2012 Annual Report
1a.Objectives (from AD-416):
1) Determine the mechanisms controlling parasite development and induction of immunity in the host bird following infection.
2) Identify factors that impact the induction of immunity induced by coccidia vaccines.
3) Develop methods to assess the development of drug resistance in isolates of Eimeria recovered in the field.
1b.Approach (from AD-416):
Live Eimeria oocysts vaccines will be improved by testing the efficacy of and study immune responses elicited by gamma-irradiated Eimeria oocysts in protecting chickens against a coccidiosis. Optimum irradiation doses will be determined for the 3 major species of Eimeria that inhibits parasite development without affecting ability to elicit immunity. A novel delivery method by encapsulating Eimeria oocysts inside gelatin beads, and subsequent application onto feed for consumption by day-old chicks will be developed. Gel beads will be formulated to resist drying, and prepared containing low numbers of Eimeria oocysts. Day-old chicks will be fed gel beads, and tested at 4-5 weeks of age for immunity against coccidiosis. A rapid method for determining drug-sensitivity of Eimeria oocysts present in poultry facilities will be developed. Cell cultures containing various anti-coccidial compounds will be inoculated with field-strains of Eimeria sporozoites to determine sensitivity to these drugs.
Eimeria acervulina, E. maxima, and E. tenella oocysts were exposed to various levels of gamma irradiation to affect the reproductive capacity of the parasites. Separate groups of chickens were inoculated with E. acervulina, E. maxima, or E. tenella oocysts that were exposed to different levels of gamma irradiation, and evaluated for vaccine uptake. Optimum levels of gamma irradiation were identified for each Eimeria species that reduced parasite replication and did not prevent development of immunity in inoculated chickens. These studies were completed in battery cages and floor pen cages, which showed possible application for vaccination against coccidiosis in the poultry industry.
Eimeria acervulina, E. maxima, and E. tenella oocysts were incorporated into an improved gel bead formulation that prolongs oocyst viability. The oocyst-incorporated gel beads were fed to day-old chickens for eliciting a protective immune response against coccidiosis challenge infection. Vaccine uptake as indicated by release of Eimeria oocysts, and induction of resistance to challenge infection was achieved. The level of immunity induced by Eimeria oocyst gel beads was substantially higher in chickens raised in floor pens, which suggests that this vaccine delivery method may be useful under poultry house conditions.
Drug sensitivity trials (DST) were conducted in chickens using laboratory strains of Eimeria acervulina, E. maxima, and E. tenella oocysts, and the anticoccidial drugs salinomycin, monensin, and nicarbazin. All laboratory strains showed complete sensitivity to the three anticoccidial drugs, which indicates that it is appropriate to use these strains in developing an in vitro assay for drug sensitivity of field isolates of Eimeria to the most commonly used anticoccidial compounds.
Delivery of Eimeria oocysts vaccine in gel beads. Vaccination against avian coccidiosis by allowing day-old chicks to ingest Eimeria oocysts is gaining greater acceptance in the poultry industry. However, the delivery of oocysts to newly hatched chicks could be improved to increase uniformity and efficiency of vaccination. In collaboration with a private company, ARS researchers in Beltsville, MD incorporated a mixture of Eimeria oocysts into gel beads that were formulated to prolong viability of the oocysts. Greater uniformity and efficiency was observed with Eimeria oocysts in gel beads, indicating that this delivery method may be useful in preventing coccidiosis in the commercial broiler and layer industries.
Jenkins, M.C., Parker, C.C., Klopp, S., Obrien, C.N., Miska, K.B., Fetterer, R.H. 2012. Gel-Bead Delivery of Eimeria Oocysts Protects Chickens Against Coccidiosis. Avian Diseases. 56(2):306-309.