Porcine circovirus
and swine influenza virus are newly emerged and recently re-emerged viral
pathogens of swine that cause substantial economic loss for swine producers.
Swine influenza subtypes H1N1 and H3N2 have re-emerged as important viral
pathogens in swine. Efficient and reliable vaccines and diagnostic reagents
are lacking for the H3N2 subtype. Mixed infections with two or more subtypes
of influenza virus may yield reassortant viral progeny that escape the
animal's existing defenses.
There is a pressing need to develop multivalent vaccines and polyvalent
differential diagnostic tests that identify viral subtypes associated
with disease outbreaks.
RESEARCH:
Evolution of swine H3N2 influenza viruses in the United States
- Webby RJ, Swenson SL, Krauss SL, Gerrish PJ, Goyal SM, Webster RG, Department
of Virology and Molecular Biology, St. Jude Children's Research Hospital.
J Virol 2000 Sep;74(18):8243-51.
During 1998, severe outbreaks of influenza were observed in four swine
herds in the United States. This event was unique because the causative
agents, H3N2 influenza viruses, are infrequently isolated from swine in
North America. Two antigenically distinct reassortant viruses (H3N2) were
isolated from infected animals: a double-reassortant virus containing
genes similar to those of human and swine viruses, and a triple-reassortant
virus containing genes similar to those of human, swine, and avian influenza
viruses. Because the U.S. pig population was essentially naive in regard
to H3N2 viruses, it was important to determine the extent of viral spread.
Hemagglutination inhibition (HI) assays of 4, 382 serum samples from swine
in 23 states indicated that 28.3% of these animals had been exposed to
classical swine-like H1N1 viruses and 20.5% had been exposed to the triple-reassortant-like
H3N2 viruses. The HI data suggested that viruses antigenically related
to the double-reassortant H3N2 virus have not become widespread in the
U.S. swine population. The seroreactivity levels in swine serum samples
and the nucleotide sequences of six additional 1999 isolates, all of which
were of the triple-reassortant genotype, suggested that H3N2 viruses containing
avian PA and PB2 genes had spread throughout much of the country. These
avian-like genes cluster with genes from North American avian viruses.
The worldwide predominance of swine viruses containing an avian-like internal
gene component suggests that these genes may confer a selective advantage
in pigs. Analysis of the 1999 swine H3N2 isolates showed that the internal
gene complex of the triple-reassortant viruses was associated with three
recent phylogenetically distinct human-like hemagglutinin (HA) molecules.
Acquisition of HA genes from the human virus reservoir will significantly
affect the efficacy of the current swine H3N2 vaccines. This finding supports
continued surveillance of U.S. swine populations for influenza virus activity.
http://jvi.asm.org/cgi/content/full/74/18/8243?view=full&pmid=10954521
Herd factors associated
with the seroprevalences of four major respiratory pathogens in slaughter
pigs from farrow-to-finish pig herds - Maes D, Deluyker H, Verdonck
M, Castryck F, Miry C, Vrijens B, de Kruif A. Department of Reproduction,
Obstetrics and Herd Health, Faculty of Veterinary Medicine, University
of Ghent, Belgium. Vet Res 2000 May-Jun; 31(3):313-27.
The objective of this study was to investigate sero-epidemiological aspects
of Mycoplasma hyopneumoniae (Mh), influenza H1N1 and H3N2 viruses and
Aujeszky disease virus (ADV) in fattening pigs from 150 randomly selected
farrow-to-finish pig herds. Different herd factors were examined as potential
risk indicators for the percentage of pigs with antibodies against the
4 pathogens. The median within-herd seroprevalences of the pathogens were:
Mh 76%, H1N1 100%, H3N2 40% and ADV 53%. There was a positive association
between the seroprevalences of both influenza viruses, and a negative
association between the seroprevalences of ADV and H1N1. The percentage
of pigs seropositive for Mh increased with the purchase of gilts and with
the season (slaughter date in March-April). The within-herd seroprevalences
of both influenza viruses were higher in the case of a higher density
of pig herds in the municipality. A higher number of fattening pigs per
pen additionally increased the risk of being seropositive for H3N2. The
percentage of pigs with anti-gE-antibodies against the wild type ADV increased
with higher airspace stocking density in the finishing unit, increasing
herd size, increasing number of pig herds in the municipality and slaughter
date in March-April.
Increased seroprevalences for these 4 respiratory pathogens were mostly
associated with pig density in the herd and its vicinity, the winter period,
and with the purchase of gilts. Purchase of gilts, number of fattening
pigs per pen and airspace stocking density are risk factors that can be
managed directly by farmers striving to attain a high respiratory health
status of pigs.
The epidemiology
and evolution of influenza viruses in pigs - IH Brown. Veterinary
Laboratories Agency-Weybridge, Addlestone, UK. Vet Microbiol 2000 May
22;74(1-2):29-46.
Pigs serve as major reservoirs of H1N1 and H3N2 influenza viruses which
are endemic in pig populations world-wide and are responsible for one
of the most prevalent respiratory diseases in pigs. The maintenance of
these viruses in pigs and the frequent exchange of viruses between pigs
and other species is facilitated directly by swine husbandry practices,
which provide for a continual supply of susceptible pigs and regular contact
with other species, particularly humans.
The pig has been a contender for the role of intermediate host for reassortment
of influenza A viruses of avian and human origin since it is the only
domesticated mammalian species which is reared in abundance and is susceptible
to, and allows productive replication, of avian and human influenza viruses.
This can lead to the generation of new strains of influenza, some of which
may be transmitted to other species including humans. This concept is
supported by the detection of human-avian reassortant viruses in European
pigs with some evidence for subsequent transmission to the human population.
Following interspecies transmission to pigs, some influenza viruses may
be extremely unstable genetically, giving rise to variants which could
be conducive to the species barrier being breached a second time. Eventually,
a stable lineage derived from the dominant variant may become established
in pigs. Genetic drift occurs particularly in the genes encoding the external
glycoproteins, but does not usually result in the same antigenic variability
that occurs in the prevailing strains in the human population. Adaptation
of a 'newly' transmitted influenza virus to pigs can take many years.
Both human H3N2 and avian H1N1 were detected in pigs many years before
they acquired the ability to spread rapidly and become associated with
disease epidemics in pigs.
Antigenic drift
in swine influenza H3 haemagglutinins with implications for vaccination
policy - JC de Jong, AP van Nieuwstadt, TG Kimman, WL Loeffen, TM
Bestebroer, K Bijlsma, C Verweij, AD Osterhaus, andEC Class. Research
Laboratory of Infectious Diseases, National Institute of Public Health
and the Environment (RIVM), Netherlands. Vaccine 1999 Mar 17; 17(11-12):1321-8.
In order to explore the occurrence of antigenic drift in swine influenza
A(H3N2) virus, we examined virus strains from outbreaks of respiratory
disease among finishing pigs in the Netherlands in 1996 and 1997 and from
earlier outbreaks. In contrast to swine H3N2 strains from the 1980s, the
recent isolates did not show significant cross-reactivity with human influenza
A(H3N2) viruses from 1972-1975 in haemagglutination inhibition tests.
These new strains form a separate branch in the phylogenetic trec of the
HA1 parts of HA. We conclude that recently there has been considerable
antigenic drift within the swine H3N2 viruses in the Netherlands and Belgium
and recommend replacement of the A/Port Chalmers/1/73 (H3N2) strain in
the current vaccine by a more recent swine H3N2 isolate.
Evaluation of a protective immunity induced by an inactivated influenza
H3N2 vaccine after an intratracheal challenge of pigs - MH Bikour,
E Cornaglia, and Y Elazhary. Virology Section, Faculte de medecine veterinaire,
Universite de Montreal, Quebec. Can J Vet Res 1996 Oct; 60(4):312-4.
A challenge study was conducted to evaluate the safety and efficacy of
an inactivated influenza H3N2 virus vaccine combined with Quil A/Alhydrogel
mixture under controlled conditions in piglets. Twenty-four piglets from
12 sows were allocated to 2 groups; injected intramuscularly with 2 doses
of the tested vaccine or with PBS at 2 wk intervals and challenged intratracheally
with 105TCID50 of the H3N2 swine influenza virus 6 d after the 2nd immunization.
Clinical and virological parameters were recorded for 4 d after the challenge.
The use of the tested vaccine produced high serum hemagglutination-inhibition
titers against the swine H3N2 strain virus. This strong immune response
suppressed all clinical signs and viral shedding and reduced pulmonary
lesions due to the challenge in the vaccinated group, without causing
any secondary effects. Our results suggest that the serum HI titers correlated
with the degree of protection induced by an inactivated swine influenza
H3N2 vaccine.
PRACTICAL APPLICATIONS:
H3N2 Subtype Continues to Spread in U.S. Swine Herds; Vaccination Effective,
But Producers Urged To Confirm Flu Strain First - MySwine.com
The new H3N2 strain of swine influenza virus is spreading quickly through
U.S. hog operations and now accounts for about half the flu cases reported,
according to veterinarians speaking at a recent tele-news conference.
"In terms of the relative number of isolates, we're seeing a 50/50
distribution of H3N2 and H1N1,"said Dr. Gene Erickson of the Rollins
Animal Disease Laboratory, North Carolina Department of Agriculture, Raleigh.
At the National Veterinary Service Laboratories (NVSL) in Ames, Iowa,
"We've had 54% as H1N1 and 46% as H3N2" since the fall of 1998,
when the first H3N2 sample was identified, through January 2000, said
Dr. Sabrina Swenson, of NVSL.
http://www.myswine.com/health/focus/swineflu.cfm
Schering-Plough
Animal Health Introduces New H3N2 Swine Flu Vaccine with Broader Protection:
USDA Issues Conditional License - MySwine.com.
After months of closely monitoring the spread and evolution of swine influenza
virus in the United States, Schering-Plough Animal Health Corporation
has introduced a new vaccine offering broader protection against the new
and costly H3N2 subtype.
The inactivated vaccine, which now contains two isolates of the new H3N2
subtype, was issued a conditional license by USDA after the company demonstrated
a "reasonable expectation of efficacy." Schering-Plough Animal
Health is pursuing full license for the product.
http://www.myswine.com/health/focus/fluvaccine.cfm
H3N2 strain of
swine influenza spreads rapidly in Missouri herds - Missouri Commercial
Agriculture News, Spring 2001.
Missouri hog producers have a new disease to contend with, according to
Tom Fangman, Commercial Agriculture swine veterinarian at the University
of Missouri-Columbia.
"It's a new strain of swine influenza--SIV H3N2--first noted in the
United States in North Carolina in 1998 and confirmed to be present in
Missouri in the fall of 1999," Fangman says. "The new influenza
strain is now being found in hog operations throughout the state.
"I suspect that a third of Missouri swine operations have been infected
and that H3N2 will continue to spread," the MU veterinarian predicts.
"What should
I do when I know I have the H3N2 strain in my herd is a question producers
might ask.
http://agebb.missouri.edu/commag/news/news17.htm
H4N6 influenza
virus isolated from pigs in Ontario - Susy Carman DVM PhD, Animal
Health Laboratory-Guelph; Chris Olsen DVM PhD, Dept Pathobiological Sciences,
School of Veterinary Medicine, University of Wisconsin-Madison, Madison,
WI; Margaret Stalker DVM PhD Dipl ACVP, Gaylan Josephson DVM Dip Path,
Animal Health Laboratory-Guelph.
Classical H1N1 influenza viruses are the most common influenza A viruses
found in swine in Ontario. H3N2 influenza viruses, similar to currently
circulating human strains, have been found in Ontario swine, but with
much lower frequency. H3N2 influenza viruses recovered from Quebec swine
in 1990 have previously been shown to be similar to earlier 1975 human
strains, suggesting that pigs act as a reservoir for human influenza virus.
Newer strains of H3N2 influenza viruses, which are triple reassortments
of human, swine and avian strains, have emerged in the USA over the last
few years. In addition, H1N2 reassortments of H1N1 and H3N2 viruses have
also been identified in American swine.
In the fall of 1999, the AHL isolated 2 influenza viruses from an Ontario
swine herd that could not be typed using either H1 or H3 antisera. The
viruses have recently been typed by reference laboratories to be a totally
avian H4N6 influenza virus, and to be similar to the influenza viruses
found to replicate in the epithelial cells of the gastrointestinal tract
of ducks. H4N6 influenza viruses are the most common influenza viruses
found in the Canadian wild duck population. The protoype virus has been
identified as A/Swine/Ontario/01911/99.
http://www.uoguelph.ca/ahl/News4-3/Swine.htm
More articles to
examine:
Efficacy and safety
of Fort Dodge Animal Health's bivalent Swine Influenza Vaccine -Javaraiah
Srinivasappa,; Catherine M. Jennen; Deborah A. Champ, Proceedings of the
32nd annual meeting of the American Association of Swine Veterinarians,
Nashville, 2001 171-
Characterization
and performance of a new bivalent, H1N1 & H3N2, swine influenza vaccine:
End-FLUence - Rich Schlueter,; Wei Lu, ; Marc Eichmeyer, Proceedings
of the 32nd annual meeting of the American Association of Swine Veterinarians,
Nashville, 2001. 213-
Characterization
of H3N2 swine influenza viruses in Iowa swine - John David Schneider;
Kyoung-jin Yoon, Proceedings of the 32nd annual meeting of the American
Association of
Swine Veterinarians, Nashville, 2001. 23-
SWINE INFLUENZA: FIELD
EXPERIENCE IN THE US WITH THE NEW STRAIN - WAGNER MA, ALLEN D. LEMAN SWINE
CONFERENCE 1999 PROCEEDINGS, 268-
EVALUATION OF ANTIBODY
RESPONSES TO AN INACTIVATED SWINE INFLUENZA VIRUS COMMERCIAL VACCINE ENDFLUENCE
IN A COMMERCIAL SWINE HERD - WILSON WD ET AL. ALLEN D. LEMAN SWINE CONFERENCE
1999 PROCEEDINGS RECENT RESEARCH REPORTS.
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