Sequential mesenteric arteriography in pony foals during repeated inoculations of Strongylus vulgaris and treatments with ivermectin

Semiselective mesenteric arteriography was performed at regular intervals (inoculation weeks [IW] 0, 11, 18, and 24) in 9 of 10 pony foals raised to be free of parasites. Fifty infective larvae (L3) of Strongylus vulgaris were administered weekly for 4 weeks, then every 2 weeks through the 20th week. Three ponies were given ivermectin (oral paste, 0.2 mg/kg of body weight) treatment at IW 8, 16 and 24. Four ponies were inoculated, but did not receive ivermectin, and a third group of 2 ponies acted as uninoculated controls. Control ponies did not have gross or arteriographic lesions, whereas the inoculated untreated ponies had gross and progressive arteriographic lesions typical of verminous arteritis. Arteriographic lesions in the ivermectin-treated inoculated ponies were not as severe those in the untreated inoculated group, and there was either a partial resolution or a lack of progression of arteriographic lesions in all treated ponies. One untreated inoculated pony did not have progressive arterial lesions as did the 3 others in the group, and may develop resistance to the parasite.     

Effects of repeated Strongylus vulgaris inoculations and concurrent ivermectin treatments on mesenteric arterial lesions in pony foals

Eight of 10 pony foals reared under helminth-free conditions were inoculated PO with 50 Strongylus vulgaris infective larvae/week for 4 weeks, at which time 1 foal died of acute verminous arteritis. Inoculation of 7 remaining foals continued at 2-week intervals for 20 weeks. Of the 7 foals, 3 were treated with ivermectin (0.2 mg/kg of body weight) in an oral paste formulation at experiment weeks 8, 16, 24; 4 foals were not treated. Two foals were not inoculated or treated and served as controls. After the first ivermectin treatment, ivermectin-treated foals had fewer days (12 +/- 2.9) with rectal temperatures greater than 38.6 C than did nontreated foals (23.3 +/- 3.8). Mean baseline rectal temperatures were 38 +/- 0.2 C. Adverse clinical reactions to ivermectin treatment were not observed in foals. Foals were euthanatized and necropsied 3 weeks after the last ivermectin treatment (week 24). Ivermectin was effective in reducing S vulgaris arterial larval and intestinal adult parasite numbers by 100% in 3 treated foals. Strongylus vulgaris arterial larvae and/or adults were recovered from all 4 nontreated inoculated foals. One nontreated inoculated foal lacked arterial larvae or active arterial lesions, indicating that protective resistance had developed in this individual. Marked gross and histopathologic lesions typical of chronic S vulgaris infection were observed in the 3 nontreated inoculated foals with arterial larvae. Repeated killing of intra-arterial S vulgaris fourth-stage larvae in ivermectin-treated foals did not exacerbate lesions associated with verminous arteritis or induce unique lesions associated with repeated destruction of arterial larvae.(ABSTRACT TRUNCATED AT 250 WORDS)     

Specific serum protein changes associated with primary and secondary Strongylus vulgaris infections in pony yearlings

The concentrations of haptoglobin, immunoglobin (Ig)G(T) and IgG were measured in the serum of four previously parasite-free pony yearlings following a single dose of 700 (Group H) or 200 (Group L) stage three Strongylus vulgaris larvae (L3) and following a reinfection with the same doses 34 weeks later. The results are compared with an uninfected control pony. The haptoglobin concentration increased during Weeks 1 to 6 and 14 to 17 after infection in the serum of the ponies receiving 200 L3, but in only one pony dosed with 700 L3 (during Weeks 1 to 16). The serum haptoglobin also increased during the first seven weeks after the second infection, in three of the four ponies following the second dose of larvae. The serum IgG(T) concentration started to increase from Week 6 or 9 in the ponies given 700 L3, reaching peaks of 44 and 32 g/litre respectively, eight to nine weeks later, compared with a peak of 16 g/litre 20 to 22 weeks after infection in ponies dosed with 200 L3. The IgG(T) concentration increased to a maximum of 25 g/litre in the serum of only one of the four ponies after the reinfection. The serum IgG concentration in all ponies increased nearly twofold during the first eight weeks after both the primary and secondary dose of larvae. It is concluded that the measurement of specific proteins is more reliable and quicker than the electrophoretic separation and quantitation of protein bands, in tracing changes in serum proteins following the artificial infection of ponies with S vulgaris larvae.     

Evaluation of ivermectin for larvicidal effect in experimentally induced Parascaris equorum infections in pony foals

A controlled test was carried out on 15 pony foals inoculated with 1,500 +/- 108.8 infective Parascaris equorum eggs. The foals were assigned to 3 treatment groups. Treatments given on postinoculation day 11 included 0.2 mg of ivermectin/kg of body weight, formulated as paste (n = 5), or liquid (n = 5), or no treatment (controls; n = 5). The foals were euthanatized on postinoculation day 25, and examined for larvae in the small intestine, lungs, and liver. Larvae were not found in foals treated with ivermectin liquid or paste, whereas significantly (P less than 0.05) higher mean numbers (960.9; range, 379 to 1,736) of 4th-stage larvae were found in the controls. Histologic and gross examination of lungs and liver revealed pathologic changes attributable to P equorum migration that were similar in all foals. Adverse reactions to treatment were not observed.     

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 than did levels measured by IHA. Antibody levels appear to increase following challenge infections of immune ponies when measured with the IFA, but not with the IHA. Significant differences in antibody titers were not seen between ponies which developed colic following challenge infections and those that did not develop colic. Antibodies were not detectable in ponies unexposed to larval migrations, but which received surgical implantation of S. vulgaris adults into the cecum.     

Integrated control of Strongylus vulgaris infection in horses using ivermectin

An attempt was made to control or eliminate Strongylus vulgaris from a closed group of three horses at pasture near Perth, Western Australia, by dosing with ivermectin on four occasions during the time of year when it was believed that environmental conditions would eliminate all the non-parasitic stages of that species. At necropsy, five months after the last dose of anthelmintic and after continually grazing the same pastures, no S vulgaris or arterial lesions were found in those horses and S edentatus, Draschia megastoma and Habronema species were also almost completely eliminated.     

Activity of closantel in the prevention of Gasterophilus and Strongylus vulgaris larval infections in equine foals and yearlings

Two controlled tests were conducted in equine foals and yearlings to determine the optimal oral dosage and the duration of activity of closantel for the prevention of Gasterophilus spp larval infections. Additional data were collected on the activity of closantel against Strongylus vulgaris larval infections. In experiment 1, 12 foals and 12 yearlings were equally allocated to 4 experimental groups, and were given oral treatments with closantel at dosages of 0 (nontreated controls), 2, 5, or 8 mg/kg of body weight every 2 months during bot season. The foals and yearlings were allowed to graze on open pasture throughout the experiment to provide a natural source for bot and helminth infections. All animals were euthanatized and necropsied 6 weeks after the final treatment. Closantel was highly effective (98.6% to 100%) at all doses in preventing Gasterophilus spp larval infections in the foals, but only the 8 mg/kg dose had significant (P less than 0.05) activity (99.7%) in the yearlings. This dose also significantly reduced the numbers of 4th-stage and immature adult S vulgaris (86.0%) in the mesenteric arteries as compared with nontreated controls. In experiment 2, 9 foals and 9 yearlings received a single oral treatment of 8 mg of closantel/kg of body weight; 3 foals and 3 yearlings were kept as nontreated controls. Groups of 6 treated (3 foals, 3 yearlings) and 2 control (1 foal, 1 yearling) animals were euthanatized and necropsied 1, 2, and 3 months after treatment. Closantel remained effective for 2 months in preventing infections of G intestinalis larvae in these foals and yearlings. Clinical signs of toxicosis were not observed in the treated animals of either study.     

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 the cranial mesenteric and ileocolic arteries on arteriography was treated with ivermectin at a dosage rate of 200 micrograms/kg of body weight. On arteriographs taken subsequently, there was evidence of regression of the lesion, and at necropsy 9 weeks after treatment, there was no arteritis or larvae in those arteries.     

Observations on the epidemiology and control of Strongylus vulgaris infections

The epidemiology and control of helminth infections in the horse were studied in four small grazing experiments between 1981 and 1984 at the University of Utrecht. At autopsy in November or December negligible Strongylus vulgaris burdens were found in the cranial mesenteric artery of four groups of ponies, which had been treated with an anthelmintic in July and subsequently transferred to a clean pasture. Considerable arterial S. vulgaris burdens were seen in three groups of ponies which were treated with an anthelmintic in July without a move to clean pasture, and in another group of ponies in 1984, which was set stocked on a pasture used for horses in 1983 and which was treated with an anthelmintic (albendazole) 2 days before turnout in April and subsequently in May, June and July. A tracer pony, grazed with this group between the middle of September and the middle of November, harboured an even higher burden of arterial S. vulgaris larvae. The arterial S. vulgaris in the latter group could not be the result of contamination of the pasture with S. vulgaris eggs before July, as in the three other groups with considerable arterial S. vulgaris burdens. Pasture larval counts showed that S. vulgaris larvae do not only overwinter, but are able to survive in considerable numbers until autumn, longer than most other gastrointestinal nematodes. There were some indications that translation of infective larvae, which overwintered on pasture in some free living stage, occurred between May and July.     

Efficacy of ivermectin in the treatment of induced Parascaris equorum infection in pony foals

Eighteen pony foals inoculated with 1,500 +/- 109 infective Parascaris equorum eggs were given 0.02 ml of ivermectin vehicle (liquid)/kg of body weight, PO, (control); 0.2 mg of ivermectin paste/kg, PO; or 0.2 mg ivermectin liquid/kg, PO, on postinoculation day (PID) 28. Foals were euthanatized on PID 42, and the small intestinal contents were examined for P equorum larvae. The mean number of fourth-stage P equorum larvae in foals treated with ivermectin paste and liquid were 3.5 and 6, respectively. Significantly (P less than 0.01) higher mean numbers of larvae (1,250) were detected in foals treated with ivermectin vehicle. Larvae recovered from foals treated with ivermectin vehicle were of significantly (P less than 0.002) longer mean length than those from foals treated with ivermectin paste or liquid. Gross examination of lungs and liver revealed similar pathologic changes from the migration of P equorum in all foals. Adverse reaction to treatment was not observed.     

Strongylus vulgaris in the tunica media of arteries of ponies and treatment with ivermectin

A preliminary investigation was made into the effect of fourth-stage Strongylus vulgaris larvae sequestered in the tunica media of ileocolic arteries of pony foals treated with ivermectin. The foals had been reared parasite-free, inoculated with infective larvae and given orally a placebo or ivermectin paste. Two foals received subsequently one or two further inoculations with larvae and treatment with ivermectin. Arteriography was used to identify the lesions in the ileocolic artery following inoculation and their regression following treatment. At necropsy, foals were examined for lesions and larvae grossly and histologically. Ivermectin was highly effective against fourth-stage larvae and those present in the media appeared not to unduly affect the integrity of the ileocolic artery. Increased numbers of larvae were not found in the media of foals receiving repeat inoculations and repeat treatments. Larvae were not found in the media of foals treated with a placebo. The major pathological changes in the arterial wall of all foals were attributed to infection with S. vulgaris and there was no strong tendency for the damaged arteries to return to normal after the S. vulgaris were removed.     

Efficacy of ivermectin in controlling Strongyloides westeri infections in foals

Twenty-eight foals whose dams were treated IM with ivermectin (200 micrograms/kg of body weight) on the day of parturition were compared with 35 foals whose dams were administered only the vehicle. The effect of ivermectin on the vertical transmission of Strongyloides westeri and foal heat diarrhea was determined by a comparison of results obtained in the 2 groups. Foals from treated mares had significantly fewer S westeri eggs per gram of feces from 17 to 28 days postpartum. There were no differences observed in the frequencies of severity of foal heat diarrhea between the treated and control groups. In another experiment, using the same foals, 32 foals were treated IM with ivermectin (200 micrograms/kg) at 21 days of age and were compared with 31 foals administered only the vehicle. Significantly fewer S westeri eggs were recovered from the ivermectin-treated foals on day 26 to day 32, the completion day of the trial.     

Evaluation of ivermectin against later fourth-stage Strongylus vulgaris in ponies at two and five weeks after treatment.

The efficacy of ivermectin against later fourth-stage Strongylus vulgaris larvae was studied in pony foals at 14 and 35 days after treatment. These foals had been reared parasite-free, inoculated with 500 infective larvae and 56 days later given either ivermectin at 200 micrograms/kg or a placebo intramuscularly. At necropsy, foals were examined for lesions and larvae grossly and histologically. Ivermectin was found to be highly effective (98.6%) against later fourth-stage larvae in five foals which were examined at 35 days after treatment, but not in five others examined at 14 days (72.5%). In some foals larvae were found in the tunica media of the ileocolic arteries. The conformation of these larvae appeared normal, but there were degenerative changes which suggested that they were dying or dead. Questions as to how the larvae attained that site and the consequences of their presence there were raised.     

Comparison of two laparoscopic treatments for experimentally induced abdominal adhesions in pony foals

OBJECTIVE: To compare laparoscopic dissection with-laparoscopic dissection combined with abdominal instillation of ferric hyaluronate gel for the treatment of experimentally induced adhesions in pony foals. ANIMALS: 12 healthy pony foals. PROCEDURE: A serosal abrasion method was used to create adhesions at 4 sites on the jejunum (day 0). At day 7 laparoscopy was performed and the adhesions observed in each foal were recorded. In group-1 foals (n = 6), the adhesions were separated laparoscopically (treatment 1). In group-2 foals (n = 6), 300 mL of 0.5% ferric hyaluronate gel was infused into the abdomen after the adhesions were separated laparoscopically (treatment 2). At day 24, terminal laparoscopy was performed and the adhesions observed were recorded. Total number of adhesions within each group was compared between day 7 and 24. Data were analyzed to determine whether an association existed between the number of adhesions on day 24 and treatment type. RESULTS: At day 24, the number of adhesions was significantly decreased within each group, compared with the number of adhesions at day 7 (group-1 foals, 10 vs 22 adhesions; group-2 foals, 3 vs 20 adhesions). Treatment 1 was associated with a significantly higher number of adhesions at day 24, compared with treatment 2 (odds ratio, 4.54; 95% confidence interval, 1.03 to 23.02). CONCLUSION AND CLINICAL RELEVANCE: Abdominal instillation of 0.5% ferric hyaluronate gel after laparoscopic dissection was a more effective technique than laparoscopic dissection alone to treat experimentally induced adhesions in pony foals. Laparoscopic adhesiolysis following abdominal surgery in foals is a safe and effective technique.     

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 treated ponies.     

In vivo activation of equine eosinophils and neutrophils by experimental Strongylus vulgaris infections

Eosinophils and neutrophils from ponies with Strongylus vulgaris-induced eosinophilia (eosinophilic ponies; activated eosinophils and neutrophils) were assayed in vitro for chemotactic and chemokinetic responses to zymosan-activated serum (ZAS) using the filter system in Boyden chambers, for Fc and complement (C) receptors using the EA and EAC-rosette assays, respectively, and for phagocytic and bactericidal activities using opsonized Escherichia coli and the acridine orange method. The responses of activated eosinophils and neutrophils in the above assays were compared with those of eosinophils and neutrophils from S. vulgaris-naive ponies without eosinophilia (noneosinophilic ponies; nonactivated eosinophils and neutrophils). Differences in cell density following centrifugation in a continuous Percoll gradient were used to further characterize the heterogeneity of activated eosinophils and neutrophils. Activated and nonactivated eosinophils demonstrated similar chemotactic responses to ZAS while activated and nonactivated neutrophils demonstrated similar chemokinetic responses to ZAS. A higher percentage of activated eosinophils and neutrophils expressed Fc and C receptors compared with nonactivated cells (P less than 0.05). Generally, higher percentages of eosinophils and neutrophils expressed C than Fc receptors. However, the percentage of neutrophils with both receptors was higher than that of eosinophils. Phagocytosis and killing of E. coli by either type of eosinophil were not consistently observed. Both activated and nonactivated neutrophils phagocytized E. coli and significant differences between the two cell types were not observed. The bacterial activity, however, of activated neutrophils was significantly greater than that obtained using nonactivated neutrophils (P less than 0.05). Activated eosinophils and neutrophils were both separated into two distinct fractions based on differences in cell densities. A higher percentage of band 2 eosinophils (density of 1.106) expressed C receptors than did band 1 eosinophils (density of 1.049) (P less than 0.05). A higher percentage of band 1 neutrophils (density of 1.072) expressed both Fc and C receptors and these neutrophils were more phagocytic and bactericidal than were band 2 neutrophils (density of 1.082) (P less than 0.05). These data suggest that equine eosinophils and neutrophils are activated by chronic S. vulgaris infections.     

Immunologic and hematologic responses in ponies with experimentally induced Strongylus vulgaris infection

Immunologic and hematologic responses were examined in 4 ponies with experimentally induced Strongylus vulgaris infection and in 5 helminth-free ponies. Two ponies were inoculated with 200 larvae and 2 were inoculated with 700 larvae of S vulgaris and then were reinoculated with the same numbers of larvae 34 weeks later. Initial response of the ponies inoculated with S vulgaris was S vulgaris antigen-induced lymphocyte response that developed 1.5 to 3 weeks after inoculation and did not persist. Development of antigen-reactive lymphocytes was followed sequentially by a biphasic complement-fixing antibody response, then biphasic eosinophilia. Antibody titer to S vulgaris antigen was higher in ponies inoculated with 700 larvae, compared with that in ponies given 200 larvae of S vulgaris. Also, the second peak in antibody titer and in absolute number of eosinophils was observed earlier in ponies inoculated with 700 larvae, compared with ponies inoculated with 200 S vulgaris larvae, and subsided before or from about 24 weeks after inoculation. The prepatent period for S vulgaris infection was 24 to 25 weeks. After reinoculation with S vulgaris, a degree of increased lymphocyte responsiveness was apparent but, by 17 weeks after reinoculation, only the primary peak in the absolute number of eosinophils indicated an anamnestic response. Essentially, antibody was not detectable after reinoculation.     

Immune responses of specific pathogen free foals to EHV-1 infection.

Four foals were raised under specific pathogen free (SPF) conditions. At 3 to 4 months of age, SPF foals and 1 other non-SPF foal were intranasally inoculated with equine herpes virus type 1 (EHV-1). Clinical signs included depression, fever, inappetence and intermittent coughing. Clinical recovery was complete by seven days but high titres of virus were detected in nasal mucus for at least 10 days after inoculation. Clinical illness was less severe in the non-SPF foal. Interferon was detected in the nasal mucus of all foals from 2 days post infection (dpi), persisting until 8 or 10 dpi. ELISA antibody was detected in serum from 6 dpi. Titres continued to rise throughout the period of observation, and were slightly stimulated by re-inoculation. EHV antibody, identified as belonging to the IgM class by the double sandwich ELISA, was detected from 6 dpi. Peak IgM titres were observed between day 10 and 18, declining to base levels by day 42. Virus neutralizing antibody was detectable in serum from day 14 and rises in titre were parallel to that of total ELISA antibody. Cellular immunity in EHV-1 infected SPF horses was examined by the antibody dependent cytotoxicity (ADCC) test and the specific lymphocyte transformation test. The ability of foal neutrophils to effect ADCC decreased significantly between 3 to 10 days after inoculation. Peripheral blood mononuclear cells (PBMC) displayed reactivity towards EHV-1 antigens from about day 14, with maximum stimulation indices being obtained between 28 and 42 dpi.