Prepared by Nigel Harvey, Senior Manager, Rentokil Environmental Services
All businesses connected with the Food Trade, whether it be raw
materials, direct food handling, manufacture, storage, distribution or
packaging, need to be aware that the presence of pests such as rodents,
insects and birds pose a potentially serious risk of product
contamination. It is therefore vitally important that steps are taken to
prevent pest problems form arising, and to have a monitoring operation in
place which ensures that should pests gain access, the problem is quickly
identified and corrective action taken.
It is also essential for those people working in these industries to be aware
of the ease with which pests can gain entry to premises, and for them to recognize
their individual and collective responsibilities with regards to
house-keeping standards, maintenance and proofing standards. The establishment
of an active and effective working relationship with their Pest Control
Contractor is a key factor in the maintenance of pest free premises.
The following notes are designed to provide basic information on pests that
are commonly encountered in the food and associated industries.
The House Mouse (Mus domesticus) is the most
common rodent pest in Britain both in business and domestic premises. The House
Mouse, will live happily outside buildings, but given the choice prefers to move
inside and live with man. It will live quite contentedly surrounded by its food
and breeds rapidly. Providing that safe, secure harbourages and food are
available the female mouse will produce litters of up to sixteen young (although
six to eight is the average) every three weeks, and she can conceive whilst
suckling her young. Young mice become sexually mature at about twelve weeks and
they start to breed. Theoretically one pair of mice in their progeny can in a
twelve month period produce close on three thousand mice! (in ideal conditions).
Normally, natural mortality is about 90%; however without effective controls,
this still leaves the potential for a very severe mouse infestation to become
established within the premises.
Inspection of incoming goods needs to be thorough as mice are often found to
have made nests in the middle of pallets of bagged goods or in packaging. They
may also come from sources outside and the proofing of the building against the
ingress of mice is very important, as it has been shown that a 10mm gap between
the door base and door threshold will allow mice to enter from exterior areas.
It therefore follows that high standards of internal maintenance are
necessary to make certain that small harbourages are not unintentionally
provided for mice. It is also important to ensure that pipe and cable runs
through walls are well proofed to restrict movement of mice within a building.
Stacked goods and equipment should be two feet clear of walls to allow
unrestricted inspection access by pest control service contractors.
Brown Rats (Rattus norvegicus) are normally
not so much of a problem inside a building as they prefer to live in burrows
outside, or are associated with rainwater and foul drainage systems. Similarly
to mice that are mainly (but not exclusively) nocturnal and forage during the
evening for food at which time they may find their way into premises. Inspection
for rats is normally associated with the environment outside the buildings
paying particular interest to undergrowth, the perimeter areas and the drainage
systems.
Rodents have been shown to carry and transmit many pathogenic bacteria
including salmonella, streptococci and in case of urine from rats, Weil's
disease. All this means they have no place at all in a food preparation,
production or distribution premises.
Prevention and detection of rodents can be combined. It is normal to have
rodenticidal food baits places in tamper resistant bait stations either
externally for rats or internally for mice around food premises. This exploits
the natural habits of both animals to explore small holes and dark places in
which they feel safe. Frequent checks of the baits in these bait stations can
show whether they have been taken by rats or mice, which means that further
treatment can be carried out, such as additional baiting points and/or, the use
of alternative or additional materials. Where suitable, the gassing of rats
using Phosphine gas in burrows in outside areas is very effective. However the
gassing of rat burrows should only be carried out by trained pest control
technicians.
The rodenticides mostly used against rodents are anticoagulants, although the
original material Warfarin is no longer used, as most mice have developed some
resistance. The newer, second generation anticoagulants are still extremely
effective, and are formulated into baits which can be liquid, whole grain and
lard based paste and into gels and dusts which are used for the treatment of
harbourages, where rodents ingest the rodenticidal material during their
grooming process.
Monitoring for rodents is requires in any food premises as, apart from the
pathogenic bacteria they may carry, they also dribble urine continuously. A mouse
produces up to eighty faecal droppings a day, a rat forty, which they leave
wherever they are, thus offering severe risk of contamination for food, albeit a
raw material of finished product. Rodent droppings represent a contamination
risk irrespective of the age of the droppings.
Prevention of rodent infestation is the key. It is important to ensure that
rodents are unable to enter any building, by sealing gaps in the fabric,
ensuring drains have U-bends, fitting wire mesh over ventilator grilles and, as
previously mentioned, ensuring the gaps under doors will not allow a mouse to
enter. The immediate surrounds and perimeter of the premises should be kept
clear of overgrown vegetation which would provide excellent cover and harbourage
for rats.
Rubbish, pallets, disused equipment etc should not be allowed to accumulate
around the outside of the building as this will be attractive to rodents to nest
in, and may often provide food residues. Refuse containment and disposal is
extremely important, no spillages from the receptacles should be allowed, lids
should be fitted and the frequency of emptying should be that they are never
over-full. Waste bin yards areas should be cleaned thoroughly at least daily.
Inside premises, care should be taken to regularly inspect voids above false
ceilings, ventilations ducts, lifts, shafts, cavity walls and partitions, which
will provide desirable harbourages for rodents, especially mice. It is advisable
to have special inspection hatches built where required so that inspection and
baiting (if required) may be carried out in those areas.
All species of rodents possess large, strong incisor teeth which continuously
grow approximately an eighth of an inch a week. Rodents gnawing on hard objects
helps keep the incisor teeth worn down to an acceptable level. As a consequence
rats and mice can cause considerable damage to fixtures and fittings including
power cables, gas and water pipes, computer network cables and alarm system
wiring. The enamel on rodents incisor teeth has a hardness greater than mild
steel. The consequences and costs in cash and human terms of these gnawing
actions are self evident.
There have been many recorded instances where fires have been
attributed to rodent damage to electrical wiring resulting in substantial
financial loss, severe damage and significant loss of productive time.
Rats and mice have also damaged reinforced plastic and rubberized hydraulic systems causing machinery malfunctions sufficient to stop
complete production lines.
In ultra sensitive areas, non-toxic indicator baits can be used, and only if
infestation is discovered would they be temporarily replaced with toxic baits
until such time that the infestation is cleared. A totally bait free system is
available using electronic infrared indicators and trapping boxes which linked
to a central control panel, with automatic contact to the service technician.
Cockroaches seek warmth, dark crevices and mainly carbohydrate foods, all of
which may be found in canteens, restaurants, kitchens and many areas food
production premises. Even the most scrupulously clean premises can be entered by
these insects, which squeeze their flat bodies through the narrowest cracks.
They eat almost anything that humans do, and readily consume anything of organic
origin, be it `pre' or `post' digestive status.
Scavengers by nature, cockroaches are a menace to health because of their
predilection for drains, sewers and rubbish. They inevitably foul more food than
they eat, leaving a trail of excreta and regurgitated material.
A paper published in Environmental Heath in 1978 details many bacteria,
viruses, protozoa and fungi carried by cockroaches, including those responsible
for salmonella food poisoning, polio and staphylococcal infections. Further
technical papers have been published that not only support these findings, but
implicate cockroaches as vectors of a wider range of diseases which are
injurious to man.
Some species of salmonella are able to remain viable in the excrement of
cockroaches for up to three months and if the humidity is exceptionally low this
period can be extended to six months. E.coli has been found to be still viable
after 32 days in the gut of a cockroach: it is obvious that the presence of
cockroaches cannot be tolerated within the food chain.
It is therefore necessary to maintain the utmost vigilance to ensure that
cockroaches cannot enter premises from adjoining buildings, either at ground
level via doors and windows, but also via underground cable and pipe runs,
drainage systems and main foul sewers. Cockroaches have been found entering
premises via recessed floor grease traps from below ground foul drains.
Regular insecticidal treatments and inspections, allied to the use of insect
detectors is recommended to guarantee that intrusions of these unwelcome pests
is noticed at an early stage, so that concentrated remedial action can be taken
by the pest control contractor.
Cockroaches (and mice) are perhaps the worlds most successful
"commercial travelers", they have been unwittingly introduced by man
into the most unlikely locations. Accommodation platforms in the North Sea and
the Antarctic Survey Stations are but two example of how these pests can
"stow away" in packed goods and equipment. It therefore follows that
the most thorough inspection of ALL incoming items for the presence of pests is
an essential part of the "first line of defence".
Flies and wasps
Flying insects, such as flies and wasps, are very much more than a nuisance,
they can be a distinct health hazard.
During mid to late summer wasps can be a serious problem in bakeries and
other food manufacturers where they are attracted by the smell of sweet products
such as jam, fondant and fruit etc. These are the worker wasps foraging for food
to take back to the nest to feed the queen wasp, who is in effect an egg laying
machine.
They feed on wide variety of food sources as well as sweet products, and
there is a risk of bacterial contamination if the wasp lands on a product. They
are also a direct psychological nuisance to workers as people are often worried
by the presence of wasps, and of course wasps will sting if excited or attacked.
If there are a large number of wasps it normally means there is a nest nearby
and this should be located and destroyed. Great care should be taken with this
operation as there can be up to thirty thousand wasps in one nest, and it is
very often more advisable to call in the services of a pest control contractor,
or indeed the environmental health department who can deal with the problem
professionally and safely. Wasps can be intercepted on the outside of a premises
by placing traps which contain a sticky fermenting liquor. Wasps are attracted
by this smell before they gain entry to the premises, they then fall into the
fermenting liquor and drown.
Flies are an even bigger health hazard then wasps. Their feeding habits of
regurgitating saliva and the contents of their gut onto a food surface prior to
sucking the liquid back up into their gut, means that they regurgitate bacteria
from whatever was their previous food source. As they have a predilection for
living, eating and breeding on faeces the results of their bacterial infection
can be understood. Flies should not be tolerated in any food premises at all!
Cleaning is essential to prevent the breeding of flies in decaying matter
anywhere around or inside premises. Special attention should be paid to gullies
and drains inside the premises and to the refuse outside. As well as thorough
cleaning, spraying of these areas with a residual insecticide will prevent fly
breeding as they will be readily killed, and any eggs they manage to lay will
not be viable. Insect screens over opening windows and doors are also very
effective. The mesh size should be small enough to prevent even the smallest
insect entering or they will find their way through. Not only does mesh
screening keep out flies and wasps, it will also keep out seasonable pests such
as Crane Flies which may blunder into the premises by error, but can still cause
serious contamination and customer complains.
As a final defence mechanism, there are ultraviolet electronic fly killers
both against flies and wasps. As ultraviolet light is highly attractive to a
wide range of flying insects, these units can also be used to monitor the level
of flying insects in the premises, and help in deciding corrective measures to
be taken. Most electronic fly killers use a high voltage discharge via an
electrical grid to electrocute the insects that fly in towards their UV lights.
The most modern type now has a rolling light emitting polymer adhesive film
which traps the insects encapsulating them for up to six months at a time
without needing any attention. Specific lures containing attractants or
pheromones have been developed to attract flies and other insects to these units
to enhance their efficiency. Shatterproof UN tubes can be fitted to these units
satisfying "glass free" requirements in food manufacturing premises.
Ants
The garden Ant ( Lasius niger) can be a seasonal pest from May to
August, Ants nests are normally outside the building in the earth but columns of
ants can often be seen foraging for food inside the premises. As they are a
social insect once food is found this is communicated to others in the nest
which means a continuous throughput of insects. They do not appear to carry any
pathogens but are a nuisance; worker ants can bite and of course can too easily
become a contaminant in a product.
Ants are best treated at the nest site outdoors with the use of insecticidal
sprays or ducts which will penetrate into the nest and eradicate the colony.
There may be many ants in the colony and the treatment may have to be repeated
two or three times. It is best to try and attack this problem before the
swarming of ants in August where the males and females grow wings and mate on
the wing in huge dense clouds. there is then a great risk of these flying ants
blundering in through windows and becoming a severe contamination problem.
Occasionally more exotic ants are found in premises, The most commonly known
of these is the Pharoahs ant (Mononorium pharaonis) and this differs
significantly from the garden ant. the Pharaohs ant is largely a protein feeder
and tends to nest inside the building in service ducts or cracks and crevices.
the ants are very tiny and straw coloured and like garden ants can be seen
trailing for food. They have been confirmed to carry a number of pathogenic
bacteria and do need to be eliminated if found. This is normally done by either
an insecticidal baiting technique or the use of an insect growth regulator,
which prevents the undertaken by professional pest control contractors who have
the technical and biological knowledge of these insects, as it may take from
three to six months to establish a satisfactory level of control.
Bird Pests
Some of the more common species of our native birds are very attracted to
food manufacturing and storage premises where they may be waste or spilt food
for them. Birds rapidly become aware as to the location of food sources and
regular feeding visits quickly become habitual. Birds will also seek out and
find local nesting
sites so that they are near to their food source. The birds that normally
create a problem within food premises are the House Sparrow (Passer
domesticus), the Feral Pigeon (Columba livia), the Starling (Sturnus
vul-aris) and to a lesser degree the Collared Dove (Streatoaelia decaocto).
In coastal mainly locations the Greater Blackbacked, Lesser Black-backed and
Herring Gulls are also considered pest species.
It is important to recognize that bird control is highly emotive subject and
control measures which include culling as a last resort, can only be undertaken
by fully trained and qualifies personnel.
As with all pest problems; prevention is better than cure
It is important, as with other pests, to reduce the attraction of a site by
ensuring cleanliness, good refuse disposal and containment, and the prevention
of food spillages becoming an attraction for these birds.
Bird nesting should not be allowed on site, the underside of loading bay
canopies and docks is often a favourite area as it provides shelter and ready
access to food spillage. Canopies and roof structures can be successfully
`netted off' with long lasting, purpose made polypropylene tensioned netting to
ensure the birds cannot gain access to these favored places. Loading doors and
van shed doors should either be of the automatic type, or kept shut whenever not
in use, or be fitted with high clarity curtain doors.
Birds carry a range of bacteria, similar to rats and mice, which are found in
their droppings or from infected respiratory droplets. Bird droppings on
finished products are unacceptable to the customer, and would certainly be
classed as a health hazard. If birds are allowed to nest they can also be a
reservoir for parasitic insects, which not only live on birds, but may transfer
to humans also. Birds nests are also found to support a range of Stored Product
Insects; it is therefore not unreasonable to suggests that stored product insect
infestations can be introduced into premises via birds and their nests, from
which they migrate to infest previously clean areas.
There as available a wide range of effective bird deterrents and control
methods which are approved by the Royal Society for the Protection of Birds, the
Ministry of Agriculture Fisheries and Food and other animal welfare
organisations. However in all cases it is essential that professional help is
sought to overcome bird problems; the penalties for unapproved or unlicensed
culling are severe.
Stored Product Insects
Wherever bulk flour, cereals, animal feed or other dry food commodities are
stored in bins or silos there is a risk of insect infestation, moulds and other
problems building up in the residues that accumulate in the structure. Food
manufacturing machinery, by its complex nature, provide harbourages for a wide
range of beetles, moths and mites.
Damage and contamination to fresh incoming ingredients can be avoided by
thorough and regular cleaning silos but this need specialist equipment and
trained staff who will take the necessary safety precautions in what is often a
potentially explosive atmosphere.
Unless silos are thoroughly cleaned, infestations of Flour Mite (Acarus
siro), Mediterranean Flour Moth (Ephestia kuhniella) or the Confused
Flour Beetle (Tribolium confusum), may build up within the structure, on
floors, walls, ledges, beams, conveyors and elevators. Bulk tankers and dirty
floor bagging machines can also transfer infestations into otherwise clean
premises.
The vacuum cleaner is the most valuable piece of equipment for cleaning mills
and plant rooms - for removing flour and other residues from the places that
cannot be reached with a brush. It must however, be remembered that the vacuum
cleaner itself can become infested with insects and so must be treated.
Insecticidal dusting powder can be sucked into the holding bag, and external
surfaces and motor compartment should be treated with an oil based spray for
electrical safety.
Quarterly cleaning and inspection schedules should be drawn up to ensure that
the fabric of the building and the outside of machines and holding bins are not
allowed to support large populations of insects. Cleaning and inspection should
also be undertaken inside machines and in silos. If on inspection insects are
found, insecticidal spraying of nonfood contact surfaces can be carried out
immediately after cleaning.
Spraying, of course cannot control insects breeding inside bagged or bulk
food, but fumigation with methyl bromide is completely successful.
Traditionally, goods can be stacked in a room or warehouse and covered with
gas-proof sheets. Gas is introduced and the stack left for a day to allow
penetration: the gas kills all stages in the development of insects. Fumigation
of whole premises with methyl bromide is a major operation usually made once a
year in the Milling trade. This is sometimes the only way to reach insects deep
inside the structure of the building, and those in the machinery and ducts. The
job must, of course, be done by competent, trained and British Pest Control
Association registered operatives, in accordance with the approved and
registered Codes of Practice.
Pallets of infested commodities can now be treated within a compact,
highly efficient thirty cubic metre fumigation bubble, using methyl
bromide or phoshine in a system that can re-absorb the gas. or be released
in a controlled and safe manner atmosphere.
Proofing
The importance of achieving and maintaining high standards of proofing cannot
be over emphasised. Many pests are opportunists and will seek out and exploit
unguarded entry points in their search for food, warmth and shelter. Effective
proofing is the first line of defence against pests; it is an essential part of
the Pest Control Programme. "It is much better to keep them out, than let
them in ". This is a very simple statement, but it encapsulates the essence
of proofing.
Proofing against pests is ongoing and should not be thought of as a
"once only" exercise. In all premises physical changes occur, these
may be due to extensions, new roofs, installation of new plant and machinery,
internal alterations with additional cable and trunking runs, the removal of old
plant, new main services etc etc. For example a plumber will frequently knock a
4" hole in a wall to put a 2" pipe through; the resulting gap is never
proofed and a permanent entry/transfer point has been unwittingly made.
Open doors and windows offer unrestricted access to flying insects, birds,
rodents as well as contaminants such as airborne seeds, birds feathers and large
and small airborne particles. Under the Food Safety Act 1995 it is clearly
stated that all windows a the are needed to be opened for ventilation purposes
should, where necessary be fitted with insect screens that can easily be removed
for cleaning purposes. Professionally made and fitted fly screen doors will also
provide a high degree of protection to manufacturing premises as well as
commercial kitchens.
Ventilation in commercial premises is also frequently via a ducted air
distribution system or through roof mounted cowls and remotely opened panel
vents. Air intake points to ventilation systems should be carefully screened
with mesh of a size to prevent flying insect entry. Roof mounted air outlets are
rarely proofed and should be examined to ensure that they will exclude birds and
insects when in the open position.
The exterior of the "building fabric" needs to be inspected (at all
levels) on a regular basis so that effective measures can promptly be taken. A
single 1" hole in brickwork will readily admit sparrows which can then
establish their nesting sites within buildings. Mice are extremely proficient
climbers and will readily scale brick walls to find entry points.
At ground level not only should the physical structure of buildings be
closely examined but great attention should be paid to doors.
Remember that any door under which you could slide a fountain pen (between
door base and door threshold) has a gap sufficiently large to admit a fully
grown mouse or a young rat. All exterior door bases should be examined and those
with large gaps enough to admit rodents should be professionally proofed with
high grade nylon bristle strip. This is equally effective on wooden, metal,
concertina, sliding and roller doors. Doors should be fitted with self closing
devices which should be checked frequently to ensure that the full closing
function is not impede. Large `goods-in' doors should be protected with plastic
strip curtain doors which are effective at reducing the chances of flying insect
and bird entry. However these doors need to be carefully specified and
installed, allowing foe type and weight most suitable foe the premises
concerned. Rapid-rise roller doors are useful in minimizing the amount of time
that the door is open; however the practice of isolation the control mechanism
to leave the door in the upright (open) position is to be strongly discouraged.
Effective pest control is a "joint responsibility" between
the client and pest control contractors, there has to be a commitment by
both parties to constantly work towards the "ideal" of
establishing and maintaining pest free premises.
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