The paper is concerned with the principles upon which coccidia of the genus Eimeria may be characterized. Reference strains for comparative purposes usually are not available and the limitations of morphological data for speciation are discussed. The value of other parameters are considered such as host and site specificity, pathogenicity, immunological specificity, pre-patent period, sporulation time, enzyme variation, and DNA buoyant density. The weight afforded to each of these parameters for specific identification may vary according to the parasite and host studied. Determinations of physiological and behavioral characteristics that are now becoming available should be included in species definitions wherever possible.

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Six experiments were conducted using broiler chickens to study the effect of selenium (Se) or vitamin E supplementation of a corn-soybean meal diet on the immune response to coccidiosis. Immunized chickens fed diets supplemented with .25 ppm Se or 100 IU vitamin E/kg of diet had increased body weight gain and feed intake and a tendency for lower feed conversion ratio than chickens fed unsupplemented diet after a challenge with 150,000 oocysts of Eimeria tenella. In two experiments, chickens fed .25 and .50 ppm of Se and immunized against E. tenella had higher body weight gain and a tendency for higher feed intake and lower feed conversion ratio than unsupplemented chickens when challenged with 150,000 oocysts of E. tenella. Except for a reduction on cecal lesion scores and blood packed cell volume in Experiments 1 and 4, respectively, no dietary effect was observed on cecal lesion score or blood packed cell volume of immunized chickens. Dietary supplementation with selenium or vitamin E reduced mortality and increased body weight gain of nonimmunized chickens infected with E. tenella in three of four experiments. These studies suggest that immunization of chickens against coccidiosis is enhanced by Se or vitamin E supplementation.

Two strains each of Eimeria acervulina and Eimeria mivati were examined for their ability to develop in the chorioallantoic membrane (CAM) of chicken embryos and the caeca of chickens. It was found that between 100 and 1000 times more sporozoites of E. acervulina were needed to produce infections in the caeca and the embryo CAM respectively. The reproduction of both species in infections of chickens was similar and a high degree of cross-protection occurred.It was found that oocysts of E. mivati differed in size and shape depending upon whether they were produced from infections of embryos or chickens. When maintained by passage in chickens they assumed size and shape characteristics of E. acervulina.These findings, with the known similarity of the life-cycle stages, pathogenicity and pathology, indicate that E. mivati is not sufficiently different from E. acervulina to be a distinct species. It is suggested that it is best referred to as E. acervulina var. mivati.

Cryptosporidium is a newly recognized, zoonotic protozoan that produces short-term, flu-like, gastrointestinal illness in immunocompetent humans and prolonged, severe, diarrhea in immunocompromised individuals. Successful completion of the life cycle, from sporozoite to infective oocyst, of isolates of Cryptosporidium from humans and calves was demonstrated in endoderm cells of the chorioallantoic membrane (CAM) of chicken embryos maintained at 37 C. The human and calf isolates of Cryptosporidium were morphologically and developmentally indistinguishable when grown in chicken embryos. The human isolate also completed its entire life cycle in the CAMs of chicken embryos maintained at 35 C and 41 C. Oocysts recovered from endoderm cells of infected CAMs produced heavy infections in suckling mice. The timing, presence, and morphology of developmental stages in CAM cells during the first eight days after inoculation of sporozoites were similar to those in enterocytes of mice inoculated with oocysts. The method described is safe and convenient for cultivating and studying Cryptosporidium in a bacteria-free environment; the system also lends itself to well-established procedures for evaluating antiprotozoan drugs.