is swine influenza ?
Swine influenza (also referred to as Swine influenza
viruses or SIV) is caused by Orthomyxoviruses which are endemic among pig populations.
Wild pigs can carry the virus intestinally, without being affected. Swine influenza
can be highly contagious among pigs, but most outbreaks cause high levels of illness
and low death rates in pigs.
Swine flu infects a number of human beings
every year, and there have been increasing numbers of reports of person-to-person
spread in recent years.
Analysis of the various virus sub-types found in
swine flu in pigs suggests a pooling of DNA, incuding genes from swine, avian
and human influenza.
Until recently, influenza viruses had been thought
to be largely 'species specific', with little risk to other species, but it has
now been established that the great epidemic of 1918 was a strain of avian flu.
of the cases in the 2009 outbreak in Mexico and the USA have been confirmed by
the World Health Organization to be due to a new genetic strain of H1N1, including
swine flu genetic content.
Note that swine influenza - swine flu - is the
accepted medical description of the disease, even though porcine flu would probably
be a little more accurate, and plain old fashioned pig flu would do just as well.
is swine influenza usually found?
The virus, a member of the Orthomyxoviridae
group, is endemic among pig populations around the world. Other strains - including
human and avian varieties - can thrive in pig populations without causing symptoms.
common is swine influenza ?
Swine influenza can reach epidemic form among
pigs but low pathogenicity forms are more common than high. Just like human flu
in humans, it is an endemic respiratory ailment.
Outside of epidemics, it
is not usually found in human beings; the US records cases in single figures in
A pandemic is defined as an epidemic that is geographically
widespread; occurring throughout a region or even throughout the world; the April
outbreak lead to over one hundred deaths, mostly in Mexico, and affected people
in a score of far-flung nations. But to call that an epidemic, let alone a pandemic,
is a sick joke. 'Normal flu' does exactly the same thing, year in, year out. The
fact that we can trace it more easily and identify the victims does not redefine
epidemic or pandemic; the fact the world panics so easily is probably little defence.
The pandemic will come; current farming methods, population density, and the fact
that millions of us fly in poorly ventilated jet aircraft is testament to that.
It will happen, but probably not yet.
swine influenza transmitted?
Infected pigs spread the 'pig flu' virus via
saliva, and nasal secretions - like human flu, it is largely an airborne infection,
and feces. In industrialised nations, pigs are 'farmed' using an industrial approach
which keeps large numbers of pigs close together, it can easily and quickly spread.
Additionally, pigs may be moved from one centre to another for breeding or other
reasons, enabling the virus (which may be at a low level and symptom-free), to
spread between centres.
In less developed countries, domestic pigs may move
more freely, over the same territory as wild pigs, enabling the virus to be constantly
on the move. Plus people and pigs live much closer together in such environments,
easing the transfer of genetically separate viruses from man to pig and vice-versa,
with the ever present risk of news forms developing.
Influenza viruses spread
not just by inhalation of aerosolized virus, but also by eye and nose contact
with droplets of respiratory secretions.
influenza be spread from person-to-person?
The disease can be spread by
infected pigs to people, through direct contact with contaminated items.
have been recorded cases of person-to-person spread.
For example, an isolated
case in 1988 resulted in multiple human infections, with antibody evidence of
virus transmission from the patient to health care workers who had close contact
with the patient.
In the same year, a healthy woman (age 32) died of pneumonia;
a swine H1N1 flu virus was detected. Four days before she became ill, the patient
visited a county fair, where there was widespread influenza-like illness among
the exhibited pigs. Tests showed that three out of four exhibitors tested had
evidence of swine flu but no serious illness was detected. The virus was also
found in some of the health care workers involved.
Pigs are susceptible
to both human and pig viruses. If a pig were infected with the pig flu virus at
the same time as a human flu virus, this could allow a new form of the pig virus
to arise with the ability to spread directly from one human being to another.
Swine flu cannot be spread through eating pork.
is most at risk?
Normally, only people who have close contact with infected
pigs are considered at risk; mostly in cultures where people and domestic fowls
live in very close proximity.
In most disease epidemics, those at risk tend
to be older people, and those weakened by immunosuppression of other ill health;
however, the 2009 flu outbreak has been characterised by deaths among young people
- a feature of the 1918 flu epidemic which killed over 20 million people worldwide,
though that epidemic originated from a strain of bird flu.
are the symptoms of swine influenza ?
The symptoms of swine flu in people
include fever, lethargy, lack of appetite and coughing. Runny nose, sore throat,
nausea, vomiting and diarrhea have also been reported.
More aggressive forms
include: fever, disorientation, stiffness of the joints, vomiting, and loss of
consciousness ending in death. The symptoms may depend on the virus strain involved.
is swine influenza diagnosed?
Initial diagnosis may depend on the individual
history, particularly recent travel and contact with pigs or swine wastes. Confirmation
will depend on laboratory tests of nose and throat swabs, plus sputum, and possibly
Is there a treatment for swine influenza
Amantadine, rimantadine, oseltamivir and zanamivir have all been used
successfully to treat swine influenza. However, the most recent swine influenza
viruses isolated from humans are resistant to amantadine and rimantadine. This
leaves the option of oseltamivir or zanamivir for the treatment and/or prevention
Is there a way to prevent infection?
those dealing with pigs, respiratory precautions when pigs show symptoms - protective
masks and eye protection as a minimum would be wise. There is a bigger question
of how the disease in pigs is dealt with, to avoid the reservoir of infection
that may be a time bomb - but that is beyond the scope of this article!
the human community, isolation and quarantine are clearly just not practical in
most places, but the time honoured approaches of exercise, good ventilation and
keeping a maximum distance from those with infection would be wise.
in the Mexico outbreak, public buildings were closed and hundreds of public events
cancelled. Schools in and around Mexico City were temporarily closed, and most
bars and restaurants in the capital were closed. People were being strongly urged
to avoid shaking hands, and the US embassy advised visitors to maintain a distance
of 2m (6 feet) from other people.
What is the mortality
rate for swine influenza ?
Very small in between epidemics; rare in pigs,
rare in human beings.
Is there an swine influenza
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 - quoted from CDC advice.
currently is no commercially available vaccine to protect humans against the virus
that is being seen in the Americas. However, vaccine development efforts are taking
Can swine influenza be controlled environmentally?
the swine influenza virus vaccines currently available may not completely eliminate
the infection, vaccination of pigs can reduce the levelsof virus shed by infected
animals, and thus reduce the potential for human exposure and zoonotic infections.
While the human influenza vaccines produced on a yearly basis contain only
human, not swine, strains of viruses, these vaccines are likely to provide some
level of protection against infection with swine viruses of the same hemagglutinin
sub-type. Thus the vaccination of farm workers may reduce the risk of human influenza
virus infection of their pigs, which in turn may reduce the risks to humans.
policies for farm employees should encourage them to remain away from work when
they are suffering from acute respiratory infections (approximately 3-7 days).
Ventilation systems should be designed to minimize re-circulation of air within
animal housing rooms. This is will reduce the exposure of pigs to viruses from
other pigs, reduce their exposure to human influenza viruses, and also reduce
exposure of workers to swine influenza viruses.
Farm workers should change
clothes prior to leaving swine barns; hand-to-face contact should be minimized
and hand-washing stations should be available throughout the animal housing areas.
Boots should be specific for the pig barns, reducing the risk of spreading infected
The known infection of pigs with waterfowl-origin influenza
viruses, the risks for reassortment of avian viruses with swine and/or human influenza
viruses in pigs, and the risk for transmission of influenza viruses from pigs
to domestic turkeys all indicate that contact between pigs and both wild and domestic
fowl should beminimized.
All doorways, windows and air-flow vents in swine
housing units should be adequately sealed or screened to prevent entrance of birds.
Although small birds such as sparrows, swallows, finches,wrens etc. are not thought
to be important in the overall ecology of influenza viruses, they may carry influenza
viruses from waterfowl faeces into barns on their bodies.
water should not be used for drinking water or for cleaning in swine facilities
(because of waterfowl faecal contamination with influenza viruses).
it may be prudent to attempt to minimize waterfowl use of farm lagoons.
and domestic fowl should not be farmed on the same premises.
Pig feed should
be kept in closed containers to prevent contamination with faeces from over-flying
These recommendations clearly cannot apply when pigs are raised
outdoors. Outdoor housing may put pigs at increased risk for infection from avian
viruses, but the animals may well be at reduced risk of passing flu amongst the
stock, and may have greater defense against infection and strionger immune systems
- research is needed in this area.
Is there legal protection
for workers and others?
All workers who may have contact with wild pigs,
or domestic pigs that have had contact with wild pigs, are entitled to full training
and education; sufficient for them to assess the risks to themselves, and for
them to be able to work in a way that minimises or removes the risks to the community.
Failure to provide full education and sufficient protective gear, including gloves,
masks, eye shields, general protective clothing (as appropriate to the job) and
handwashing facilities, would almost certainly be seen by the courts as negligence,
particularly if this led to confirmed disease spread.
and Further Information Sources
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Article written by Andrew Heenan BA (Hons), RGN, RMN