Abstracts: Swine Influenza (also called swine
flu, hog flu and pig flu) is a respiratory disease of
pigs caused by influenza virus (type A) responsible for
outbreaks of influenza in pigs in the United States,
Mexico, Canada, South America, Europe (including the
United Kingdom, Sweden, and Italy), Kenya, Mainland
China, Taiwan, Japan and other parts of Eastern Asia.
Swine Influenza viruses cause high levels of illness and
low death rates in pigs. Influenza viruses usually
circulate among swine throughout the year, but most
outbreaks occur during the late fall and winter similar
to outbreaks in humans.
There are four main type A influenza virus subtypes that
have been identified in pigs: H1N1, H1N2, H3N1 and H3N2.
However, most of the recently isolated influenza viruses
from pigs have been type A H1N1 viruses. The swine
influenza virus (type A H1N1) was first isolated from a
pig in 1930. This virus is spreading from
person-to-person, probably in much the same way that
regular seasonal influenza viruses spread. The H1N1
virus was originally referred to as “swine flu” because
laboratory testing showed that many of the genes in this
new virus were very similar to influenza viruses that
normally occur in pigs in North America. But further
study has shown that this new virus is very different
from what normally circulates in North American pigs.
Pigs can be infected by avian influenza, human influenza
viruses as well as swine influenza viruses. The
influenza virus has been known as a pathogen in the
human population since at least the 16th century. It has
got a unique ability to cause recurrent epidemics and
global pandemics due to rapid genetic re-assortments
that cause fast and unpredictable antigenic changes in
important immune targets leading to recurrent epidemics
of febrile respiratory disease every 1 to 3 years. Each
century has witnessed some pandemics rapidly progressing
to all parts of the world due to emergence of a novel
virus to which the overall population holds no immunity.
The influenza viruses can re-assort (i.e. swap genes)
and new viruses, a mix of swine, human and/or avian
influenza viruses can appear leading to development of
new novel strain for which humans do not have the
immunity. Like all other influenza viruses, swine
influenza viruses also change constantly.
Recently, human cases of H1N1virus infection have been
reported in several parts of the world and
human-to-human transmission of the virus appears to be
ongoing - representing a real pandemic threat. WHO has
now upgraded the phasing of pandemic swine flu influenza
from Phase - 3 to Phase - 5.
Transmission of swine influenza virus from pigs to
humans is not common and if at all the infection is
passed on from pigs to humans, it is called zoonotic
swine flu. People who work with pigs, especially people
with intense exposures, are generally at increased risk
of infection. Outbreaks of swine flu are now resulting
due to human-to-human transmission. Infected person
cough or sneeze and the infected droplets get onto their
hands, drop onto surfaces, or are dispersed into the
air. Other person can breathe such contaminated air, or
touch infected hands or surfaces, and can be exposed.
Therefore, to prevent spreading of swine flu, people
should cover their mouth and nose with a tissue while
coughing, and wash their hands regularly.
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