Efficacy of ivermectin against gastrointestinal nematodes of cattle in Denmark evaluated by different methods for analysis of faecal egg count reduction.
The efficacy of ivermectin (IVM) against gastrointestinal nematodes in Danish cattle was assessed by faecal egg count reduction test (FECRT). Six cattle farms with history of clinical parasitism and avermectin use were included. On the day of treatment (Day 0), 20 naturally infected calves per farm (total n = 120) were stratified by initial faecal egg counts (FEC) and randomly allocated to a treatment group dosed with 0.2 mg IVM kg-1body weight s.c. (IVM; n = 10) or an untreated control group (CTL; n = 10). Individual FEC were obtained at Day 0 and Day 14 post-treatment and pooled faeces by group were cultured to isolate L3 for detection of Ostertagia ostertagi and Cooperia oncophora by qPCR. Treatment efficacies were analysed using the recommended WAAVP method and two open-source statistical procedures based on Bayesian modelling: 'eggCounts' and 'Bayescount'. A simulation study evaluated the performance of the different procedures to correctly identify FEC reduction percentages of simulated bovine FEC data representing the observed real data. In the FECRT, reduced IVM efficacy was detected in three farms by all procedures using data from treated animals only, and in one farm according to the procedures including data from treated and untreated cattle. Post-treatment, O. ostertagi and C. oncophora L3 were detected by qPCR in faeces of treated animals from one and three herds with declared reduced IVM efficacy, respectively. Based on the simulation study, all methods showed a reduced performance when FEC aggregation increased post-treatment and suggested that a treatment group of 10 animals is insufficient for the FECRT in cattle. This is the first report of reduced anthelmintic efficacy in Danish cattle and warrants the implementation of larger surveys. Advantages and caveats regarding the use of Bayesian modelling and the relevance of including untreated cattle in the FECRT are discussed.
Section for Bacteriology, Pathology and Parasitology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870 Frederiksberg C, Denmark. Electronic address: miap@vet.dtu.dk.
Miguel
M
Peña-Espinoza
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlægevej 100, 1870 Frederiksberg C, Denmark.
Stig M
SM
Thamsborg
Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Grønnegårdsvej 8, 1870 Frederiksberg C, Denmark.
Matthew J
MJ
Denwood
Section for Bacteriology, Pathology and Parasitology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870 Frederiksberg C, Denmark; Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Grønnegårdsvej 8, 1870 Frederiksberg C, Denmark.
Markus
M
Drag
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlægevej 100, 1870 Frederiksberg C, Denmark.
Tina V
TV
Hansen
Section for Epidemiology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870 Frederiksberg C, Denmark.
Vibeke F
VF
Jensen
Section for Bacteriology, Pathology and Parasitology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870 Frederiksberg C, Denmark; Norwegian Veterinary Institute, Ullevålsveien 68, PO Box 750 Sentrum, N-0106, Oslo, Norway.
Heidi L
HL
Enemark
D000818:Animals; D000977:Antiparasitic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002417:Cattle; D003718:Denmark; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D007411:Intestinal Diseases, Parasitic / Q000188:drug therapy / Q000469:parasitology; D007559:Ivermectin / Q000008:administration & dosage / Q000494:pharmacology*; D010028:Ostertagia / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D010270:Parasite Egg Count; D010273:Parasitic Diseases, Animal / Q000188:drug therapy / Q000469:parasitology; D060888:Real-Time Polymerase Chain Reaction; D014251:Trichostrongyloidea / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
D000977:Antiparasitic Agents; D007559:Ivermectin
Bayesian modelling; Cattle; Faecal egg count reduction test; Gastrointestinal nematodes; Ivermectin; Real-time PCR