Efficacy of Coccivac against field isolates of chicken Eimeria
Steve H. Fitz-Coy
Schering-Plough Animal Health, Union NJ
steve.fitz-coy@spcorp.com
This report includes a series of
tests to compare the antigenicity of coccidia isolated from recent field samples
against those in Coccivac. Based on the data, the antigens in Coccivac provided
good protection against field isolates.
The objective of the study was to determine the incidence of field strains of
Eimeria that show differences in antigenic properties from those antigens in the
Coccivac vaccine. Field isolates collected from 60 broiler and breeder pullet
farms across the USA. The chickens (n=70/group) were inoculated per os with one
dose of Coccivac-B or Coccivac-D during the first week of life. Inoculated birds
were placed into floor pens on clean wood shavings, then grown to approximately
35 days of age. Following immunization, birds were tagged and placed into
assigned treatment groups. Attempts were not made to purify the inocula, but to
standardize the E. maxima level to 100,000 sporulated oocysts per bird. Birds
from the immunized group and their un-immunized hatch-mates were challenged with
inocula of field isolates. The un-immunized hatch-mates served as the positive
controls. Birds kept in the challenge phase between 144 to 156 hr, the following
processes were followed: euthanasia, necropsy and intestines examined grossly
for coccidial lesions using a 0 to 4 scoring system. Mucosal scrapings taken
from the duodenal loop, jejunum, ileum and ceca were then placed on microscope
slides for microscopic evaluations. Microscopic evaluation (scored 0 to 4) was
made using a compound light microscope. Severity of infection (0 = no parasite,
1 = 1 to 10 per field, 2 = 11 to 20 per field, 3 = 21 to 40 per field and 4 =
> 50 per field for E. maxima).
Birds immunized with Coccivac and challenged with field isolates demonstrated
substantial immunity as determined by the level of parasitism in the immunized
birds vs the non-immunized groups for E. acervulina, E. tenella and E. maxima.
The average level of protection provided by Coccivac against the three
predominant species of field isolates of Eimeria (E. acervulina, E. maxima and
E. tenella) were: 97%, 86% and 91%, respectively.