In man the causative agent is commonly found to be some granulation or vegetation occurring in the structure of the aortic valves.
These, when sufficiently large, repeatedly strike the wall of the vessel during the movement of the valves, and excite inflammation in the part struck; or it may result from a portion of blood clot liberated from the interior of a large vessel being carried away and arrested in a smaller one, producing a plugging of the vessel, or embolism.
In the horse the disease is most commonly seen in the anterior mesenteric artery and in that part of the aorta in immediate proximity to it. It is the result of irritation excited in the vessel by the presence of worms. The parasites Strongylus armatus frequently take up their abode here, and by their presence induce inflammation in the vessel wall.
The vessel, which is at first thickened, becomes soft and very much like a piece of wet wash-leather. Its elasticity is impaired or altogether lost, and in consequence it gradually yields to the pressure of the blood stream, and ultimately becomes dilated and forms an aneurism. On the internal surface there is frequently to be found a quantity of coagulated fibrine, in which the parasites are embedded.
The chief symptoms of this disease are wasting, and diarrhoea, and periodical subacute abdominal pain. The animal is dull and listless, tucked up in the belly, feeds indifferently, and sometimes refuses food altogether. If a sharp look-out be kept, small red worms will be found in the excrement.
In these cases the partial plugging of the mesenteric artery diminishes the quantity of blood flowing towards the intestine. The function of that organ is therefore imperfectly performed, resulting in periodical attacks of diarrhoea, colic, and a general unthriftiness of the affected animal.
The patient sometimes brightens up and appears to have recovered, when recrudescence of the disease occurs, and he goes back in condition, and may succumb to the disease.
In all cases of this kind the treatment will succeed in proportion to the injury done to the vessel, and the amount of obstruction to the blood-flow resulting from the degree of dilatation, and the extent to which the vessel has been narrowed by the coagulation of fibrine within it. Very many cases are hopeless, and if they do not die it would be real economy to have them destroyed at once. Some recover, only, however, to be a future trouble to whoever may possess them.
These facts should be present to the mind of all persons who are called upon to treat cases of this kind.
As we have already indicated, the treatment of this disease is very uncertain. The affected animal should be placed in a well-littered box, and everything should be done to keep up the strength of the body. Food easy of digestion is of the first importance here. Malt meal and linseed, crushed oats and bran, with a very small quantity of sweet chaff, all well scalded, will be found for the most part suitable.
It is no use trying to destroy the parasites; they are beyond our reach, and cannot be influenced by medicines; but they may sooner or later leave the vessel of their own accord and pass into the intestine.
When pain appears it must be combated and controlled by the administration of repeated small doses of opium. A little bicarbonate of potash with chloride of sodium may be administered with the food, and repeated small doses of turpentine and aromatic spirits of ammonia should be given in combination with tincture of cinchona as a stimulant and tonic.