Immunisation against coccidiosis in chickens: Tests under simulated field conditions

Abstract

SUMMARYTwo trials designed to examine the effect of a vaccine against coccidiosis were carried out with commercial replacement layers. The effect of vaccination was evaluated by challenging vaccinated and non-vaccinated chickens. In the first trial chickens vaccinated at 14 days of age were compared with non-vaccinated, medicated chickens fed robenidine at 66 ppm throughout and with unmedicated chickens kept in the same house. In the second trial birds were vaccinated at 7 days of age and compared with non-vaccinated birds on a 'Pancoxin' stepdown programme and with chickens maintained coccidia-free by feeding robenidine at 66 ppm throughout.The vaccine was composed of two attenuated strains of E. mivati and E. tenella, and virulent laboratory strains of three or four other species of Eimeria. Resistance of the chickens to E. acervulina, E. brunetii and E. maxima and partial resistance to the other species developed within 3 weeks. In general, immunity increased and was high against all species, although less complete in the case of E. mivati and, when judged by lesion scores, E. tenella.

Studies on the immunogenicity of seven attenuated lines ofEimeriagiven as a mixture to chickens

“…However, in birds partially immune to E. tenella the presence of severe caecal lesions may not necessarily be accompanied by lowered body weight gains (Long et al, 1980). Long et al (1982) also found lesions of E. tenella in commercial replacement layers that had been given TA oocysts when 2 weeks of age and then challenged with virulent strains 6 to 20 weeks later. It is possible that the administration in this study of a greater number of TA oocysts might have given better results, but a dose of 1 x 10 3 oocysts had previously been used by Long and Millard (1979) and by Long et al (1982) as a standard dose.…”

“…Long et al (1982) also found lesions of E. tenella in commercial replacement layers that had been given TA oocysts when 2 weeks of age and then challenged with virulent strains 6 to 20 weeks later. It is possible that the administration in this study of a greater number of TA oocysts might have given better results, but a dose of 1 x 10 3 oocysts had previously been used by Long and Millard (1979) and by Long et al (1982) as a standard dose. A precocious line of E. tenella recently selected by McDonald (personal communication) is being evaluated in this laboratory as a replacement for the TA line in a live attenuated vaccine.…”

“…Studies by Long andMillard (1977, 1979) and Long et al (1982) showed that careful control of the initial exposure of young chickens to a combination of five virulent and (the then available) two attenuated lines could result in effective immunisation. The work described in this paper differs from that cited above in two important respects.…”

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

“…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). For these reasons, an egg-adapted line of E. tenella (derived after >100 passages) has been included in a commercial vaccine (Livacox ® ) (Shirley and Bedrnik 1997;Williams 2002a, b).…”

“…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. Since the serial passage of E. tenella in embryonating chicken eggs commonly results in the emergence of a line significantly less pathogenic in chickens compared with 'field strains' but immunogenic (Long et al 1982), an embryo-adapted line (after more than 100 passages) has been incorporated into the Livacox ® vaccine (Shirley and Bedrnik 1997). Eimeria tenella Rt3+15 has the potential to cause moderate caecal lesions in young chickens (Richards, unpublished).…”