Symptoms. First phase.—Disseminated encephalitis.—The symptoms vary with the phases of evolution of the parasite and of the disease which it causes. After the six-hooked embryos have penetrated to the brain, the animals affected lose appetite and show a certain degree of dulness, which is all the more marked inasmuch as the animals usually affected are young, and therefore should appear bright and alert. Then follow wasting and depression; the animals remain stationary for whole hours together, the head being carried low or inclined to one side. At this stage disturbance in vision and irregularities in movement may appear.
Fig. 216.—An adult gid tapeworm (Tænia cœnurus). Natural size. (After Railliet.)
Fig. 217.—Sexually mature segment of the gid tapeworm (Tænia cœnurus). cp, Cirrus pouch; gp, genital pore; n, nerve; ov, ovary; sg, shell gland; t, testicles; tc, transverse canal; ut, uterus; v, vagina; vc, ventral canal; vd, vas deferens; vg, vitellogene gland. × 20. (After Deffke.)
The eyesight is almost always affected, but the symptoms may vary widely. In some cases the patients seem to be absolutely blind, and strike against any obstacle in their way; in others the power of vision seems to be lost only on one side. All that can be discerned objectively is an inequality in the pupils, together with retraction or dilatation, convergent or divergent strabismus, nystagmus, etc. The humours of the eye appear infected, but examination with the ophthalmoscope reveals lesions of more or less extensive neuro-retinitis.
The visual disturbance is of central origin. The powers of movement may be affected in numerous ways, which at times are extremely difficult to estimate with accuracy. Sometimes the gait is uncertain, inco-ordinated, and hesitant; at others the animal shows lameness or loss of control over a front or hind limb, or over two limbs simultaneously (either the two front or hind limbs or the diagonal limbs), or it may be absolutely unable to stand.
It walks obliquely, or the front or hind limbs collapse; or again, it may persistently lie down, a fact which makes the shepherd think it is suffering from paralysis. On examination, however, no true indications of paralysis can be found; sensation and motor power are both preserved in a modified form.
Fig. 218.—Brain of a lamb infested with young gid bladderworms (Cœnurus cerebralis). Natural size. (After Leuckart.)