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Swine Flu Epidemic in North America
Swine influenza is a respiratory disease of pigs caused by type
A influenza viruses. Sometimes it may spread to Humans
and cause flu-like symptoms.
The virus is influenza A virus, carrying the designation H1N1. It is a
hybrid reassorted virus and contains DNA typical to avian, swine and
human viruses, including elements from European and Asian swine
viruses. It clasically causes outbreaks from Mid March to mid May and
commonly causes fever, headache, fatigue and cough. As yet, none of
the Eight Swine flu cases diagnosed in US has proved fatal, though
sources report about 80 fatal cases in Mexico in the past few weeks.
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, a total of 12 human infections
with swine influenza were reported from 10 states in the United
States. Since March 2009, a number of confirmed human cases of a
new strain of swine influenza A (H1N1) virus infection in California,
Texas, and Mexico have been identified.
In the Federal District of Mexico, surveillance began picking up cases
of ILI starting 18 March. The number of cases has risen steadily
through April and as of 23 April there are now more than 854 cases of
pneumonia from the Mexican capital. Of the Mexican cases, 18 have
been laboratory confirmed in Canada as Swine Influenza A/H1N1,
while 12 of those are genetically identical to the Swine Influenza
A/H1N1 viruses from California. The US has 8 confirmed cases within
America and has tested atleast 14 specimens from Mexico, of which
seven tested positive.
Mean Prevalence of Influenza in U.S
New England — 1.5%
Mid-Atlantic — 2.9%
East North Central — 1.9%
West North Central — 1.7%
South Atlantic — 2.2%
East South Central — 2.5%
West South Central — 4.8%
Mountain — 1.5%
Pacific — 3.0%
National average- 2.4%
The regions currently affected have always showed an infection rate
higher than the national average.
WHO has now activated its Strategic Health Operations Center (SHOC)
-its command and control center for acute public health events.
Life Cycle of Swine Flu virus-
Birds like Ducks, geese and swans are common reservoirs of Influenza
virus and can harbor the virus without showing symtoms of the
Pigs most commonly get infected with flu viruses from other pigs
(swine flu), but also can get infected with flu viruses from birds (avian
flu), and from people (human flu). This cross-species spread of flu
viruses can lead to new types of flu viruses. Pigs may sometimes
harbor the virus without exhibiting any overt symtoms.
Signs of swine flu in pigs include:
• coughing (“barking”)
• discharge from the nose
• breathing difficulties
• going off feed
Studies have shown that 30% to 50% of commercial U.S. swine have
been infected with swine flu. H1N1 and H3N2 swine flu viruses are
endemic among pig populations in the United States.. Recent studies
have shown that 15% to 25% of swine farmers might have been
infected with swine flu viruses, as well as about 10% of veterinarians
Why are Pigs important in this cycle?
Replication of avian influenza viruses in pigs may allow them to adapt
to and be able to efficiently infect mammals, and ultimately be
transmitted to people. In addition, pigs can serve as hosts in which
two (or more) influenza viruses can undergo quot;genetic reassortment.quot;
At this time, there are four main influenza type A virus subtypes that h
ave been isolated in pigs: H1N1, H1N2, H3N2, and H3N1. However,
most of the recently isolated influenza viruses from pigs have been H3
N2 and H1N1 viruses.
The reassortant H3N2 and H1N1 viruses currently circulating widely
and causing disease throughout the swine population of the United
States all contain human influenza virus genes.
From Pigs to Humans-
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).
Families of swine owners who visit the farm atleast four times a week
are also susceptible.
Humans to other Humans-
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. Influenza normally affects
the very young and the very old, but these age groups have not been
heavily affected in Mexico.
People infected with flu typically have fever (often high), cough,
body aches, headaches, fatigue and runny or stuffy nose.
Vomiting and diarrhea may also occur.
CDC recommends the use of oseltamivir or zanamivir for the
treatment and/or prevention of infection with swine influenza viruses.
These medicines should be started in the first 2 days of being ill to be
Diagnosis of swine influenza A (H1N1) virus infection should be
considered in patients with febrile respiratory disease and who
1) live in San Diego and Imperial Counties, California, or Guadalupe
County, Texas, or traveled to these counties or
2) who traveled recently to Mexico or were in contact with persons
who had febrile respiratory illness and were in the two U.S. counties or
Mexico in the 7 days preceding their illness onset.
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.
Swine influenza viruses were first isolated in the United States in
The most well known is an outbreak of swine flu among soldiers in Fort
Dix, New Jersey in 1976. The virus caused disease with x-ray evidence
of pneumonia in at least 4 soldiers and 1 death.The virus was transmit
ted to close contacts in a basic training environment, with limited trans
mission outside the basic training group.
The virus circulated for a month and then disappeared just as
mysteriously. The swine influenza A virus collected from the Fort Dix s
oldier was named A/New Jersey/76 (Hsw1N1)
The number of isolates testing positive for Flu has been steadily
increasing over the years. The H1N1 strain has been specialy noted for
rapid increase since 2006-07. The Human H1N1 strain is genetically
different from H1N1 strain seen in Swines.
Infection Control of Ill Persons in a Healthcare Setting
• Place all suspected cases in a single-patient room with the door
• The ill person should wear a surgical mask when outside of the
patient room, and should be encouraged to wash hands
frequently and follow respiratory hygiene practices.
• Cups and other utensils used by the ill person should be washed
with soap and water before use by other persons.
• Standard, Droplet and Contact precautions should be used for all
patient care activities, and maintained for 7 days after illness
onset or until symptoms have resolved.
• Personnel providing care to or collecting clinical specimens from
suspected or confirmed cases should wear disposable non-sterile
gloves, gowns, and eye protection (e.g., goggles) to prevent
• Cover your nose and mouth with a tissue when you cough or
sneeze. Throw the tissue in the trash after you use it.
• Wash your hands often with soap and water, especially after you
cough or sneeze. Alcohol-based hands cleaners are also
• Try to avoid close contact with sick people.
• If you get sick, CDC recommends that you stay home from work
or school and limit contact with others to keep from infecting
• Avoid touching your eyes, nose or mouth. Germs spread that
Center For Disease Control –
World health organization –
National Pork board -
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