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A ProMED-mail post
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International Society for Infectious Diseases
[The following is [1] a statement of the research program of the United
States Department of Agriculture (USDA) Agricultural Research Service
(ARS), and [2] the outcome of a study of the cross-reactivity of serum
samples from US pigs against the new swine origin 2009 H1N1 influenza virus
(S/O H1N1). The results of this analysis indicate that pre-existing
immunity induced by swine influenza viruses circulating in the US may not
protect pigs against the new S/O H1N1 influenza virus presently circulating
in people. - Mod.CP]
[1]
Date: Tue 26 May 2009
Source: USDA, ARS (Agricultural Research Service) [edited]
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 1st step was to evaluate whether current US 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 US could protect against the 2009 H1N1
influenza 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.
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 US 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 are used to designate the subtype
of the virus.
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 US 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, CDC has reported about one case of human infection with a swine
influenza virus every one to 2 years.
Recent ARS research results: 2009 H1N1 influenza virus:
ARS researchers tested serum samples from pigs previously infected with US
swine influenza viruses or vaccinated with commercial vaccines to determine
whether US commercial swine herds are susceptible to the new swine origin
(S/O) H1N1 influenza virus. They found that there was limited cross
reactivity against the new S/O H1N1 influenza virus. This suggests that
pre-existing immunity induced by swine influenza viruses previously
circulating in the US may not protect pigs against the new S/O H1N1
influenza virus presently circulating in people. Importantly, vaccines
currently used to protect pigs on US swine farm operations against swine
influenza viruses may not be effective against the new S/O H1N1 influenza
virus.
Next step: ARS scientists will be testing the efficacy of swine influenza
virus vaccines in a pig vaccination challenge to determine whether
measurable antibody titers detected in vaccinated pigs correlate with
protection against the new virus.
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 US 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:
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
More information about the HINI (swine) influenza virus:
- USDA H1N1 webpage
- APHIS H1N1 webpage
- CDC H1N1 webpage
- AAAS Swine Flu
--
communicated by:
ProMED-mail rapporteur Mary Marshall
******
[2]
Date: Tue 26 May 2009
Source: USDA, ARS (Agricultural Research Service) [edited]
Recent results from studies with the new swine origin H1N1 influenza A virus
------------------------------------------
Project:
Serologic cross-reactivity of serum samples from US pigs against the new
swine origin H1N1 influenza virus
Purpose of study:
An important concern is to address whether US commercial swine herds are
susceptible to the new swine origin (S/O) H1N1 influenza virus.
Experiment:
The new S/O H1N1 influenza A virus isolated from a person in California in
March 2009 (A/CA/04/2009) was obtained from CDC and grown in vitro (that
is, in a permissive cell line). The standard hemagglutination inhibition
(HI) test was used to investigate whether serum samples from pigs infected
or vaccinated with US H1N1 swine influenza virus could prevent the
A/CA/04/2009 virus from agglutinating (clumping) red blood cells (this test
indicates the presence of antibodies that prevent the influenza virus from
attaching to red blood cells and is therefore indicative that the animal
has protective antibodies).
38 serum samples from pigs infected between 1999-2008 with 19 H1N1 swine
influenza viruses in US commercial swine operations were tested in the
standard HI test. The 19 H1N1 swine influenza viruses selected for this
study represented all 4 phylogenic (genetically characterized) clusters of
all the endemic H1 swine influenza viruses known to circulate in the US.
An additional 17 serum samples from pigs vaccinated with 5 different
commercial products used to vaccinate pigs against H1N1 swine influenza
virus in the US were tested by the standard HI test.
Results:
11 of the 38 serum samples from pigs infected with US H1N1 swine influenza
viruses had a measurable HI titer against the A/CA/04/2009 H1N1 influenza
virus. Only 2 of the commercial vaccines tested induced a measurable HI
titer against the A/CA/04/2009 H1N1 influenza virus.
Conclusion:
Limited cross-reactivity of serum samples from pigs infected with the US
swine influenza viruses or vaccinated with commercial vaccines was
demonstrated against the new S/O H1N1 influenza virus (A/CA/04/2009) as
measured by the standard HI test. The results of this experiment suggest
that pre-existing immunity induced by swine influenza viruses circulating
in the US may not protect pigs against the new S/O H1N1 influenza virus
presently circulating in people. Importantly, vaccines currently used to
protect pigs in US swine operations against swine influenza virus may not
be effective against the new S/O H1N1 influenza virus.
Next steps:
ARS scientists will test the efficacy of swine influenza virus vaccines in
a pig vaccination challenge model to determine whether the measurable HI
titers detected in vaccinated pigs correlate with protection.
--
communicated by:
ProMED-mail rapporteur Mary Marshall
[see also:
Influenza A (H1N1) - worldwide (49): case counts 20090528.1984
Influenza A (H1N1) - worldwide (48): case counts 20090527.1972
Influenza A (H1N1) - worldwide (47): China, epidemiology 20090526.1962
Influenza A (H1N1) - worldwide (46): case counts 20090526.1960
Influenza A (H1N1) - worldwide (45) 20090525.1951
Influenza A (H1N1) - worldwide (44): case counts 20090525.1945
Influenza A (H1N1) - worldwide (43): case counts 20090523.1931
Influenza A (H1N1) - worldwide (42) 20090523.1929
Influenza A (H1N1) - worldwide (41): case counts 20090522.1921
Influenza A (H1N1) - worldwide (40): case counts 20090521.1906
Influenza A (H1N1) - worldwide (30): case counts 20090516.1831
Influenza A (H1N1) - worldwide (20): case counts 20090510.1741
Influenza A (H1N1) - worldwide (10): case counts 20090504.1675
Influenza A (H1N1) - worldwide 20090430.1636
Influenza A (H1N1) "swine flu": worldwide (07), update, pandemic 5
20090429.1622
Influenza A (H1N1) "swine flu": Worldwide 20090427.1583
Influenza A (H1N1) virus, human: worldwide 20090426.1577
Influenza A (H1N1) virus, human - New Zealand, susp 20090426.1574
Influenza A (H1N1) virus, human - N America (04) 20090426.1569
Influenza A (H1N1) virus, human - N America (03) 20090426.1566
Influenza A (H1N1) virus, human - N America (02) 20090425.1557
Influenza A (H1N1) virus, human - N America 20090425.1552
Acute respiratory disease - Mexico, swine virus susp 20090424.1546
Influenza A (H1N1) virus, swine, human - USA (02): (CA, TX) 20090424.1541
Influenza A (H1N1) virus, swine, human - USA: (CA) 20090422.1516
Influenza A (H1N1) virus, swine, human - Spain 20090220.0715
2008
---
Influenza A (H1N1) virus, swine, human - USA (TX) 20081125.3715
2007
---
Influenza A (H2N3) virus, swine - USA 20071219.4079
Influenza, swine, human - USA (IA): November 2006 20070108.0077]
..................cp/msp/sh
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