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  Contributed Papers: Oral Presentations
Vaccines


Acquisition of immunity to Eimeria maxima in newly hatched chickens given 100 oocysts.

H. D. Chapman, P. L. Matsler, and M. E. Chapman
Department of Poultry Science,
University of Arkansas, Fayetteville, AR 72701
Corresponding author email address: dchapman@uark.edu

The acquisition of immunity to E. maxima by chicks infected 18 hr post-hatch with a single dose of 100 oocysts was investigated. In the first experiment, birds were moved each day to clean cages in order to prevent the possibility of secondary infection resulting from ingestion of oocysts passed in their feces. Immunity was measured at 4 wk of age by calculation of oocyst production following challenge with 500 oocysts or weight gain following challenge with 100,000 oocysts. Large numbers of oocysts were produced by infected birds following challenge although numbers were significantly less than those from birds that had been reared in the absence of infection (susceptible controls). The weight gain of infected birds following challenge was significantly greater than that of susceptible controls but less than that of unchallenged controls. Thus only partial protection had been acquired, whether parasite replication or bodyweight gain was used to assess the extent of immunity development. In a second experiment, acquisition of immunity at 4 wk by chicks infected 18 hr post-hatch with 100 oocysts of E. maxima and reared in floor-pens in contact with their droppings was investigated. Infected birds produced no oocysts following challenge and weight gains were not significantly different from the unchallenged controls indicating that full immunity had developed by 4 wk. It is concluded that if oocysts of Eimeria species are used to vaccinate day-old chicks, re-infection by oocysts present in the litter is necessary for the establishment of protective immunity.





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