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.
Williams PF, Brooks SP, Cooper DR.Sir, — We wish to report the death of a foal due to a parasitic lesion caused by Parascaris equorum..P equorum is reported to cause periodic colic, enterilis, obstructive colic with occasional rupture of the small intestine. However, personal communications with other veterinarians and our experience indicate fatal cases are not as common as indictaed in the literature.
Sutoh M, Saheki Y, Ishitani R, Inui S, Narita M, Hamazaki H, Yokota T.This is the first report on Eimeria leuckarti infection in foals in Japan. Seven Thoroughbred or Angloarabian foals 2 to 7 months of age raised in the Hidaka district, Hokkaido, were infected with E. leuckarti. They died of severe alterations caused by the larval migration of Strongylus vulgaris, and were examined over a period from 1970 to 1973. Protozoa of this species were observed in the small intestine in all the foals. They were found mostly in vacuoles of the cytoplasm of monoclear cells in the lamina propria at or near the tip of villi. Various stages of gametocytes, oocysts, and micro...
Genchi C, Malnati G.Strongyloides westeri larvae transmission by mare milk in foals has been studied; the results show the importance of this route for parasite penetration.
Kates KC, Colglazier ML, Enzie FD.The efficacy of oxibendazole against gastrointestinal parasites of horses was evaluated by the critical test method. Naturally infected ponies of various ages were given single oral doses of 5, 10, or 15 mg-kg of bodyweight. The drug was highly effective against adult large strongylids (Strongylus vulgaris, S edentatus, S equins), adult small strongylids (especially species of the genera Cylicostephanus, Cylicocyclus, Cyaathostomum, and Triodontophorus), and adult and larval stages of the large pinworm, Oxyuris equi. There was no apparent dose-related differences in efficacy. Oxibendazole was ...
Ardans A, Walters G.Treatment with 3 formulations of cambendazole (paste, pellets, and suspension) was compared with thiabendazole treatment in 181 Quarter Horses (females and intact and altered males) of different ages in 2 experiments. The mean output of strongyle eggs, as measured by eggs per gram of feces (epg), was reduced by at least 95% by the 3 formulations of cambendazole compared with pretreatment epg and epg in simultaneously nonmedicated horses. Eggs of Parascaris equorum were seen in 19 of the younger horses in experiment I. Parascaris eggs were not seen in postmedication fecal samples from 14 horses...
Drudge JH, Lyons ET, Wyant ZN, Tolliver SC.The occurrence of 2nd and 3rd instars of Gasterophilus intestinalis and Gasterophilus nasalis was determined in 476 horses during the 22-year period from 1951 to 1973. Overall, G intestinalis infected 98.7% of the horses and averaged 168/horse; whereas G nasalis infected 80.7% of the horses and averaged 52/horse. Aggregate average total numbers for G intestinalis ranged from a low of 50 in September to a high of 229 in March, and for G nasalis, from a low of 14 in September to a high of 82 in February. Horses were infected by 2nd or 3rd instars of both species on a year-round basis. Differenti...
Erbsloh JK.A short account is given of babesiosis (equine biliary fever) caused by the tick-borne protozoan Babesia equi and B. caballi, endemic in the Cape Province of South Africa. The clinical picture, diagnosis and treatment are described. In the absence of any prophylactic measures, prognosis is poor; control of the parasites in the tick-infested areas is essential.
Greatorex JC.The clinical manifestations of a diarrhoeic syndrome of horses with ulceration of the mucosae of the colon and caecum are described. Patients could be divided into three groups according to their presenting symptoms and the disease is probably caused by the thrombo-embolism associated with migrating larvae of Strongylus vulgaris. The differential diagnosis, prognosis and treatment are outlined with particular reference to the use of antithrombotic agents.
Ogbourne CP.Studies on the epidemiology of Strongylus vulgaris infection of the
horse. International Journalfor Parasitology 5: 423426. Observations are reported on the size and age
structure of Stronglyus vulguris populations recovered from the anterior mesenteric artery and its
main branches of horses slaughtered at regular intervals throughout a year. Marked seasonal variations were found in the mean monthly numbers of worms present. During spring/early summer the
numbers were relatively low and a large proportion of the arteries had no worms in them at all.
Thereafter, the arterial worm burdens q...
Pauli B, Althaus S, Von Tscharner C.Migrating fourth-stage larvae of Strongylus vulgaris, a parasite of equines, damage the intima of the anterior mesenteric artery and its larger branches and induce thrombus formation on the injured sites. As the time of larval passage through each of these branches has been exactly determined in earlier experiments, the aim of the present studies is to contribute to a more complete understanding of repair mechanisms in the process of time after thrombotic vascular injuries. Methods: five foals were separated individually to specially cleaned stables and given anthelmintic treatment till the ag...
Slocombe JO, McCraw BM.Four pony foals were inoculated with Strongylus edentatus infective larvae and on days 3 and 4 postinfection two of the ponies were treated with thiabendazole, each at the rate of 440 mg/kg of body weight. Total circulating eosinophil counts in untreated ponies increased to over 1700 per cu mm after the second week postinfection. In the treated ponies as well as in an uninfected untreated pony eosinophil counts did not increase beyond 100 per cu mm. At necropsy on day 35 postinfection the cecum, colon and omentum of treated ponies were normal and few tracks were present on the surface of the l...
Drudge JH, Lyons ET, Tolliver SC.Three formulations of cambendazole were evaluated for anthelmintic activity by critical testing method in 21 horses. Cambendazole suspension was administered via stomach tube at the dose rate of 10 mg/kg to 3 horses and at the dose rate of 20 mg/kg to 3 horses. Cambendazole paste was given intraorally to 8 horses, and the pellet formulation was fed to 7 horses at the dose rate of 20 mg/kg. Anthelmintic activity of cambendazole was similar for all dose rates and formulations. Gasterophilus intestinalis, Gasterophilus nasalis, Draschia megastoma, Anoplocephala perfoliata, and Anoplocephala magna...
Lyons ET, Swerczek TW, Tolliver SC, Drudge JH.At 4 days of age, an orphan horse foal born on a pasture was placed in a parasite-free stall. It was euthanized at 205 days of age and examination revealed numerous. Parascaris equorum specimens, ranging from 3.0 mm to adult size, indicating reinfections in the stall over an extended period of time. Initial infection of the foal was from stages on pasture. The foal had been observed repeatedly eating its own feces and the question is posed as to whether "recycling' of P. equorum eggs several times by coprophagy allowed time for embryonation and reinfection to occur.
Bailey M, Kent J, Martin SC, Lloyd S, Soulsby EJ.The concentrations of serum proteins (beta 1, beta 2, gamma, alpha 1, alpha 2 globulins and albumin) and absolute numbers of eosinophils, neutrophils and lymphocytes were examined in 64 naturally infected horses and ponies in which the number of larvae of Strongylus vulgaris in the cranial mesenteric artery and the severity of the lesion of verminous arteritis could be determined. The horses were grouped according to the number of larvae found and the severity of the arteritis. The results demonstrated that, although some significant deviation from a random distribution occurred in certain of ...
Reitsma JF.A report on infection with Dictyocaulus arnfieldi in a number of ponies and one horse in which complete clinical recovery was obtained following treatment with albendazole (Valbazen), administered by oral route at a dosage of 25 mg/kg of body weight twice daily for five days.
Malek IA, Baharudin F, Peng TL, Sabri J.Equine strongyles are harmful gastrointestinal parasites affecting horses' health and productivity. In tropical regions, environmental conditions, including temperature and soil type, significantly influence the development and survivability of strongyle larvae. This study aims to assess the development and survival of third-stage larvae (L3) of strongyles under different temperatures and soil types commonly found in Malaysia. Faecal samples from five adult horses aged between 22-24 years that were kept under a semi-intensive management system and had no history of recent anthelmintic treatmen...
Austin RJ, Dies KH.The protozoan, Klossiella equi was found in the kidneys of an aged Shetland mare raised in the Fredericton area of New Brunswick. This is the first published report of K. equi in a horse in Canada. The microscopic appearance of the parasite in the kidney is described. A brief discussion of other conditions seen in the horse is also presented.
Folz SD, Pax RA, Klei TR, Thomas EM, Ash KA, Conder GA, Bennett JL.An in vitro assay involving the use of a horse strongyle (Strongylus edentatus) and the micromotility meter has been developed to test for equine anthelmintic activity. Three commercially available equine anthelmintics (dichlorvos, ivermectin, and pyrantel pamoate) and an investigational drug (p-toluoyl chloride phenylhydrazone) were evaluated in this assay at four concentrations. After a 24-h incubation, greater than or equal to 10 micrograms/ml of all four drug treatments significantly (P less than or equal to 0.05) reduced the motility of ensheathed L-3 S. edentatus larvae, thereby indicati...
Mayhew IG, Brewer BD, Reinhard MK, Greiner EC.A fifth stage Strongylus vulgaris migrated through the spinal cord of a 2-year-old, male donkey resulting in progressive paraparesis and then tetraplegia. A profound neutrophilic pleocytosis was detected on analysis of cerebrospinal fluid. The parasite appeared to have entered the mid-lumbar spinal cord, migrated to the cranial thoracic segments, exited, then re-entered the spinal cord a few segments craniad. It then traveled further cranially and was found in the third cervical spinal cord segment. Some parts of the lesion were remarkably free from tissue necrosis, hemorrhage and inflammation...
Kumar S, Yokoyama N, Kim JY, Bork-Mimm S, Inoue N, Xuan X, Igarashi I, Sugimoto C.Theileria equi is a tick-transmitted intraerythrocytic protozoan parasite in equids. Equine merozoite antigen (EMA)-1 and EMA-2 of T. equi have been identified as immunodominant proteins co-expressed on the surface of extra-erythrocytic merozoites. Additionally, only the EMA-2 is shed into the cytoplasm of infected erythrocyte or inside the erythrocytic membrane during their early developmental stage. In this study, we initially performed West-Western blot analysis on Triton X-100-insoluble erythrocytic skeleton collected from a healthy horse, using a glutathione S-transferase (GST)-tagged rec...
Duncan JL, McBeath DG, Best JM, Preston NK.The efficacy of fenbendazole against immature stages of Trichonema spp., Strongylus vulgaris and Strongylus edentatus was evaluated. Naturally infected 6 to 12 month old ponies were given single, oral doses of 0, 15, 30 and 60 mg/kg of body weight. A dose response relationship was noted between increasing dose levels and efficiency against larval trichonemes and migrating stages of S. vulgaris and S. edentatus. Dose levels of 30 mg/kg and higher removed 93 per cent of mucosal stages of Trichonema spp., while doses of 60 mg/kg removed 83 per cent and 89 per cent of the migrating larvae of S. vu...
Lyons ET, Drudge JH, Tolliver SC.Critical tests were conducted in 11 naturally infected horses to evaluate the anthelmintic activity of parbendazole. Single doses at the rates of 30, 20, 10, 5, or 2.5 mg/kg of body weight were administered by stomach tube to 1, 4, 2, 2, and 2 horses, respectively. Parbendazole was active against Parascaris equorum, Oxyuris equi, Strongylus vulgaris, Strongylus edentatus, and small strongyles throughout the range of doses. Generally, small numbers of P equorum were present, but apparently a dose rate higher than 2.5 mg/kg is necessary for complete clearance. Removal of O equi was virtually 100...
Anderson WI, Picut CA, Georgi ME.Heavy renal infection in a pony with Klosiella equi resulted in moderate diffuse tubular nephrosis and tubular rupture. Multifocal non-suppurative interstitial nephritis was associated with ruptured tubules. Ultrastructural examination of sporoblasts demonstrated both the presence of a bilaminated membrane encasing organisms and nuclear budding. Endogenous corticosteroid production probably led to the development of an immune-compromized state and subsequent extensive parasitic replication.
Kudrnáčová M, Langrová I, Maršálek M, Jankovská I, Scháňková S, Brožová A, Truněčková J.The occurrence of Hypoderma diana (Diptera: Hypodermatidae) in a herd of 15 horses was observed during a 4-year period (2010-2013) in northwest Bohemia. During this period, infestation by the warble fly H. diana increased from 12.5% in 2010 to 53.3% in 2013. Nodules were observed on the neck, back, stomach, legs, and head. The incidence of H. diana was probably influenced by the presence of a specific host mouflon (Ovis orientalis musimon).
