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Topic:Larvae
Larvae in relation to horses refers to the immature stages of various parasitic organisms that can infect equine hosts. These larvae can originate from different species of internal and external parasites, such as gastrointestinal nematodes and bots. The presence and development of larvae in horses can lead to various health issues, including digestive disturbances, weight loss, and colic. Common parasitic larvae affecting horses include those of Strongylus vulgaris, Parascaris equorum, and Gasterophilus spp. Understanding the life cycle, transmission, and impact of these larvae is essential for effective parasite management and control in equine populations. This page compiles peer-reviewed research studies and scholarly articles that explore the biology, pathology, and management strategies related to larval parasitism in horses.
Effect of ivermectin treatment on eosinophilic pneumonia and other extravascular lesions of late Strongylus vulgaris larval migration in foals. Eighteen parasite-free pony foals were infected orally with 500 third stage larvae of Strongylus vulgaris. At 56 days after infection, six ponies were treated with intramuscular ivermectin (22, 23-dihydroavermectin B1); six were treated with oral ivermectin; and six were not treated. Necropsy was done 91 days after infection to study the pathologic effects of migrating S. vulgaris larvae and to determine the efficacy of ivermectin in attenuation of S. vulgaris-induced lesions. Larval migration induced eosinophilic inflammation of the liver, spleen, mesenteric, colic and cecal lymph nodes, and ...
In vitro induction of lymphocyte responsiveness by a Strongylus vulgaris-derived mitogen. Proliferation in vitro of peripheral blood lymphocytes both from horses infected with Strongylus vulgaris and from helminth-free ponies was observed in the presence of extracts of the fourth and fifth stage larvae and adults of S. vulgaris. In addition, S. vulgaris extracts induced transformation in cultures of peripheral blood lymphocytes from sheep and dogs and in mouse spleen cell cultures. Nylon wool non-adherent, T cell enriched fractions of lymphocytes from both mice and horses were stimulated by the S. vulgaris larval mitogen while no proliferation was observed in cultures containing ny...
The elimination of equine strongyles and hematological and pathological consequences following larvicidal doses of thiabendazole. Twelve horses were divided into three groups and given various doses of a mixed species strongyle inoculum, representing light, moderate, and heavy infections. Three weeks after the larval inoculations, three animals from each group were given larvicidal doses of thiabendazole (TBZ) (440 mg kg-1 on two consecutive days); one animal from each group served as a non-medicated control. Treatment was repeated three weeks later. One treated animal from each group was designated for long-term study; others were necropsied to study adult and larval parasite loads. Six of the twelve animals with strong...
Efficacy of ivermectin in injectable and oral paste formulations against eight-week-old Strongylus vulgaris larvae in ponies. A controlled test method was used to evaluate the efficacy of injectable micelle and oral paste formulations of ivermectin (22,23-dihydroavermectin B1) against 8-week-old Strongylus vulgaris larvae in experimentally infected pony foals. The dosage level of the drug in both formulations tested was 0.2 mg/kg. Ponies were euthanatized and necropsied 5 weeks after treatment. Based on the recovery of live vs dead S vulgaris from mesenteric arteries, both formulations were greater than 99% effective. Increased weight gains and marked reductions in the severity of arterial lesions were observed in tr...
Effectiveness of fenbendazole against later 4th-stage Strongylus vulgaris in ponies. Twelve pony foals (reared worm-free) were inoculated with Strongylus vulgaris. Approximately 8 weeks later, 4 of the foals were given fenbendazole (10% suspension) at a dosage rate of 10 mg/kg of body weight daily for 5 days and 4 foals were given the suspension at a dosage rate of 50 mg/kg daily for 3 days; the remaining foals were given a placebo. All treatments were administered by stomach tube. Fenbendazole was 99.6 and 97.9% effective in the 2 treatment groups, respectively, in eliminating later 4th-stage S vulgaris larvae located near the origin of major intestinal arteries. On microscop...
SEM study of Strongylus vulgaris larva-induced arteritis in the pony. This paper describes the histological and scanning electron microscopical examinations of the right colic artery of eight ponies. Lesions all had large thrombi surrounding a larva or larvae, with arterial wall thickening. Endothelial shape change, degeneration and loss were present. Fibrin-platelet red blood cell aggregates were present on endothelial surfaces as well as on the surface of thrombi. Damage to the intima appeared to produce the conditions for progressive thrombus formation.
Transmission of equine cyathostomes (Strongylidae) in central Texas. After foaling, 6 mares and their foals were placed on equine parasite-free pastures. Observations of fecal nematode eggs and pasture larvae indicated peak cyathostome egg production occurred in late August and early September, with greatest numbers of larvae on the forage appearing during October. Two foals were necropsied for parasitologic evaluations at approximately 155 days of age. Both had approximately 100,000 adult cyathostomes, mostly Cylicostephanus longibursatus, Cylicocyclus nassatus and Cyathostomum catinatum. However, there were nearly 7 times more cyathostome larvae (189,004) in ...
Transfer of adult Strongylus vulgaris via stomach tube. Patent infections with Strongylus vulgaris were established in 6 of 8 helminth-free ponies given 41 to 101 adult worms via nasogastric tube. The parasites were removed from the cecum and ventral colon and transferred within 1 to 2 hours of the death of the donor horses. Eggs were found in the feces of the recipients in 2 or 3 days; egg counts reached maximum, 28 eggs per gram of feces, at 4 weeks after ponies were inoculated. In 6 ponies euthanatized 3 to 7 weeks after parasitic transfers were done, 28% of the inoculated worms were found alive at necropsy. A 7th pony was maintained as a donor ...
Alternate grazing of horses and sheep as control for gastro-intestinal helminthiasis in horses. Gastro-intestinal helminth infections of a group of three yearling mare Shetland ponies, which were set-stocked on a small pasture from February until September, were compared with those of a similar group of ponies, which grazed a similar pasture from February to July and subsequently was removed to a pasture which had been grazed by sheep from April to July. In addition both groups were treated with cambendazole when the latter group was removed to the sheep pasture. Pasture larval counts and worm counts demonstrated that the group grazed after the sheep acquired considerably smaller burdens...
Antibody responses of ponies to initial and challenge infections of Strongylus vulgaris. An indirect fluorescent antibody assay (IFA) was developed using Strongylus vulgaris third stage larvae (L3) as antigens. Observations using the IFA indicate that a species-specific antibody response to S. vulgaris L3 develops in S. vulgaris-infected ponies and that some surface L3 antigens are shared by adult worms. Sequential antibody levels against S. vulgaris were measured in strongyle-naive and in immune ponies following initial and challenge infections using the IFA and an indirect hemagglutination assay (IHA). Antibody levels measured by IFA increased faster following initial infections...
The activity of closantel as an equine antiparasitic agent. Eighteen pony foals were experimentally infected with 500 third stage larvae of Strongylus vulgaris at 2 weeks, and at 2, 4, 6 and 8 months after birth. For the duration of the study, all foals were kept in the same pasture with their mothers to allow natural infection with other parasites by exposure to a contaminated environment. Twelve of the foals were utilized in groups of 3 and treated orally five times at two month intervals starting at one month of age with closantel at doses of 5, 10, 20 or 40 mg kg-1. Ten months after birth the foals were necropsied to determine the parasitic burdens...
[Contribution to the parasitic fauna of the GDR (German Democratic Republic). 7. Occurrence of Gasterophilus larvae (Diptera: Gasterophilidae) in horses]. Observations were carried out from May 1977 to May 1980 on occurrence, fauna, and seasonal dynamics of Gasterophilus spp. in 2,539 horses for butchering from all districts of the German Democratic Republic and also in 79 horses after control against gasterophilosis. 99.98% of the 13,742 second and third instar larvae of horses for butchering were Gasterophilus intestinalis, only 0.02% Gasterophilus nasalis. Out of 7,765 larvae passed after control measures Gasterophilus intestinalis dominated with more than 96%. Only in four districts of the German Democratic Republic Gasterophilus nasalis was...
The prevalence of Gasterophilus intestinalis in horses in northern England and Wales. The stomachs of 448 horses from northern England and Wales were examined for Gasterophilus larvae, and 237 (52.7%) were found to be infected with G. intestinalis. Larvae were present in stomachs examined during each month of the year except August. Second instar larvae occurred from September through February and third instars were present from November through July. Adult fly activity began in August as indicated by the presence of eggs on horses. The life-cycle of G. intestinalis in northern England and Wales is outlined from the data presented. The mean instar burdens were 15.7 second and 3...
Effectiveness of ivermectin against later 4th-stage Strongylus vulgaris in ponies. Twelve pony foals were reared worm-free and inoculated with Strongylus vulgaris. Approximately 8 weeks after they were inoculated, 6 foals were given ivermectin IM at a dosage rate of 200 micrograms/kg of body weight and 6 were given a placebo. All foals were necropsied 35 days after treatment. Ivermectin was 98.9% effective in eliminating later 4th-stage S vulgaris larvae located near the origin of major intestinal arteries and in reducing clinical signs and permitting resolution of lesions associated with verminous arteritis. One pony foal reared on pasture and with evidence of arteritis of ...
Controlled tests of pastes of dichlorvos and thiabendazole against induced Strongyloides westeri infections in pony foals in 1973-1974. In 1973-1974, 4 controlled tests were performed in pony foals (n = 17) raised parasite-free and experimentally infected with Strongyloides westeri. Administration of infective larvae by stomach tube in 1 test resulted in low-grade infections and tended to invalidate the test. Intraoral and percutaneous (intra-aural) administration of larvae resulted in suitable test infections for 1 and 2 tests, respectively. A paste formulation of dichlorvos at 36.3 mg/kg of body weight removal from 4 ponies. Treatment of 4 the dosage rate of 44 mg/kg was consistently effective (greater than 99% to 100%) for ...
Ivermectin: activity against larval Strongylus vulgaris and adult Trichostrongylus axei in experimental infections in ponies. Activity of ivermectin, administered IM at the dosage rate of 200 micrograms/kg of body weight, was evaluated in controlled tests against migrating larvae of Strongylus vulgaris and adult Trichostrongylus axei in experimental infections in 6 ponies raised worm-free. Ponies were given 2,190 or 2,400 infective 3rd-stage larvae of S vulgaris at 7 days before treatment and 22,000 or 22,750 infective 3rd-stage larvae of T axei at 42 or 45 days before treatment. Three ponies were given ivermectin plus vehicle, and 3 ponies were given the vehicle only; the ponies were euthanatized 7 or 9 days after t...
Irradiated larval vaccination of ponies against strongylus vulgaris. Nonimmune pony foals 9 to 12 mo of age were vaccinated with third-stage Strongylus vulgaris larvae (L3) irradiated with 70, 100, or 130 Kr of gamma radiation. Ponies receiving per os inoculations of L3 irradiated with 70 or 100 Kr were protected from the clinical disease and lesions associated with challenge infections of 4,300 L3, when compared to nonvaccinated controls. Similarly, the numbers of worms from the challenging population recovered from successfully vaccinated animals were significantly lower than from nonvaccinated controls. The degree of resistance that develops in individuals c...
Efficacy of injectable and oral paste formulations of ivermectin against gastrointestinal parasites in ponies. A controlled test was used in ponies to compare the antiparasitic efficacy of ivermectin (22,23-dihydro-avermectin B1) in an injectable micelle solution administered IM with the efficacy of the same drug in an oral paste formulation. Parasite infections were naturally acquired in southern Louisiana. The drug was tested in both formulations at a dosage level of 0.2 mg/kg of body weight. Ivermectin in both formulations tested had an efficacy greater than 98% against Gasterophilus intestinalis and G nasalis larvae. Trichostrongylus axei, Habronema spp, Strongylus vulgaris, S. edentatus, and speci...
[Artificial infestation of horses with the eggs of the stomach botfly (Gastrophilidae)]. 10 foals were artificially infected for the first time with eggs of Gastrophilus intestinalis, G. veterinus, G. haemorrhoidalis, G. inermis, G. nigricornis. 63 to 67% of the 1st stage larvae die in the first period of life after emergence from the egg, at the moment of invasion into the skin and at the beginning of the migration. In 40 to 45 years after the infection most larvae (73 to 82%), depending on their specific belonging, were found in the stomach, duodenum and rectum.
Controlled tests of fenbendazole against migrating Strongylus vulgaris in ponies. Sixteen pony foals were reared worm-free and inoculated with Strongylus vulgaris. On day 7 after inoculation, 12 ponies were given a fenbendazole 10% suspension at dose rate of 50 mg/kg of body weight by stomach tube. On day 8 after inoculation, 8 of these ponies were given the 2nd treatment of the anthelmintic and on day 9, 4 of these ponies were given the 3rd treatment. (The other 4 of the 16 ponies were given only tap water, as controls.) The ponies were necropsied at death or on day 28 after inoculation. Fenbendazole was effective in minimizing the appearance of clinical signs associated w...
Effect of diethylcarbamazine on Strongylus vulgaris infection in ponies. Shetland ponies (n = 4) were given diethylcarbamazine orally at a dose level of 22 mg/kg/day for 1 week before they were inoculated with 800 third-stage larvae of Strongylus vulgaris. Treatment was continued for 86 (1 pony) or 200 days (3 ponies) after the inoculation. As compared with the changes seen in a similarly inoculated group of ponies (group 2) which were not treated, diethylcarbamazine did not prevent the clinical or pathologic changes due to the migrating larvae. Fewer adult parasites were recovered at necropsy from treated ponies than from nontreated (group 2) ponies, even when tre...
A random walk model for the migration of Strongylus vulgaris in the intestinal arteries of the horse. A study of the migration of fourth stage larvae of the parasite Strongylus vulgaris in the intestinal arteries of the horse is presented. It is established, that the larvae migrate along the arteries in almost straight lines. It is suggested that this is primarily due to their ability to sense the curvature of the vessel wall, and not, as might have been expected, because of an ability to sense the direction of blood flow. A larva will sometimes alter its direction of motion when encountering a small off-branching artery. This behaviour suggests, that the migration of S. vulgaris larvae can be...
Efficacy of ivermectin against cutaneous Draschia and Habronema infection (summer sores) in horses. Thirty-one horses with naturally occurring summer sores were given a single IM injection of 0.2 mg of ivermectin (22,23-dihydroavermectin B1)/kg during the summer of 1980. Larvae of Draschia and/or Habronema spp were recovered from biopsy samples taken from 21 of 25 horses (84%) on the day of anthelmintic treatment. There was a marked clinical improvement in 26 horses (84%) 7 days after ivermectin was given. The typical summer sore was replaced by healthy pink granulation tissue at 7 days and this healed after 1 to 5 weeks. Biopsy samples were taken from 21 of these horses 1 to 6 weeks after t...
Habronemic blepharoconjunctivitis in horses. Habronemic blepharoconjunctivitis was characterized clinically by raised yellow gritty plaques in the palpebral and bulbar conjunctivae. Lid granulomas and blepharitis were observed in some cases. On histologic examination, mast cells, eosinophils, and collagenolysis was found in most sections, but if only one section was examined an erroneous diagnosis of mastocytosis could have been made. Treatment consisted of larvicidal mixtures for lid lesions and organophosphate ophthalmic drops along with corticosteroids for the conjunctivitis. If the cornea was damaged by the gritty conjunctival plaque...
Recovery of helminths postmortem from equines. I. Parasites in arteries, subperitoneum, liver and lungs. The entire gastro-intestinal tract and viscera of the abdomen and thorax, including the heart, aorta and its branches to the viscera, are removed from the carcass. All the branches of the aorta, with the exception of the A. gastrica sinistra, are dissected from the intestinal tract, and subsequently each branch is isolated from the mesentery, fat, pancreas, kidneys, etc. Usually, the A. ileocolica is grossly enlarged due to chronic arteritis with thrombus formation caused by 4th stage larvae, 4th moult and 5th stage Strongylus vulgaris. Descriptions of methods to examine the subperitoneal tiss...
Recovery of helminths postmortem from equines. II. Helminths and larvae of gasterophilus in the gastro-intestinal tract and oestrids from the sinuses. The tongue, pharynx, oesophagus and gums are examined for larvae of gasterophilus spp., and the nose and sinuses for oestrid larvae. The gastro-intestinal tract is divided into separate specimens-stomach, small intestine, caecum, ventral colon, dorsal colon, descending colon and rectum- and each is examined separately. Aliquots of ingesta of 1/4 by mass of the stomach and 1/10 by mass of the small intestine, caecum, ventral colon and dorsal colon are collected for microscopic examination. Each part of the wall of the caecum, ventral and dorsal colon is washed and specimens are collected for su...
