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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Development of Control and Intervention Strategies for Avian Coccidiosis

Location: Animal Parasitic Diseases

2013 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.


3.Progress Report:
A mixture of Eimeria acervulina, E. maxima, and E. tenella oocysts were exposed to an optimum level of gamma irradiation to affect the reproductive capacity of the parasites. Newly hatched broiler chicks were inoculated this mixture of gamma-irradiated E. acervulina, E. maxima, or E. tenella oocysts and evaluated for vaccine uptake. Control groups included non-immunized chicks and chicks inoculated with non-irradiated Eimeria oocysts. All chickens were infected at 3 weeks of age with a high dose of a mixture of E. acervulina, E. maxima, and E. tenella oocysts, and weight gain and feed conversion efficiency were measured over the infection period. Chickens immunized with irradiated or non-irradiated oocysts displayed complete protection against avian coccidiosis. These findings indicate that irradiated Eimeria oocysts may be useful as a vaccine 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. Chickens raised under poultry house conditions and vaccinated via gel beads or spray administration displayed complete protection against a high dose Eimeria oocysts challenge. These findings indicate that gel bead delivery of Eimeria oocysts is a efficacious way of immunizing chickens against avian coccidiosis in poultry houses.

An in vitro drug-sensitivity assay was developed wherein drug-sensitive E. tenella sporozoites were shown to be sensitive to the 2 most common ionophore drugs, salinomycin and monensin. Cultures of chicken cells were inoculated with E. tenella sporozoites in the presence or absence of salinomycin or monensin. Cells were harvested after 2 hr or 24 hr, and E. tenella invasion and development was assessed by quantitative PCR and immunolabeling with antisera specific to E. tenella. The number of E. tenella parasites observed in cell culture was 10-fold less in cells treated with either ionophore drug compared to untreated cells. These findings suggest that in vitro drug sensitivity testing is a good alternative to animal studies.


4.Accomplishments
1. Development of an in vitro drug-sensitivity test for Eimeria. Medication of poultry feed with ionophore drugs or synthetic chemicals represents a major way to control avian coccidiosis in the poultry industry. However, this approach has become less efficacious because of drug-resistance in Eimeria parasites. While there are several different anti-coccidial drugs available, it is impossible to know a priori which drug to use on a particular farm because there are no rapid tests for estimating drug-sensitivity in the resident Eimeria population. An in vitro cell culture assay was developed that utilizes chicken cells that are inoculated with E. tenella sporozoites in the presence or absence of ionophore drugs salinomycin or monensin. The effect of these drugs on parasite invasion and development was measured by using molecular methods, such as quantitative PCR, or direct staining methods with immune sera specific for E. tenella. These assays indicate that in vitro cell culture is a viable alternative to conducting drug-sensitivity studies in chickens because it is more rapid and less costly, and avoids the use of animals to obtain insight on Eimeria drug-resistance in a broiler house.


Review Publications
Fetterer, R.H., Miska, K.B., Mitchell, A.D., Jenkins, M.C. 2013. The use of dual-energy X-ray absorptiometry (DEXA) to assess the impact of Eimeria infections in broiler chicks. Avian Diseases. 57(2):199-204.

Kim, S., Faris, L., Cox, C., Summers, L., Jenkins, M.C., Fetterer, R.H., Miska, K.B., Dalloul, R. 2012. Molecular characterization and immunological roles of avian IL-22 and its soluble receptor IL-22 binding protein. Cytokine. 60:815.

Last Modified: 7/31/2014
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