Symptoms. The symptomatology of this disease may clinically be divided into three well-marked periods:
I. Primary period. The primary phase commences with the penetration of the embryos of the parasite into the body, firstly into the intestine, and then into the liver by ascending the bile ducts. This phase occurs during the last months of the year, October, November, and December, and is rarely accompanied by alarming symptoms. At this time the sheep appear in good health, the summer being over, and the animals, being well nourished and fat, are able to resist the first attacks of the parasite, so that even an observant shepherd only notices a little dulness, want of condition, and muscular weakness. It requires a carefully trained eye to note these very general symptoms, for the bodily condition only changes very slowly and progressively, the appetite remaining good. Experienced butchers, however, in the districts where distomatosis is common, readily detect this condition. The animals make little resistance when handled.
Fig. 158.—Drawing from a microscopic preparation showing a fluke in the tissue of the liver. a, Necrotic liver tissue; b, atrophic liver cells; c, spines on the fluke, showing the outline of the body. (After Schaper, 1890, Pl. III., Fig. 5.)
Nevertheless, even in this primary phase, the conditions are not always as above sketched, and a certain number of deaths may occur. Gerlach has mentioned the possibility of death by cerebral apoplexy, in consequence of the young distomata penetrating to the brain. Moussu has certainly never seen such a complication, but has seen death from hepatitis, perihepatitis, and secondary pericarditis in animals gravely infested. The young embryos, whether they penetrate only by the bile ducts, as has been stated, or are carried to the liver by the blood stream, often excavate canals in the substance of the gland before establishing themselves in the bile ducts. They make their way as far as Glisson’s capsule, and may even penetrate it; and as they carry with them innumerable intestinal germs, when they arrive viâ the bile ducts, they set up hepatitis, perihepatitis, with the formation of numerous false membranes, or even infectious fibrinous peritonitis. Should the patients die during this phase one finds young distomata at the surface of the liver, or even in the thickness of the false membranes.
Fig. 159.—Tabular diagram of the occurrence of the common liver fluke (Fasciola hepatica) during different months of the year. a, Cattle; b, sheep; c, swine. (After Leuckart, 1889, p. 301, Fig. 147.)
When infestation is discrete the appearances are quite different. Careful breeders have even stated that at this period the young sheep appear to show a greater tendency to fatten.
II. Second period. In the primary phase deaths are exceptional; they only become common towards the end of the winter. During the second or middle period (December and January) the patients lose flesh, appear less active, show less regular appetite and greater thirst. The conjunctiva becomes pale and swollen, the sclerotic has a bluish tint, and the eyelids are somewhat infiltrated. The wool appears drier and less curly; locks of wool part readily from the skin, and the individual fibres become dry and fragile.
