the young, or larvÊ 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 principal 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 pronounced 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
retarded, 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 succumb 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 mass
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 associated 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 assets of the
South by an additional $33,000,000. The principal 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 classes of animals. This decreased
value reacts and fixes the valuation of all cattle which remain in the
infected territory, thereby reducing the assets 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 succumb 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 advertisement 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 encumbrances 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 competition 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 assured that their lands and cattle would not become infested
with fever ticks. Could this assurance 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 passed, 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 passed 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 larvÊ 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 arsenic.
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 assured.
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 arsenical 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 arsenical 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, arsenic stock
and tar stock, which must not be mixed except in the diluted dipping bath.
Arsenic stock requires the following materials ready to hand before
starting:
Pounds.
Caustic soda 4
White arsenic 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 circumstance, the heat created by mixing the materials should be
insufficient to dissolve all the arsenic.
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 arsenic, 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
arsenic. The secret of success is to work the arsenic 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
arsenite 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 arsenic. In that
case, put the kettle over the fire, heat nearly, but not quite, to boiling,
and stir. As soon as the solution of arsenic 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 arsenic 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 molasses. Test it by letting about a teaspoonful drip from the
paddle into a glass of water (a glass 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 glass 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 glass 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.