Parasites Of Horses Research Articles

Equine parasites: diagnosis and control - a current perspective

Equine parasites: diagnosis and control - a current perspective

Equine cyathostomins: a review of biology, clinical significance and therapy

The small strongyles of horses, also known as cyathostomins, are considered the most prevalent and pathogenic parasites of horses today. The clinical syndrome of larval cyathostominosis which occurs as a result of mass emergence of inhibited stages has a high fatality rate despite the best standard of care given to affected horses. Management of the challenge level of cyathostomins to prevent the syndrome is preferable. Many different management programmes have been tried over the past two decades, with mixed success. Programmes have relied heavily on repeated use of anthelmintic treatments throughout the life of a horse. The widespread incidence of resistance to certain anthelmintics is reducing these options. An understanding of the biology of cyathostomins, risk factors for infection and appropriate strategic use of still effective anthelmintics is essential for the future management of this parasite group. This review highlights the necessity to use currently available anthelmintics that are appropriately suited to the biology of cyathostomins, and to maintain heir efficacy through an appropriate treatment strategy.

Intestine ultrastructure of the facultative parasite Halicephalobus gingivalis (Nematoda: Panagrolaimidae)

Abstract Halicephalobus gingivalis, classified as a free-living nematode, is a known facultative parasite of horses, zebras and humans. However, detailed information concerning its internal morphology is lacking, especially in relation to possible adaptations to its lifestyle as a facultative parasite. The research presented here uses TEM and PI staining to analyse the morphology of the intestine of H. gingivalis. Specimens cultured under different conditions were included to determine if differences in ultrastructure are induced by culturing method. TEM analysis revealed that the intestinal tract comprises a single layer of cells in which nine pairs of nuclei can be distinguished. Further, unusual dichotomously and trichotomously branched microvilli were observed next to finger-like cylindrical microvilli, the latter being the most commonly described form in nematodes. Finally, three different types of secretion vesicles, i.e., spherical (type I), thread-like (type II) and enlarged globular (type III), occurred independently from each other along the intestinal tract. The relationship of morphological adaptations of the microvilli to parasitism in nematodes is discussed.

Prevalência de Cryptosporidium spp e Giardia sp em eqüinos estabulados no Jockey Club de Santa Maria - RS, Brasil

O Cryptosporidium spp. e a Giardia sp. são atualmente reconhecidos como os principais patógenos entéricos com potencial zoonótico. O presente estudo visou estabelecer a prevalência desses protozoários em eqüinos hospedados no Jockey Club de Santa Maria, RS, Brasil, no período de 19 de maio a 30 de junho de 2007. Foram coletadas amostras de fezes, diretamente da ampola retal, de 64 animais. As amostras de fezes foram processadas por meio do método de centrifugação-flutuação de Faust modificado. Posteriormente essas amostras foram visualizadas ao microscópio óptico para a pesquisa de cistos e oocistos. Os resultados encontrados revelaram a presença de Cryptosporidium spp. em 75% (48/64) das amostras. Cistos de Giardia sp. não foram encontrados nas amostras de fezes analisadas. A freqüência de Cryptosporidium spp. nas diferentes faixas etárias foi de 83,3% (15/18) nos potros até dois anos de idade, 71% (22/31) nos jovens entre dois e cinco anos e 80% (12/15) nos adultos. Os resultados demonstram que o Cryptosporidium spp. está amplamente disseminado na população de eqüinos do Jockey Club de Santa Maria e pode representar uma fonte de infecção significativa para a população da região.

Sequence heterogeneity in the 18S rRNA gene within Theileria equi and Babesia caballi from horses in South Africa

A molecular epidemiological survey of the protozoal parasites that cause equine piroplasmosis was conducted using samples collected from horses and zebra from different geographical locations in South Africa. A total of 488 samples were tested for the presence of Theileria equi and/or Babesia caballi using the reverse line blot hybridization assay. Ten percent of the samples hybridized to the Theileria/ Babesia genus-specific probe and not to the B. caballi or T. equi species-specific probes, suggesting the presence of a novel species or genotype. The small subunit of rRNA gene (18S; ∼1600 bp) was amplified and sequenced from 33 of these 488 samples. Sequences were compared with published sequences from the public sequence databases. Twelve distinct T. equi and six B. caballi 18S rRNA sequences were identified. Alignments demonstrated extensive sequence variation in the V4 hypervariable region of the 18S rRNA gene within T. equi. Sequence variation was also found in B. caballi 18S rRNA genes, although there was less variation than observed for T. equi. Phylogenetic analysis based on 18S rRNA gene sequences revealed three T. equi clades and two B. caballi clades in South Africa. The extent of sequence heterogeneity detected within T. equi and B. caballi 18S rRNA genes was unexpected since concerted evolution is thought to maintain homogeneity within repeated gene families, including rRNA genes, in eukaryotes. The findings reported here show that careful examination of variants of the 18S rRNA gene of T. equi and B. caballi is required prior to the development of molecular diagnostic tests to detect these parasites in horses. Species-specific probes must be in designed in regions of the gene that are both conserved within and unique to each species.

A review of the use of moxidectin in horses

SummaryMoxidectin has broad‐spectrum anti‐nematodal and anti‐arthropodal activities in the horse but is not effective against tapeworms or flukes. Moxidectin and ivermectin have the same efficacy against internal, adult parasites of horses. Moxidectin, however, is highly effective in eliminating encysted and hypobiotic larval stages of cyathostomins, whereas ivermectin is not. Treatment of horses with moxidectin results in an egg‐reappearance period (ERP) of 15–24 weeks. Because of its long ERP, moxidectin is labelled to be used at 12 week intervals. Moxidectin may provide protection against infection by ingested cyathostomin larvae for 2–3 weeks after it is administered.The larvicidal activity of moxidectin has often been compared to that of fenbendazole administered at either 7.5 or 10 mg/kg bwt for 5 consecutive days. The efficacy of fenbendazole, when administered daily for 5 consecutive days at 7.5 or 10 mg/kg bwt, against all stages of cyathostomins is often less than that of moxidectin because resistance of cyathostomins to benzimidazoles is prevalent worldwide, and the 5 day course of fenbendazole does not overcome this resistance. There are now reports of resistance of ascarids to moxidectin. Overt resistance of cyathostomins and a shortened egg re‐emergence period after treatment with moxidectin have been reported. Rapid removal of manure by natural fauna can significantly reduce larval nematode concentrations and thereby reduce intervals of anthelmintic treatment. Of the macrocyclic lactones, moxidectin has the least deleterious effect on faecal fauna.

Illustrated identification keys to strongylid parasites (strongylidae: Nematoda) of horses, zebras and asses (Equidae)

The Equidae (the horse, Equus caballus, the ass, Equus asinus, zebras and their hybrids) are hosts to a great variety of nematode parasites, some of which can cause significant morbidity or mortality if individual hosts are untreated. Worldwide the nematode parasites of horses belong to 7 suborders, 12 families, 29 genera and 83 species. The great majority (19 of 29 genera and 64 of 83 species) are members of the family Strongylidae, which includes the most common and pathogenic nematode parasites of horses. Only the Strongylidae are included in this treatise. The Strongylidae (common name strongylids) of horses – nematodes with a well-developed buccal capsule, a mouth collar with two leaf-crowns, and a strongyloid (common name of superfamily Strongyloidea) copulatory bursa – can be separated into two subfamilies: Strongylinae (common name strongylins), usually large or medium-sized with a globular or funnel-shaped buccal capsule; and Cyathostominae (common name cyathostomins), usually small to medium-sized with a cylindrical buccal capsule. The increased attention to strongylid nematode parasites of horses has resulted in the need for updated diagnostic keys to these parasites using readily recognizable characters and the most recent literature on their systematics. Because the cyathostomins have been historically difficult to identify, and because they have emerged as the most significant nematode pathogens of horses, we provide a brief nomenclatural and taxonomic history and an introduction to the morphology of this group. This treatise is intended to serve as a basic working tool—providing easy identifications to genus and species of adult strongylid nematodes of equids. All strongylid nematodes normally parasitic in horses, the ass (and their hybrids), and zebras are included. The keys are illustrated with line drawings and halftone photomicrographs of each species. A short discussion of the systematics of the genus and species is provided for each genus following the species descriptions. Species diagnoses and a synonymy of each species is provided. Geographic distribution, prevalence, and location in host are also given for each species.

Presence of Gasterophilus (Leach, 1817) (Díptera: Oestridae) in horses in Rio Grande do Sul State, Brazil

ABSTRACT With the purpose of verify the presence of larvae from the genus Gasterophilus in the Rio Grandedo Sul State, a study was undertaken using 395 horses taken to slaughter in the city of Pelotas. Thematerial analysis revealed that 126 animals (31,90%) presented infection, with 100 animals (25,32%)infected by Gasterophilus nasalis , and 47 animals (11,90%) infected by G . intestinalis . These resultsalso represent the first report of the definite establishment of G. intestinalis as a horse parasite inBrazil. The probable implications of G. intestinalis occurrence in Brazil are discussed. Key words: Gasterophilus; G. nasalis; G. intestinalis. * Laboratorio de Doencas Parasitarias da Faculdade de Veterinaria, UFPel, Pelotas, Brasil.** Setor de Parasitologia, Departamento de Microbiologia, Instituto de Ciencias Basicas da Saude, UFRGS, PortoAlegre, Brasil. INTRODUCTIONThe genus Gasterophilus (Diptera, Oestridae)includes eight species of flies whose larvae causegastrointestinal myiasis in equids

Cloning and characterization of genes encoding α and β subunits of glutamate-gated chloride channel protein in Cylicocyclus nassatus

The invertebrate glutamate-gated chloride channels (GluCls) are receptor molecules and targets for the avermectin–milbemycin (AM) group of anthelmintics. Mutations in GluCls are associated with ivermectin resistance in the soil dwelling nematode Caenorhabditis elegans and the parasitic nematode Cooperia oncophora. In this study, full-length cDNAs encoding α and β subunits of GluCl were cloned and sequenced in Cylicocyclus nassatus, a common and important cyathostomin nematode parasite of horses. Both genes possess the sequence characteristics typical of GluCls, and phylogenetic analysis confirms that these genes are evolutionarily closely related to GluCls of other nematodes and flies. Complete coding sequences of C. nassatus GluCl-α and GluCl-β were subcloned into pTL1 mammalian expression vector, and proteins were expressed in COS-7 cells. Ivermectin-binding characteristics were determined by incubating COS-7 cell membranes expressing C. nassatus GluCl-α and GluCl-β proteins with [ 3H]ivermectin. In competitive binding experiments, fitting the data to a one site competition model, C. nassatus GluCl-α was found to bind [ 3H]ivermectin with a high amount of displaceable binding (IC 50 = 208 pM). Compared to the mock-transfected COS-7 cells, the means of [ 3H]ivermectin binding were significantly different for C. nassatus GluCl-α and the Haemonchus contortus GluCl (HcGluCla) ( p = 0.018 and 0.023, respectively) but not for C. nassatus GluCl-β ( p = 0.370). This is the first report of orthologs of GluCl genes and in vitro expression of an ivermectin-binding protein in a cyathostomin species. These data suggest the likelihood of a similar mechanism of action of AM drugs in these parasites, and suggest that mechanisms of resistance may also be similar.

Expression of recombinant β-tubulin alleles from Cylicocyclus nassatus (Cyathostominae)

Small strongyles (Cyathostominae) are common nematode parasites of horses that have developed resistance to the benzimidazole anthelmintics used to control their populations. Evidence suggests that the principal mechanism of resistance involves a phenylalanine-to-tyrosine mutation at codon 200 in the beta-tubulin proteins that are components of microtubules. Other works, however, suggest that a phenylalanine-to-tyrosine mutation at codon 167, or alternative mechanisms, may be involved. As part of an ongoing project examining the role that these two beta-tubulin mutations may play in benzimidazole resistance, we have cloned the wild-type allele and the two alleles with the phenylalanine-to-tyrosine mutations at codons 167 and 200 of the beta-tubulin isotype 1 gene from the small strongyle Cylicocyclus nassatus. In this work, we describe the construction of expression vectors containing these alleles and their expression in Escherichia coli.

External Parasites on Horses

Arthropod parasites of horses include internal bots that infest the digestive tract, mites that burrow in the skin and feed on the skin surface, ticks that infest the ears as well as the skin, lice that either suck blood or feed on skin, blood sucking flies and mosquitoes that range in size from biting gnats just observable with the naked eye to the large black horse flies which are almost one inch long. Non-biting flies such as house flies and face flies are also important in producing fly worry, irritation and disease transmission. This document is ENY-283 (IG139), one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date May 1980. Revised March 2006. ENY-283/IG139: External Parasites on Horses (ufl.edu)

A multicenter evaluation of the effectiveness of Quest ® Gel (2% moxidectin) against parasites infecting equids

Controlled trials with a common protocol were conducted in Idaho, Illinois and Tennessee to evaluate anthelmintic effectiveness of Quest ® Gel (QG; 2% moxidectin) against lumenal parasites in horses. Candidate horses were required to have naturally acquired nematode infections, as confirmed by presence of strongylid eggs in feces. At each site, 24 equids were blocked on the basis of pretreatment strongyle fecal egg counts (EPG) and randomly assigned to treatments within blocks. Within each block of two animals, one received QG on Day 0 at a dosage of 0.4 mg moxidectin/kg b.w. and one was an untreated control. Body weights measured the day before treatment served as the basis for calculating treatment doses. Horses assigned to treatment with QG received the prescribed dose administered orally with the commercially packaged Sure Dial™ syringe. Horses were necropsied 12–14 days after treatment, and lumenal parasites and digesta were harvested separately from each of five organs, including the stomach, small intestine, cecum, ventral colon and dorsal colon. Parasites from stomachs and small intestines were identified to genus, species and stage. Micro- (i.e., <1.5 cm) and macroparasites (i.e., >1.5 cm) in aliquots from the cecum, ventral colon and dorsal colon were examined in aliquots of approximately 200 parasites until at least 600 parasites had been identified to genus, species and stage or until all parasites in the 5% aliquot were examined, whichever occurred first. Data were combined across sites and analyzed by mixed model analysis of variance to assess the fixed effect of treatment and random effects of site and block within site. Because QG does not contain a cestocide, efficacy of QG against tapeworms was not significant ( P > 0.05). Based on geometric means, however, efficacy of QG was greater than 90% ( P < 0.05) against 38 species and developmental stages of cyathostomes, strongyles, bots, larval pinworms and ascarids encountered in at least 6 of 36 control horses in the combined data set. None of the horses treated with moxidectin exhibited evidence of adverse effects. Study results demonstrate QG, administered to horses with naturally acquired endoparasite infections at a dosage of 0.4 mg moxidectin/kg b.w., was highly effective against a broad range of equine parasitic infections.

Prevalence of gastrointestinal parasites in horses

Prevalence of gastrointestinal parasites in horses

Anoplocephala perfoliataof horses – significant scope for further research, improved diagnosis and control

Anoplocephala perfoliata is the commonest tapeworm parasite of horses and is incriminated as a significant cause of clinical disease (e.g., ileocaecal intussusception, caeco-caecal intussusception and/or caecal perforation), particularly in horses chronically infected with large numbers of worms. The high prevalence (approximately 20-80%) of the parasite in some countries suggests an increased risk of clinical cases. In spite of research, there is still a paucity of information regarding the pathogenesis of the disease, the epidemiology of the parasite in different geographical regions and there are significant limitations with the diagnosis of infection. The present article provides an account of the biology, epidemiology and pathogenic effects of A. perfoliata, the diagnosis of infection and treatment. It highlights some gaps in knowledge of the parasite and the disease it causes, and suggests opportunities for future research and prospects for improved diagnosis, prevention and control.

Evaluation of the Efficacy of Oral Paste Formulations of Ivermectin against Gastrointestinal Parasites in Horses

The anthelmintic efficacy of oral paste formulations of ivermectin against gastrointestinal parasites in horses was evaluated, using fifteen active racehorses in which nematodes had been detected in their gastrointestinal tracts by fecal examination. A single dose of ivermectin was given orally to twelve horses of the treatment groups at a dosage rate of 200 μg/kg in order to obtain and identify gastrointestinal parasites in their feces for 3 days after treatment. Small strongyles, strongyles, and Parascaris equorum were found passed in feces up to post-treatment day (PTD) 2, but they were no longer observed on PTD 3. Horse bot fly Gasterophilus spp. larvae were found on PTD 2 and 3. The percentages of small strongyles found on PTD 1 were 75-100% (88% on average), and the rest were found (12% on average) on PTD 2. The nematodes were 16 species from 7 genera, of which 11 species were identified as small strongyles. In the fecal examination conducted on PTD 14, all horses of the treatment groups showed negative for nematode eggs. No abnormalities were observed in general clinical signs of the treated horses for 14 days after treatment. Three non-treated horses of the control groups still showed positive for nematode eggs on PTD 14. These results confirm that when ivermectin was given orally to horses at a dosage rate of 200 μg/kg, small strongyles, strongyles, and P. equorum, were excreted in feces up to PTD 2, and Gasterophilus spp. larvae on and after PTD 2, demonstrating the potent anthelmintic efficacy of ivermectin against these parasites.

Occurrence of gastrointestinal parasites in horses in metropolitan Perth, Western Australia.

To assess the occurrence of gastrointestinal parasites in horses in Perth. To apply polymerase chain reaction (PCR) for the identification of some species of encysted larval cyathostomes. Between February and September of 2000, the gastrointestinal tracts of 29 horses submitted to a local knackery and Murdoch University Veterinary hospital in Perth were examined post mortem for the presence of gastrointestinal parasites. The gastrointestinal tract was divided into six sections, which were screened for the presence of parasites such as Gasterophilus sp, Anoplocephala sp and Parascaris equorum. Samples of contents were taken for worm counts. Cyathostomes were found in 28 of the 29 horses. Eighteen species of gastrointestinal helminths were identified. Twelve of these were cyathostomes, with the four most common species being Cyathostomum catinatum, Cylicocyclus nassatus, Cylicostephanus longibursatus and Cylicostephanus goldi. The large strongyle, Triodontophorus serratus, was found in three of the horses but species of Strongylus were not found. In contrast to a study conducted on horses from this region in 1985, cyathostomes were the most common gastrointestinal parasites found. The four most common cyathostome species found in the present study correlated well with findings of studies in other locations. The high number of cyathostomes may be due to the increase in resistance to anthelmintics among the species, and to improper anthelmintic use. The apparent reduction in number of large strongyles may be due to the widespread use of ivermectin, which is very effective against these parasites, and also possibly because some larvae may not have been detected.

Inhibition of equine cyathostomes to glucosinolate hydrolysis products

Cyathostome nematodes have become the central focus of concerns related to internal parasites of horses due to their pathological and persistent effects on the growing and mature horse (Murphy and Love, 1997). Current anthelmintic treatments have, however, led to resistance and alternative control measures are required. Glucosinolate hydrolysis derivatives have a wide range of biological activities, and have previously been shown to inhibit root nematodes (Brown and Morra, 1997). The aim of the study was to examine whether cyathostome nematode eggs could be inhibited by glucosinolate hydrolysis products.An in vitro egg hatch assay was set up using eggs extracted from the faeces of naturally infected horses (Kassai, 1999). The egg suspension (containing approximately 100 eggs) were incubated with nine different concentrations (range: 20-10,000 ppm) of the glucosinolate hydrolysis products (allyl isothiocyanate (C), allyl nitrile (N) and phenethyl isothiocyanate (P). A control was set up in which water replaced the hydrolysis product. The number of eggs and larvae were counted using an inverted microscope. Statistical differences between treatments were assessed using General Linear Model, ANOVA.

Anthelmintic resistance in nematodes of horses.

Suppressive anthelmintic treatment strategies originally designed to control Strongylus vulgaris in horses were extremely successful in reducing morbidity and mortality from parasitic disease. Unfortunately, this strategy has inadvertently resulted in the selection of drug-resistant cyathostomes (Cyathostominea), which are now considered the principal parasitic pathogens of horses. Resistance in the cyathostomes to benzimidazole drugs is highly prevalent throughout the world, and resistance to pyrantel appears to be increasingly common. However, there are still no reports of ivermectin resistance in nematode parasites of horses despite 20 years of use. It is unknown why resistance to ivermectin has not yet emerged, but considering that ivermectin is the single most commonly used anthelmintic in horses most parasitologists agree that resistance is inevitable. The fecal egg count reduction test is considered the gold standard for clinical diagnosis of anthelmintic resistance in horses, but diagnosis is complicated by lack of an accepted standard for the performance of this test or for the analysis and interpretation of data. Presently there is very little data available on the molecular mechanisms of anthelmintic resistance in cyathostomes; beta-tubulin gene is the only anthelmintic-resistance associated gene that has been cloned. The increasingly high prevalence of anthelmintic-resistant cyathostomes must be taken into account when designing worm control programs for horses. Strategies to decelerate further selection for drug resistance thereby extending the lifetime of currently effective anthelmintics should be implemented whenever possible. Considering the nature of the equine industry in which horses often graze shared pastures with horses from diverse locations, transmission and widespread dispersal of resistant parasites is virtually assured. A proactive approach to this problem centered on understanding the molecular basis of anthelmintic resistance in cyathostomes is required if we are to expect chemical control of nematodes in horses to remain a viable element of parasite control in the future.

World association for the advancement of veterinary parasitology (WAAVP): second edition of guidelines for evaluating the efficacy of equine anthelmintics

These guidelines have been designed to assist in the planning, operation and interpretation of studies which would serve to assess the efficacy of drugs against internal parasites of horses. Although the term anthelmintic is used in the title and text, these guidelines include studies on drug efficacy against larvae of horse bot flies, Gasterophilus spp., which are non-helminth parasites commonly occurring in the stomach of horses. The advantages, disadvantages and application of critical and controlled tests are presented. Information is also provided on selection of animals, housing, feed, dose titration, confirmatory and clinical trials, record keeping and necropsy procedures. These guidelines should assist both investigators and registration authorities in the evaluation of compounds using comparable and standard procedures with the minimum number of animals.

Equine Immunity to Parasites

Helminths are among the most significant parasites of horses in developed countries. This article examines immune responses against helminth parasites and the implications that immunologic investigations have on vaccine development, improvement of diagnostic procedures, and disease eradication.