Evaluation of prevalence and clinical implications of anthelmintic resistance in gastrointestinal nematodes in goats.
OBJECTIVE
To determine prevalence of resistance to all anthelmintics that are commonly used to treat gastrointestinal nematodes (GINs) in goats.


METHODS
Prospective study.


METHODS
777 goats.


METHODS
On each farm, goats were assigned to 1 of 5 treatment groups: untreated controls, albendazole (20 mg/kg [9.0 mg/lb], p.o., once), ivermectin (0.4 mg/kg [0.18 mg/lb], p.o., once), levamisole (12 mg/kg [5.4 mg/lb], p.o., once), or moxidectin (0.4 mg/kg, p.o., once), except on 3 farms where albendazole was omitted. Fecal samples were collected 2 weeks after treatment for determination of fecal egg counts (FECs), and percentage reductions were calculated by comparing data from anthelmintic-treated and control groups. Nematode populations were categorized as susceptible, suspected resistant, or resistant by use of guidelines published by the World Association for the Advancement of Veterinary Parasitology.


RESULTS
Resistance to albendazole was found on 14 of 15 farms, and resistance to ivermectin, levamisole, and moxidectin was found on 17, 6, and 1 of 18 farms, respectively. Suspected resistance to levamisole and moxidectin was found on 4 and 3 farms, respectively. Resistance to multiple anthelmintics (albendazole and ivermectin) was found on 14 of 15 farms and to albendazole, ivermectin, and levamisole on 5 of 15 farms. Mean overall FEC reduction percentages for albendazole, ivermectin, levamisole, and moxidectin were 67, 54, 94, and 99%, respectively.


CONCLUSIONS
Anthelmintic resistance in GINs of goats is highly prevalent in the southern United States. The high prevalence of resistance to multiple anthelmintics emphasizes the need for reexamination of nematode control practices.
Mortensen
Lars L
LL
Danish Center for Experimental Parasitology, Department of Veterinary Microbiology, Section for Parasitology, Royal Veterinary and Agricultural University, DK-1870 Frederiksberg C, Denmark.
Williamson
Lisa H
LH
Terrill
Thomas H
TH
Kircher
Robin A
RA
Larsen
Michael
M
Kaplan
Ray M
RM
D015766:Albendazole / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology* / Q000627:therapeutic use; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D005260:Female; D005845:Georgia / Q000453:epidemiology; D015511:Goat Diseases / Q000188:drug therapy* / Q000453:epidemiology / Q000469:parasitology; D006041:Goats; D007411:Intestinal Diseases, Parasitic / Q000188:drug therapy / Q000453:epidemiology / Q000662:veterinary*; D007559:Ivermectin / Q000494:pharmacology / Q000627:therapeutic use; D007978:Levamisole / Q000494:pharmacology / Q000627:therapeutic use; D008297:Male; D009348:Nematoda / Q000187:drug effects*; D009349:Nematode Infections / Q000188:drug therapy / Q000453:epidemiology / Q000662:veterinary*; D010270:Parasite Egg Count / Q000662:veterinary; D021261:Parasitic Sensitivity Tests / Q000662:veterinary; D015995:Prevalence; D011446:Prospective Studies; D011897:Random Allocation; D013022:South Carolina / Q000453:epidemiology
D000871:Anthelmintics; D007978:Levamisole; D007559:Ivermectin; D015766:Albendazole