Fig. 160.—The large American fluke (Fasciola magna), natural size. (Stiles, Annual Report, U.S.A. Bureau of Agriculture, 1901.)
This phase is accompanied by very marked anæmia, rapid exhaustion during movement, and inability to run for any length of time.
The different methods of examination reveal nothing specially striking, except that the valvular sounds of the heart are sharper, and that trifling œdema occurs under the thorax and abdomen.
Microscopic examination of the fæces reveals the presence of eggs of distomata. The sheep rapidly become thin from about the end of January, even although the appetite persists and nourishing food is given.
III. Third, or wasting, period. The decline, which sets in about February, appears extremely obstinate, and resists all treatment.
The patients become feeble, eat less, and digest badly. Submaxillary œdema, common to advanced wasting diseases, then appears. If the sheep are removed from the fold to pasture, the swelling of the submaxillary space is very noticeable. It consists in an indolent œdematous tumefaction, which disappears when the animals are travelled, but reappears when grazing on account of the low position in which the head is then held.
The condition then becomes complicated with diarrhœa, and soon grows alarming. On examination, extensive dropsy may often be found in the thorax, pericardium, and abdomen.
Death results from exhaustion; the animals do not appear to suffer, but become extraordinarily anæmic, and perish without a struggle. The blood is simply rosy in colour, like gooseberry syrup; the clot is soft and gelatinous; the number of red blood corpuscles has fallen from about seven millions to a few hundred thousand.
Icterus is rare, though certain cases have been described where it has appeared during the last and even during the middle stage.
When animals begin to die in a district which has long been infested, the losses are enormous, the condition sometimes constitutes a perfect scourge. It should be remarked, however, that all those affected do not die; animals kept under good conditions may even survive for several months, although greatly wasted.