London's Pulse: Medical Officer of Health reports 1848-1972

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City of London 1957

[Report of the Medical Officer of Health for Port of London]

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could not be introduced into the Port for the simple reason that there are insufficient rats to
enable the spread of infection. Nevertheless, fifty-six rats were sent to the Laboratory and
were examined for plague with negative results.
(3) Arrangements in the district for deratting ships, the methods used, and if done by a commercial
contractor, the name of the contractor.
(a) The burning of sulphur at the rate of 3-lbs. per 1,000 cubic feet of space for a period of
not less than six hours.
The destruction of rats, whether it be by the open pot method or by sulphur gas in cylinders,
is efficient and the great advantage is that when applied in the holds of ships, the crew need
not be put ashore. Unfortunately a number of countries have, for some time past, refused to
accept as valid, International Certificates, where this method of rat destruction has been employed;
consequently it has fallen out of use.
(b) The generation of hydrocyanic acid gas by various methods. For the destruction of
rats a concentration of HCN at the rate of 2-ozs. per 1,000 cubic feet of space is required
with a minimum of two hours contact.
(c) "1080" and "Warfarin". The employment of "-1080" has been used regularly throughout
the docks for some time with highly satisfactory results both on shore and in ships. An
increasing number of ships have been deratted by this method in preference to the use of
cyanide, resulting in a considerable saving of time and cost to the shipowner.
Although satisfactory results have been obtained from the use of "Warfarin" a suitable bait
has yet to be found, particularly in granaries, with which to mix the poison, so that rats will
take it continuously in preference to grain and other forms of cereal on which they are normally
feeding.
(d) Trapping. Trapping is seldom employed save for the destruction of isolated rats which
have escaped a major poisoning operation or which have not yet established themselves.
The following are the names of the firms approved for carrying out the deratting of ships:—
Messrs. Associated Fumigators Ltd. Messrs. Fumigation Services Ltd.
Messrs. London Fumigation Co. Ltd. Messrs. Ridpests Ltd.
Messrs. Scientex (Southern) Ltd. Messrs. Insecta Laboratories Ltd.
TREATMENT OF MICE INFESTATIONS
In some respects mice are more difficult than rats to eradicate by customary methods of control
especially where there is adequate attractive food near or forming remote harbourage in which to
hide and breed. Such conditions are often provided in dock warehouses where cargo is stored and
left undisturbed for indefinite periods.
Once the mice have become established in the centre of bulk food, two characteristics of the
mice make control almost impossible — they will not venture far from the harbourage and they can
live without water for a considerable time; therefore, having the food of choice immediately
available and no craving for water they can live inside the stack probably unobserved while they
continue to breed and destroy the cargo.
Any attempt to poison them by ingestion of toxic substances would involve a risk of poisoning
the cargo in one way or other and, to avoid any misadventure, it remains to persevere with poison
baits and traps around and about the boundaries of the stacks.
In general circumstances this method is laborious and only partially successful, particularly in
a warehouse that is not rodent-proof.
It is true that claims of successful operations have been carried through by experimental
teams, but the circumstances have been rather suitable to the experiment and not those usually
encountered in old dock warehouses.
There are three main factors to consider in controlling these pests:—
(a) To provide mice-proof warehouses.
(b) To prevent infested cargo entering the warehouse.
(c) To stow the cargo in such a manner as to afford inspection and necessary action.
To adopt a system of suitable cargo stowage is not always possible owing to labour difficulties
and warehouse economics, but measures to comply with warehouse construction and admission of
cleaner cargoes have met with some success.
As an example, mice infestations in London Dock have given rise to anxiety for some years and,
despite all efforts made to combat the pests, the results have not been encouraging. The real
cause of the trouble arose from the importation and stowage of millet seed sprays in rather flimsy
containers already infested with mice from the exporting country. Damage to the containers
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