Part 65 (2/2)
Pasteur has further added to our knowledge of the disease by showing that a virus capable of cultivation exists in the nervous system, especially in the lower part of the brain (medulla oblongata) and in the anterior part of the spinal column. He has further shown that that portion of the nervous system which contains the virus, the exact nature of which has not yet been demonstrated, will retain it for a very long time if kept at a very low temperature or if left surrounded by carbolic acid; but if the nerve matter, which is virulent at first, is exposed to the air and is kept from putrefaction by substances which will absorb the surrounding moisture, it will gradually lose its virulence and become inoffensive in about fifteen days. He has also further shown that the action of a weak virus on an animal will prevent the development of a stronger virus, and from this he has formulated his method of prophylactic treatment. This treatment consists in the successive inoculation of portions of the nerve matter containing the virus from a rabid animal which has been exposed to the atmosphere for thirteen days, ten days, seven days, and four days, until the virulent matter which will produce rabies in any unprotected animal can be inoculated with impunity. A curious result of the experiments of Pasteur is that an animal which has first been inoculated with a virus of full strength can be protected by subsequent inoculations of attenuated virus repeated in doses of increasing strength.
Innumerable attempts have been made to discover the causative agent, and investigators have announced the finding of many of the lower forms of animal and vegetable life as the pathogenic factor. Among the recently described causes, certain protozoanlike bodies found in the ganglionic cells in 1903 by Negri, and termed Negri bodies, are of a very suggestive nature. Negri claims that these bodies are not only specific for rabies, but that they are protozoa and the cause of the disease. His work has been corroborated by investigators in all parts of the scientific world. An examination of the vitality of these bodies will show a striking resemblance to the vitality of an emulsion of the virulent tissue. Thus, they have been found to be quite resistant to external agencies, such as putrefaction, drying, etc., and are about the last portion of the nerve cell to survive the advance of decomposition.
They are also found in more than 96 per cent of the cases of rabies examined, but have not been proved to exist in other diseases.
Valenti states, as his strongest evidence of the protozoan nature of the bodies, that the virus of rabies is neutralized in test tubes by quinin, while no other alkaloid has this property. As a result of the work performed in the New York City Board of Health laboratory, Park claims that Negri bodies are found in animals before the beginning of visible symptoms, and evidence is given that they may be found early enough to account for the infectiousness of the central nervous system. These bodies are now almost universally considered as diagnostic of rabies, and in the pathological laboratory of the Bureau of Animal Industry their detection in the nerve cells of the brain suffices for a diagnosis of rabies without animal inoculations. In case these granular bodies are not found in a suspected animal, the plexiform ganglion is next examined, and should negative results still be obtained, the inoculation of rabbits is then made as a last resort. It is indeed rare that positive results are obtained from the latter method after the first two methods have been negative, but it has occurred occasionally in cases in which the animal had been killed in the early stages of the disease.
_Symptoms._--From the moment of inoculation by the bite of a rabid dog or other rabid animal or by other means, a variable time elapses before the development of any symptoms. This time may be eight days or it may be several months; it is usually about four weeks. The first symptom is an irritation of the original wound. This wound, which may have healed completely, commences to itch until the horse rubs or bites it into a new sore. The horse then becomes irritable and vicious, and it is especially susceptible to moving objects, excessive light, noises, the entrance of an attendant, or any other disturbance will cause the patient to be on the defensive. It apparently sees imaginary objects; the slightest noise is exaggerated into threatening violence; the approach of an attendant or another animal, especially a dog, is interpreted as an a.s.sault and the horse will strike and bite. The violence on the part of the rabid horse is not for a moment to be confounded with the fury of the same animal suffering from meningitis or any other trouble of the brain. But in rabies there is a volition, a premeditated method, in the attacks which the animal will make, which is not found in the other diseases. Between the attacks of fury the animal may become calm for a variable period. The writer attended a case in which, after a violent attack of an hour, the horse was sufficiently calm to be walked 10 miles and only developed violence again an hour after being placed in the new stable. In the period of fury the horse will bite at the reopened original wound; it will rear and attempt to break its halter and fastenings; it will bite at the woodwork and surrounding objects in the stable. If the animal lives long enough it shows paralytic symptoms and falls to the ground, unable to use two or more of its extremities, but in the majority of cases in its excesses of violence it does physical injury to itself. It breaks its jaws in biting at the manger or fractures other bones in throwing itself on the ground and dies of hemorrhage or internal injuries. At times throughout the course of the disease there is an excessive sensibility of the skin which, if irritated by the touch, will bring on attacks of violence.
Throughout the course of the disease the animal may have appet.i.te and desire water, but on attempting to swallow has a spasm of the throat which renders the act impossible. This latter condition, which is common in all rabid animals, has given the disease the name of hydrophobia (fear of water).
In a case under the care of the writer a horse, four weeks after being bitten on the forearm by a rabid dog, developed local irritation in the healed wound and tore it with its teeth into a large ulcer. This was healed by local treatment in 10 days, and the horse was kept under surveillance for more than a month. On the advice of another pract.i.tioner the horse was taken home and put to work; within 3 days it developed violent symptoms and had to be destroyed.
_Diagnosis._--The diagnosis of rabies in the horse is to be made from the various brain troubles to which the animal is subject; first by the history of a previous bite of a rabid animal or inoculation by other means; second, by the evident volition and consciousness on the part of the animal in its attacks, offensive and defensive, on persons, animals, or other disturbing surroundings. The irritation and reopening of the original wound or point of inoculation is a valuable factor in diagnosis. Diagnosis after death may be made by microscopic examination for Negri bodies or by the inoculation of rabbits, as already mentioned.
Recovery from rabies may be considered as a question of the correctness of the original diagnosis. Rabies is always fatal.
_Treatment._--No remedial treatment has ever been successful. All the anodynes and anesthetics, opium, belladonna, bromid of potash, ether, chloroform, etc., have been used without avail. The prophylactic treatment of successive inoculations is being used on human beings, and has experimentally proved efficacious in dogs, but would be impracticable in the horse unless the conditions were quite exceptional.
DOURINE.
By JOHN R. MOHLER, V. M. D., _a.s.sistant Chief, Bureau of Animal Industry_.
Dourine (also known as maladie du cot, equine syphilis, covering disease, breeding paralysis) is a specific infectious disease affecting under normal conditions only the horse and a.s.s, transmitted from animal to animal by the act of copulation, and due to an animal parasite, the _Trypanosoma equiperdum_.
_History._--It is described as having existed as early as 1796 in the Eastern Hemisphere, and was more or less prevalent in several of the European countries, including France, Germany, Austria, and Switzerland, during the first half of the nineteenth century. Its presence was recognized for the first time in the United States in 1886, when an outbreak occurred in Illinois. Since then the existence of the disease has been observed at irregular intervals in numerous other States, including Nebraska, Iowa, Montana, Wyoming, New Mexico, North Dakota, and South Dakota.
_Symptoms._--There are many variations in the symptoms of dourine, and this is particularly true of the disease as it occurs in this country.
Two distinct stages may be noted which vary somewhat from those described in textbooks, but probably no more than could be expected when differences of climatic conditions and methods of handling are taken into consideration.
The first stage chiefly concerns the s.e.xual organs and therefore differs somewhat in the male and female. In the second stage the symptoms indicating an affection of the nervous system are more prominent and are not dependent upon the s.e.x of the animal.
Following a variable period of incubation of from 8 days to 2 months, there is seen in the stallion an irritation and swelling about the p.e.n.i.s and sheath. In a few days small vesicles or blisters may appear on the p.e.n.i.s, which later break, discharging a yellowish, serous fluid and having irregular, raw ulcers. The ulcers show a tendency to heal rapidly, leaving scars which are permanent. There may be more or less continuous dripping from the urethra of a yellowish, serouslike fluid.
Stallions may show great excitement when brought in the vicinity of mares, but service is often impossible because of the fact that a complete erection of the p.e.n.i.s does not occur.
In the mare the first symptoms may be so slight as to be overlooked. The disease, being the result of copulation, usually begins with inflammation of the v.u.l.v.a and v.a.g.i.n.a. There may be a mucopurulent discharge, which may be slight or profuse in quant.i.ty, agglutinating the hairs of the tail. The mare may appear uneasy and urinate frequently.
Vesicles may appear on the external v.u.l.v.a and mucous membrane of the v.u.l.v.a and v.a.g.i.n.a which later rupture and form ulcers. On the dark skin of the external v.u.l.v.a the scars resulting from healing of the ulcers are white, more or less circular in outline, from one-eighth to half an inch in diameter, and pitlike. This depigmentation of the skin about the external genitals is permanent.
Urticarial eruptions or plaques which break out over various parts of the body are a frequent symptom seen in animals of either s.e.x. These are sharply defined and edematous swellings of the skin about the size of a half dollar or may be even larger. The usual locations of these plaques are the croup, belly, and neck.
The intensity of the symptoms mentioned which are significant of the early stage of the disease may vary to a wide extent and in many instances be so mild as to escape the attention of any but the most careful observer. They commonly disappear after a brief period. The apparent recovery, however, is not permanent, for such animals after a period of variable length manifest const.i.tutional or nervous symptoms.
These may not appear for several months or even years. They consist of a general nervous disorder with staggering, swaying gait, especially in the hind limbs. The animal generally becomes emaciated, the abdomen a.s.suming a tucked-up appearance. The first indication of paralysis will be noted in traveling, when the animal fails to pick up one of the hind feet as freely as the other, or both may become affected at the same time, at which time knuckling is a common symptom. Labored breathing is occasionally noted. When the paralysis of the hind limbs starts to appear the disease usually progresses rapidly. The horse goes down, is unable to rise, and dies in a short time from nervous exhaustion. The appet.i.te usually remains good up to the last.
Although a case of dourine may now and then recover, as a rule the disease is present in the latent stage. Bad weather, exposure, insufficient feed, and complicating diseases like influenza, distemper, or in fact any condition which tends to lower the vitality of the animal, may hasten the termination of the disease.
_Diagnosis._--The complement-fixation test furnishes by far the most reliable means of diagnosis and is especially valuable in a chronic affection of this character, when the symptoms manifested are variable and frequently so obscure as to escape observation. This is a laboratory test requiring special facilities and the services of a trained bacteriologist.
<script>