Lesions. No lesions can be detected on a simple examination of the dead bodies. Gilbert has mentioned a change in the blood; Trasbot, chronic inflammation of the pia mater and of the lumbo-sacral portion of the spinal cord. German writers have described sclerotic changes in the posterior portions of the cord. Moussu has carried out a large number of examinations, but has never found these lesions, either on anatomical or on histological investigation, and he considers that they are not by any means present in all cases.
Besnoit and Morel, who carried out a very remarkable anatomical and pathological study of the disease, used Nissl’s staining method, but only found very discrete changes in the cord (vacuoles in the motor cells of the anterior horns). They found, however, significant lesions of neuritis in the peripheral nerves.
Causation. The cause is as yet little understood, and it is difficult to prove how the forms of neuritis described by Besnoit are brought about.
The disease was not known in France before the introduction of Merinos, and former investigators referred it to heredity, consanguinity, precocity, and even to sexual excitement. German writers declare that it seems more particularly to attack rams and the better-bred varieties. In reality, the disease occurs in all flocks, and in all kinds of sheep indiscriminately; it attacks ewe lambs and young castrated lambs as well as rams. Moussu is absolutely of this opinion, and for want of more precise information agrees with Trasbot, and, he believes, with Besnoit, that the symptoms shown may possibly be referred to a chronic intoxication.
Diagnosis. The diagnosis is difficult during the early stages, but when the pruritus becomes manifest there can no longer be room for doubt.
Cases of paraplegia might perhaps be mistaken for paraplegia due to cœnurosis, but in the latter case there is no pruritus.
Prognosis. The prognosis is extremely grave, observation having shown that all the patients die after a longer or shorter time.
Treatment. Until now treatment has proved absolutely useless, and it would seem the best course to slaughter the animals before wasting becomes marked.