Eimeria tenella Infection: Does It Affect Humoral Immune Responses to Heterologous Antigens?

Abstract

R. Becker at Iowa State College, Ames; it is not known whether this isolate still exists. The reason for the extended presence of fourth generation meronts in Roudabush's material is not readily apparent. Although the isolate of E. nieschulzi that Roudabush studied may have been contaminated with another species, his drawings and measurements fit so closely with other observations on this species, that we consider this possibility to be unlikely. He did not state how many oocysts were inoculated except that larger inocula were given when rats were to be examined for early endogenous stages. Marquardt (1966, loc. cit.) gave rats inocula ranging from 500,000 to 8 million oocysts; the larger numbers were given when tissues were to be examined early in endogenous development. In this laboratory, we have found that more than 1 million oocysts must be given to a rat of 60-75 g for death to occur, whereas Becker (1934. Coccidia and coccidiosis of domesticated, game and laboratory animals and of man. Collegiate Press, Ames, Iowa) stated that as few as 30,000 oocysts might cause the death of a rat. Therefore, it is unlikely that Roudabush (1937, loc. cit.) employed inocula larger than those we have employed in our various studies with the Landers Isolate. There are some differences between the timing of fourth generation merogony in this study and that of Marquardt (1966, loc. cit.) despite the use of the same isolate. Marquardt (1966, loc. cit.) found meronts from 144 to 168 hr whereas we found them somewhat earlier, but not as late: 136 to 156 hr PI. In the earlier study, larger inocula were used, thereby probably spreading out the infection in time. In the present study, only relatively small inocula were used, thereby limiting the span of time any individual stage would be found. In addition, studying living stages limits the amount of time that the tissue can be examined compared to fixed and stained tissue, and because of the nature of the preparations, the earliest stages of an asexual generation are difficult to find. The different techniques seem to account for the variation in the time and rate of development. This investigation was supported by Colorado Agricultural Experiment Station project number 337.