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presentation, with 1 dog lost to follow-up. Discussion Our work represents a novel case series, with outcome information, on dogs outside of the US (Canada) with detected hookworm, A caninum , anthelmintic resistance markers. Before our study, there
are beginning to fail because of the development of anthelmintic resistance in parasites. Anthelmintic resistance among gastrointestinal tract nematodes of small ruminants has been documented in many countries, with multidrug resistance becoming a
Abstract
Objective—To determine prevalence of resistance to all anthelmintics that are commonly used to treat gastrointestinal nematodes (GINs) in goats.
Design—Prospective study.
Animals—777 goats.
Procedure—On each farm, goats were assigned to 1 of 5 treatment groups: untreated controls, albendazole (20 mg/kg [9.0 mg/lb], PO, once), ivermectin (0.4 mg/kg [0.18 mg/lb], PO, once), levamisole (12 mg/kg [5.4 mg/lb], PO, once), or moxidectin (0.4 mg/kg, PO, 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 and Clinical Relevance—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. (J Am Vet Med Assoc 2003;223:495–500)
Abstract
Objective—To determine the prevalence and clinical implications of anthelmintic resistance in cyathostomes of horses.
Design—Prospective study.
Animals—80 horses on 10 farms in a 5-county region of northeast Georgia.
Procedure—On each farm, horses were stratified in descending order according to pretreatment fecal egg count (FEC), blocked into groups of 4, and then randomly assigned to 1 of 4 treatment groups: no treatment (controls), and treatment with pyrantel pamoate, fenbendazole, or ivermectin. Fecal samples were collected 24 hours prior to treatment and 2, 4, and 6 weeks after treatment for determination of FEC. Mean percentage of reduction in FEC was then calculated for each treatment group. For horses from each farm, the efficacy of each anthelmintic was categorized on the basis of mean percentage of reduction in FEC at 2 weeks after treatment (< 80% reduction = ineffective; 80 to 90% reduction = equivocal; and > 90% reduction = effective).
Results—Pyrantel pamoate was effective at reducing FEC in horses from 7 farms, ineffective in horses from 2 farms, and equivocal in horses from 1 farm. Fenbendazole was ineffective at reducing FEC in horses from 9 farms and equivocal in horses from 1 farm. Ivermectin was effective at reducing FEC in horses from all 10 farms.
Conclusions and Clinical Relevance—Results suggest that cyathostome resistance to fenbendazole is highly prevalent, and resistance to pyrantel pamoate is high enough to warrant concern. Resistance to ivermectin was not detected. On the basis of these data, it appears that ivermectin continues to be fully effective in horses. However, too few farms were used in this study to determine the prevalence of cyathostome resistance to ivermectin. Therefore, the efficacy of ivermectin should continue to be monitored closely. (J Am Vet Med Assoc 2001;218:1957–1960)
contortus . 3,4 Although the use of these products has often been effective at controlling parasitism by H contortus in the short term, marked anthelmintic resistance has been documented 1,5 in recent decades because overuse or underdosing has
Abstract
Objective—To determine prevalence of anthelmintic resistance in cyathostome nematodes of horses in the southern United States.
Design—Cross-sectional study.
Animals—786 horses on 44 farms and stables in Georgia, South Carolina, Florida, Kentucky, and Louisiana.
Procedure—Fecal egg count (FEC) reduction tests were performed on 44 large farms and stables. Horses on each farm were treated with an oral paste formulation of fenbendazole, oxibendazole, pyrantel pamoate, or ivermectin at recommended label dosages. A mixed linear model was fitted to the percentage reduction in FEC, accounting for differences among farms, states, ages, treatments, and treatment by state interactions.
Results—By use of a conservative measure of resistance (< 80% reduction), the percentage of farms with anthelmintic-resistant cyathostomes was 97.7%, 0%, 53.5%, and 40.5% for fenbendazole, ivermectin, oxibendazole, and pyrantel pamoate, respectively. Mean percentage reductions in FEC for all farms were 24.8%, 99.9%, 73.8%, and 78.6% for fenbendazole, ivermectin, oxibendazole, and pyrantel pamoate, respectively. Pairwise contrasts between states for each treatment revealed that in almost all instances, there were no significant differences in results between states.
Conclusions and Clinical Relevance—The prevalence of resistance found in this study was higher than that reported previously, suggesting that anthelmintic resistance in equine cyathostomes is becoming a major problem. Furthermore, data from these 5 southern states, which are geographically and physiographically distinct, were remarkably similar. This suggests that drug resistance in cyathostomes is highly prevalent throughout the entire southern United States and probably nationwide. (J Am Vet Med Assoc 2004;225:903–910)
Abstract
The primary aim of this article is to provide an overview of several selected skin conditions in livestock species. Topics include ectoparasites in alpacas, antler velvet in reindeer, immune-mediated disease in goats, ectoparasites in pigs, Culicoides allergic dermatitis and parapox infection in sheep. When dealing with skin disease in livestock, it is important to collect a detailed history and undertake a thorough clinical examination to include the axilla, groin, limbs and feet. While the diagnosis will often be anticipated from the history and presentation, it is important to consider a differential diagnosis list and appropriate diagnostic testing before embarking on a poly-pharmacy approach to “rule out” causes of disease. This is particularly important where morbidity is high and the livestock of perceived high value to the keeper/owner, such as goats and small-breed pigs, or when the skin condition is long standing/chronic. Ideally, the management plan should sequentially clarify the role of microbial infection and then ectoparasites before considering less common allergic and autoimmune conditions. Skin cytology is an invaluable in-house diagnostic method that can support the findings of culture. Taking skin samples for histopathology and possibly culture may prove valuable once other diagnostic methods have been explored. Given the need to protect the use of parenteral antimicrobials, topical antimicrobial therapies can be deployed successfully. The repeated use of macrocyclic lactones (avermectins) must be balanced in terms of the risks of promoting anthelmintic resistance versus controlling or eradicating the ectoparasites that have, ideally, been specifically identified.
Effective control of strongyles, particularly cyathostomes, is becoming increasingly difficult in horses as anthelmintic resistance becomes more commonly recognized. Only 3 drug groups, the benzimidazoles, avermectins, and pyrantel salts, have
observations of shortened ERPs in more contemporary compounds (macrocyclic lactones). 3–5 Anthelmintic resistance is an inherited trait passed from adult parasites to their offspring, and genetic reversion to susceptibility was shown to not occur in a 40-year
