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A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Fri 12 Nov 2010
Source: CDC Online Newsroom [edited]
Reports of human infections with swine origin influenza A (H3N2)
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The 12 Nov 2010 FluView reports 2 human infections with swine origin
influenza A (H3N2) viruses in the United States. Test samples from 2
patients submitted by Wisconsin and Pennsylvania have been confirmed at the
CDC [Centers for Disease Control and Prevention] as positive for swine
origin triple-reassortant (tr) H3N2 influenza viruses -- viruses that
normally infect pigs. While human infection with swine influenza viruses is
rare, it can occur. This is most likely to occur when people are in close
proximity to infected pigs, such as in pig barns and livestock exhibits
housing pigs at fairs.
Both of the patients with confirmed trH3N2 infection reported in FluView
were in the vicinity of live pigs. Dates of illness onset in the 2 patients
are more than 6 weeks apart and the viruses from the 2 patients have some
genetic differences, confirming that these 2 cases are not linked. Ongoing
investigations in both states have not shown any evidence of community
transmission of these viruses. The most likely scenario at this point is
that these are 2 isolated cases of human infection with swine influenza
viruses that, while very rare, do occur from time to time. Both patients
have fully recovered from their illnesses; however, these 2 cases do
underscore the importance of human and animal surveillance for influenza.
These 2 cases reported in FluView bring the total number of human
infections with swine origin influenza viruses reported to CDC since 2005
to 18. Previously, 3 of these reports had been swine origin A (H3N2)
viruses. The Pennsylvania and Wisconsin cases bring the number of reports
swine origin A (H3N2) infections in humans in the United States to 5. The
viruses identified in Pennsylvania and Wisconsin are similar to viruses
that infected a patient in Iowa in September 2009, a patient in Kansas in
August 2009 and a patient in Minnesota in May 2010.
Swine Influenza (swine flu) is a respiratory disease of pigs caused by type
A influenza viruses that regularly causes outbreaks of influenza in pigs.
Swine flu viruses cause high levels of illness and low death rates in pigs.
Swine influenza viruses may circulate among swine throughout the year, but
most outbreaks occur during the late fall and winter months similar to
outbreaks in humans. There are 4 main influenza type A virus subtypes that
have been isolated in pigs: H1N1, H1N2, H3N2, and H3N1. Most flu viruses
circulating in pigs are referred to as "triple-reassortant" viruses because
these flu viruses contain genes from human, swine and avian influenza viruses.
Most commonly, cases of human infection with swine-origin influenza viruses
occur in people with direct exposure to pigs. The patient in Pennsylvania
lives in an area where live pigs are farmed and the patient in Wisconsin
became sick 2 days after attending a state fair where pigs were exhibited.
It's important to note that swine influenza viruses are not transmitted to
humans by food. You can not get swine influenza from eating pork or pork
products. Eating properly handled and cooked pork and pork products is safe.
In the past, CDC received reports of approximately one human infection with
a swine influenza virus every one to 2 years, but in the past few years,
about 3 cases have been reported per year. Increased reporting of human
infections with swine influenza could be the result of increased influenza
testing capacity and capabilities in public health laboratories.
These trH3N2 viruses are different from the 2009 H1N1 virus that has been
circulating in the United States since late April 2009. They are also
different from human seasonal influenza A (H3N2) viruses that typically
circulate among people during the flu season. Swine trH3N2 viruses commonly
circulate in pigs in North America, but rarely infect humans. These viruses
are different from the swine classical H1N1 or swine trH1N1 influenza
viruses that also circulate in pigs in North America because they have H3N2
surface antigens. Tr H3N2 viruses first emerged in North American swine
herds in the late 1990s. The H3 and N2 genes which 1st emerged in swine flu
viruses originated from human seasonal H3N2 influenza viruses that
circulated globally among humans in the late 1990s.
Although the vast majority of instances of human infection with animal
influenza viruses do not result in human to human transmission, each case
should be fully investigated to be sure that such viruses are not spreading
among humans and to limit further exposure of humans to infected animals if
infected animals are identified. Surveillance for both seasonal and novel
influenza viruses is conducted by the CDC and its state and local health
partners year round.
For more information about swine influenza, see:
Weekly US surveillance updates are published in FluView and posted at:
--
communicated by:
ProMED-mail Rapporteur Mary Marshall
[There are 4 main influenza type A virus subtypes that have been isolated
in pigs: H1N1, H1N2, H3N2, and H3N1. Most flu viruses circulating in pigs
are referred to as "triple-reassortant" viruses because these flu viruses
contain genes from human, swine, and avian influenza viruses.
Swine triple-reassortant H3N2 influenza viruses commonly circulate in pigs
in North America, but rarely infect humans. The total number of human
infections with swine origin influenza viruses reported to the CDC since
2005 had been 16, and 3 of these reports had been swine origin A (H3N2)
viruses. The Pennsylvania and Wisconsin cases described above bring the
number of reports swine origin A (H3N2) infections in humans in the United
States to 5, and the total of swine origin A influenza A viruses to 18.
The dates of illness onset in the 2 patients are more than 6 weeks apart
and the viruses from the 2 patients have some genetic differences,
confirming that these 2 cases are not linked.
Swine flu viruses cause high levels of illness and low death rates in pigs.
Swine influenza viruses may circulate among swine throughout the year, but
most outbreaks occur during the late fall and winter months similar to
outbreaks in humans.
Transmission of swine (tr) influenza a viruses to humans has been rare,
even in individuals occupationally exposed to pigs. With the exception of
the swine-origin A (H1N1) 2009 pandemic virus human-to-human transmission
has occurred rarely, if at all.
The HealthMap/ProMED-mail interactive map of the United States, showing the
locations of the states of Pennsylvania and Wisconsin, can be accessed at
[see also:
Influenza (13): WHO update 20101111.4092]
...................cp/ejp/sh
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