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Title: IMMUNOLOGICAL VARIABILITY OF FIVE GEOGRAPHICAL AND TEMPORAL STRAINS OF EIMERIA MAXIMA

Author
item Danforth, Harry
item BARTA, JOHN - UNIV OF GUELPH, CANADA
item FERNANDO, M - UNIV OF GUELPH, CANADA

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Avian coccidiosis, an intestinal disease caused by a small protozoan parasite, is estimated to cost the U. S. poultry industry over $350 million in losses annually. This disease has been partially controlled over the last 50 years by the use of anticoccidial compounds usually mixed prophylactically in the feed. However, parasite resistance to anticoccidials has become an increasing problem during the last 10 years, and the present sensitivity studies were undertaken to determine the extent of this resistance in coccidia collected from various areas of the U.S. The results showed that anticoccidial resistance is increasing. In addition, sensitivity testing of individual poultry production complexes is necesssary to determine which anticoccidials will effectively control the coccidia for that particular complex. Use of this data will extend the life of anticoccidials for the control of avian coccidiosis.

Technical Abstract: The ability of different strains of Eimeria maxima to induce cross- protective immunity was tested with 2 laboratory strains (USDA strain #68 isolated from the eastern shore of Maryland 15 years ago and a University of Guelph strain isolated from an Ontario broiler house 23 years ago) and 3 recent field strains. The relative sensitivity of each of these strains to a variety of anticoccidial compounds was also evaluated. Chicks were immunized at 1 day of age and challenged at 10 days of age, testing all possible combinations of immunizing and challenge strain. Six days post-challenge, chicks were killed and weight gains and lesions scores were determined and compared to unimmunized and challenged and unchallenged age-matched controls. Three of the coccidial strains were fully cross-protective against each other by both measures. These were the 2 laboratory strains and the North Carolina strain. When the remaining 2 strains (Maryland and Florida) were used as immunizing strains only those chicks challenged with the homologous strain were protected. Reciprocally, no other strains protected chicks against the Florida and Maryland strains. Thus in some field situations, immunization with a live E. maxima vaccine may necessitate incorporation of strains isolated locally from the field in order to adequately protect against subsequent infections. Drug sensitivity studies showed differences between the 2 laboratory strains and the 3 recently isolated field strains. No correlation was seen between cross-protection and sensitivities to anticoccidials.