numerous and varied as they have been unsuccessful. Traps and poisons
have been the agencies of destruction, but until some highly
communicable epizootic peculiar to rodents shall have been discovered,
absolute eradication of the rat can be considered as nothing less than
impossible.
A recognized authority on plague, Major Morehead, of the Indian
Medical Service, states that “rat destruction is of doubtful value,”
referring, of course, to trapping and poisoning when those measures
are used solely without auxiliary measures. He agrees with Japanese
authorities in their arguments that as rat populations decrease, the
breeding rate among survivors increases, due, obviously, in part at
least, to increased food supply and harboring facilities. Such a
result is assured where rat proofing is not accomplished at the same
time. This latter procedure, by destroying rat harborages and cutting
off food supplies bring about conditions unfavorable to breeding.
The total eradication of rats in a locality is not absolutely
necessary, however, to the eradication of plague. If the rat
population is kept within fairly low limits, rat centers destroyed,
and such rat population as does exist well scattered and not
congested, it is ventured that rat plague will disappear from a
locality. Plague among rats in San Francisco ceased to appear when the
number of rodents was reduced some 50 per cent, but such reduction was
accomplished only after six months of ceaseless endeavor, which
included also the rat proofing of the bakeries, stables, and markets
in the city.
It is a logical supposition that close contact is just as essential
for the propagation of plague among rats as it is for the spread of
certain communicable diseases among human beings, the increase of
cases being in direct proportion to the density of population and
closeness of contact.
RAT PROOFING OF PRIMARY IMPORTANCE.
Without the general enforcement of rat proofing antiplague measures
are bound to be more or less temporary and decidedly unsatisfactory.
This subject is of immense importance to the public, both from a
sanitary and a commercial standpoint, but the latter aspect of the
question is more apt to prove of interest to most communities.
The measures necessary to render buildings rat proof are the same,
however, whether they be instituted for sanitary or for commercial
reasons. Rat proofing will, therefore, be considered entirely from a
sanitary standpoint; but it can be understood that granaries,
bakeries, butcher shops, packing houses, dwellings, and other places,
if rat proofed for sanitary reasons, are just as much protected from
depredation of the rat as though the work had been performed for
commercial reasons alone.
Rat proofing has a twofold objective. It serves as a protection to the
inmates of a building, and excludes rodents from sources of food
supplies and harboring places. While rat proofing should be enforced
as a general measure in all plague-infected localities, it is
imperatively demanded in premises whereon have occurred cases of human
or rodent plague.
Plague-infected localities or places that contain food must be
rendered impervious to rats in order to insure the success of other
preventive measures. Rats can be trapped or poisoned only when other
food supply is excluded. A rat will enter a trap for food or will eat
poisoned preparations not because of their greater attractiveness, but
because of their greater availability. It therefore follows that rat
proofing of food supplies is a prerequisite to success in rat
eradication. The food depots requiring attention in the order of
importance are stables, meat markets, bakeries, restaurants,
groceries, warehouses, and private dwellings.
It is logical to suppose that the most common mode of infection is by
reason of plague rats dying in the walls, roofs, or floorings of human
habitations. As soon as the rat’s body is cold the fleas abandon it
for another rat, some domestic animal, or human being. The risk to
human inmates in such infected houses, therefore, is evident.
That rat proofing is a valuable measure is shown by the reports of the
British Plague Commission where are mentioned the results following
the use of rat-proof “go-downs” and those not so constructed.
Additional evidence is presented by the fact that appalling epidemics
of plague have ravaged India and the China coast, whereas in the
Philippine Islands but few people die of the disease. It would appear
that the comparatively few cases in the Philippine Islands were due to
the fact that most Philippine dwellings are rat proof by reason of
being elevated from the ground and the fact that the walls are thin
and offer no refuge whatever to rats.
RAT PROOFING IS EXPENSIVE.
The almost insuperable obstacle that will usually confront the
sanitary authorities in such work will be either the financial
inability of the unfortunate community or the sordid unwillingness to
make any expenditure that does not promise personal gain.
When the influence of the mosquito in the transmission of yellow fever
was proven, recourse was had to mosquito proofing of both the sick and
the well as a preventive measure. Rat proofing in plague is just as
rational and necessary, but the financial expenditure contemplated
thereby has been of such proportion as to cause the majority of
sanitary authorities in different parts of the world to dismiss the
idea as impossible.
To properly rat proof a city undeniably requires enormous
expenditures, but no antiplague campaign was ever waged without an
immense outlay of both money and labor. If allowed to progress
unchecked, however, plague, either through ravages of the population
or through commercial interference, is ruinous. To fight plague,
therefore, is the only alternative, and a costly campaign should be
anticipated and prepared for in advance. To merely put out traps and
poisons without the preliminary rat proofing required can be
productive of little good and no permanency. Such a plan of campaign
may be attractive because of its relative cheapness, but any city or
country that relies wholly on such measures is practicing false
economy and deferring the day of reckoning.
It becomes evident, therefore, that rat proofing is of the greatest
value as an antiplague measure, and that practical results to be
expected are much greater than with any other method.
As has already been stated, the individual premises on which plague
either among rodents or human beings has occurred demand first and
immediate attention. The work should be extended as rapidly as
possible from the point of infection so as to include the entire block
and neighboring blocks.
While the chief energies should be centered on plague-infected foci,
similar work should be carried on simultaneously throughout the city.
METHODS OF RAT PROOFING.
If plague occurs in the grounds of dwellings the following course
should be pursued: All planked-over areas, including sidewalks, that
might possibly shelter a rat should be removed, leaving either bare
ground or, at the option of the owner, gravel or concrete used, the
gravel being preferable. Small sheds should be elevated, or their
ground floors concreted. Wood sheds should probably be left without
flooring, wood kindling or other contents being piled on elevated
platforms provided for the purpose. Stables on the premises should be
treated as indicated in a subsequent paragraph relating to these
structures.
The garbage depository must be given most careful attention. It should
be a metal receptacle, preferably a galvanized can, water-tight to
prevent seepage which would attract rats, and there should be a
closely fitting lid. A can 2 feet in height without cover will not be
proof against the incursion of rats.
The rat proofing of chicken yards is a difficult task as most chickens
in private families are fed on table scraps, thereby attracting and
supporting a fair quota of rats. The entire inclosure should be
protected by wire fencing 6 feet high and of a mesh not larger than a
half inch. Ordinary poultry netting is inadequate, the mesh being too
large. The edge of the yard should be of concrete construction, the
concrete extending 1 foot upward and 2 feet inward. If, on any
subsequent inspection, rats have been found to have burrowed into the
inclosure, the entire area should be concreted, sand or earth being
allowed as a top dressing.
It would seem sufficient to confine these specifications to a feeding
pen, but in practice this will not suffice, as a mere pretext of such
a place would be built, and the housewife would continue to throw
scraps into the unprotected yard.
The dwelling house itself should receive the most careful attention.
If it is a small frame structure the cheapest and most effective means
of rendering it free from rats is by elevating it, the minimum height
being 1½ feet, measured from the most dependent joist. At the same
time, all underpinning should be freed of rubbish or other material.
It is not sufficient to raise the structure a few inches so as to
permit the entrance of cats and other enemies of the rat. Such height
and exposure must be secured as to deprive all rodents of cover.
If the house is of more substantial structure, and always if it has a
cellar or basement, concrete or some other rat-proof material should
be adopted. If sound foundation walls of stone or brick exist, then
only the addition of a concrete floor is necessary. The stopping up of
rat holes in any substance pervious to rats is at best a poor
expedient.
The grounds must be rendered rat proof by piling all loose materials
at such an elevation as will preclude rat harborage. All rubbish
should be burned or otherwise destroyed. All basement windows should
be properly protected against the ingress of rats, and if the _Mus
rattus_ be present, even second and third story windows should not be
considered too high to afford them entrance.
All loose materials on the premises should be properly piled, even
though they are in a rat-proof cellar. It is not probable that the
_Mus decumanus_ would remain or breed in any place where it could not
burrow; but no encouragement should be offered to any rodent let in by
carelessly left open doors. There have been cases where the black rat
has lived, increased, and overrun a house which was structurally rat
proof, but in which there was allowed easy access through open windows
and doors, and great piles of loose materials and dunnage furnish
harborage.
Stables are of twofold importance because they provide a source of
food supply for rats and furnish harborage. All grain must be kept in
a metal lined box or granary. A small stable is sufficiently rat proof
if it has an elevation of 2 feet with clear underpinning, provided the
floor is rendered impervious to falling grain. Barns of larger extent
are best made rat proof by concrete flooring tight on the ground, and
the area walls should be of concrete 1 foot high or of galvanized iron
of standard thickness. The ingredients of concrete should be specified
as to quality and quantity.
The windows of stables should be screened, especially if black rats be
present. To render a large livery stable rat proof, however, is hardly
practicable, owing to doors being open almost continuously, but rat
proofing even in such buildings will destroy rat harborage and limit
rat invasions to an occasional migratory rodent. With concrete
flooring and protected feed pens it should be an easy task to keep
such a building free from rats.
Finally, manure pens should be rat proof or the manure thrown into the
corner of the rat-proof stable, provided there is frequent cartage.
RAT-PROOFING ORDINANCES SHOULD BE SPECIFIC.
Any law or ordinance providing for rat proofing should specifically
state the minimum thickness of concrete and cement. Concrete 4 inches
deep with one-half inch dressing of cement or 1-inch asphalt answers
very well. Area walls if of concrete should be 6 inches thick, and the
floors should have sufficient slant to allow drainage.
Any expedient as galvanized iron sunk into the ground and made flush
with the flooring will not prove of practical value, as it allows
rat-harboring space to exist beneath the flooring, and sooner or later
rats will gain access thereto by burrowing under the iron gratings or
through the wooden flooring.
Meat markets should have concrete floors with cement or asphalt
dressing, the floors to be close on the ground and surrounded by
properly constructed foundation walls of stone or brick in cement.
Water-tight metal cans should be provided for all scraps, and
especially for the sawdust with its admixture of fine pieces of meat.
Bakeries and restaurant kitchens should be treated in the same way as
meat markets. Packing houses, slaughter pens, warehouses, and food
depots in general should be concreted.
The water front demands the greatest attention. The piers and wharves
should be of concrete or steel construction. The shipping should be
shored off from the dock, and all lines properly rat guarded. When not
in use, gang planks should be lifted. Notwithstanding these
precautions, rats will be imported from time to time, and the only
practical way to prevent their getting ashore will be the systematic
and routine fumigation of ships by the quarantine authorities.
The rat proofing of sewers is open to argument. Of all places in a
city the sewer is certainly the one where rats can die with the least
danger to the human population. For this reason the sewer should be
the last structure in a municipality to be made rat proof. The
movements and migrations of rats should be controlled to the extent of
making corner catch basins their sole means of entrance and exit to
sewers. The small and large iron-pipe mains require no attention in
this respect, but where mains are constructed of brick, and especially
where they are old and in bad repair, they should be repaired, all rat
runs leading from the sewer walls being stopped up and all blind
sewers being closed. By this means there will be prevented the
breeding of rats in these areas.
The rat proofing of catch basins by any method that would not also
block the entrance to the basin seems hardly possible. Properly
trapped basins, however, will be found almost as effective and just as
desirable.
To attain efficient rat proofing requires necessary laws or ordinances
and public sentiment favoring their enforcement. Dead-letter laws that
form no small part of many city statutes attest the fact that
favorable public opinion is almost indispensable to their enforcement.
However, well-drafted laws, clear and specific in requirement and
impartially and consistently enforced, inevitably lessen and destroy
opposition.
In the foregoing are contained general principles necessary to rat
proofing in the case of an outbreak of plague. Due allowance will have
to be made, however, for local conditions, and special considerations
as they arise, as no unvarying plan will be practical of application
in every instance.
CHOICE OF ARCHITECTURE AND BUILDING MATERIALS.
Cities and countries have from time to time wholly revolutionized
their type of buildings and constructive materials for either
commercial or æsthetic reasons. It is suggested that ports having
trade relations with countries where plague prevails should bear in
mind the advisability of taking advantage of this fact and revise
their building laws with the view to rendering all new buildings rat
proof.
Concrete has been advocated for purposes of rat proofing because of
its durability and relative cheapness. Concrete flooring or side walls
can be made more durable, however, by embedding therein steel netting
of 1 or 2 inch mesh. By this method the cost of construction will
probably be reduced, as a thinner layer of concrete would be
sufficient, and the metal would be protected, thereby adding
stability. Such construction at the same time would be doubly rat
proof.
THE INEFFICIENCY OF BACTERIAL VIRUSES IN THE EXTERMINATION OF RATS.
By M. J. ROSENAU,
_Surgeon, U. S. Public Health and Marine-Hospital Service, Washington,
D. C., now Professor of Preventive Medicine, Harvard University
Medical School_.
INTRODUCTION.
Rats are notoriously resistant to bacterial infections. About the only
exception is the plague bacillus. Plague among rats occurs both in
endemic and epidemic form. When we recall that this virulent disease,
which spreads readily from rat to rat, neither eradicates these
rodents nor, as a rule, makes any appreciable inroads on the number of
rats, we can hardly expect that an artificially induced bacterial
disease would be successful. No other known bacterial infection has
such a virulence for rats as the plague bacillus has maintained.
Epizootics of bacterial nature, therefore, can not be classed among
the natural enemies of the rat. Despite this fact persistent efforts
have been made to create artificial epizootics to combat these
dangerous and destructive rodents, but with little success.
The bacterial viruses that have been used for the destruction of rats
and mice belong to the colon-typhoid group[AL] and excite enteritis of
different characters and a septicemia.
Footnote AL:
More particularly the hog-cholera group, which includes the
para-typhoid organisms.
In 1889 Loeffler discovered and described a bacillus which he called
the bacillus of mouse typhoid (_B. typhi murium_). He isolated this
organism from a spontaneous epidemic which occurred among white mice
in the Hygienic Institute at Griefswald.[AM] He determined that this
bacillus not only caused the death of his mice in the laboratory, but
also that the infection was taken into the system of the mouse by
ingestion. He found the cultures to be especially virulent for field
mice (_Arvicola arvalis_). Loeffler gives a complete description of
the bacillus which, from a biologic standpoint, is the parent stock of
almost all subsequent work along this line. The bacillus used by
Danysz and other workers is either identical with or very closely
allied to Loeffler’s bacillus of mouse typhoid.
Footnote AM:
Loeffler, F.: Ueber Epidemieen unter den im hygienischen Institute
zu Griefswald gehalten Mäusen und über die Bekämpfung der
Feldmausplage. Centblt. f. Bakt., Orig., vol. 11, 1892, pp. 129–141.
In 1892 Loeffler[AN] personally undertook a campaign against the field
mice in Thessaly and reported satisfactory results. The depredations
carried on by the mice were checked within eight to nine days.
Footnote AN:
Loeffler, F.: Die Feldmausplage in Thessalien und ihre erfolgreiche
Bekämpfung mittels des _Bacillus typhi murium_. Centblt. f. Bakt.,
Orig., vol. 12, 1892, p. 1.
The English commission[AO] threw doubt upon the Thessaly operations
and concluded that the bacillus as a means of destruction of mice has
no value. They found the method to be expensive, affecting only one
species of mice; further, that the epidemic-like spread of the disease
in the fields was not sufficiently investigated, and that the infected
material retains its virulence only for eight days and does not permit
of being used in continued bad weather.
Footnote AO:
Wien. landw. Zeit. 1894, p. 783.
Loeffler’s optimistic report, however, stimulated many similar trials
with varying success. Practically all these efforts were directed
against mice, until 1900, when Danysz took up the subject from the
standpoint of the rat and plague.
Danysz found that Loeffler’s _Bacillus typhi murium_ proved to be
pathogenic for ordinary mice (_Mus musculus_) and for field or harvest
mice (_Mus arvicolis_), but not for rats.
The culture isolated by Laser[AP] in 1892 was pathogenic for field
mice (_Mus agrarius_); this organism killed 70 of the 76 mice which
were used as experiment animals at the Hygienic Institute at
Königsberg.
Footnote AP:
Laser, Hugo: Ein neuer für Versuchsthiere pathogener Bacillus aus
der Gruppe der Frettschen-Schweinseuche. Centblt. f. Bakt., Orig.,
vol. 11, 1892, p. 184.
Mereshkowsky[AQ] in June, 1893, isolated an organism belonging to this
group from a ground squirrel known as the Zisel (_Spermophilus
musicus_). This culture killed domestic and field mice when placed in
their food, but was not pathogenic for rats.
Footnote AQ:
Mereshkowsky, S. S.: Ein aus Zieselmäusen ausgeschiedener und zur
Vertilgung von Feld-resp. Hausmäusen geeigneter Bacillus. Centblt.
f. Bakt., Orig., vol. 17, 1895, p. 742.
The Japanese investigator Issatchenko,[AR] in 1898, briefly described
a bacillus obtained by him from gray [white?] rats, which proved
virulent for rats and mice.
Footnote AR:
Issatchenko, B.: Untersuchungen mit dem für Ratten pathogenen
Bacillus. Centblt. f. Bakt., Orig., vol. 31, 1902, p. 26.
Each of these various bacilli is of such variable virulence that it
could not be used for the destruction of all species of these rodents.
Danysz[AS] therefore conceived the notion that it would be of great
interest first to extend the field of action of one of these organisms
by increasing its virulence so that it would attack other species of
rodents, and then maintain this increased virulence at its highest
point.
Footnote AS:
Danysz, J.: Un microbe pathogène pour les rats (_Mus decumanus_ et
_Mus rattus_) et son application à la destruction de ces animaux.
Ann. Inst. Pasteur, vol. 14, 1900, p. 193.
In 1900 Danysz isolated a bacillus from a spontaneous epidemic among
harvest mice. This organism was a cocco-bacillus presenting the
general characteristics of the colon-typhoid group and resembling the
bacillus of Loeffler—_B. typhi murium_. From the first this bacillus
showed a slight pathogenicity for gray rats (_M. decumanus_). Out of
10 animals fed with a culture of this microbe 2 or 3 would die;
several others would sicken and recover; others appeared completely
refractory. The fact that a certain number of the rats fed with these
cultures always succumbed led to the hope that it would be possible to
increase the virulence of this particular microbe by the generally
accepted methods—that is to say, by a certain number of passages from
rat to rat.
Danysz first tried to increase the virulence of the organism by this
means, but he found that successive passages from rat to rat, whether
by feeding or by subcutaneous injection, ended by enfeebling rather
than increasing the virulence of the microbe. He found that it was
rarely possible to go beyond 10 to 12 passages. Sometimes the series
was stopped at the fifth passage, or even sooner, by the survival of
all the animals undergoing experiment. The result was exactly the same
if, instead of alternating each passage through the animal by a
culture in bouillon or agar, the bodies of animals dead of a preceding
passage were fed to others.
It was therefore plain that in the evolution of an epidemic caused by
this microbe it was necessary to take account of the indisputable
diminution of the virulence of the microbe, as well as the natural
resistance of the survivors.
Passage of cultures in collodion sacs inclosed in the peritoneal
cavities of rats was tried, both in interrupted series and by
alternating each sac culture with a culture in bouillon or on agar,
but the end was invariably a notable diminution of virulence when
administered by the digestive tract.
Finally, after long and painstaking procedures, Danysz obtained a very
virulent culture that, contained in flasks and kept from the influence
of light and air, preserved its virulence for several months. Planted
on agar it preserved its virulence without appreciable diminution for
two months under laboratory conditions. In bouillon, in flasks, or in
tubes stoppered with cotton it altered very rapidly.
DESCRIPTION OF THE ORGANISM.
A culture of Danysz’s virus obtained from the Pasteur Institute had
the following characteristics:
The organism is a cocco-bacillus showing distinct motility. Stains
well by the ordinary stains, but does not stain by Gram’s method.