Eimeria tenella: Reproduction, pathogenicity and immunogenicity of a strain maintained in chick embryos by serial passage

Control of poultry coccidiosis: changing trends

“…The attenuated lines of Eimeria parasites can be developed through repeated selection for early maturation (precociousness) or by serial passage through embryonated eggs (Long 1972;Jeffers 1975). The most important feature of these attenuated lines is their reduced proliferative capacity resulting in less damage to the intestinal epithelium after one passage through the gut.…”

Reproductive characteristics of a precocious vaccine line (Rt3+15) of Eimeria tenella in embryonating chicken eggs

“…The corresponding reproductive indices were 500, 1,800 and 1,300 from respective passages. It is likely that the lower reproductive indices achieved in the present study compared with that of Long (1972) relate to an insufficient adaptation to the growth in chicken embryo and precocious nature of Rt3+15 E. tenella line. Further experimentation is required to verify whether the pathogenicity and/or immunogenicity of E. tenella Rt3+15 in chickens change as it adapts to chicken embryos over a large number of passages and to establish its reproductive characteristics in embryos and, subsequently, in chickens.…”

“…Long (1965,1966) first demonstrated that some species of Eimeria could complete their endogenous development in the chorioallantoic membrane of the chicken embryo. Subsequently, Long (1972Long ( , 1973 also showed that the continuous passage of E. tenella in embryos resulted in an adaptation, associated with a reduction of pathogenicity, size of the schizonts (asexual stages) and a change in the site of development, compared with the original, 'parent' line of the parasite. Serial passage of E. tenella in embryonating chicken eggs usually results in the development of a line of parasite which is significantly less pathogenic to chickens compared with wild-type strains while remaining immunogenic (Long et al 1982).…”

“…Nonetheless, it should be possible to achieve higher oocyst yields and enhanced embryo-adaptation (leading to decreased embryonic mortality) through increased serial passage in eggs, thereby maintaining immunogenicity in the vaccinated host. For instance (using an inoculation dose of 10,000 sporozoites per egg), Long (1972) reported embryonic mortalities of 29, 7 and 0% during passages 1, 37 and 38, respectively. The corresponding reproductive indices were 500, 1,800 and 1,300 from respective passages.…”

The effect of some anticoccidial drugs on the development of immunity to coccidiosis in field and laboratory conditions

“…Six days later all the birds were weighed, killed and the intestines examined for coccidial lesions. Caecal lesions were scored as described by Long (1972). Intestinal lesions were scored as described by Johnson and Reid (1970).…”