Topic:Anthelmintic Resistance
Anthelmintic resistance in horses refers to the reduced effectiveness of deworming agents, known as anthelmintics, in controlling parasitic worm populations. This phenomenon arises when parasites develop the ability to survive treatments that previously were effective at standard doses. Anthelmintic resistance is a growing concern in equine management, as it can lead to increased parasite burdens and associated health issues in horses. Common parasites affected by resistance include small strongyles (cyathostomins) and ascarids (Parascaris spp.). This page compiles peer-reviewed research studies and scholarly articles that explore the mechanisms, prevalence, and management strategies related to anthelmintic resistance in equine populations.
A survey of helminth control practices in equine establishments in Ireland. We report the results of a survey to assess the attitudes of horse owners and managers of equine businesses in Ireland to the control of helminth parasites, and the extent to which veterinary practitioners are involved in providing advice on parasite control of horses. Replies to our questionnaire indicated that there is a high level of awareness on the need for helminth control, typically leading to several doses of anthelmintic being administered to each animal every year. While a majority of respondents (61%) were concerned about the issue of anthelmintic resistance, only a few were of the ...
Comparative use of faecal egg count reduction test, egg hatch assay and beta-tubulin codon 200 genotyping in small strongyles (cyathostominae) before and after benzimidazole treatment. A survey on benzimidazole (BZ) resistance in small strongyles was performed on three farms in the tenth region in Chile. Samples from a total of 100 horses were tested using the faecal egg count reduction test (FECRT), the egg hatch assay (EHA) and an allele-specific PCR for the detection of beta-tubulin isotype 1 genes coding for phenylalanine (phe) or tyrosine (tyr) at codon 200. In the past, BZ-type drugs have been used within anthelmintic campaigns on all the three farms. This has predictably led to a high degree of BZ resistance at the Valdivia and Riñihue farms and to a lesser degree at...
Sustainable use of anthelmintics in grazing animals. It is suggested that the major factor in avoiding the development of anthelmintic resistance is the percentage of worms that do not encounter the anthelmintics (worms in refugia). This in turn is determined by the numbers of larvae on pasture, the percentage of animals treated and whether any stages in the host can avoid the action of anthelmintic. To maintain anthelmintic efficacy the percentage of worms in refugia must be sufficiently large. In cattle, this should involve treating only first-year animals and using a different pasture each year for calves. For sheep, only animals that have to...
Risk factors for high endoparasitic burden and the efficiency of a single anthelmintic treatment of Danish horses. A questionnaire survey regarding endoparasite control practices in Danish horse herds was carried out in 1995. The participating veterinarians and herd owners were sampled using convenience and purposive sampling. In the analysis of risk factors for development of a high endoparasitic burden (> 200 eggs per gram faeces) 903 horses were sampled and the analysis of the efficiency of a single anthelmintic treatment was based on 605 horses. The following factors had a significant effect on the endoparasitic burden: herd type, age of the horses, use of pasture rotation, anthelmintic treatment of ho...
Evaluation of tests for anthelmintic resistance in cyathostomes. Resistance, especially to the anthelmintic benzimidazoles (BZ), has been reported in horse cyathostomes world-wide. Diagnosis of resistance has traditionally been made by faecal egg count reduction (FECR) trials, however, this technique has limitations. Some of the shortcomings may be resolved by refining the test or by using an in vitro test. FECR tests and the larval development assay (LDA) were performed on adult horses held on 15 different horse properties across a wide geographical area of NSW, Australia. FECR were measured before and 10-14 after days treatment with oxibendazole (OBZ), mo...
Helminth control used by trainers of thoroughbreds in England. A telephone survey was conducted of the methods used to control parasitic worms at 106 thoroughbred training yards. Most of the horses were allowed access to grass and were therefore at risk of infection. The control methods relied primarily on the use of anthelmintics and appeared reasonably successful because only 44 per cent of trainers reported observing clinical signs of nematode infections. They dosed their horses frequently, 40 per cent treating every four to six weeks and 25 per cent treating every seven to eight weeks. New arrivals on yards were usually treated with anthelmintic but t...
International harmonisation of anthelmintic efficacy guidelines (Part 2). The "International Co-operation on Harmonisation of Technical Requirements for Registration of Veterinary Medicinal Products (VICH)" is an international programme of co-operation between regulatory authorities and the animal health industries of the European Union, Japan and the United States of America which aims to harmonise the technical requirements for the registration of veterinary medicinal products. Australia and New Zealand participate as active observers. The objective of this second paper is to present additional guidelines established by the Working Group on anthelmintic guidelines...
Nematodes and liver fluke in New Zealand. Abstract A general review of the epidemiology, significance and control of nematode parasitism of sheep, goats, cattle and deer in New Zealand, the emergence of anthelmintic resistance and its effects, and the search for parasite control strategies that reduce reliance on anthelmintic use, is provided. The research that has formed the basis for present levels of understanding of this complex and important topic is summarised and sources of further information are indicated. Aspects of nematode infections of horses, pigs, dogs and cats, and the history of the liver fluke, Fasciola hepatica, in ...
Cyathostome fecal egg count trends in horses treated with moxidectin, ivermectin or fenbendazole. Commercial preparations of fenbendazole (Safe-Guard, Intervet), ivermectin (Eqvalan, Merial) or moxidectin (Quest, Fort Dodge) were administered once to horses scheduled for routine parasiticide treatment. In total, 93 horses from six cooperating farms were used in the study. Computer generated, random allocation of horses to treatment group was conducted at each farm. Fecal egg counts were determined for all horses on trial days 0, 56, 84 and 112, with corresponding calendar dates that were unique to each farm. Only strongyle egg counts from animals which were positive at day 0 were used for ...
Prevalence and clinical implications of anthelmintic resistance in cyathostomes of horses. To determine the prevalence and clinical implications of anthelmintic resistance in cyathostomes of horses. Methods: Prospective study. Methods: 80 horses on 10 farms in a 5-county region of northeast Georgia. Methods: 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 dete...
Antimicrobic and anthelmintic resistance. Antimicrobial and anthelmintic resistance are growing issues for the equine practitioner. The development of antimicrobial or anthelmintic resistance is a source of significant concern because of increased frequency of treatment failures and increased treatment costs. In addition, antimicrobial resistance may have important consequences for public health. Only through judicious use can the efficacy of antimicrobials and anthelmintics be prolonged. This article discusses the development of resistance and suggestions for control.
A study to evaluate the field efficacy of ivermectin, fenbendazole and pyrantel pamoate, with preliminary observations on the efficacy of doramectin, as anthelmintics in horses. The efficacy of ivermectin, fenbendazole, pyrantel pamoate and doramectin was evaluated under field conditions at 2 sites in the Free State Province of South Africa. The study involved 25 horses at each site, divided into 5 groups of equal size. Ivermectin, fenbendazole and pyrantel pamoate were administered orally at doses of 0.2, 10 and 19 mg/kg respectively. Doramectin was administered by intramuscular injection at a dose of 0.2 mg/kg. Treatment efficacy was based on the mean faecal egg count reduction 14 days post treatment. At site A a faecal egg count reduction of 100% was found after tr...
Continuance of studies on Population S benzimidazole-resistant small strongyles in a Shetland pony herd in Kentucky: effect of pyrantel pamoate (1992-1999). Research on benzimidazole-resistant Population S small strongyles began in a Shetland pony herd in 1974 at the University of Kentucky and has continued for over 25 years. The present update, for the period 1992-1999, evaluated activity of pyrantel pamoate (PRT) in field tests in the pony herd. Additional critical tests with PRT and oxibendazole (OBZ) were done in foals born in the herd. Activity of PRT was initially excellent in field tests, based on epg/lpg count data, but declined rapidly during the second full year of pyrantel treatments. Critical test data for small strongyles indicated ef...
Benzimidazole resistance in equine cyathostomes in Slovakia. The present study included 19 stud farms, including 243 horses, that were investigated for the occurrence of anthelmintic resistant cyathostomes. The number of horses on the farms varied from nine to more than 100, and horses of all ages were included. A minimum of seven horses were used for faecal egg count reduction (FECR) tests. The anthelmintics included were: fenbendazole (paste formulation), ivermectin (paste formulation) and pyrantel (powder). Resistance to benzimidazoles was detected on 14 farms, with FECR values ranging from 65.1 to 86.3%. Larval cultures after fenbendazole treatment ...
Parasite control methods used by horse owners: factors predisposing to the development of anthelmintic resistance in nematodes. One hundred and fifty horse owners, primarily private owners and riding schools, replied to a questionnaire concerning the practices they used to control parasites. Twenty-seven had experienced a parasite problem. Faecal samples from 188 horses selected at random showed that worm control practices were generally successful; however, many owners were not following recommendations for slowing the development of resistant parasites. In 1996, 86 per cent of the owners were using either three or two classes of anthelmintic a year, and they used a median of six doses with a range from one to 11. App...
Prospects for controlling animal parasitic nematodes by predacious micro fungi. Resistance against anthelmintics is widespread, particularly in parasitic nematode populations of small ruminants. Several new techniques or supplements have been developed or are under investigation. Biological control (BC) is one of these new methods. The net-trapping predacious fungus Duddingtonia flagrans produces thick walled resting spores, chlamydospores, which are able to survive passage through the gastrointestinal tract of cattle, horses, sheep and pigs. Under Danish climatic conditions it has been shown that the number of parasite larvae on pasture and the worm burden of the grazing...
Pharmacology of anthelmintic resistance in cyathostomes: will it occur with the avermectin/milbemycins? Anthelmintic-resistance has emerged as a problem in several animal industries. In the horse, cyathostome resistance to all available treatments except for the avermectin/milbemycins means that these drugs provide the cornerstone of control. Ivermectin has been available for several years; the related compound moxidectin is more recent. Although we do not know for sure, aspects of moxidectin such as its persistent action and its efficacy against mucosal stages of cyathostomes, may enhance the rate of development of resistance. On the other hand, selection pressure would be reduced if the persis...
Pathogenicity of cyathostome infection. Cyathostomes are now the principle parasitic pathogen of the horse: a remarkable transformation during the last 25 years from virtual obscurity to focus of attention in equine parasitology. This rise to prominence coincides with the marked decrease in prevalence of large strongyle infections as a result of widespread use of modern anthelmintic compounds. On the basis that strongyle-associated diseases continue to commonly occur in the absence of these large strongyle species, clinical attention has turned to the pathogenicity of cyathostomes. Although many horses harbour burdens of tens of tho...
Parasite diversity and anthelmintic resistance in two herds of horses. Diversity of parasite populations was compared between two herds of horses, one a regularly treated herd the other a feral herd which has bad no anthelmintic treatment for at least 25 years. Eggs obtained from fecal samples of both herds were tested for anthelmintic resistance by use of an in-vitro larval hatch/development assay (LDA), DrenchRite. A fecal egg reduction test was also performed with the domesticated herd using fenbendazole, pyrantel pamoate and ivermectin. Cyathostomes were the predominant group of worms present in both herds. Trichostrongylus axei was seen in both herds, but St...
Historical perspective of cyathostomes: prevalence, treatment and control programs. Small strongyles are highly prevalent in horses and can be found worldwide. Even though over 50 species of these parasites have been described, about 10 species comprise the bulk of the total number present in horses. Efforts to control small strongyles and other equine internal parasites have been undertaken for many years. Some of the early medications and control measures provided questionable activity against endoparasites; whether effective or not, they could be detrimental to the horse. Beginning in the early 1900s, scientific effort was used to evaluate activity of antiparasitic compoun...
Alternative approaches to control of cyathostomes: an African perspective. Cyathostomes are common nematode parasites of horses, donkeys and mules in developing countries. These equids usually work on a daily basis and this includes transportation of goods, crops and people. Stress, associated with work, and limited nutrition often result in a loss of condition, and cyathostomid nematodes may, then, cause clinical disease. Because anthelmintics are not always accessible or affordable in many parts of Africa, or there may be anthelmintic resistance to current remedies, management practices are often used as an adjunct to chemotherapy. This paper discusses some current...
Current concerns about control programs in temperate climates. Efforts to control cyathostome nematodes in temperate climates have not been uniformly successful, as evidenced by contemporary reports of clinical disease and widespread anthelmintic failure. Indeed, effective control is confounded by numerous factors, including ignorance of local transmission patterns, confusing or conflicting control recommendations, and use of ineffective anthelmintics or regimens. Most of these problems are universal rather than being climatically unique, and it is important to recognize that they are mere symptoms of larger and more comprehensive problems. The most basic...
Frontiers in anthelmintic pharmacology. Research in anthelmintic pharmacology faces a grim future. The parent field of veterinary parasitology has seemingly been devalued by governments, universities and the animal industry in general. Primarily due to the success of the macrocyclic lactone anthelmintics in cattle, problems caused by helminth infections are widely perceived to be unimportant. The market for anthelmintics in other host species that are plagued by resistance, such as sheep and horses, is thought to be too small to sustain a discovery program in the animal health pharmaceutical industry. These attitudes are both alarmi...
Species-specific amplification by PCR of ribosomal DNA from some equine strongyles. The first and second internal transcribed spacer sequences of 28 morphologically-defined species of horse strongyle were characterized, and specific oligonucleotide primers were designed for some species based on the nucleotide differences. Utilizing these primers, a PCR approach was developed for the specific amplification of ribosomal DNA of Strongylus vulgaris, Cyathostomum catinatum, Cylicocyclus nassatus, Cylicostephanus longibursatus or Cylicostephanus goldi. The method allowed the species-specific amplification of parasite DNA derived from faecal samples and/or copro-cultures, demonstra...
Persistence of the efficacy of a moxidectin gel on the establishment of cyathostominae in horses. A controlled trial was carried out to evaluate the persistence of the effect against small strongyles of a 2 per cent moxidectin gel administered orally to foals at a dose rate of 0.4 mg/kg bodyweight. Five of nine helminth-free foals were treated on day 0, and the remaining four foals were used as controls. On days 0, 7, 14, 21 and 28 all nine foals were infected experimentally with 200,000 small strongyle larvae. Three treated and two control foals were necropsied on day 42 and the rest on day 43. Fourteen species of small or medium sized small strongyles were found in the control foals, 10 ...
Survey of anthelmintic resistance on Danish horse farms, using 5 different methods of calculating faecal egg count reduction. This study reports on the prevalence of anthelmintic resistance in strongyles of horses in Denmark. Of 5 methods used for the calculation of faecal egg count reduction (FECR) the method recommended by the World Association for the Advancement of Veterinary Parasitology, for the detection of resistance in sheep was the most sensitive procedure for detecting resistance. Using this method benzimidazole resistance was detected on 33 of 42 farms (79%) examined. Pyrantel was tested on 15 farms and FECR tests indicate resistance on 3 (30%) farms. On 2 farms on which resistance to pyrantel was detecte...