TEXAS OR TICK FEVER

New Zealand Mail, 29 January 1902, Page 58

TEXAS OR TICK FEVER

The sixteenth annual report of the Bureau of Animal Industry, Washington, ITS.A., lately to hand, contains j some reports of continued experiments ; by Dr. Schroeder, the superintendent of i the experiment station, which possess i great interest to the cattle-owners of i tins State. Dr. Schroeder conducted a ! series of experiments in the. growing •of noil-infected ticks, and afterwards j infected them. An effort was made to j grow ticks on annnais refractory to : 'Texas fever. Horses, mules, dogs, j sheep, goats, rabbits, guinea pigs, and ■ pigeons were used, but the ticks per- ; sistently refused to take hold of and ! grow upon any of the animals named. |He has since been assured, however, | that they occasionally grow on horses j and mules in the Southern States. He | determined to see wiiat could be done j by using very young calves, which are j practically immune from Texas fever, j All his experiments are given in de- ! tail, but here it will only be necessary | to state that ticks from cows obtained i from the fevered regions of the Soutli- ; era States were placed on two very ' young calves when they matured ; they were placed in a bottle, the mouth of | which was plugged with cotton wool, where they deposited their ova, and the latter hatched in due course. The young ticks were placed on a cow and calf, and were found not to produce the j disease. Ticks collected from the cow, ! and subsequent generations of those | ticks, were all found to be non-infec- ; tious. It was found, however, that , when any of these ticks were placed on cows from the Southern States that had passed through the fever and had the organisms in their blood, they became pathogenic, their progeny never failing to produce Texas fever when placed on Northern susceptible cattle, i During those experiments an important discovery was made —namely, that it is possible to carry infection by means of insects other than ticks from an infected to a susceptible animal. Two cases of the kind are stated by Dr. Schroeder. In a field where the clean cattle were kept, and separated from the infected paddock by a ditch and two lines of fence, a cow was found |to bo suffering from Texas fever, alj though no ticks were found on her, nor i on any of the other cattle in the same j field. A second case, a cow, had re- { ceived a hypodermic injection of blood j from a Southern cow, and died from ! its effects. A fly caught on her body : after death was found to have its abdo- : men distended with blood. This blood ! was pressed out on a slide, and examin- ! ed under the microscope, and was seen to contain many almost perfect corpuscles, nearly every one of which was infected with a large Texas fever parai site. Eleven days after the death of j this cow another cow in the same en- | closure was observed to be passing j bloody urine, and she died nineteen days after the symptoms were first observed. No ticks were found on her, nor on any of the cattle in the same field. The case was one of true Texas fever, and from these two cases the doctor thinks it is reasonable to assume that flies, and possibly other blood-sucking insects and external parasites, may carry infection from one animal to another; ! but lie thinks the cases must bo very rare, and that no general outbreak can be produced in this manner.

On the vitality of the cattle tick he records an instance in which he placed a number of female ticks in a cotton-stoppered name, and kept them in a warm room. The time which elapsed from the day the adult ticks were collected until the day when a host was provided for the young ticks was 168 days, or very nearly the half of the year. Dealing with tlie persistence of the Texas fever organism in the blood of cattle, he cites an experiment of two calves, from four to five months old, which received a hypodermio injection of blood drawn from the jugular vein of two Southern cows. One was inoculated with blood from the North Carolina cow whose case has been so often cited. She arrived at the experiment station in 1889, and her blood is still virulent. The two calves suffered an attack of Texas fever, so mild in character that it would have escaped notice without careful examination of tlie blood. The blood of those calves was afterwards injected into two Northern cows, both of which passed through a severe form of Texas fever, and one died and the other made a slow recovery. From these facts, and tlie permanently infectious character of the blood of Southern cattle, which has been repeatedly demonstrated, it appeared to the doctor that the organism of Texas fever is in some manner retarded in its growth in tlie blood of immune cattle, either by the production of an anti-toxin of insufficient strength to destroy it entirely, or some alteration in the .system of the cattle about which nothing is known; that is to .say, the cause which prevents the multiplication of tiie organism is a modification of its environment and not of its own character, otherwise it would fail to display the power of rapid multiplication, which is seen whenever it reaches the blood of a new host not previously infected. If an antitoxin were produced, the doctor reasoned, the injection of large quantities of blood or blood serum from immune cattle into susceptible cattle would be equivalent to transferring a portion of tlie immunity of tlie former to the latter. A number of cows were inoculated with 10 c.c. of blood from a Southern cow, and then quantities of serum up to 100, 300 and 100 c.c. at different times, but nothing was gained from this experiment.

In the course of carrying out this experiment. however. Dr. Shroedcr deduced a fact which it would be well for Queensland cattle-owners to carefully note —namely, that the injection of a large quantity of infectious blood causes diseases of no greater severity than the injection of a small quantity. A dose of 10 cubic centfinetres seems sufficient, but lie recommends that that quantity should be tlie minimum dose. With a 10 c.c. dose we may feel quite certain that ail attack of the affection has occurred. even if it was too mild to be diagnosed by tlie ordinary methods witliin the reacli of general practice; uitii a smaller dose an element of uncertainty remains.