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Topic:Parasites
Parasites are organisms that live on or within a host, deriving nutrients at the host's expense. In horses, parasitic infections can affect various systems, including the gastrointestinal tract, skin, and respiratory system. Common equine parasites include strongyles, ascarids, tapeworms, and bots. These parasites can lead to a range of health issues, from mild discomfort to severe disease, depending on the type and burden of the infestation. This page compiles peer-reviewed research studies and scholarly articles that explore the biology, life cycle, and impact of parasites on equine health, as well as strategies for diagnosis, treatment, and prevention of parasitic infections in horses.
Characteristics of a recent isolate of Sarcocystis neurona (SN7) from a horse and loss of pathogenicity of isolates SN6 and SN7 by passages in cell culture. An isolate of Sarcocystis neurona (SN7) was obtained from the spinal cord of a horse with neurologic signs. The parasite was isolated in cultures of bovine monocytes and equine spleen cells. The organism divided by endopolygeny and completed at least one asexual cycle in cell cultures in 3 days. The parasite was maintained by subpassages in bovine monocytes for 10 months when it was found to be non-pathogenic to gamma interferon knockout (KO) mice. Revival of a low passage (10th passage) of the initial isolate stored in liquid nitrogen for 18 months retained its pathogenicity for KO mice. Mero...
Prevalence of Neospora hughesi and Sarcocystis neurona antibodies in horses from various geographical locations. Parasite-specific antibody responses to Neospora antigens were detected using the immunofluorescent antibody test (IFAT) and immunoblot analysis in select equine populations. For comparison, a naturally infected Neospora hughesi horse and an experimentally inoculated Neospora caninum horse were used. In addition, all samples were tested for antibodies to Sarcocystis neurona by immunoblot analysis. A total of 208 samples was evaluated. The equine populations were derived from five distinct geographic regions. Locations were selected based on distribution of Didelphis virginiana, the native Nort...
Comparison of Sarcocystis neurona isolates derived from horse neural tissue. Sarcocystis neurona is a protozoan parasite that can cause neurological deficits in infected horses. The route of transmission is by fecal-oral transfer of sporocysts from opossums. However, the species identity and the lifecycle are not completely known. In this study, Sarcocystis merozoites from eight isolates obtained from Michigan horses were compared to S. neurona from a California horse (UCD1), Sarcocystis from a grackle (Cornell), and five Sarcocystis isolates from feral opossums from Michigan. Comparisons were made using several techniques. SDS-PAGE analysis with silver staining showed...
Initiation of a Sarcocystis neurona expressed sequence tag (EST) sequencing project: a preliminary report. To accelerate genetic and molecular characterization of Sarcocystis neurona, the primary causative agent of equine protozoal myeloencephalitis (EPM), a sequencing project has been initiated that will generate approximately 7000-8000 expressed sequence tags (ESTs) from this apicomplexan parasite. Poly(A)(+) RNA was isolated from culture-derived S. neurona merozoites, and a cDNA library was constructed in a unidirectional lambda phage cloning vector. Sixty phage clones were randomly picked from the library, and the cDNA inserts were amplified from these clones using the T3 and T7 primers that fl...
Ultrastructure of schizonts and merozoites of Sarcocystis neurona. The ultrastructure of Sarcocystis neurona schizonts and merozoites was studied in specimens derived from cell culture and from the brains of infected mice. Schizonts and merozoites were located in the host cell cytoplasm without a parasitophorous vacuole at any stage of development. Merozoites divided by endopolygeny. Fully formed merozoites had a pellicle, numerous polysomes and ribosomes, smooth and rough endoplasmic reticulum, 22 subpellicular microtubules, 9-16 dense granules, 25-75 micronemes, a plastid, a Golgi complex, 1-3 mitochondria, a conoid, 2 apical rings, 2 polar rings, 0-6 lipid...
In vitro quantitative analysis of (3)H-uracil incorporation by Sarcocytis neurona to determine efficacy of anti-protozoal agents. Parasite-specific incorporation of (3)H-uracil was used to assess the replication of Sarcocystis neurona, a protozoal parasite associated with equine protozoal myeloencephalitis (EPM). Anti-protozoal drugs, pyrimethamine (0.01, 0.1 and 1.0microg/ml PYR), sulfadiazine (5microg/ml; SDZ), sulfamethoxazole (5microg/ml; SMZ), diclazuril (100ng/ml; DCZ), atovaquone (0.04ng/ml; ATQ), tetracycline (5microg/ml; TET) and the herbicide glyphosate (1.5 and 4.5mM; GLY) were studied with varying S. neurona parasite densities (2x10(1)-1.2x10(6)merozoites/well). A microtiter plate format was used to test thes...
Sporocyst size of isolates of Sarcocystis shed by the Virginia opossum (Didelphis virginiana). The Virginia opossum (Didelphis virginiana) is a definitive host for multiple Sarcocystis species including Sarcocystis neurona, one of the causative agents of equine protozoal myeloencephalitis (EPM), a severe, neuromuscular disease of horses. Size and morphologic characteristics of isolates of Sarcocystis shed by the opossum were examined to determine if differences were useful in discriminating between the isolates and/or species. Collections of sporocysts from 17 opossums were molecularly characterized and measured using an ocular micrometer. The mean sporocyst size of isolates of S. neuro...
Caecal impactions managed surgically by typhlotomy in 10 cases (1988-1998). Surgical management of caecal impactions has included several different procedures suggested over the years. Complete bypass of the caecum through an ileocolic or jejunocolic anastomosis has become common practice for first time caecal impaction management, especially when dysfunction is suspected. In our practice, however, caecal impactions have been managed surgically by typhlotomy alone and of the 10 cases (July 1988-June 1998), 9 underwent surgery for first time caecal impactions, received a typhlotomy, and had survived an average of 43 months at time of case review. At the time of surgery...
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.
Equine protozoal myeloencephalitis. Recent advances in the understanding of the parasite life cycle, epidemiology, clinical signs, diagnosis, treatment, and prevention of EPM are reviewed. The NAHMS Equine '98 study and a controlled retrospective study from The Ohio State University College of Veterinary Medicine identified a number of risk factors associated with development of the disease. The national annual incidence of EPM was 1% or less depending on the primary use of the animals. Increased disease risk was associated with age (1-5 and > 13 years of age), season (lowest in winter months and increasing with ambient tempe...
Caecocaecal and caecocolic intussusceptions associated with larval cyathostomosis in four young horses. This report describes the clinical and pathological features of 4 horses affected by caecocaecal or caecocolic intussusceptions associated with larval cyathostomiasis. In each case, there was clinical and/or pathological evidence of concurrent larval cyathostomosis. They all demonstrated variable signs including diarrhoea, pyrexia, weight loss and subcutaneous oedema and cyathostome larvae were identified in the faeces of 3 of the horses. These cases highlight the need to consider caecal intussusceptions as a possible complication in horses affected by larval cyathostomosis, especially where s...
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...
Hydatidosis: dynamics of transmission. Hydatidosis is a widespread zoonosis infecting a large number of animals and humans. Echinococcus granulosus has the smallest taenia adult of the cestodes but with the largest larva. Its morphologic and biologic features were identified with DNA analysis. Different strains were separated according to the intermediate hosts: sheep, cattle, pigs, horses, camels. Definitive host are canids, mostly dogs, where the worm grows to adulthood in several months. The eggs are scattered in the pasture by wind and water and are ingested by various hosts. The larvae migrate through the intestinal wall and p...
Investigation of an outbreak of tapeworm-associated colic in a training yard. A novel serological assay which measures IgG(T) specific for a 12/13 kDa protein of the equine tapeworm Anoplocephala perfoliata was used as part of a colic outbreak investigation. A training/rehabilitation yard for Thoroughbreds and Arabs was found to have an increasing incidence of colic over a 5 year period, culminating in a peak incidence of 1.15 episodes/horse year at risk. Four animals suffered from ileal impaction colic which necessitated surgical management. A case-control study design suggested a strong association between tapeworm infection and colic, with evidence of a dose-response...
Animal trypanosomiasis in South America. Current status, partnership, and information technology. Animal trypanosome species of economical importance in South America include T. vivax and T. evansi. Both species are described in Brazil, Bolivia, Colombia, French Guyana, Peru, Suriname, and Venezuela. In Argentina and Guyana, only T. evansi and T. vivax are found, respectively. Our studies on T. vivax indicated that the parasite was spreading around 1.3 km per day in Bolivia. We found severe leukopenia in bovines from Pantanal (Brazil) and the Department of Santa Cruz (Bolivia). Because it can cause immunosuppression, the importance of trypanosomiasis control in ensuring success of vaccinat...
Larval cyathostomiasis. Over the past few years, cyathostomiasis has become increasingly recognized as a clinical problem of horses in the United States. Clinical cyathostomiasis has been reported frequently in Europe for a considerable time. This clinical syndrome is usually related to the sudden release of large numbers of the larval stages of small strongyles from the mucosa of the large intestine. Typical clinical signs include diarrhea, ventral abdominal edema, pyrexia, colic, weight loss, and poor body condition. Hypoalbuminemia and the presence of large numbers of small strongyles being passed in the feces are...
Phylogenetic analysis of partial mitochondrial cytochrome oxidase c subunit I and large ribosomal RNA sequences and nuclear internal transcribed spacer I sequences from species of Cyathostominae and Strongylinae (Nematoda, Order Strongylida), parasites of the horse. Three nucleotide data sets, one nuclear (ITS-2) and two mitochondrial (COI and l-rRNA), have been investigated in order to determine relationships among species of Strongylinae and Cyathostominae, intestinal parasites of the horse. The data exhibited a strong mutational bias towards A and T and in the COI gene, silent sites appeared to saturate rapidly partly due to this substitution bias. Thus, the COI gene was found to be less phylogenetically informative than the l-rRNA and ITS-2 genes. Combined analysis of the l-rRNA and ITS-2 genes supported a monophyletic clade of the cyathostomes with T...
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...
Tests for cooperative behaviour between stallions. Breeding groups with multiple stallions occur sympatrically with single-stallion breeding groups in feral horse, Equus caballus, populations. Mutualism and reciprocal altruism between stallions have been proposed to explain the origin and functioning of multistallion bands. However, empirical support for these hypotheses is contradictory and incomplete. Furthermore, there are no explicit tests of the predictions that each hypothesis makes about stallion behaviour and social structure. We compared nine multistallion and 18 single-stallion bands in the Kaimanawa Ranges, New Zealand. Compared wit...
Trichinella in horses: a low frequency infection with high human risk. After the initial report in 1976 of a trichinellosis epidemic caused by the consumption of infected horsemeat, 12 other outbreaks have been described in Europe. Since the first serious human outbreak several experiments have confirmed the susceptibility of horses to Trichinella species and the rapid disappearance of specific antibodies in this host that prevents the use of serological methods for routine screening. A review of the distribution of parasite burdens in muscles of naturally or experimentally infected horses indicates that the tongue is the most likely sample to contain detectable ...
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 ...
Homogeneity of Trypanosoma evansi isolates from domestic and sylvatic mammals from the Pantanal of Mato Grosso. 'Mal de Cadeiras' is a disease which causes great mortality in horses in the Pantanal Matogrossense region, Brazil. The agent of this disease is Trypanosoma evansi, a kinetoplastid flagellate which belongs to the Trypanosomatidae family, classified into the Salivarian section. Transmission occurs mechanically by haematophagous Diptera, mainly by Stomoxys sp. and Tabanus sp. and vampire bats. Outbreaks of Mal de Cadeiras in horses result in economic losses, thus limiting their use in cattle raising. Ten isolates of T. evansi recently derived from coati (Nasua nasua, Carnivora, Procyonidae), hor...
Dermatitis associated with “hypopodes” in a horse: the first case reported in Italy. The authors report, for the first time in Italy, a case of dermatitis of "hypopodes" origin in a horse. The hypopodes are a particular nymphal stage of mites of the suborder Astigmata. The "hypopus" is non-feeding, lacks a mouth and has a ventral suctorial plate with suckers and conoids for attaching itself to insects as a mode of dispersal. Some of these larval stages can enter into the hair follicles and into the subcutaneous layers causing lesions similar to mange. There are few reports of dermatitis in horses specifically associated with the presence of hypopodes and these have been attrib...
The beta-tubulin gene of Babesia and Theileria parasites is an informative marker for species discrimination. A fragment of the beta-tubulin gene was polymerase chain reaction (PCR) amplified from genomic DNAs of Babesia bovis, Babesia bigemina, Babesia divergens, Babesia major, Babesia caballi, Babesia equi, Babesia microti, Theileria annulata and Theileria sergenti. Single amplification products were obtained for each of these species, but the size of the amplicons varied from 310 to 460 bp. Sequence analysis revealed that this variation is due to the presence of a single intron, which ranged from 20 to 170 bp. The extensive genetic variability at the beta-tubulin locus has been exploited to develop...
Polydipsia in a foal with renal helminthiasis. This research article presents the case of a five-month-old foal showing intense thirst and excessive urination, which was found to be associated with renal helminthiasis – a rare condition characterized […]
Secondary structure model for the ITS-2 precursor rRNA of strongyloid nematodes of equids: implications for phylogenetic inference. In order to maximise the positional homology in the primary sequence alignment of the second internal transcribed spacer for 30 species of equine strongyloid nematodes, the secondary structures of the precursor ribosomal RNA were predicted using an approach combining an energy minimisation method and comparative sequence analysis. The results indicated that a common secondary structure model of the second internal transcribed spacer of these nematodes was maintained despite significant interspecific differences (2-56%) in primary sequences. The secondary structure model was then used to refine...
