Higher incidence of Eimeria spp. field isolates sensitive to diclazuril and monensin after live coccidiosis vaccination with Paracox™-5
H.W. Peek and W.J.M. Landman
w.landman@gdvdieren.nl
Animal Health Service Ltd., P.O. Box 9,
7400 AA Deventer, the Netherlands
Abstract
Twenty Eimeria spp. field isolates originating from Danish, German, Greek,
Italian, Portuguese and Rumanian broiler farms were subjected to anticoccidial
drug sensitivity testing. The anticoccidial drugs tested were diclazuril (Clinacox®)
and monensin (Elancoban®) at a concentration of 1.1 mg/kg and 103 mg/kg
respectively. The assay was performed in experimental battery cages. Broiler
chickens fed with anticoccidial drugs were infected with a defined number of
sporulated oocysts of the Eimeria spp. field isolates. An infected unmedicated
control group was given the same inoculum and served as positive control while
an uninfected unmedicated group was used as negative control. Coccidial lesion
scores, oocysts shedding and weight gain were used as parameters. Based on the
percentages of reduction of mean lesion scores of the infected medicated birds
compared to the infected non-medicated chicks, the results show that resistance
is common amongst European coccidiosis field isolates, especially E. acervulina
(68 and 53% resistance for diclazuril and monensin, respectively). Resistance is
less frequent amongst E. maxima (38 and 50% resistance to diclazuril and
monensin, respectively) and E. tenella isolates (23 and 38% resistance to
diclazuril and monensin, respectively). Statistical analysis by the Chi-Square
test showed a highly significant influence of the coccidiosis prevention program
(live coccidiosis vaccination with Paracox™-5 versus anticoccidial drugs in
feed) on the sensitivity pattern of Eimeria spp. field isolates to both
diclazuril (P = 0.000) and monensin (P = 0.001). When looking at coccidia
species and anticoccidial drug level, a significant effect of vaccination on the
sensitivity profile of E. acervulina to monensin (P = 0.018), E. tenella for
diclazuril (P = 0.007) and E. maxima to diclazuril (P = 0.009) was found –
thus, in half of the cases. The present study shows that sensitivity to the
anticoccidial drugs diclazuril and monensin is more frequent in Eimeria spp.
field isolates originating from broiler farms where a coccidiosis vaccination
policy was followed.