Part 17

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.

It grows well at ordinary room temperature, also in the incubator, and on all the ordinary media. In bouillon it produces a uniform cloudiness in twenty-four hours. A slight scum forms after several days’ growth, which falls to the bottom when shaken. In Dunham’s solution it grows well, but produces no indol in twenty-four hours’ growth.

It does not coagulate milk.

It grows the whole length of the stab in gelatin, forming small whitish colonies in the deeper portions of the tube. It does not grow over the entire surface of the gelatin tube; does not liquefy gelatin.

It grows under anærobic conditions.

It ferments glucose bouillon, but not lactose bouillon. In glucose bouillon it produces 1-CO_{2}, 5-H. It also produces H_{2}S.

From a general biological standpoint it is plain that this bacillus belongs to the para-typhoid group, and is very similar to the bacillus of hog cholera as well as the _Bacillus icteroides_, also _B. enteritidis_, so far as its morphological and cultural characteristics are concerned.

In the following table the fermentations produced by various members of this group upon certain carbohydrates are shown:

─────────────┬────────┬───────────┬────────┬────────┬────────┬───────── Organism. │Lactose.│Saccharose.│Maltose.│Mannete.│Glucose.│Levulose. ─────────────┼────────┼───────────┼────────┼────────┼────────┼───────── B. typhosus │ − │ − │ − │ − │ − │ − B. dysenteriæ│ − │ − │ − │ − │ − │ [AT] Shiga │ │ │ │ │ │ B. dysenteriæ│ − │ − │ − │ − │ − │ [AT] Kruse │ │ │ │ │ │ B. │ │ │ │ │ │ para-typhosus│ − │ − │ + │ + │ + │ + A │ │ │ │ │ │ B. │ │ │ │ │ │ para-typhosus│ − │ − │ + │ + │ + │ + B │ │ │ │ │ │ B. para colon│ − │ − │ + │ + │ + │ + B. acidi │ + │ − │ + │ + │ + │ + lactici │ │ │ │ │ │ B. hog │ − │ − │ + │ + │ + │ + cholera │ │ │ │ │ │ B. typhi │ − │ − │ + │ + │ + │ + murium Danysz│ │ │ │ │ │ B. icteroides│ − │ − │ + │ + │ + │ + B. │ − │ − │ + │ + │ + │ + enteritidis │ │ │ │ │ │ B. coli │ + │ + │ + │ + │ + │ + communis │ │ │ │ │ │ ─────────────┴────────┴───────────┴────────┴────────┴────────┴─────────

Footnote AT:

Or bubble.

EXPERIMENTS UPON RAT VIRUS IN THE HYGIENIC LABORATORY.

In 1901 I made an investigation of this pathogenic microbe (_B. typhi murium_) applied to the destruction of rats under laboratory conditions.[AU] One hundred and fifteen rats were fed with the cultures in various ways during the course of these experiments with the virus. Of these, 46 died—less than half.

Footnote AU:

Rosenau, M. J.: An investigation of a pathogenic microbe (_B. typhi murium_ Danysz) applied to the destruction of rats. Bull. No. 5 of the Hygienic Laboratory, U. S. Mar. Hosp. Serv., Washington, 1901, 11 p.

Most of the rats used were the gray rat (_M. decumanus_ or _norvegicus_) and the tame white rat. A few (8) of the wild black or house rats (_M. rattus_) were used.

The virus is in reality pathogenic for these three kinds of rats when ingested. No special difference was noted in its effects upon the various species.

As the work progressed it soon became evident to me that the result depended largely upon the amount of the culture ingested. By starving rats for a day or two and then giving them all they could be induced to eat and drink of the cultures, a very positive result was obtained. In one instance of 27 rats so fed all died within a week. If the rats are given a small amount the effect is uncertain—only a few die. In one instance I fed 70 rats with 4 agar tubes and only 7 died. Feeding them a second time with very large quantities 9 more died. The survivors were then fed with all they could be induced to eat every day for a week without effect.

It seems plain, therefore, that a large primary dose proves fatal, and a small dose is not only uncertain, but produces an immunity. This is a very important factor, for it is likely that in the wild state rats would often partake of an amount too small to cause death. Such rats may then subsequently eat large amounts of the culture with impunity.

It would seem then that, after all, the virus is not so different from the laying of a chemical poison, depending as it does for its effect upon the amount ingested. A chemical poison, however, does not possess the disadvantage of producing an immunity. Another disadvantage possessed by the virus is the rapid deterioration in virulence which occurs when it is exposed to the action of air and light, or when it becomes dry, as is very apt to happen when laid out for rats in the wild state.

Since these early experiments, tests have been made of various rat viruses in the Hygienic Laboratory, and the results are given in the following pages:

AZOA.

Series 1. Single feeding of azoa in oatmeal. Rats starved twenty-four hours before feeding. Three out of eight animals died in four, five, and seven days, respectively. Micro-organisms resembling the predominant one of azoa could not be isolated from their hearts’ blood. The organs of these dead rats were fed to fresh rats with the result that one of the three died. It must be mentioned that the mortality among our fresh rats was nearly as high as that in the experimental animals from a disease probably due to infection with an animal parasite.

Series 2. Daily feedings with azoa in oatmeal. Five white rats fed with the mixture, a constant supply being kept in the cage. These animals were picked rats freshly obtained from the dealer. One rat died after seven days. It was heavily infested with lice. The azoa organism could not be found in the blood. The rest remained well after twenty-five days.

Series 3. Black tame mice, daily feedings. One of the five died after seven days. The rest remained well after fourteen days.

These experiments indicate that azoa is not pathogenic for white rats and black tame mice to a degree rendering it applicable for vermin extermination on a practical scale, provided that its action is no more pathogenic for the wild than for the tame species.

RATITE.

The manufacturers recommend a single feeding of this substance rather than a continued exhibition of the virus.

Series 1. Five white rats starved twenty-four hours and then fed with a mixture of ratite and oatmeal. Subsequent daily feedings with plain oatmeal. Picked animals fresh from the dealer. One animal died after twelve days; too much putrefied for further examination; had been heavily infested with lice. The remaining rats are well after twenty-five days.

Series 2. Five black tame mice fed as above. Three were found dead after eighteen days and the other two after nineteen days. Further experiments were not made, as putrefaction was too far advanced when they were found. The room in which they were kept had been unusually cold just before their death owing to a sudden and unexpected drop in the external temperature.

Ratite does not appear to be very pathogenic for white rats. All the five mice fed with ratite died in eighteen to nineteen days (much longer than the advertised incubation period of the infection), but their death could be reasonably attributed to unusual cold. This part of the test is therefore invalidated except that the animals lived considerably longer than would be expected from the literature furnished by the manufacturers, which says that the effects of laying the virus will be apparent in eight to ten days.

DANYSZ VIRUS.

Twelve tubes of Danysz virus were sent to the laboratory for examination April 7 by the Independent Chemical Company, agent for Danysz Virus Company (Limited). The label stated “Keep in a cool place and at above temperature; use before May 15, 1909.”

The virus was kept at 15° C. until April 13, when it was turned over to Passed Asst. Surg. W. H. Frost, who made the following tests:

One tube opened. Cultures made on two agar tubes were found to correspond in cultural characteristics with the bacillus of Danysz virus as generally described. The remainder of the tube prepared according to directions in accompanying circular, using stale dry bread 2 ounces and suspension of the culture in normal salt solution.

Series 1. Approximately equal parts, then fed to six white rats in individual cages, they having not been fed for twenty-four hours previously. Rats all ate greater part of infected food.

Five rats of series 1 died within five to seven days and were partly eaten before being removed from the cage. The pathological changes in all cases were chiefly enlargement and congestion of spleen and liver, and in some cases inflammation of small intestine. In each case an organism was obtained, usually in pure culture, from one or more organs, corresponding culturally and morphologically with cultures taken from original tube.

Series 2. April 14: Rats all ate greater part of infected food. Transferred to large cage containing nine other white rats. Nine other white rats exposed to infection by being placed in a large cage with the rats of series 1. Four of the nine rats of this series died in four to seven days after eating infected rats.

Pathological changes and results of cultures from internal organs the same as with series 1. Autopsy and cultures impossible in one case, where body was almost completely devoured.

Series 3. May 5: Three of the six surviving rats (one from series 1, two from series 2) were placed in individual cages, deprived of food for twenty-four hours, then fed each with one-third agar tube cultures of Danysz virus (the same used in the original feeding). All three ate practically all the virus given.

All three of these rats remain alive and well after two months.

Summary.—Series 1. Six rats each fed one-twelfth to one-sixteenth agar culture Danysz virus. Five died within five to seven days.

Series 2. Nine rats exposed to infection by being placed in cage with series 1. Four died within eight to twelve days after death of first rat of series 1.

Series 3. Three of the surviving rats (1 from series 1 and 2 from series 2) fed each with one-third agar tube of original Danysz virus as used in series 1. None died.

TRANSATLANTIC RATIN.

A can of this substance labeled “Transatlantic ratin” was furnished by the American agents representing the Bacteriological Laboratory, Copenhagen, Denmark. The can bore the date January 26, 1909, and was stated to be “effective for six months from date of production.”

On April 13, 1909, this sample was given to Passed Asst. Surg. W. H. Frost for examination, and he obtained the following results:

April 13, 1909: Can of ratin opened with aseptic precautions. Contents mixed with about equal bulk of clean fresh lard.

A portion of this about equal to one tablespoonful fed to each of six white rats previously deprived of food for twenty-four hours. All the rats ate some of the bait at once. Feeding at 2 p. m.

April 14: Five rats very sick, having convulsions; partially paralyzed. One dead.

April 15: Three more rats found dead. Remaining 2 recovering.