infection with the 2009 H1N1 influenza virus circulating
in people. This research study also evaluated whether pre-existing titers in
pigs previously infected with endemic H1N1 swine influenza viruses circulating
in the U.S could protect against the 2009 H1N1 influenza virus. Second was to
address whether meat, blood and tissue from pigs infected with the new 2009
H1N1 Influenza A Virus would be free of infectious virus.
Classical swine influenza virus infections are enzootic among pigs in North
America. Sporadic cases of human infection with swine influenza virus have been
reported in the United States and elsewhere. Worldwide, more than 50 human
cases of swine influenza virus infection, mostly due to classical swine
influenza virus, have been documented in the past 35 years, with the greatest
risk of infection among people with occupational exposure to live pigs.
ARS Veterinary Medical Officers Amy Vincent and
Kelly Lager are leading ARS's swine influenza virus research program.
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Experts believe pigs can act as a "mixing vessel" for the
reassortment of avian, swine and human influenza viruses, and might play an
important role in the emergence of novel influenza viruses that could be
capable of causing a human pandemic similar to the virus in the current
outbreak.
Between the 1930s and the 1990s, the most commonly circulating swine
influenza virus among pigs-classical swine influenza A, known as H1N1-underwent
little change.
However, by the late 1990s, multiple strains and subtypes of triple
reassortant swine influenza viruses-whose genomes include combinations of
avian, human and swine influenza virus gene segments-had emerged and became
predominant among North American pigs. The 2009 H1N1 influenza virus is also a
triple reassortent, but its lineage is different than the H1N1 influenza
viruses currently circulating in U.S. pigs.
Background
The genetic makeup of swine influenza viruses is identical to other
influenza A viruses and consists of 8 segments of RNA that code for different
proteins. Influenza viruses have the ability to exchange these segments,
creating new genetically different viruses. Two major surface glycoproteins
(proteins with a carbohydrate attached), called hemagglutinin (H) and
neuraminidase (N), are how influenza A viruses are identified. These
glycoproteins also determine the host range, antigenicity and the pathogenicity
of the viruses. The hemagglutinin and neuraminidase proteins are important
targets for diagnostics and used to designate the subtype of the virus.
For
more information about ARS research on H1N1 (swine) influenza viruses, contact:
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Cyril Gay, ARS
Senior National Program Leader,
Animal Health
cyril.gay@ars.usda.gov
301-504-4786
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Currently 16 different hemagglutinins and 9 neuraminidases have been
identified. The majority of these viral subtypes are found in waterfowl, with
only a few combinations being found in humans and swine.
Swine influenza virus (SIV) is one of the primary causes of respiratory
disease in growing pigs and can lead to major economic losses. Currently, only
H1N1, H1N2, and H3N2 subtypes are circulating in the U.S. swine population.
Pigs have long been considered a potential source for new and novel
influenza viruses that infect humans, as they have receptors on their cells
that bind both mammalian and avian influenza viruses, increasing the
opportunity for the exchange of genetic segments of the virus.
Previously, the CDC have reported approximately one case of human infection
with a swine influenza virus every one to two years.
Project 1: Serologic cross-reactivity of serum samples from U.S pigs
against the new 2009 H1N1 influenza virus
This study addressed whether U.S commercial swine herds are susceptible to
the 2009 A/H1N1 influenza viruses isolated from persons in California, New
York, and Mexico. ARS researchers tested serum samples from pigs inoculated
with swine influenza viruses that are known to circulate in the U.S or
vaccinated with commercial vaccines to determine if U.S commercial swine herds
are susceptible to the new H1N1 influenza virus. They found that there was
limited cross reactivity against the new 2009 A/H1N1 influenza viruses. This
suggests that pre-existing immunity induced by swine influenza viruses
previously circulating in the U.S may not protect pigs against the new 2009
A/H1N1 influenza viruses presently circulating in people. Importantly, vaccines
currently used to protect pigs on U.S swine farms operations against swine
influenza viruses may not be effective against the new 2009 A/H1N1 influenza
viruses.
Next step: ARS scientists will test the efficacy of a select subset
of swine influenza virus vaccines tested in this first study, and evaluate
their effectiveness in a pig vaccination challenge study to determine whether
measurable antibody titers in pigs correlate with protection against the new
A/H1N1 Influenza Virus.
More information about this study
Project 2: Four-pig pathogenesis study with the 2009 A/H1N1 influenza
virus
This study addressed whether meat, blood, and tissue from pigs infected with
the new 2009 A/H1N1 influenza virus are free of infectious virus. ARS
researchers tested four 5-week-old cross-bred pigs from a herd free of swine
influenza virus. The pigs were inoculated with an infective dose of the 2009
A/H1N1 influenza virus isolated from persons in California. Pigs were observed
daily for clinical signs of disease and nasal swabs and fresh samples from
lung, tonsil, inguinal lymph node, liver, spleen, kidney, skeletal muscle
(ham), and colon contents were tested by the most sensitive virus detection
assays. Live 2009 A/H1N1 influenza virus was only detected in the respiratory
tract of infected pigs and the virus did not appear to spread and replicate in
other tissues.
Next step: ARS scientists will conduct a larger study to evaluate
tissues at additional time points (1, 3, 5, and 7 days dpi).
More information about this study
ARS Swine Influenza Research Program
The ARS research program focuses on tracking the evolution of swine
influenza viruses and their potential impact on the swine industry. The Agency
also tracks the ability of current vaccines to protect swine from new virus
isolates.
Because of the emergence of novel influenza viruses in U.S. pigs, USDA-ARS
at NADC in collaboration with USDA's Animal and Plant Health Inspection Service
and CDC created an interagency agreement in 2008 to address the need for
monitoring the swine influenza virus. Having this agreement already in place
has enabled the rapid response to evaluate the zoonotic potential of the 2009
H1N1 influenza virus.
ARS also supports a proposed USDA-APHIS swine influenza surveillance program
by providing additional characterization of emerging swine influenza virus
(SIV) isolates as they are identified through the surveillance program.
ARS Research Projects
More
information about the HINI (swine) influenza virus:
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Genetic
and Antigenic Characterization of North American H1 Swine Influenza Viruses
Study
of Influenza A Viruses
Characterization
of Swine Influenza Virus Isolates
Influenza
Pandemic Preparedness
ARS Publications
The Role of Swine in the Generation of Novel
Influenza Viruses
Characterization of an Influenza A Virus Isolated
from Pigs During an Outbreak of Respiratory Disease in Swine and People During
a County Fair in the United States
Swine Influenza Viruses: A North American
Perspective
Protection of Weaned Pigs by Vaccination with Human
Adenovirus 5 Recombinant Viruses Expressing the Hemagglutinin and the
Nucleoprotein of H3N2 Swine Influenza Virus
H1N1 virus
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The Roles of Influenza Virus Haemagglutinin and
Nueleoprotein in Protection: Analysis Using Vaccinia Virus Recombinants
Overcoming Maternal Antibody Interference by
Vaccination with Human Adenovirus 5 Recombinant Viruses Expressing the
Hemagglutinin and the Nucleoprotein of Swine Influenza Virus
Isolation of Reassortant H2N3 Avian/Swine Influenza Virus
from Pigs in the United States
Limited Susceptibility and Lack of Systemic
Infection by an H3N2 Swine Influenza Virus In Intranasally Inoculated
Chickens
Failure of Protection And Enhanced Pneumonia with a US
H1N2 Swine Influenza Virus in Pigs Vaccinated With an Inactivated Classical
Swine H1N1 Vaccine
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