Part 18

_Passed Assistant Surgeon, United States Public Health and Marine-Hospital Service_.

To appreciate the great importance and absolute necessity of rat proofing as an antiplague measure, it is only necessary to consider the results that have followed its use as compared with other measures that have been relied on in recent years in combating this disease. These were, briefly, disinfection, evacuation, or destruction of buildings in infected areas, preventive inoculations, and destruction of rats either by poison or by trapping.

Plague was formerly believed to be communicable by aerial transmission and through the agency of fomites. Sanitarians have, therefore, put great faith in disinfection procedures, but the results have never been satisfactory, and it is only necessary to consider the method of transmission of plague to perceive the fatuity of bactericidal measures. Measures intended for the destruction of fleas are also of relatively small value. It is well worth while to destroy all fleas possible, but if those infesting the rat population escape, the efforts will have had little effect in preventing the spread of plague. It is only those fleas that infest rats and their habitats that are of importance in relation to the transmission of disease, and it is only by rat proofing that their destruction in rat burrows and runs can be accomplished.

Rat-proofing of individual buildings is of no recent date, but new emphasis was laid on rat-proofing as a separate and distinct antiplague measure by Passed Assistant Surgeon Mark J. White in an article written in the fall of 1907.[AK]

Footnote AK:

Journal American Medical Association October 19, 1907.

Disinfecting procedures must be regarded as of minor importance in plague prevention, except in pneumonic cases where its use is imperative. It is not intended to depreciate the value of disinfection, but rather to estimate its exact value as an antipest measure. Time and money should not be wasted nor a feeling of false security engendered by using an ineffective measure when others, as rat proofing, of much greater value are at hand. As an example of this might be cited an outbreak of plague in one of the refugee camps during the recent epidemic of the disease in San Francisco. This camp covered several blocks and housed between two and three thousand people. The camp grounds throughout and the houses were disinfected and disinfected well. At the same time, every effort was made to poison and trap rats. Notwithstanding these precautions, cases continued to occur, but when the houses were elevated there followed an immediate cessation of plague cases in the camp.

Another case of infected premises proved equally refractory to disinfection. The place was a large two-story frame dwelling located in the center of the city and in a good neighborhood. The yard was planked, as was also a part of the basement, the latter being used as a storeroom. On November 1 there occurred in this dwelling a fatal case of human plague, and plague rats were found at the same time. The place was disinfected in the usual manner and thorough measures were taken to trap and poison rats with apparent subsidence of infection, but on January 22 a plague rat was trapped, followed by another on January 31, after which the occupant of the building vacated it in great alarm. All planking was then removed from the yard and basement and concrete substituted by the owner, the place thereby being rendered thoroughly rat proof, and no plague rats were subsequently taken from that dwelling or in its immediate neighborhood.

In 1902 the plague outbreak was almost wholly confined to the Chinese colony. Chinatown was made the battle ground, and among other measures rat proofing was enforced, with the result that after the fire it was by far the most sanitary district in the city of San Francisco from a structural point of view. The buildings when erected were made rat proof from cellar to garret. The Chinese had had their lesson, and to their credit it must be stated that they responded with a greater show of intelligence than did some of the residents in surrounding districts.

Adjacent to the Chinese colony is the Latin quarter. In the rebuilding of this section, no attention was paid to rat proofing; consequently many of the buildings consisted of small shacks set on the ground or abutting some insanitary stable, and were therefore ideal rat harbors. On account of these conditions the natural results followed. Chinatown, on the other hand, which had contributed in the previous epidemic almost the entire number of plague cases during the epidemic of 1907, did not furnish more than two or three of the plague cases reported; that is, less than 2 per cent of the total cases reported, while the Italian colony, including North Beach district, probably furnished over 50 per cent of the total.

The evacuation or burning of buildings can hardly be called a successful measure any more than a retreat can be styled a victory; moreover, there can be no question from an economic standpoint as to the value of rat proofing over abandonment except in a few isolated cases of dilapidated insanitary property.

Schemes and plans for demurization, total or partial, have been as 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.