Species Differentiation in the Coccidia from the Domestic Sheep

Abstract

The literature on coccidia and coccidiosis in sheep was reviewed in detail by Thomson and Hall (1931), who called attention to the difficulty of determining whether the oocysts in the feces represent five distinct species, as described in the literature, or whether these oocysts were simply variants of a single species. On the basis of oocyst studies Balozet (1932) concluded that there are five valid species in sheep, and he redefined Eimeria parva, E. nina-kohl-yakimovi, E. faurei, E. arloingi, and E. intricata. Balozet considered the colorless, spherical oocysts described as E. galouzoi by Yakimov and Rastegaeva (1930) to be spherical variants of E. nina-kohl-yakimovi. Becker (1934) followed Balozet in recognizing five valid species, and suggested that further study is needed to establish the identity of E. aemula, described by Yakimov (1931). The present survey of the coccidia from domestic sheep was undertaken to determine the validity of identifications based on the morphology of the o6cyst and, in the event this proved to be feasible, to ascertain the species infecting sheep in the United States. The results obtained indicate that the unsporulated o6cyst is a reliable criterion for diagnosis, that the five species recognized by Balozet are valid, and that E. galouzoi and E. aemula are probably not valid. In addition to the valid species of coccidia heretofore recorded from ovine hosts, two new species of the genus Eimeria from sheep are described on the basis of o6cysts. With relatively costly domestic animals such as sheep, cattle, and swine, it is impracticable for the diagnostician to conduct experimental infections on coccidia-free hosts for the purpose of confirming oocyst identification. In view of this difficulty it is believed that detailed descriptions and supplementary figures of the unsporulated o6cyst constitute the most practical form of identification now available for the determination of the species of coccidia of sheep.