The Life Cycle of Four Intestinal Coccidia of the Domestic Rabbit

Although infections with coccidia have long been recognized among domestic and game animals, considerable confusion still exists concerning classification of various species of coccidia, their life cycles and methods of control. Coccidia are of great economic importance to animal industry. Zoologists, pathologists and investigators in related fields have contributed information toward the control of these parasitic protozoa and one of the factors which aids in an intelligent interpretation of this problem is derived from a study of life cycles. While the control of coccidiosis is not entirely dependent upon a definite knowledge of the life cycles, such information does add appreciably, and in turn aids in instituting prophylactic measures. In the domestic rabbit, Oryctolagus (Hobbs, 1931), five species of Eimlteria occur. Four of these multiply in the epithelial cells of the small intestine and one in the epithelium of the bile passages. Early workers in this field failed to differentiate all four of these species because they often dealt with mixed infections. Kessel and Jankiewicz (1931) clarified the situation by differentiating all four on the basis of the morphological structure of their oocysts. Accepting this differentiation it has been possible to segregate the four species, and establish pure infections of each in coccidia-free rabbits, thus enabling one to determine their endogenous life cycles. The species which is parasitic in the bile ducts was first noticed by Leeuwenhoek in 1674. He described bodies in the bile of rabbits which Dobell (1922) believes were the o6cysts of Eimeria stiedae. Hake (1839), according to Wenyon, first described the pathology of coccidiosis in the liver and duodenum of the rabbits, although he believed the o6cysts to be pus globules associated with carcinoma of the liver. No attempt was made, however, by the first investigator to differentiate between the species inhabiting the liver and intestine. It was not until 1879 that Leuckart proposed the name Coccidiztum perforans for the coccidia he found to inhabit the intestine, and it is assumed that he described, for the most part, the species now known as Eimeria perforans. Remak (1845) first noted o6cysts in the intestinal mucosa and Kauffmann (1847), according to Wenyon, observed that the o6cysts segmented into four separate sporocysts if kept in water. Stieda (1865) corroborated this observation and noticed in addition that within each sporocyst two elongated structures developed. These are now known as sporozoites. Balbiani (1884) proved that the sporocysts produce two sporozoites and a small residual body. It was Lindemann (1865), however, who recognized the parasitic nature of these cysts and called them Molocystis stiedae. In 1875 Schneider established the genus Eimeria for the coccidium of the mouse, and Leuckart's genus, Coccidium, is now considered a synonym for Eimneria.