A contagious disease, the precise cause of which has not yet been determined. It is essentially a disorder of the equine species. It occurs in relatively low-lying districts along the eastern coast of South Africa, and appears to be in some way connected with climatic conditions. Its partiality for low, damp regions, especially during heavy rains, and its comparative absence in dry summers, clearly show that wet favours its development.
In particularly dry summers very little of the disease is observed, but when the seasons are wet and rain continuous then horse sickness prevails. February, March, and April are months during which it is most prevalent. For a long time it was looked upon as anthrax, and having regard to the suddenness with which it sometimes appears, the rapidity with which it runs its course, and the post-mortem symptoms of the malady, such an assumption was not without reason. It was, however, shown by Lieut-colonel Dunn in 1887, that the anthrax bacillus was not present in the blood, and that whatever the cause of the disease may be, it could no longer be regarded as anthrax.
Although we have hitherto failed to determine the precise cause of the malady there is no doubt as to the inoculability of it.
Dr. Edington showed that it could be transmitted by inoculating the blood of a diseased horse directly into the body of a healthy one; but, strange to say, the serous fluid which is effused into the tissues in the course of the disease when inoculated into a healthy horse does not produce it.
Speaking of the cause, Captain J. T. Coley, C.V.S., in an able article in the Veterinary Record says: - "It is at present undiscovered, but probably is a very minute micro-organism, as under the highest power of the microscope, and with the present methods of staining, it is invisible; and it passes through the best-made filters, as proved by the fact that filtered blood serum (infectious) when injected produces the disease, so also does infectious blood when injected or given per orem. Yet none of the serous fluids infiltered into the tissues as a result of the disease produce it when inoculated.
"The following are theories and ideas as to the possible modes of infection, viz. ingestion, inhalation, inoculation. At present one is unable to determine if natural infection takes place by only one or more of these channels, but probably all the above methods of infection are concerned in the spread of the disease, as will be gathered from the following results which I have noted."
The organism evidently requires heat and moisture for its propagation and vitality, appears to have a miasmatic origin, and to be transmitted by dews, fogs, and winged insects.
"Ingestion. - Animals which eat dew-laden grass grown in an infected district invariably suffer from the disease, but they can eat the same grass with comparative impunity when saturated with rain. I have known instances of dew-laden grass cut in kloof or valley and given to stabled animals which contracted the disease; and of dew-laden grass from the same kloofs which was well dried in the sun the day after cutting, was also given to stabled animals a few yards distance without any fatal results."
Inhalation. - I believe inhalation plays an important part in the introduction of the disease into the system. I have known two animals which were taken out of a troop and were ridden a few hours through the dense fog in a kloof contract the disease and die in ten or eleven days later, although, with the exception of mosquito inoculation, there was no other apparent mode of infection, as these animals did not get an opportunity of eating or drinking while away from their station, and they were the only two animals that died from the disease. Edington records one case of spontaneous infection from a horse suffering from the disease to its companion standing in the next stall, the animals being able to smell each other.
"Inoculation undoubtedly is a very probable mode of infection, and more than likely mosquitos and other winged insects act as hosts and intermediary bearers, when one considers the vast numbers in which they are bred in stagnant water of kloofs saturated with dew. All the preventive measures enumerated hereafter are more or less preventive against inoculation by mosquitos."
There are two varieties of the disease known by the Dutch names, dunpaard-ziekte and dikkopaard-ziekte. In the former the symptoms are, as a rule, comparatively absent until just before death. The animal appeal's in perfect health and vigour, and within an hour characteristic symptoms may appear, such as hurried respiration, animal lies down and gets up again immediately, soon followed by death in a few minutes.
"The symptoms usually seen in the dikkop form appear some days before death, and gradually become well defined towards the end, viz. the neck, head, and lips become swollen, in some cases enormously, the eyes close, and the lower lip droops."
"A sub-variety of this disease is called 'Blawtong', or bluetong, when the swelling of the neck and head is not marked, but mostly confined to the tongue, which presents a livid blue colour, due to intense venous congestion."
"Owing to the absence of symptoms until just before the onset of death, it was believed the disease was of very short duration. The foregoing symptoms are all that is generally noticed by farmers and horse-keepers, but if the animals in horse-sickness districts, or which have been through such districts, are carefully inspected and their temperature taken daily, the first symptoms discovered will be fever about the seventh or eighth day after infection; and if my memory serves me correctly, when investigating this disease under the supervision of Dr. Edington, the incubation periods in animals experimentally inoculated was from six to eight days. A noteworthy feature about the temperature is that it gradually rises, and seldom, if ever, is below the previous day's temperature, taken at the same time. The morning and evening temperature will be higher than that of the previous day, although the morning temperature may be below that of the previous evening, but will be higher than that of the previous morning, and so gradually increases to 105°, and in some cases to 107° Fahrenheit, until the final stage is reached, when it suddenly drops to normal or below it."
"The primary rise of temperature is soon followed by a dusky-yellow pinkish discoloration of the conjunctiva, which is congested, and invariably petechial or stellate spots are present, which are always well marked; and generally there is a watery discharge from the eyes, and a peculiar dry husky breathing can be detected on auscultation at the trachea. In a day or two these symptoms become more marked, and are followed by oedema of the conjunctiva and eyelids, swelling of the orbital fossa, injection of the nasal mucous membranes, swelling of the neck along the jugular furrows, and in the dikkop, or big-head variety, the head and neck may be swollen to an enormous size, the eyes closed up, and the conjunctiva protruding. These symptoms are followed by weariness. The animal stands lazily, rests its head on the manger or against the wall, resting one leg then the other, and in final stages refuses food, although in the beginning appetite is unimpaired; breathing increased to thirty or over per minute, pulse small, quick, and hard, which soon becomes feeble, often intermittent, and auscultation of the heart generally gives tumultuous or palpitating sounds. There is a jugular pulse, animal lies down and soon gets up again. About this stage a yellow clear fluid discharges from both nostrils. On auscultation at the thorax, the breathing is audible, and of a gurgling sound, which gives one the impression there is a fluid in the bronchial tubes; respiration is hurried and laborious, the animal falls or lies down, and dies suddenly. Frequently, a few minutes before death, a great quantity of white froth is blown from the nostrils, and almost invariably at death this froth appears at the mouth and nose, which retains its form, and does not become fluid till some time after death."
"This froth is the yellow fluid mixed with air from the lungs, and, according to Edington, is blood serum. The commonly observed symptoms are usually evident about the tenth day, and death takes place about ten or fourteen days after infection, and in the dikkop variety a day or two later."
"In 1898 I tried inter-tracheal injections of iodine on a case of the dikkop variety, and in twenty-four hours I was so much surprised at the improvement which took place that I decided to give this treatment a further test, and try if possible to perhaps improve on the iodine solution, which I found to give me the only satisfactory results."
"The inter-tracheal injections used were as follows: -
Iodine, grs. iv. Pot. lod. grs. xii. 01. Terebinth, m. xv Glycerine, 3i. Aqua, boiled, 3i. Injected once or twice daily.
Iodine, grs. iv. Pot. Iod. grs. xii. A. Carbolic, m. xv. Glycerine, 3iss. Aqua, boiled, 3i."
"Of thirty-six animals treated in this way seven recovered, twenty-three died within twenty-four hours, and six died in from two to six days from date of admission."
"In some cases this treatment caused the animal undue disturbance, and coughing for about an hour after the injection; also, if given every twelve hours for two or three days the urine became blood-stained, and on post-mortem examination the kidneys were much enlarged, congested, a livid blue colour on surface, and capsule, if anything, more easily detached than normal."
"The following season I used intravenous injections, which gave more satisfactory results, besides causing practically no disturbance to the animal, so discontinued the inter-tracheal injections."
"B as follows: - Iodine, grs. iv. Pot. Iodide, grs. xv. Glycerine. Aqua, boiled, 3i."
"A noteworthy feature of this treatment is the immediate effect it has on the temperature."
"In the majority of cases the temperature drops from one or two degrees within twenty-four hours after the first injection, and a gradual decrease of temperature afterwards is a favourable sign; also, the ecchymosis on the conjunctiva is much improved in twenty-four hours."
"If the disease is discovered the first or second day of the fever, two or three injections usually effect a cure. If the animal is only treated early enough in the disease the chances of recovery are greatly increased."
"All the recorded cases developed undoubted clinical symptoms of horse sickness."
"In my hands over 66 per cent of such cases recovered; but I do not claim that all horses with a rise in temperature were suffering from the disease, as coincidences are bound to occur, but I claim that the greater number of them, if left untreated or treated by old methods, would have died of horse sickness."