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All rats for examination for plague, either by post mortem and subsequently, if necessary, by
bacteriological examination, are promptly sent to the Central Public Health Laboratory at
Colindale. The bodies are placed in polythene bags which in turn are placed inside metal boxes,
sealed and labelled so that there is no risk of the escape of any rat fleas during their transit to
the Laboratory. The boxes are, of course, delivered by hand.
The rat population of the Port is now so small and is under such strict control that it can be
said to be almost certain that the arrival of a plague infected rat, even should it manage to
get ashore, would be highly unlikely to have any serious significance. In other words, an
epizootic could not be introduced into the Port for the simple reason that there are insufficient
rats to enable the spread of infection. Nevertheless, eighty-nine 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 31bs. per 1,000 cubic feet of space for a period
not less than six hours. This method is seldom used in the Port of London.
(b) The generation of hydrocyanic acid gas by various methods. For the destruction of rats
a minimum concentration of HCN at the rate of 2ozs. per 1,000 cubic feet of space is
required with a minimum of two hours exposure.
(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. A
substantial 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 baithas yet to be found, particularly in granaries, with which to mix the poison
so that rats will take is 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.
(e) Methyl Bromide. This is a very effective and lethal fumigant which has been used in
this Port as an insecticide, particularly in the dry fruit industry. It has considerable
penetrating powers and is not difficult to disperse after an operation. It is also possible
to use this gas as a rodenticide and where there is an infestation of rodents and insects
the combined problem can be solved with one operation.
The following are the names of the firms approved for carrying out the deratting of ships:—
London Fumigation Co. Ltd. Rentokil Laboratories Ltd.
The P. & 0. Orient Line Contra-Pest Service Ltd.
RODENT CONTROL ON LIGHTERS
Rat-proofing, which in essence means the elimination of harbourages entirely or at least
denying access by rats to such spaces that must remain, was continuously encouraged and
an increasing percentage of craft inspected showed no indications of rats aboard. Harbourages
usually consist of obscure spaces behind wooden linings and lockers into which the rats find
or gnaw access and where they can breed with reasonable security. Having been denied access
to these spaces, the rats resort to the bilges unless the drain holes at the bulkheads are
restricted by a grill or perforated plate. Not all the lighters have been rat-proofed yet, but those
that have not been so treated, mostly units of small fleets, are gradually being absorbed into larger
businesses by which the principles of rat-proofing have already been accepted and put into
practice. Naturally, the outstanding benefits have accrued to those lighters normally trading with
rat attractive cargoes.
During the year, experiments to determine the feasibility of installing permanent poison
baiting measures with anti-coagulant substances were not successful and, apart from poisonbaiting
on a few specific occasions, rodents were exterminated by fumigation with sulphur
dioxide or methyl bromide. Where harbourages can be exposed, sulphur dioxide is a simple and
effective rodenticide, otherwise the extra penetrating and lethal properties of methyl bromide
are preferred. Incidentally, methyl bromide at high concentrations is becoming increasingly
popular for disinsecting cargoes in lighters since any stray rodents are killed simultaneously.
Nearly nine hundred such fumigations were carried out during the year and, as a result of close
collaboration with the Industry, all facts and figures were submitted to the Port Health Authority
for their information.
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