Organophosphates for Animal Health
Both pets and farm animals can suffer infestations of external parasites.
These make their lives a misery and can spread infections and transmit
disease. In pet animals, fleas are the most
common parasite encountered; in farm animals, lice, mange mites, scab mites,
blowfly and ticks are the principal
problems. Distressing enough on their own, these parasites can even lead to secondary
problems - for example, flea bites often cause allergic dermatitis, and in
farm animals lice and mange can lead to loss of wool or hair.
Responsible owners of animals want to protect their charges from these
infestations. Indeed, it is obligatory to protect farm animals from infestations under the
Farm Animal Welfare Codes. Failure to do so can lead to prosecution for neglect. It is
also in a farmer's best interest financially, as healthy animals are more productive.
Over the years there has been a range of products available with which
to treat affected animals and to prevent infestation by these parasites. Among these are a number of products which have
organophosphates (OPs) as their principal active ingredient - the most common are
some sheep
dips and flea treatments for pets.
What are OPs?
'OP' is an abbreviation for organophosphate and describes a huge
range of chemicals with a very wide spectrum of physical and chemical properties.
Just as the word 'alcohol' encompasses a wide range of products -
everything from the lethally poisonous methanol, through industrial chemicals and cleaning
agents to the everyday wine, beer or spirits which most people enjoy in moderation - the
OP category is a broad one and generalisations are difficult.
The very few OPs which have been chosen for use in animal medicines
were selected, based on a combination of efficacy and wide safety factors, as being most
appropriate to deal with specific target pests by practical means of application.
At the doses used in animal medicines, OPs are able to
target external
parasites without causing any harm to the host animal. OPs used around the
world to treat animals include diazinon, cythioate, fenthion, phosmet, dichlorvos, propetamphos and
tetrachlorvinphos.
OPs used in animal medicines generally come in liquid
form and when diluted are used as dips. Or they can be formulated for direct
application such as via a flea collar, pet spray and 'spot on' for pets.
Alternatives to OPs have always been available. However, OPs are
frequently the preferred choice of treatment are because they provide efficacious,
safe and cost
effective control of a wide range of pests.
Can anyone put an OP product on the market?
No. Under both EU and UK law, before any animal treatment is
sold, it must go through a stringent licensing procedure to obtain what is called
a 'Marketing Authorisation'. It must be proved that the product is efficacious (in
this case, that it is effective against the parasite), is of good quality and is safe to the users, the environment and to animals.
Manufacturers spend many millions of pounds to produce extensive test results, which must
be presented for review by independent experts at the regulatory authority. The instructions for use are approved,
with the authorities determining what precautions and other safety advice should be
included.
By law, all animal medicine authorisations are routinely and
continuously reviewed and may be revoked at any time should the need arise. Manufacturers
and veterinary surgeons are obliged to report to the licensing authority any adverse
reactions to any animal medicines both in animals and humans. OP sheep dips, which have
been in the spotlight for the past few years, have been subject to additional extensive
reviews, with examination of new data
from manufacturers and other research organisations. OP products remain on
the market, and many people choose to use them.
For substances such as OPs, some of which have been in
world wide use for many decades, the manufacturers' data is backed by a vast
library of published material documenting independent research and
experience of use. The use of these products continues to be studied.
Sales Controls
Veterinary surgeons who dispense medicines and animal health
distributors who sell to farmers are trained and qualified by examination. Every time a
farm animal is treated, the treatment must by law be recorded and the animal or its
produce (eggs or milk) may not enter the food chain until a specified period has passed
following medication (called the
'withdrawal period').
A manufacturer of an animal medicine does not decide the retail outlet
for its product; only the licensing authority can determine whether a product may go on
general sale or should be restricted to sale via these qualified agents. Products which
can be bought from the pet shop or supermarket are, by definition, those which are deemed
by the authorities to be safe in untrained hands. Even these products are, however,
accompanied by carefully worded instructions which must be followed.
User Safety
Advice on user safety is given on product labels and is
regularly reviewed and updated. For sheep dips this includes, for example, reference to
the purchase and use of protective clothing both for handling the concentrates in the
preparation of the dip bath and using the diluted product during the dipping procedure as
well as disposal of left over dip. OP dips are now supplied in specially
designed closed transfer packaging systems to reduce even further the
possibility of any contact from the concentrate to the person making up the
dip. For pet products, advice is given on use and storage of the product, handling the
product and the animal after treatment, and disposal of the product after
use.
Following independent investigation in the early 1990s by
the Health and Safety Executive and others, it became apparent that some
users of OP sheep dips were not following the label instructions stipulated by
the authorities as necessary for their personal safety. Accordingly, a certification and
registration scheme was introduced and only people registered under the scheme are allowed
to buy OP sheep dips.
For those who prefer not to obtain a certificate, or who find the
wearing of appropriate protective clothing unacceptable, many farmers choose
to have their sheep dipped by professional contractors. There is also a wide
range of alternative products available. But whatever product is used, it is essential that the manufacturers'
official authorised instructions are followed, for the safety of user, animal and
consumer, and to ensure effective use of the product.
Further reading:
HSE / VMD / DETR publication 'Sheep Dipping' AS29 (rev2) available
free from HSE Books, PO Box 1999, Sudbury, Suffolk CO10 6SF. Telephone numbers of local
Health & Safety Executive offices are in the telephone directory.
The Veterinary Medicines Directorate
(the executive agency responsible for licensing animal medicines in the UK) can be
contacted on +44 (0)1932 336911.
The National Proficiency Tests Council (the executive agency
responsible for administration of the sheep dipping certificate) on +44 (0)1203 696553.
Reviewed October 2007
See also:
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