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

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City of London 1964

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

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To a great extent the International Sanitary Regulations assist in the prevention of rodents
being imported by sea, for all foreign-going ships are obliged to have a Deratting or Deratting
Exemption Certificate according to the conditions on board at the time of irspection by the Port
Health Authority issuing the Certificate. The certificate must be on the prescribed form and is
valid for six months. A thorough inspection must be made of all compartments of the ship when
empty to provide the comprehensive, information to be recorded on the Certificate. Similar action
is taken in respect of coasting ships, an appropiate certificate is issued and remains valid for
four months.
Apart from these requirements all ships are inspected on arrival at the terminal berth for
evidence of rodents and the procuring of specimens for bacteriological examination, particularly
from those ships arriving from ports that are likely to be ur are infected with plague. It is customary
to attend all ships in order of priority as soon as practicable after arrival at the berth and,
if possible, before any disturbance aboard so as to gain the advantage of more conclusive rodent indications
The incidence of rodents being imported into the Docks by land transport has gradually
diminished and this can be attributed partly to the more hygienic construction of installations and
routine attention given to them by health authorities. However, it has been noted that transportation
of agricultural produce tends to attract mice, which are more elusive than rats and create
circumstances which call for specific modes of control. Cargoes of seeds from the Continent have
been particularly vulnerable to mice infestations, while grains, animal feed and organic material
are more attractive to rats. As with the land transports, so with the water-borne traffic it has been
noted that where the standard of sanitation has been raised, the incidence of infestations has
been proportionately reduced, and the transport enterprises have been encouraged accordingly.
The range of chemical rodenticides used during the year included, sulphur dioxide, hydrogen
cyanide, methyl bromide, blood anti-coagulant, sodium-fluoroacetate and sodium-fluoroacetimide.
Not one of these alone is a panacea for all circumstances and conditions. It has been customary
to use methyl bromide or sulphur dioxide on lighters, sodium-fluoroacetate and sodium-fluoroacetimide
aboard ships and the anti-coagulants in shore premises as a general principle. Hydrogen
cyanide has slowly lost popularity as a fumigant on vessels in favour of methyl bromide, particularly
when the compartments have contained infested cargo, since the latter has more penetrating
qualities and acts as an insecticide as well as rodenticide. Because of relative operational
simplicity, sulphur dioxide has found popularity with lighters in need of deratting. The pungent
nature of the gas reduces risks of fatality among the semi-skilled labour force employed, and
it is quite effective as a rodenticide when properly applied.

The overall results for the year are quite satisfactory and the rodents actually recovered inc lude:-

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This represents a numerical drop compared with last year, when 3,131 rats and 2,601 mice were
destroyed, although there has been no relaxation of effort. The reduction may well be due to the
consistent drive to eliminate rodent harbourages ashore and afloat.
The number of dead rodents actually recovered is but one facet of the work. When the fecundity
of these pests is considered, the full effect of continuous control must include the arrest of
the enormous breeding potential. The decline of infestation aboard sea-going ships was almost
dramatic, while operations on the harbour lighters proved to be of immense value in preventing the
spread of infestations around the Port, In providing a reliable check on the health of the rats in
the Port and,of course, in reducing the number resident to breed and cause economic losses to
food and property. Of the 64 rats submitted for bacteriological examination to the Public Health
Laboratory Service, none were found to be affected with P.pestis.
Continuous Control of Rats on Sea-going Ships.
In recent years, some ship owners, in an endeavour to reduce the rat population aboard their
vessels, have had them fitted with permanent boxes, containing warfarin, a blood anti-coagulant
bait. As these baits must remain rat attractive for fairly long periods a fungicide is added to the
prepared baits to prevent deterioration.

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