ROCKY MOUNTAIN SPOTTED FEVER INVESTIGATION AND ERADICATION.

Field investigations.-The field investigations of the distribution and spread of Rocky Mountain spotted fever throughout the 10 Rocky Mountain and Pacific coast States in which the disease has been discovered, were continued during 1916 in cooperation with the health agencies of the different States. Two officers, Surg. L. D. Fricks, in charge, and Asst. Surg. Liston Paine have been detailed to this duty.

The most important results of the investigations reported during 1915 were the abrupt and extensive spread of the disease into southeastern Montana, the invasion of a heretofore uninfected State, South Dakota, and a further smaller extension, investigated at the request of the Commissioner of Indian Affairs, across the Deschuttes River, on the Warm Springs Indian Reservation in northern Oregon.

In contrast to this extension of spotted fever of the previous year the most important observation bearing upon the prevalence of the disease made during the present season has been the marked reduction of cases reported from certain territory, for many years recognized as foci of infection, along the Snake River Valley in Idaho. Heretofore this valley has been considered the center of Rocky Mountain spotted fever infection. The reduction of case incidence from certain localities in this region has been progressive and so pronounced that it can hardly be considered accidental, and it has occurred without any special effort having been made to control the disease, other than the changes and alterations which have followed the rapid development of the entire section. During the season of 1915 an officer of the service was detailed to make an investigation of the influence of live-stock movement, sheep grazing, and other factors which might have a bearing on the extension or the restriction of the disease in this territory.

Quarantine regulations. The accumulated data bearing upon the spread of Rocky Mountain spotted fever indicate that the disease is disseminated by means of infected adult ticks attached to large animal hosts during the spring and early summer months. In the migrations and movements of domestic animals the attached ticks are frequently and necessarily carried many miles by their hosts, and if the ticks are infected, may originate foci of infection in other localities. The extension and dissemination of the disease are in part accounted for in this manner. In order to prevent this spread, particularly by domestic animals, a regulation was promulgated and incorporated as a part of the Interstate Quarantine Regulations, as approved by the Secretary of the Treasury January 15, 1916, prohibiting the interstate shipment of live stock from infected territory during the season from March 15 to June 15 unless previously freed from all ticks. The regulation provides that common carriers shall not accept for interstate shipment, and no person shall offer for interstate shipment, any cattle, horses, sheep, goats, elk, deer, or hogs originating in a locality where Rocky Mountain spotted fever is known to exist, unless said shipment is accompanied by a certificate from a Federal, State, or local health authority, or an inspector of the Bureau of Animal Industry of the United States Department of Agriculture, or a State veterinarian or his deputy, stating that the

said animals are free from all attached wood ticks, or have been freed thereof by hand picking, spraying, or dipping in a disinfectant solution of sufficient strength and for a sufficient time to kill all ticks attached to said animals, such hand picking, spraying, or dipping to be accomplished immediately prior to leaving infected territory. It is expected that this regulation will in large part prevent the dissemination of ticks conveyed through the ordinary transportation channels and will ultimately have considerable influence in preventing the further extension of the disease.

Eradication.-In connection with the field investigations of Rocky Mountain spotted fever efforts toward the eradication of the disease from the Bitter Root Valley, Mont., were continued during the year, the methods employed being as follows: (1) Education of the people concerned as to the mode of transmission of the disease, the consequent danger from tick bites, and the precautions which should be taken for their prevention. (2) Efforts to secure from the State authorities the enactment of proper laws and regulations restricting the grazing of horses and cattle on the west side of the Bitter Root Valley. This has been urged for three years, or since it was determined that the dipping of these animals was inadequate for proper tick destruction. Certain regulations have been passed, but a stronger law is required. (3) Tick destruction: The methods employed in tick destruction during the present year have been: (a) Dipping and hand picking of domestic animals. (b) Eradication of small wild animals. (c) Sheep grazing.

The practical difficulties in the way of eradicating Rocky Mountain spotted fever from the Bitter Root Valley by the dipping of domestic animals alone have been previously reported. These are, the location and the brief period of attachment on their hosts of the adult tick, Dermacentor andersoni; the fact that immature forms of the tick do not attach to animals which are dipped and the unfavorable weather conditions existing in the valley during the early spring months, at which season the ticks are most voracious. The present season emphasized the correctness of these observations. Because of prolonged cold weather the regular dipping of live stock was impossible, and it was necessary to depend to a great extent on hand picking the ticks from domestic animals at short intervals. Where animals are numerous this procedure is both laborious and unsatisfactory, and for this reason it has been strongly recommended to State officials that the grazing of horses and cattle on the tickinfested territory of the west side of the valley be prohibited, exception being made of a limited number of milk cattle and work stock commensurate to the needs of each resident family.

The following comprises a list of the live stock in the three tick districts, covering an area of approximately 60 square miles, together with the treatment employed in each instance for the eradication of ticks:

Victor district: Cattle, range, 245; cattle, pasture, 216; total, 461. Horses, range, 34; horses, pasture, 30; total, 64. Sheep, four small bands; total, 260.

Treatment: Cattle dipped, 541; hand picked, 341. Horses dipped, 116; hand picked, 26. All sheep were examined at intervals for live wood ticks, but none were found.

Hamilton district: Cattle, range, 83; total, 83. Horses, range, 38; horses, pasture, 14; total, 52.. Goats, pasture, 130; total, 130. Hogs, pasture, 30; total, 30. Sheep, three small bands; total, 100.

Treatment: Cattle dipped, 103; hand picked, 112. Horses dipped, 88; hand picked, 4. Goats dipped, 130. Hogs dipped, 60. The sheep were examined for wood ticks and a small percentage of live ticks were found on one band, recently introduced on to heavily infested territory.

Gold Creek district: Cattle, range, 288; total, 288. 59; total, 59.

Treatment: Cattle dipped, 393; hand picked, 125.

159.

Horses, range,

Horses dipped,

Destruction of small rodent animals: Only the adult spotted fever ticks are directly affected by the dipping process, as they alone attach to the larger domestic animals. In order to reach the immature forms, larvæ and nymphs, the destruction of their small rodent hosts has been urged by the Public Health Service since the beginning of the spotted-fever campaign in 1911. It appears that between these two methods of tick destruction the latter, for several practical reasons, will prove more effective in the Bitter Root Valley.

The methods employed in the destruction of small rodents, principally Citellus colombianus, during the present season have been (1) shooting, (2) trapping, (3) poisoning with strychnine. The area over which the rodent animals are being destroyed includes the dipping districts and adjacent territory, approximating 100 square miles in extent. The use of the squirrel destroyer or carbon-bisulphide pump has been abandoned in the valley, first because of the expense in time and labor required for its operation, and also because of its inefficiency probably due to the loose, sandy soil encountered in this region.

Shooting: Sixty thousand .22-caliber rifle cartridges have been utilized in destroying small animals during the present season; of these 35,000 were distributed to landowners and other responsible but unemployed hunters, while the remainder were used by a small force of regular hunters employed in shooting and trapping outside of the cultivated lands. The results obtained from the distribution of smallcaliber ammunition show it to have been an extremely economical expenditure.

Trapping: There is less sport to the farmer boy in trapping than in shooting ground squirrels, but 25 No. 1 steel traps will require only a little time and attention while going about the ordinary farm work, and will collect a continuous toll from the squirrels throughout the entire season. The farmers on the west side of the valley have been encouraged to use this method of squirrel destruction.

Poisoning: Of the different measures employed for the destruction of small animals in the tick-infested territory of the Bitter Root Valley properly prepared grain, poisoned with strychnine, has given the best results. It should be understood, however, that complete extermination of the small animals has not been attempted, and probably is not necessary for spotted-fever control. Twenty bushels of hulled oats, or groats, have been distributed during the present season. This was prepared by freshly coating the grain with a mixture of raw starch, strychnine alkaloid, salt, and saccharine. Unhulled

grain is not suitable for the destruction of Citellus colombianus, because this species of rodent does not pouch its food, but as a rule immediately hulls and eats it.

The best time for poisoning ground squirrels is very early in the spring, as soon as they are out and before the grass is up. This period is very brief, for with the appearance of the green grass the squirrels can not be poisoned profitably. Later on, when the young rodents first appear and the grass and weeds begin to dry, this method of destruction can again be used successfully.

Sheep grazing: It has previously been pointed out that sheep can be used both as tick removers in a purely vehicular capacity, and also as tick destroyers through their deleterious action, directly and indirectly exercised upon the ticks themselves. In order that the full effect of the former method may be secured it is necessary that a large number of sheep be grazed over the same territory in the same direction for successive years. Tick eradication effected in this way by sheep movement has been observed on the east side of the Bitter Root Valley. Further observations made in Elmore County, Idaho, during the present season seem to substantiate the validity of those previously reported from the Bitter Root Valley. In Elmore County it was found that over a strip of country 40 miles wide and 150 miles long, just north of the Snake River, where more than 100,000 sheep have moved north each spring from their winter quarters on the river, no case of spotted fever has occurred during the past 17 years. North of this territory, where the sheep are sheared and begin to range in all directions, the average incidence of spotted fever cases is from 75 to 100 yearly. The only distinctive differences detected between the spotted fever free territory and that adjoining, from which cases have been reported annually, were those of shearing and sheep movement.

On the west side of the Bitter Root Valley the grazing of outside sheep has been tried, but for economic reasons the slower method of encouraging the west-side farmers, so far as possible, to replace their horses and cattle with small bands of sheep has been found the sounder policy. Many small bands have been started within the past two years, and the results thus far obtained in both tick destruction and in money returns have been good.

Incidence of Rocky Mountain spotted fever: The following table gives the number of cases and deaths of Rocky Mountain spotted fever during 1915:

The spotted-fever season for 1916 has not yet been completed, but judging from the reports in hand there appears to have been a noticeable reduction in cases for the present year.

Laboratory investigations and publications: The following laboratory investigations were made at the field laboratory at Victor, Mont., and in the Hygienic Laboratory in connection with Rocky Mountain spotted-fever work.

The following table shows the number of rodents received and examined for plague during the year:

The effects of strychnine sulphate upon the California valley quail were studied and the findings published in the Public Health Reports for December 10, 1915. This alkaloid has had an extensive use in the eradication of ground squirrels, and at various times the effect which grain poisoned by this substance might have upon valley quail has been questioned. Accordingly experiments were conducted to determine the minimum lethal dose of strychnine for quail and the amount producing toxic symptoms under natural conditions. It was found that quail are relatively insusceptible to strychnine and that under natural feeding conditions there is no mortality from this cause.

A comparative study of the efficacy of brilliant green agar, as advised by Krumwiede, Pratt, and McWilliams Journal Infectious Diseases, vol. 15, No. 1), and Endo's media for the isolation of B. typhosus from stools was made. In a number of instances the bril liant green proved superior to the Endo media.

Experiments were also carried on to determine the length of time B. typhosus remained viable when planted with feces from typhoid patients in Krumwiede's brilliant green media containing 1 per cent agar. The organism was readily isolated after 4× hours The object of this experiment was to devise a method by which cultures could be made from suspected typhoid patients and carriers at a distance from the laboratory. This meda, containing 1 per cent agar, is of semisolid consistency and can be placed in a small shell vial. These vials are then mailed in double containers, such as 1s used by the United States Publie Health Service, to the place where the cultures are to be made. There they are inoculated with from 1 to 2 grams of feces and returned by mail to the laboratory.

Certain experiments with pediculus vestimenti, received from Senior Surg C. C. Pierce, on special duty at the Mexican border, were performed during the year. A number of hee collested from typhus patients and normal persons were micerated and extend it to gunea | 25, while sections were made and examined of others The results of the guinea pig moculations were negative, and no detit,te conclusions could be made from the sextions exam ned.

Experiments were made to determine a numerical relation be tween the quantity of bica hang powder necessary to sterilize a so'i tion of orgatae matter and its oxygeni consulted valie. A solution of peptome was used, and it was found that the amount of chlorine regres varies according to the oxygen consumed value of the orgat matter.

Research work which remains uncompleted relates to the possible use of glycerine for delayed examat on of water, with especial