The life of the cattle tick is thus spent largely on cattle, and although the young, or larvae may live for a long time on the ground in the summer season, they can not mature except as parasites on cattle and horses. We have purposely omitted various details of the life history, including that of the male, as they are not necessary to an understanding of our present subject--Texas fever. How this is transmitted we will proceed to consider.
Before the enforcement of the Federal quarantine southern cattle sent north during the spring and summer months carried on their bodies large numbers of the cattle ticks, which, when matured, would drop off and lay their eggs in the northern pastures. After hatching, the young ticks would soon get upon any northern cattle which happened to be on the pasture. So soon as they attached themselves to the skin they inoculated the cattle, and Texas fever would break out a week or more thereafter. For many years there had been a growing suspicion that the cattle tick was in some way concerned in the spread of Texas fever, and the facts which supported this supposition finally became so numerous and convincing that a series of experiments was inaugurated by the Bureau of Animal Industry which served to show that the tick is abundantly able to carry the disease to a herd of healthy cattle, and, in fact, is probably the only agent concerned in the transmission of the disease from southern cattle to susceptible northern animals.
_Injurious effects of cattle ticks._--Unfortunately many cattle owners who have always been accustomed to see both ticks and ticky cattle on their farms are not inclined to attach much importance to these parasites, and, as a rule, through lack of appreciation of their damaging effects, placidly consider them as of little consequence. That ticks may be detrimental to their hosts in several ways has probably not suggested itself to these stockmen, who are most vitally affected, and it therefore seems necessary to emphasize the fact that, in addition to their relation to Texas fever, they may also be injurious to cattle as external parasites. While the power of transmitting Texas fever is undoubtedly the most dangerous property possessed by the cattle tick and is the princ.i.p.al cause for adopting stringent measures looking to its complete eradication, nevertheless there still remain other good reasons for the accomplishment of this achievement.
These secondary objections to the presence of ticks on cattle consists in the physical harm they do to the host aside from the production of the specific disease of Texas fever. True, a few parasites may remain on cattle indefinitely without causing any noticeable effect, but it is not uncommon to notice bovine animals on pastures with their hides heavily infested with these pests. In such cases it can readily be seen that the continuous sucking of blood causes more or less impoverishment of the circulation. The animal must therefore be fed more in order to meet the demands of the parasites in addition to the ordinary needs of the host. If the ticks are removed from the body, the bites inflicted are often distinguished by small, inflamed or reddened areas somewhat swollen, with perforations of the skin which may allow the entrance of various kinds of disease germs, and showing that more or less irritation of the hide is produced by these parasites. This condition, together with the loss of blood, frequently induces an irritable state and evidence of uneasiness commonly known as "tick worry," which results in the loss of energy and other derangements of the animal"s health. It may in some cases, especially in hot weather, become so p.r.o.nounced that the animal will lose flesh in spite of good pasturing, thereby reducing the vitality and rendering it more susceptible to the inroads of disease. Moreover, if the infestation of ticks is not controlled, the cattle may be so reduced in condition that growth is r.e.t.a.r.ded, and, in the case of young animals, they may never become fully developed, but remain thin, weak, and stunted--a condition that has been termed "tick poverty"--and easily succ.u.mb to other diseases as a result of lowered vitality. In milch cows this debilitating influence of the numerous ticks is shown in a greatly reduced milk supply. This should not appear strange when it is considered that some animals harbor several thousand of the bloodsucking parasites. If these parasites are crushed, it will be found that their intestines are completely filled with a dark, thick ma.s.s of blood abstracted from the animal host and containing nutriment that should go to the formation of milk, flesh, and the laying on of fat. In some rare cases the large number of bites on a limited area of skin may be followed by infection with pus-producing organisms, giving rise to small abscesses which may terminate in ulcers. The discharge from these sores, or in some cases the mere oozing of blood serum through the incision made by the mouth parts of the ticks, keeps the hair moist and matted together, and the laying and hatching of fly eggs in these areas give rise to infestation with destructive maggots, causing ulcers and other complications that require medical treatment. These statements regarding the secondary injurious effects of cattle ticks also apply to those ticks which have been previously spoken of as harmless so far as Texas fever is concerned, and, in fact, to all external parasites. Therefore, it is just as important to eradicate the cattle ticks for reasons other than those a.s.sociated with Texas fever as it is to exterminate lice, fleas, and other vermin.
Furthermore, cattle ticks, aside from the losses sustained by their purely parasitic effects, are the greatest menace to the profitable raising and feeding of cattle in the South, because they are an obstacle to cattle traffic between the infected and noninfected districts.
_Loss occasioned by cattle ticks._--The economic aspect of the tick problem is unquestionably of the greatest practical interest, since the fundamental importance of all the other questions which surround it depends upon the actual money value involved. A careful and conservative estimate made in 1916 placed the annual loss caused by the ticks in the United States at $40,000,000, and indicated that the ticks also lowered the a.s.sets of the South by an additional $33,000,000. The princ.i.p.al items in these losses are set forth below.
It is well known that those animals coming from an infected district and sold in the "southern pens" of northern stockyards bring about one-half a cent less per pound than the quoted market price. The handicap that is placed on the southern cattle raiser as a result of this decrease in value of his stock will average at this figure $3 per head, allowing an individual weight of 600 pounds for all cla.s.ses of animals. This decreased value reacts and fixes the valuation of all cattle which remain in the infected territory, thereby reducing the a.s.sets of the cattle industry of that section. In addition there is a very great loss from the decrease in flesh and lack of development of southern cattle occasioned by the parasitic life of the ticks from without and by the blood-destroying and enervating properties of the protozoan parasites from within.
The presence of the tick among the cattle of the South not only lessens the value of the cattle on the hoof but causes the gradings of hides that have been infested with ticks as No. 4 quality. The same hide, if free from tick marks, would grade No. 2. The difference in price between these two grades of hides is 3 cents a pound. As the hide of a southern steer weighs about 42 pounds, the presence of the tick in the hide causes a loss in the hide alone of more than $1.26 a hide. It has been shown that the cost of tick eradication is only about 50 cents a head, so that if the counties make a systematic campaign to eradicate the tick, the increase in value of the hide alone would pay for the cost of tick eradication and leave the farmer a net profit of about 76 cents a hide.
The shrinkage in the milk production of cattle harboring many ticks will average 1 quart a day, which in the aggregate is a heavy loss. The damage resulting to the southern purchaser of northern purebred or high-grade cattle is another item of no small moment. About 10 per cent of all such cattle taken into the South die of Texas fever, even after they are immunized by blood inoculations, and about 60 per cent of them succ.u.mb to Texas fever when not so treated. As they are usually very expensive animals and of a highly valued strain of blood, the loss in certain cases is excessive and in others almost irreparable, owing to the possible extinction of some particular type especially selected for the improvement of the herd.
Another instance in which it is difficult to figure the injury done by the ticks is in the case of death of nonimmune cattle in the tick-free pastures of the South. Such animals are as susceptible to Texas fever as nonimmune northern cattle, and inasmuch as there is in many States only one out of every four farms infested with ticks, the cattle on the remaining farms will in many cases contract Texas fever when exposed to the fever tick.
These losses can scarcely be computed, as the death rate depends so much on the season of the year when exposure occurs and on the age of the animal affected. However, the deaths among such cattle are considerable, although this fact is little appreciated or understood by many outside the infected area.
On rare occasions a small outbreak of Texas fever occurs north of the quarantine line as a result of improperly disinfected cars, of unscrupulous dealers breaking the quarantine regulations, or of some accidental condition. Such damage, however, is slight, but should be considered in summing up the loss occasioned by the fever tick.
The advertis.e.m.e.nt which a breeder obtains and the sales which are made by having his stock in the show ring are usually lost to the cattle raiser in the infected area who aspires to display his animals in the North, as they are barred from most of these exhibitions. On the other hand, the southern farmer is not given an opportunity to see and be stimulated by the fine specimens of northern cattle which might be shown at southern stock exhibits, for the reason that the danger of contracting Texas fever is too patent to warrant such exposure. A heavy expense is incurred by the Government and the States in enforcing the regulations that apply to the quarantine line.
Another loss which is indirectly sustained by the southern cattle industry through increased freight rates is the cost, to the railroad companies, of cleaning and disinfecting the cars that carry cattle and in providing separate pens for them at various places.
These statements are sufficient to indicate that the loss to the quarantined section from the cattle tick is something enormous. Such a series of enc.u.mbrances as those recorded could be carried by the cattle industry of no other section of the country than the South, whose excellent pastures, rich soil, and salubrious climate are the only reasons for its ability to overcome such obstacles in meeting the compet.i.tion of the West; and it is the inherent capacity of the South for greatly increasing its herds and enlarging its pasture lands that makes the actual loss even secondary to the potential loss from restrictions necessitated by the presence of the cattle tick. This potential loss may be described as the difference between the value of the cattle industry of the South to-day and the extent to which this industry would be increased if farmers and ranchmen were a.s.sured that their lands and cattle would not become infested with fever ticks. Could this a.s.surance be given, the beneficial effects would extend over the entire country, because the market of the northern breeder would thereby become greatly extended.
These appalling losses and annual sacrifices of the cattle raisers of the infected district can be entirely effaced, and this at a small proportionate cost; for, with enthusiastic stockmen, satisfactory State legislation, sufficient money, and a corps of trained inspectors, the cattle tick may be exterminated, and every dollar expended in this work will be returned many times during each succeeding year.
_The so-called period of incubation._--After the young ticks have attached themselves to cattle the fever appears about 10 days thereafter in midsummer. When the weather is cool, as in autumn, this period may be a little longer. The actual period of incubation may be shorter, for if blood from a case of Texas fever is injected into the blood vessels of healthy cattle the fever may appear within five days. When cattle graze upon pastures over which southern cattle have pa.s.sed, the time when the disease appears varies within wide limits. When the animals have been put upon pastures immediately after southern cattle have infected them with ticks, it may take from 30 to 60 days, or even longer, before the disease appears.
This will be readily understood when we recall the life history of ticks.
The southern cattle leave only matured ticks which have dropped from them.
These must lay their eggs and the latter must be hatched before any ticks can get upon native cattle. The shortest period is thus not less than 30 days if we include 10 days for the period of incubation after the young ticks have attached themselves to native cattle. When the infection of pastures with ticks has taken place early in the season, or when it is cold, the period is much longer, because it takes longer for the eggs to hatch.
If native cattle are placed upon pastures which have been infected with ticks some time before, the disease will appear so much sooner, because the young ticks may be already hatched and attack the cattle at once. It will be evident, therefore, that the length of time between the exposure of native cattle on infected fields and the appearance of the disease depends on the date of original infection, and on the weather, whether cold or hot.
When native cattle are placed upon fields on which young ticks are already present, they will show the fever in 13 to 15 days if the season is hot.
The fever appears before the ticks have matured. In fact, they are still small enough to be overlooked. In any case very careful search should be made for them in those places which they prefer--the thighs, escutcheon, and udder. After the acute stage of the fever has pa.s.sed the ticks begin to swell up and show very plainly. (Pl. XLVI, figs. 6 and 7.)
_Prevention._--It is generally accepted that if southern cattle are entirely free from that species of tick known as _Margaropus annulatus_ they can be allowed to mingle with the most susceptible animals without danger. Furthermore, it has been learned from the study of the life history of the cattle tick and by observation that this tick infests pastures only transiently, never permanently, and will not mature except upon cattle or equines, that its extermination is possible, and that the disease it causes may be prevented. Therefore the various methods with these results in view should be directed toward the destruction of ticks on cattle as well as their eradication from the pastures.
METHODS OF ERADICATING THE TICKS.[7]
In undertaking measures for eradicating the tick it is evident that the pest may be attacked in two locations, namely, on the pasture and on the cattle.
In freeing pastures the method followed may be either a direct or an indirect one. The former consists in excluding all cattle, horses, and mules from pastures until all the ticks have died from starvation. The latter consists in permitting the cattle and other animals to continue on the infested pasture and treating them at regular intervals with agents destructive to ticks and thus preventing engorged females from dropping and reinfesting the pasture. The larvae on the pasture, or those which hatch from eggs laid by females already there, will all eventually meet death.
Such of these as get upon the cattle from time to time will be destroyed by the treatment, while those which fail to find a host will starve in the pasture.
Animals may be freed of ticks in two ways. They may be treated with an agent that will destroy all the ticks present, or they may be rotated at proper intervals on tick-free fields until all the ticks have dropped. The method most generally used is dipping the cattle in a solution of a.r.s.enic.
The pasture-rotation method is not only more complicated, but the necessary tick-free fields are seldom available.
DIPPING.
The dipping vat is the best and cheapest means of applying the tick-destroying solution. The great advantage of dipping over spraying and applying remedies by hand lies in the fact that thoroughness of the treatment is practically a.s.sured.
When eradication is undertaken, all the cattle, and also the horses and mules if they harbor ticks, are treated regularly every two weeks during the part of the year that the temperature is favorable to treatment, until the ticks have disappeared. The purpose of the treatment is to destroy all ticks that get on the animals before they have had a chance to mature and drop, thus preventing them from reinfesting the pasture, farm, or range. If the treatment used were absolutely effective in destroying each and every tick on the animals treated there would be no renewal of the infestation after the treatment is begun. The cattle would act simply as collectors of ticks which would be destroyed regularly by the treatment applied every two weeks. It is probable, however, that in most instances, either because of the lack of efficiency of the dip or imperfect application, or because of failure to dip all cattle systematically, some ticks escape treatment and reproduce, thus prolonging the time that otherwise would be required for eradication.
If ticks apparently disappear from the cattle after they have been under treatment for some time, the dipping should not be discontinued until a number of careful inspections show that the cattle are free of ticks. If ticks continue on cattle until cold weather and then finally disappear it should be borne in mind that in all probability eradication has not been accomplished and that there may be engorged females, unhatched eggs, and inactive seed ticks on the farm or range, and that even if the cattle should remain free of ticks during the winter they may become reinfested the following spring. In any case in which ticks disappear from the cattle and treatment is discontinued, the cattle should be watched very carefully for ticks until ample time has elapsed to leave no doubt that eradication has been accomplished.
As a general rule it has been found that if dipping is begun in March and systematically and thoroughly done, all cattle being dipped every 14 days until November, complete eradication will be secured. In dipping, each animal should be completely covered by the dip. To prevent any animals from going through the vat without becoming wet all over, a man, provided with a forked stick, should be stationed at the middle of the vat to shove under those that have not been completely submerged.
Dipping is the only really satisfactory method of treating animals for ticks. In cases of emergency, however, or where there are not cattle enough within a radius of several miles to warrant the construction of a vat in which all the cattle of the community may be dipped, spraying may be advisable. In spraying animals the work should be done with great thoroughness and every portion of the body treated. An animal can not be sprayed properly unless it is tied or otherwise held, nor can good results be obtained unless the hair and skin are thoroughly wetted.
_Preparation and use of a.r.s.enical dips._[8]--After experimenting for many years to discover a practical method for dipping cattle to destroy ticks without injury to the cattle, the Bureau of Animal Industry has developed a very satisfactory a.r.s.enical dip. Two formulas are given for homemade dips, one known as the "S-B" (self-boiled) and the other as the boiled dip. The former is the one usually employed.
_The S-B dip._--The formula calls for two stock solutions, a.r.s.enic stock and tar stock, which must not be mixed except in the diluted dipping bath.
a.r.s.enic stock requires the following materials ready to hand before starting: Pounds.
Caustic soda 4 White a.r.s.enic 10 Sal-soda crystals 10
There should be also some means for heating the solution in case, as sometimes happens because of impure materials, lack of skill, or some unforeseen circ.u.mstance, the heat created by mixing the materials should be insufficient to dissolve all the a.r.s.enic.
In a 5-gallon kettle or metal[9] pail place the 4 pounds of caustic soda, add 1 gallon of cold water, and stir with a stick until the caustic soda is practically all dissolved. Without delay begin adding the white a.r.s.enic, in portions of a pound or two at a time, as fast as it can be dissolved without causing the solution to boil, stirring all the time. If the liquid begins to boil, stop stirring and let it cool slightly before adding more a.r.s.enic. The secret of success is to work the a.r.s.enic in fast enough to keep the solution very hot--nearly but not quite at the boiling point. The result should be a clear solution, except for dirt. If the liquid persistently remains muddy or milky, it may be because the operation has been conducted so fast that much water has been boiled out and sodium a.r.s.enite is beginning to crystallize, so add another gallon of water and stir. If the solution does not then clear up, the caustic soda must have been very low grade, and the undissolved substance must be a.r.s.enic. In that case, put the kettle over the fire, heat nearly, but not quite, to boiling, and stir. As soon as the solution of a.r.s.enic is complete, dilute to about 4 gallons, add the sodium carbonate, and stir until dissolved.
_Cautions._--It is necessary to avoid splashing. Hence never work hurriedly; stir deliberately and regularly; do not dump in the a.r.s.enic and sal soda, but carefully slide them in from a grocer"s scoop held close to the side of the pail and to the surface of the liquid. Perform the whole operation in a well-ventilated place and avoid inhaling steam.
After the solution has become cold add water to make it to exactly 5 gallons,[10] mix well, let settle, and draw off into containers which can be tightly corked or otherwise closed. Jugs or demijohns are best, but tin cans will serve if occasionally inspected for leaks which may occur after a time through the action of the solution upon the solder of the can.
Tar stock is prepared thus: In a large metal pail dissolve three-fourths of a pound of caustic soda in 1 quart of water, add 1 gallon of pine tar, and stir thoroughly with a wooden paddle until the mixture, which at first looks streaked and muddy, brightens to a uniform, thick fluid somewhat resembling mola.s.ses. Test it by letting about a teaspoonful drip from the paddle into a gla.s.s of water (a gla.s.s fruit jar or a wide-mouth bottle will do) and stirring thoroughly with a sliver of wood. It should mix perfectly with the water. Globules of tar which can be seen by looking at the gla.s.s from underneath and which can not be blended with the water by repeated stirring indicate that more caustic-soda solution is needed. In that case make up more caustic-soda solution of the same strength and add it, not more than a pint at a time, with thorough stirring, until the desired effect is produced.
If an appropriate gla.s.s vessel for making the test is not at hand, take a little of the mixture between the fingers, then dip the fingers under water and try to rub off the tar. It should leave the fingers perfectly clean after a little rubbing with water. If an oily coating remains, more caustic-soda solution is needed. Such an extra addition of caustic soda will be required only in case of a very low-grade chemical or a very highly acid tar. The tar stock should be kept in closed containers, such as a pail with a friction top.
The quant.i.ty of S-B a.r.s.enic stock or of tar stock made in one operation can be varied as desired, provided the above-given proportions of the ingredients are adhered to. But one should attempt to work the S-B formula on a larger scale only after skill and experience have been acquired.
_The boiled dip_ is less convenient than the S-B dip, but the final composition and effect of dipping baths prepared from the two are the same.
To make a 500-gallon bath provide:
Sal-soda crystals 24 pounds.
White a.r.s.enic 8 pounds.
Pine tar 1 gallon.
Put 25 gallons of water into a kettle or tank of from 40 to 50 gallons"
capacity, heat to boiling, and add the sal soda. When this has dissolved add the white a.r.s.enic, then boil and stir for 15 minutes or longer, until the white a.r.s.enic has entirely disappeared. If intended for immediate use cool to 140 F. (by addition of cold water if desired), then pour in the pine tar in a thin stream while constantly and vigorously stirring the solution. Immediately empty the liquid into the dipping vat, which has already been three-fourths filled with water, and stir thoroughly.
All the utensils must be free from greasy or oily matter which would coat the a.r.s.enic and hinder its solution. The operation of boiling requires constant attention to avoid loss by foaming. Hard water may be used, but in that case considerable undissolved material, which, however, does not contain any a.r.s.enic, may be left after boiling.
For a stock solution to be kept on hand and used when needed add no tar, but after the solution has become cold make it up to 25 gallons, stir well, let settle, and draw off into containers which can be well closed. In this case the tar stock previously described is also required.