A fatal affection among horses implicating the spinal and cerebral membranes appears to have been known for a long period in various parts of the world. In the United States of America cerebro-spinal meningitis is recorded to have been investigated in 1850. In Germany it was known in 1865, and in Egypt ten years later. About the year 1881 a fatal form of paralysis attracted notice in this country, and Professor Axe described outbreaks which occurred almost simultaneously in Essex, London, and Norfolk. A peculiarity of the disease at the time was its limitation to certain parts of the year, the majority of cases occurring between the end of February and the beginning of May. Mares seemed to be more susceptible to the affection than horses, and animals of all ages were attacked. Climatic conditions did not appear to have any marked influence on the progress of the malady. When it was first recognized in 1881 the weather was cold and wet, but since then cases have been observed in the latter part of the summer during hot bright weather.
On the first appearance of the affection it was looked upon as a totally new malady which had probably been introduced from America.
Percival in his Hippo Pathology refers to a form of epizootic paralysis occurring on cold wet pastures in spring and autumn. Professor Axe mentions an article by Mr. Small in the Veterinarian for 1857 describing outbreaks of paralysis occurring in his district in that year. Other writers have also mentioned cases of the periodical occurrence of a form of paralysis in different parts of the country, and there is very little doubt that these cases were of the same character as those which have been recently designated cerebro-spinal meningitis.
With regard to the propagation of the disorder Professor Axe notices the communication of the disease to other animals than the horse. On this part of the subject he says: - " At the time when the disorder prevailed in the county of Essex, Mr. Ellis, veterinary surgeon of Maldon, resolved upon trying the efficacy of venesection. Several horses were consequently bled, and the blood removed from them was, contrary to instructions, thrown down in a yard adjoining the stables. During the day large numbers of sparrows were observed to partake freely of the clot, and after a short period to become paralysed in their wings, and unable to rise from the ground. On the following day a sow and a dog, which had also consumed some of the blood, were similarly affected, the latter so much so as to lead to his destruction. Several young pigs, offspring of the sow referred to, were at the same time seized with convulsive twitchings of the voluntary muscles, accompanied by a greater or less degree of paralysis. These latter animals, it should be mentioned, had not partaken of the blood of the horse, but were at that time subsisting exclusively on the milk of the dam."
Indications of the disease in the majority of instances appear suddenly, but in other cases before there is any appearance of paralysis the animals show some premonitory signs of drowsiness, unsteadiness in their movements, catching the toe in the ground in walking. More commonly, however, without any warning the affected horse is found down and almost incapable of moving. In many cases the loss of power is apparent in the posterior half of the body, and during the progress of the affection nearly all the muscles of motion are involved. Sometimes the loss of power is particularly marked in muscles connected with swallowing, so that the animals cannot take fluid or solid; in other instances the power to eat and drink remains, while paralysis gradually extends over the body. In the advanced stages of the disease excitement is frequently present, alternating with spasmodic contraction of some of the muscles. The excitement may be followed by total loss of consciousness, or it may be exaggerated and end in frenzy. These symptoms usually indicate that a fatal termination is at hand. During the course of the disease the temperature is but little affected, and, excepting when complications arise, the pulse and respiration are nearly normal. On post mortem examination it has been found that the membranes of the brain and spinal cord are charged with blood, and effused blood and serum are frequently found on the brain and spinal cord. The digestive and respiratory organs, and also the spleen and kidneys, show considerable changes in their texture.
A. Portion of spinal con! showing engorgement of vessels and hemorrhagic points and patches in cerebro-spinal meningitis.
B. Arteritis. - Portion of aorta laid open, showing patches of arteritis.
C. Arteritis. -Transverse section oi artery infiltrated with inflammatory products, (a) Leucocyt tunica adventitial or external coat. (b) Leucocytes infiltrating tunica media or middle coat. (c) Leucocytes causing irregular thickening of tunica intima or internal coat. D. Arteritis. Longitudinal section of inflamed artery, (a) Leucocytes infiltrating vessel wall.
No satisfactory explanation has been given of the origin of the disease. It has been looked upon as infectious, and recent experience of the malady goes to prove pretty conclusively that it is so. The fact of its recurrence occasionally and under very different conditions is sufficient in itself to prove that it is not due to any of the ordinary causes. Whatever the cause may be, it is quite certain that it only exists at intervals, and also that it affects a considerable number of animals in the district in quick succession. The cessation of the disease is sometimes as sudden as its appearance.
Of the different plans of treatment which have been tried none has proved so successful as to claim any pre-eminence. Laxatives, cold applications to the head, and in cases where muscular spasms in the neck, for example, are present, injections of morphine have been tried with partial success.
For the prevention of the spreading of the affection it is desirable to remove healthy animals from the immediate neighbourhood of the sick. Efficient cleansing and disinfection of the stables in which sick horses have stood must on no account be neglected, and a complete change of food is also desirable.