+ Site Statistics
+ Search Articles
+ PDF Full Text Service
How our service works
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ Translate
+ Recently Requested

Evaluation of a larval development assay (DrenchRite) for the detection of anthelmintic resistance in cyathostomin nematodes of horses



Evaluation of a larval development assay (DrenchRite) for the detection of anthelmintic resistance in cyathostomin nematodes of horses



Veterinary Parasitology 121(1-2): 125-142



A larval development assay (LDA, DrenchRite) was evaluated to determine the effectiveness of this method in detecting anthelmintic resistance in cyathostomin nematodes of horses. A total of 15 horse farms from Georgia and South Carolina (USA) and Population S ponies from the University of Kentucky (USA) were included in this study. Nematode eggs were extracted from pooled fecal samples and placed into the wells of a DrenchRite plate for testing against thiabendazole (TBZ), levamisole (LEV) and 2 ivermectin (IVM) analogs (IVM-1, IVM-2). After a 7-day incubation larvae in each well were counted and data were analyzed by logistic regression. Resistance status of each farm for different drugs was determined in a separate study using a fecal egg count reduction test. LDA were performed on the 15 farms once, however, the Population S cyathostomins were assayed on 3 separate occasions to estimate the consistency of results between assays. Mean TBZ LC50 for oxibendazole resistant, suspected resistant and sensitive farms were 0.2015, 0.1625, and 0.1355 microM, respectively. For LEV, mean LC50 for PYR resistant, suspected resistant and sensitive farms were 1.590, 1.8018 and 1.4219 microM, respectively. All 15 farms had worms susceptible to IVM; mean LC50 for IVM-1 and for IVM-2 were 7.5727 and 87.9718 nM, respectively. A linear mixed model was fitted to the data to determine the relationship between LC50 and LC95 and resistance status for each farm. No meaningful relations were found. Consistency of assays varied between drugs, being best for TBZ and worst for LEV and IVM-1. All farms in this study had benzimidazole-resistant nematodes; therefore usefulness of DrenchRite for discriminating susceptibility versus resistance to this drug class could not be accurately assessed. Moreover, since all farms tested were sensitive to IVM and resistance to this drug class has not yet been reported in cyathostomins, it is not possible to assess accurately the usefulness of DrenchRite LDA for detecting IVM resistance at this time. Assay results for LEV suggest that LEV in a LDA does not yield data that is useful in estimating PYR efficacy in vivo. Based on results for PYR/LEV, the current high prevalence of benzimidazole resistance, no known cases of IVM resistance, and the sometimes extreme variation in results seen in many of the assays, DrenchRite LDA cannot be considered a useful tool for the diagnosis of resistance in cyathostomins of horses at present.

Please choose payment method:






(PDF emailed within 0-6 h: $19.90)

Accession: 048993478

Download citation: RISBibTeXText

PMID: 15110410

DOI: 10.1016/j.vetpar.2003.09.016


Related references

Larval development assay for detection of anthelmintic resistance in cyathostomins of Swedish horses. Veterinary Parasitology 128(3-4): 261-269, 2005

Evaluation of a larval development assay for the detection of anthelmintic resistance in Ostertagia circumcincta. International Journal for Parasitology 27(3): 305-311, 1997

Evaluation of the Egg Hatch Assay and the Larval Migration Inhibition Assay to detect anthelmintic resistance in cattle parasitic nematodes on farms. Parasitology International 61(4): 614-618, 2012

A larval development test for the detection of anthelmintic resistance in nematodes of sheep. Research in Veterinary Science 49(2): 198-202, 1990

A microlarval development assay for the detection of anthelmintic resistance in sheep nematodes. Veterinary Record 130(20): 442-446, 1992

Standardization of larval development assay for detection of anthelmintic resistance in Haemonchus contortus. Journal of Veterinary Parasitology 17(1): 21-25, 2003

Anthelmintic therapy of equine cyathostomin nematodes - larvicidal efficacy, egg reappearance period, and drug resistance. International Journal for Parasitology 48(2): 97, 2018

Evaluation of egg hatch assay for detection and risk analyses of antihelmintic resistance in strongylid nematodes of horses. Revista Scientia Parasitologica 5(1/2): 33-38, 2004

Arrested larval development and anthelmintic resistance in cattle nematodes. Parasitology Today 4(4): 106, 1988

Larval development test for detection of anthelmintic resistant nematodes. Research in Veterinary Science 45(1): 50-53, 1988

Reliability and reproducibility of the larval paralysis test as an in vitro method for the detection of anthelmintic resistance of nematodes against levamisole and morantel tartrate. Veterinary Parasitology 30(3): 223-232, 1989

Modelling the development of anthelmintic resistance in cyathostomin parasites: The importance of genetic and fitness parameters. Veterinary Parasitology 269: 28-33, 2019

Lack of Cyathostomin sp. reduction after anthelmintic treatment in horses in Brazil. Veterinary Parasitology 194(1): 35-39, 2013

Anthelmintic resistance in nematodes of horses. Veterinary Research 33(5): 491-507, 2002

Control of anthelmintic resistance in nematodes of horses. Irish Veterinary Journal 47(7): 320-325, 1994