North American Influenza (Swine Flu)
What is Swine Influenza?
Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A
influenza virus 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. The classical swine flu virus (an influenza type A H1N1 virus) was first
isolated from a pig in 1930.
How many swine flu viruses are there?
Like all influenza viruses, swine flu viruses change constantly. Pigs can be
infected by avian influenza and human influenza viruses as well as swine
influenza viruses. When influenza viruses from different species infect pigs,
the viruses can reassort (i.e. swap genes) and new viruses that are a mix of
swine, human and/or avian influenza viruses can emerge. Over the years,
different variations of swine flu viruses have emerged. At this time, there are
four main influenza type A virus subtypes that have been isolated in pigs: H1N1,
H1N2, H3N2, and H3N1. However, most of the recently isolated influenza viruses
from pigs have been H1N1 viruses.
Swine Flu in Humans
Can humans catch swine flu?
Swine flu viruses do not normally infect humans. However, sporadic human
infections with swine flu have occurred. Most commonly, these cases occur in
persons with direct exposure to pigs (e.g. children near pigs at a fair or
workers in the swine industry). In addition, there have been documented cases of
one person spreading swine flu to others. For example, an outbreak of apparent
swine flu infection in pigs in Wisconsin in 1988 resulted in multiple human
infections, and, although no community outbreak resulted, there was antibody
evidence of virus transmission from the patient to health care workers who had
close contact with the patient.
How common is swine flu infection in humans?
In the past, CDC received reports of approximately one human swine influenza
virus infection every one to two years in the U.S., but from December 2005
through February 2009, 12 cases of human infection with swine influenza have
been reported.
What are the symptoms of swine flu in humans?
The symptoms of swine flu in people are expected to be similar to the symptoms
of regular human seasonal influenza and include fever, lethargy, lack of
appetite and coughing. Some people with swine flu also have reported runny nose,
sore throat, nausea, vomiting and diarrhea.
Can people catch swine flu from eating pork?
No. Swine influenza viruses are not transmitted 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. Cooking pork to an internal temperature of 160°F
kills the swine flu virus as it does other bacteria and viruses.
How does swine flu spread?
Influenza viruses can be directly transmitted from pigs to people and from
people to pigs. Human infection with flu viruses from pigs are 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. Human-to-human transmission of
swine flu can also occur. This is thought to occur in the same way as seasonal
flu occurs in people, which is mainly person-to-person transmission through
coughing or sneezing of people infected with the influenza virus. People may
become infected by touching something with flu viruses on it and then touching
their mouth or nose.
What do we know about human-to-human spread of swine flu?
In September 1988, a previously healthy 32-year-old pregnant woman was
hospitalized for pneumonia and died 8 days later. A swine H1N1 flu virus was
detected. Four days before getting sick, the patient visited a county fair swine
exhibition where there was widespread influenza-like illness among the swine.
In follow-up studies, 76% of swine exhibitors tested had antibody evidence of
swine flu infection but no serious illnesses were detected among this group.
Additional studies suggest that one to three health care personnel who had
contact with the patient developed mild influenza-like illnesses with antibody
evidence of swine flu infection.
How can human infections with swine influenza be diagnosed?
To diagnose swine influenza A infection, a respiratory specimen would generally
need to be collected within the first 4 to 5 days of illness (when an infected
person is most likely to be shedding virus). However, some persons, especially
children, may shed virus for 10 days or longer. Identification as a swine flu
influenza A virus requires sending the specimen to CDC for laboratory testing.
What medications are available to treat swine flu infections in
humans?
There are four different antiviral drugs that are licensed for use in the US for
the treatment of influenza: amantadine, rimantadine, oseltamivir and zanamivir.
While most swine influenza viruses have been susceptible to all four drugs, the
most recent swine influenza viruses isolated from humans are resistant to
amantadine and rimantadine. At this time, CDC recommends the use of oseltamivir
or zanamivir for the treatment and/or prevention of infection with swine
influenza viruses.
Is the H1N1 swine flu virus the same as human H1N1 viruses?
No. The H1N1 swine flu viruses are antigenically very different from human H1N1
viruses and, therefore, vaccines for human seasonal flu would not provide
protection from H1N1 swine flu viruses.
Swine Flu in Pigs
How does swine flu spread among pigs?
Swine flu viruses are thought to be spread mostly through close contact among
pigs and possibly from contaminated objects moving between infected and
uninfected pigs. Herds with continuous swine flu infections and herds that are
vaccinated against swine flu may have sporadic disease, or may show only mild or
no symptoms of infection.
What are signs of swine flu in pigs?
Signs of swine flu in pigs can include sudden onset of fever, depression,
coughing (barking), discharge from the nose or eyes, sneezing, breathing
difficulties, eye redness or inflammation, and going off feed.
How common is swine flu among pigs?
H1N1 and H3N2 swine flu viruses are endemic among pig populations in the United
States and something that the industry deals with routinely. Outbreaks among
pigs normally occur in colder weather months (late fall and winter) and
sometimes with the introduction of new pigs into susceptible herds. Studies have
shown that the swine flu H1N1 is common throughout pig populations worldwide,
with 25 percent of animals showing antibody evidence of infection. In the U.S.
studies have shown that 30 percent of the pig population has antibody evidence
of having had H1N1 infection. More specifically, 51 percent of pigs in the
north-central U.S. have been shown to have antibody evidence of infection with
swine H1N1. Human infections with swine flu H1N1 viruses are rare. There is
currently no way to differentiate antibody produced in response to flu
vaccination in pigs from antibody made in response to pig infections with swine
H1N1 influenza.
While H1N1 swine viruses have been known to circulate among pig populations
since at least 1930, H3N2 influenza viruses did not begin circulating among US
pigs until 1998. The H3N2 viruses initially were introduced into the pig
population from humans. The current swine flu H3N2 viruses are closely related
to human H3N2 viruses.
Is there a vaccine for swine flu?
Vaccines are available to be given to pigs to prevent swine influenza. There is
no vaccine to protect humans from swine flu. The seasonal influenza vaccine will
likely help provide partial protection against swine H3N2, but not swine H1N1
viruses.
Source:
http://www.cdc.gov/
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