[The following stages may be noticed in sheep suffering from fascioliasis. Gerlach recognized four stages, based on the varied relations that the flukes contract with the liver of their host. These periods are sometimes very marked, but at others, owing to subsequent infections, the features become merged and so obliterated. But when a single infestation occurs they are very marked.
Fig. 142.—Fasciola hepatica: egg from liver of sheep. o, operculum, e, segmenting ovum. The rest of the space is occupied by yolk cells, the granules in three only being shown. × 680. (After Thomas.)
[The first period is called the PERIOD OF IMMIGRATION. This occurs at the fall of the year and generally passes unperceived, as the young flukes do little harm to the liver. It varies from four to thirteen weeks. Gerlach has remarked upon cases of death from apoplexy at this period.
[The second period is the PERIOD OF ANÆMIA. This occurs in November and December. The sheep at first fatten rapidly, but later the mucous membranes become pale and of a yellowish hue, and the sheep become sluggish and cease to feed. The fæces are normal, but may contain fluke ova.
[The third period is the PERIOD OF WASTING. This corresponds with the beginning of January—about three months after the entry of the larvæ. Emaciation now becomes very marked, the skin and mucous membranes blanched, temperature variable and marked by an irregular curve; respiration laboured and quick; appetite regular; abortion frequently occurs in pregnant ewes; pressure on the back causes the animals to fall; local œdemas occur, the most perceptible in the submaxillary space, extending below the larynx and over the cheeks and parotids (called “bourse,” “boule” in France; “watery poke” or “cockered” in England). Death usually occurs at this period, but a fourth stage may occur.
[The fourth period is the PERIOD OF MIGRATION OF THE FLUKES. This is a period of convalescence and recovery, generally in May and June.—F. V. T.]
Oxen suffer less in general, but even in these animals “stray” hepatic flukes are occasionally found in the lungs, enclosed in thick-walled cysts.
Pathological Anatomy.—The bile-ducts are conspicuous on the surface of the liver. They are thickened and much dilated and in parts saccular, and considerable atrophy of the liver cells accompanies the condition. Histologically there is immense proliferation of the epithelium of the bile-ducts leading to “adenomata.”