Page:Tropical Diseases.djvu/1005

Rh Theileria is the title reserved for a number of bacillary or coccoid forms. Theileria parva (Fig. 253) is the parasite of "East Coast fever" of African cattle.

Another piroplasm, P. mutans, is commonly found in the blood of cattle suffering from "East Coast fever," together with the specific parasite Th. parva. In the case of the latter the forms in the blood consist entirely of gametocytes; in P. mutans, on the other hand, the quadruple forms in the

Fig. 252.—Piroplasma canis. (After Nuttall.)

erythrocytes apparently represent a stage of the schizogony. Therefore direct inoculation of blood containing Th. parva does not produce the disease, whereas infection with P. mutans invariably occurs, if schizonts of this species are present in the inoculated blood. The schizogonic stage of Th. parva is apparently passed in the internal organs such as the spleen. Splenic puncture in the diseased animals reveals bodies bearing a rough resemblance to a sporulating quartan malaria parasite known as "Koch's bodies"; it is thought that these bodies, which are capable of reproducing the disease on re-inoculation, represent the schizogonic cycle in the splenic cells.

Fig. 253.—Theileria parva. (After Theiler.)

Nuttallia is a small oval or pear-shaped piroplasm, also multiplying in the form of a cross. Two kinds are known: one, N. equi, causes piroplasmosis in horses in southern Europe; the other, N. herpestidis, is found in the mongoose.

Anaplasma, a small coccoid body, perhaps to be included with the piroplasms and apparently causing great destruction of the red cells, has been described by Theiler in cattle. These bodies are arranged either in the centre of the cell or radially; hence the names A. centrale and A. marginale have been applied to them. According to some authorities they are not parasites at all, but merely represent a degeneration of the red cell.

Within the red cell the piroplasm consists of little save vacuolated protoplasm and a simple nucleus. The parasites are said to exhibit a certain amount of amœboid movement, and, when free from the cell, to be capable of independent