Coccidiosis in Turkeys: Patterns of sensitivity to diclazuril following vaccination with Coccivac-T vaccine
Marcelo Lang1; Steve Fitz-Coy
1corresponding author
A series of trials were conducted to
determine the efficacy of Clinacox (diclazuril) in turkey flocks against
isolates collected from farms using different control programs for coccidiosis.
Isolates of coccidia were collected from farms that:
(1) Used only Coccivac-T vaccine in the year prior to collection
(2) Used Clinacox for six months, followed by an ionophore drug prior to
collection
(3) Used Clinacox for six months, followed by Coccivac-T prior to collection.
Three groups of poults did not receive medication and were challenged with
sporulated oocysts coming from each of the three sources (infected, unmedicated
controls, IUC). Three groups of poults received feed with diclazuril and were
inoculated with oocysts coming from one of the above sources. Another group
received diclazuril-free feed and was not challenged, serving as the unmedicated,
unchallenged control (UUC).
Growth rate at the end of 6 days post-challenge was depressed by an average of
37% on the IUC groups as compared to the UUC group. The average gross lesion
score of IUC birds was 2.0 and a microscopic parasite score of 3.27 (range 0 to
4, the higher the score the greater the severity) was assessed, compared to no
lesions and zero parasite burden in the UUC birds.
Index scores were determined using growth, gross lesions, microscopic parasitism
and livability; A higher index score indicates better efficacy. The average
indexes for the isolates obtained from source 1 were 40 and 96, for IUC and
diclazuril medicated birds, respectively. The average score for the samples
collected from source 2 were 35 and 60, for IUC and diclazuril medicated birds,
respectively. The average score for the samples collected from source 3 were 35
and 86, for IUC and diclazuril medicated birds, respectively.
The infectivity of the isolates was severe and similar on the IUC birds
regardless of source. On the other hand, the response of the isolates to
medication with diclazuril was different. Birds challenged with isolates from
sources 1 and 3 (where Coccivac-T vaccine had been used) showed better response
to medication than birds challenged with isolates from source 2, where
diclazuril had been used, but no vaccination was applied.
Using Coccivac-T vaccine in rotation with diclazuril appeared to provide a
sparing effect on the efficacy of the drug.