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Alien
Plants Get Up Your Nose
By Kelly Scott
<kelly.scott@adelaide.edu.au>
Millions are suffering in a rising
national epidemic of allergies and asthma caused by the spread of
alien plants in the Australian environment.
"There's
no doubt at all, invasive plants are a massive national health
problem - but not one that is widely recognised by either the
public or the healthcare community," says Dr Rachel McFadyen,
CEO of the Cooperative Research Centre for Australian Weed
Management on World Asthma Day on May 2.
"They make
life miserable for millions of people. And the worst plants
actually make you allergic to a whole lot of things you weren't
allergic to before."
Dr McFadyen said that when the
drugs being taken for allergies and asthma, the doctor visits,
hospitalisations, lost productivity and time off work are all
accounted for, the total cost could exceed a billion dollars per
year. The drugs alone have been estimated to be worth $300m
annually.
The good news, says Dr McFadyen, is that it is
possible to control some of the worst offending plants quite
cheaply - compared with solving other major health problems -
using biological control.
Besides allergies and asthma,
alien plants also bring with them other health concerns - deadly
fruits and seeds, skin irritants, thorns, spines and stings and
livestock poisons.
"Despite some successes, the
continued spread of certain invasive plants is increasing the
health impact on the nation," Dr McFadyen says. "It is
our goal, by 2020, to stop the introduction of any more dangerous
plants - and to cut back the extent of existing ones."
The
worst offenders include plants like parthenium weed and annual
ragweed, which over-stimulate the individual's immune system,
giving them new allergies to other plants. In susceptible
individuals both can cause gross facial swelling, allergic eczema
and infected sinuses. They have even driven some people from their
homes and jobs. Others include privet and annual ryegrass - which
is developing resistance to herbicides.
"Fortunately,
through biological control, the abundance of these first two nasty
introduced plants is in decline - and is a good example of how
controlling a weed can achieve a useful healthcare outcome,"
Dr McFadyen says.
Unfortunately, she adds, many of the
worst health offenders have escaped from people's gardens - and
it is up to home owners and other land owners to play their part
in combating a national health problem.
The NSW Asthma
Foundation advises gardeners to avoid plants with wind-borne
pollen, and choose native grasses in preference to imported lawns.
"We must also all be aware of the risk we pose to community
health when we let plants escape from our gardens and establish in
the wild," says Dr McFadyen.
Of the 25 major seasonal
allergens in Australia around 20 of them are introduced species,
says Dr Tim O'Meara of the Woolcock Research Institute at Sydney
University
"Native species may also be very important,
but they are less well characterized as allergen sources. The
introduced species that are know to drive allergies include
pasture grasses such as ryegrass and paspalum, trees such as birch
and olive and weeds such as ragweed, plantain and parietaria.
"In
Australia, pollens are generally associated with hay fever, known
as allergic rhinitis, which affects 20-40% of adults. We do not
see a clear association with asthma, except in the case of
thunderstorm asthma when pollen grains rupture to a size that
readily penetrates deeper into the airways and causes airway
narrowing, even in people with no previous history of asthma."
In
the US and Europe the pollens from a number of plants introduced
into Australia are also found to be associated with asthma, Dr
O'Meara says. This may be a result of the stronger seasonality of
the pollens in US and Europe. In Australia the pollen seasons all
tend to blend together, so it is hard to tease out an effect on
asthma - which is a chronic disease - due to a single species.
Some of the plants associated with both rhinitis and asthma in the
Northern hemisphere are ragweed, parietaria, olive and birch.
"An
example of the impact of introduced species on allergies is the
association between ragweed and autumn hay fever. In the Northern
Rivers area of NSW, an area known to have a ragweed problem, 35
per cent of people are allergic to ragweed. Many suffer hay fever
in the months of March-April when ragweed releases its pollen into
the air."
One plant which is a growing problem both as
an environmental weed and as cause of allergies is the olive tree,
which is spreading in the wild in SA. Near infested areas it can
account for up to 40 per cent of the airborne pollen on some days,
says Flinders University researcher Dr David Bass.
"Pollen
from olive trees can exacerbate asthma and a range of other
allergic conditions. In the Mediterranean area and in California,
olives are widely distributed and its pollen is one of the most
important causes of respiratory allergy," he says.
"Olive
pollen is also cross-reactive. If someone is exposed and
sensitized to olive pollen they may react to other allergens such
as ryegrass."
Toxic plants which pose a risk to
children and pets include thornapple and castor oil seeds, arum
lily and blackberry nightshade.
"Although we spend a
lot of money controlling weeds in Australia each year, very little
is actually targetted at those plants which represent major health
problems," Dr McFadyen says.
"At present only one
out of 23 problem plants posing a significant respiratory or toxic
threat has received federal funding for control. We know that if
we cut back the abundance of a plant which causes health problems,
the health problems decline and so does the dependence on drugs
and healthcare.
"This is a clear case when a modest
investment in controlling invasive
plants can reap major
national health benefits, make life better for
millions of
people and help reduce the swelling cost of healthcare."
More
information:
Dr Rachel McFadyen, Weeds CRC, 0409 263 817
(Sunday 1 May), 07 3362 9388 (wk)
Peter Martin, Weeds CRC, 0429
830 366 (Sunday 1 May), or 08 8303 6693 (wk)
Please Visit:
http://www.weeds.crc.org.au
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