Critical tests with oxibendazole against gastrointestinal parasites of ponies.

Twenty ponies were allotted to 4 groups of 5 ponies each, and oxibendazole was orally administered at dose levels of 5, 10, 15, and 20 mg/kg. In the 3 groups of ponies given the largest doses, efficacy against 3 species of Strongylus was between 92 and 100% and that against small strongylids of the genera Cyathostomum, Cylicocyclus, Cylicodontophorus, and Cylicostephanus was more than 99%. All adults and 95 to 100% of larvae of the pinworm Oxyuris equi were removed. In the group of ponies given 5 mg/kg, 86 to 100% of the large strongylids and 84 to 100% of the small strongylids were removed, as were all larval and adult pinworms. Trichostrongylus axei was found only in 4 of the 5 ponies given 5 mg/kg; results were encouraging, but not consistent. Almost all of the Parascaris equorum were found in this group of ponies; no anthelmintic activity was detected at this dose level. Oxibendazole removed approximately 99% of small strongylid 4th-stage larvae. No efficacy against the larval stages of Gasterophilus intestinalis and against Habronema spp and Setaria equina was observed.     

The development of immunity to Parascaris equorum infection in the foal

Following infection with 8000 Parascaris equorum eggs in two- to four-week-old foals reared under worm-free conditions a high percentage of the infective dose completed its tissue migration and returned to the small intestine. Patent infections were establisehd between 81 and 104 days after infection and high faecal egg counts were recorded. A group of six- to 12-month-old foals, which had been either reared under worm-free conditions or exposed to natural ascarid and strongyle infections on pasture, received a similar infection of 8000 P equorum eggs. Compared with the younger foals there was a marked reduction in the number of larvae reaching the small intestine. Also, patent infections were established less frequently (50 per cent of cases) and, when present, the faecal egg counts remained low.     

Identification of foals infected with Parascaris equorum apparently resistant to ivermectin

During September 2002, routine fecal examinations performed on 16 Thoroughbred foals residing on a farm outside Toronto, Ontario, Canada, revealed low to moderate numbers of Parascaris equorum eggs in feces from 9 of the 16. All foals were then treated with ivermectin at a dose of 220 to 280 microg/kg (100 to 127 microg/lb), p.o., and fecal egg counts were repeated 12 days later. Fecal P. equorum egg counts increased between the first and second fecal examination in 7 foals, were unchanged in 1, and decreased in 5. Fecal samples were collected 13 days after treatment from 21 additional foals that had been treated with ivermectin at the same dose, and P. equorum eggs were detected in 12 of the 21. For all 37 foals, high P. equorum egg counts (> or = 100 eggs/g of feces) 12 to 13 days after ivermectin treatment were significantly more likely in foals that had been regularly treated with ivermectin since birth and permanently resided on the farm, compared with foals that had been treated with other anthelmintics or had an unknown deworming history. Collectively, these data suggested that P. equorum in these foals was resistant to ivermectin administered at the recommended dose.     

Comparison of the efficacy of ivermectin, oxibendazole, and pyrantel pamoate against 28-day Parascaris equorum larvae in the intestine of pony foals

Sixteen helminth-free pony foals were inoculated with a mean (+/- SD) 2,000 (+/- 545.5) infective Parascaris equorum eggs (day 0). Foals were allocated to replicates of 4, and treatments within each replicate were assigned at random. Treatment administered on postinoculation day (PID) 28 included no treatment (control), 0.2 mg of ivermectin/kg of body weight, 10 mg of oxibendazole/kg, or 6.6 mg of pyrantel base (pamoate)/kg. Paste formulations of the anthelmintics were administered orally. The foals were euthanatized 14 days after treatment (PID 42) and examined for P equorum larvae in the small intestine. The mean +/- SD (and range) numbers of fourth-stage P equorum larvae recovered from nontreated foals and those treated with ivermectin, pyrantel, or oxibendazole were 1,603.8 +/- 1,026.8 (305 to 2,480), 29.3 +/- 55.8 (0 to 113), 413.0 +/- 568.1 (0 to 1,204), or 889.5 +/- 1,123.1 (1 to 2,345), respectively. Compared with the value for control (nontreated) foals, treatment with ivermectin, pyrantel, and oxibendazole was 98.2, 74.2, and 44.5% effective, respectively, when administered 28 days after experimentally induced infection with P equorum. Adverse reactions attributable to treatment were not observed.     

Borrelia burgdorferi infections with special reference to horses. A review

This review discusses the literature on B. burgdorferi infections in view of the rising incidence of this infection in general and the increasing concerns of horse owners and equine practitioners. Lyme disease, the clinical expression of Borrelia infections in man is an important health problem. The geographic distribution of B. burgdorferi infections in equidae should resemble that of human cases because the vector tick involved, Ixodes ricinus, feeds on both species and, indeed, the infection has been established many times in horses. However, a definite diagnosis of the disease "Lyme borreliosis" in human beings as well as in horses and other animals is often difficult to accomplish. Although a broad spectrum of clinical signs has been attributed to B. burgdorferi infections in horses, indisputable cases of equine Lyme borreliosis are extremely rare so far, if they exist at all.     

Borrelia burgdorferi infections with special reference to horses. A review

Summary This review discusses the literature on B. burgdorferi infections in view of the rising incidence of this infection in general and the increasing concerns of horse owners and equine practitioners. Lyme disease, the clinical expression of Borrelia infections in man is an important health problem. The geographic distribution of B. burgdorferi infections in equidae should resemble that of human cases because the vector tick involved, Ixodes ricinus, feeds on both species and, indeed, the infection has been established many times in horses. However, a definite diagnosis of the disease "Lyme borreliosis" in human beings as well as in horses and other animals is often difficult to accomplish. Although a broad spectrum of clinical signs has been attributed to B. burgdorferi infections in horses, indisputable cases of equine Lyme borreliosis are extremely rare so far, if they exist at all.     

Determination of anthelmintic efficacy against equine cyathostomins and Parascaris equorum in France

This article reports the results of a faecal egg count reduction test on 4 farms in France, as an integrated part of the routine deworming strategy against horse cyathostomins and Parascaris equorum. Treatment with fenbendazole (FBZ) or ivermectin (IVM) was evaluated in yearlings on Farms 1 and 2 and treatment with pyrantel embonate (PYR) was tested on Farms 3 and 4. Calculation of the arithmetic mean faecal egg count reduction and the 95% confidence intervals (95% CI) around the mean was performed using bootstrap analysis. For equine cyathostomins, resistance to FBZ was found with an arithmetic mean reduction of 48.8% (95% CI: 1.9–69.3%). On Farms 1 and 2, horses with reduced efficacy were identified. PYR was found to be effective against cyathostomins, with an arithmetic mean reduction of 95.3% (95% CI: 84.6–99.8%), as well as IVM (100%). For P. equorum, both FBZ and PYR were effective (100% reduction). The efficacy of IVM, however, was low (45.5%; 95% CI: 0–96.3%). These results confirm that FBZ resistance in equine cyathostomins is present in France and that anthelmintic resistance to IVM is present in P. equorum. This study underlines the necessity to evaluate the efficacy of horse deworming strategies on a regular basis under field conditions.     

Acute small intestinal obstruction associated with Parascaris equorum infection in young horses: 25 cases (1985-2004)

AIMS: To retrospectively evaluate the medical and surgical records of horses with acute small intestinal obstructions associated with Parascaris equorum infection; to describe the gastrointestinal lesions; and to determine the outcome of cases with such lesions. METHODS: Records of 25 horses with acute small intestinal obstruction associated with P. equorum between 1985 and 2004 were reviewed to determine signalment, history, physical examination, surgical or post-mortem findings, and outcome. RESULTS: All horses except one were less than 12 months old. Standardbreds were over-represented in the population studied. Sixteen horses (72%) had been administered anthelmintics, including pyrantel (n=8), ivermectin (n=7), and trichlorphon (n=1), within 24 h prior to the onset of colic. Of the 25 cases reviewed, 16 had simple obstructive ascarid impactions (SOAIs), and nine had complicated obstructive ascarid impaction (COAI) including volvulus (n=6) or intussusception (n=3), both concurrent with ascarid impaction of the small intestine. Short-term survival (discharge from hospital) occurred in 79% of horses treated for SOAI, and was 64% for all horses. Long-term survival (>1 year) occurred in 33% of horses with SOAI, and the overall long-term survival was 27% for all horses. Formation of adhesions was the most frequent finding associated with death for horses that did not survive long-term. CONCLUSIONS AND CLINICAL RELEVANCE: The incidence of anthelmintic treatment within 24 h of the onset of colic in this study population (72%) was higher than that previously reported. Resistance of P. equorum to ivermectin recently reported in Ontario may be associated with increased ascarid burdens, predisposing horses to ascarid impaction. The long-term survival of these horses was better than that reported previously.     

Effects of low and high temperatures on viability of Parascaris equorum eggs suspended in water

Microcentrifuge tubes containing 5000 eggs of Parascaris equorum suspended in water were frozen at -5, -10, -15, -20, and -80 degrees C for 1-168 h and then thawed at a room temperature. Other samples of P. equorum eggs suspended in water were inserted into wells in the heated metal block of a thermal DNA cycler. Block temperatures were set at 5 degrees C incremental temperatures from 40 to 100 degrees C. At each temperature setting microcentrifuge tubes containing P. equorum eggs were removed 1 and 5 min later. Both, frozen and heated egg suspensions as well as untreated control suspensions were then incubated to test of viability based on the development of infective larvae inside viable eggs. We found out that eggs of P. equorum in water can retain viability and infectivity after freezing and that eggs survive longer at higher freezing temperatures. Our results also indicated that when water containing P. equorum eggs reached temperatures of 60 degrees C or higher within 1 min, the viability of eggs was lost.     

Macrocyclic lactone-resistant Parascaris equorum on stud farms in Canada and effectiveness of fenbendazole and pyrantel pamoate

The aims of studies in 2002 and 2003 on three farms with 76 foals naturally infected with Parascaris equorum were to (i) identify if the nematode was resistant to ivermectin and moxidectin, and (ii) confirm the effectiveness of fenbendazole and pyrantel pamoate for the parasite. Twelve clinical trials, each with a Fecal Egg Count Reduction Test, were conducted on two Thoroughbred and one Standardbred farms in southwestern Ontario, Canada. In each trial, Parascaris eggs/g feces were estimated for each foal pre- and post-treatment using the Cornell-Wisconsin double flotation and Cornell-McMaster dilution techniques. On each farm and for each trial, foals were randomized into treatment groups. Treatments were ivermectin, moxidectin, fenbendazole, pyrantel pamoate administered at the manufacturers' recommended dosages, and some foals were untreated. The overall efficacy for ivermectin was 33.5% (19 foals) and for moxidectin 47.2% (28 foals). Fenbendazole (16 foals) and pyrantel pamoate (21 foals) were highly effective for P. equorum each at 97.6%. For fenbendazole, 15 foals had 100% and for pyrantel pamoate 17 foals had >97% with 14 at 100%.     

Parascaris equorum in foals and in their environment on a Swedish stud farm, with notes on treatment failure of ivermectin

Environmental contamination and the egg excretion pattern of the ascarid Parascaris equorum (Nematoda) was investigated in relation to anthelmintic treatment on a Swedish stud farm. Faecal samples from 15 foals, dewormed every 8th-week with a paste formulation of ivermectin at the standard dose rate of 0.2 mg/kg bodyweight, were collected at five sampling occasions between August and November 2006. In addition, soil samples were obtained from four paddocks used by these foals in November 2006. The number of eggs per gram (epg) was counted in both faeces and soil. Egg excretion started when the foals were 3-4 months, and reached the highest levels when they were approximately 5-month-old, and was then followed by a decline. Egg excretion seemed to be unaffected by ivermectin despite these foals were dewormed at regular intervals. In four out of five foals examined 10 days after treatment, epg actually increased. In contrast, when either fenbendazol or pyrantel embonate were used instead of ivermectin, treatments were effective. The number of eggs in soil was significantly higher in the permanent paddock compared to in the temporarily used soil paddock and in the summer paddocks.     

A field evaluation of oxibendazole in horses infected with benzimidazole resistant small strongyles

Horses with a history of frequent benzimidazole (BZD) treatment were used in a trial to assess the effectiveness of oxibendazole (OBZ). Initial investigations established that these animals were infected with small strongyles resistant to thiabendazole (TBZ), mebendazole (MBZ), cambendazole (CBZ), oxfendazole (OXF) and fenbendazole (FBZ).The herd was subsequently divided into four groups and received TBZ, CBZ, OBZ, or no treatment. OBZ effectly reduced fecal egg counts. Similar reductions were not observed with TBZ or CBZ.     

Evaluation of serum osteocalcin and CTX-I in Ardenner horses with special reference to juvenile interphalangeal joint disease

The first aim of this study was to establish a profile of age-related normal serum concentrations of osteocalcin (OC) in Ardenner horses. For this first part, blood samples from 49 healthy Ardenner horses were collected. The second aim was to study two biochemical markers of bone metabolism, OC and a carboxy-terminal cross-linking telopeptide of type I collagen (CTX-I), in 30 young Ardenner horses during 1 year. Amongst them, 17 showed lesions of juvenile degenerative joint disease in the distal forelimbs. A specific radioimmunoassay for equine OC was used to measure the serum concentration of the marker. The serum concentration of CTX-I was measured using a commercially available human assay validated for use in the horse. The effect of age, sex, season and health status (with or without lesions) was assessed. Levels of OC fall between birth and the adult stage: this decrease being most marked between birth and 1 year of age. This age-related decrease of OC was confirmed in the 30 young Ardenner horses, but CTX-I levels remained constant in this group. The Levels of the two markers changed significantly with the season with higher concentrations during the winter. No significant difference was shown either between the two sexes or between the two health statuses.     

Observations on the transmission, immunology, clinical signs and chemotherapy of dourine (Trypanosoma equiperdum infection) in horses, with special reference to cerebro-spinal fluid.

This paper is a record of observations on the transmission and clinical signs of dourine in naturally infected cases of known duration, and of temporal and quantitative aspects of the immune response in blood and cerebro-spinal fluid. Included in the record are observations on the presence of Trypanosoma equiperdum parasites in these body fluids and methods for their detection. There is evidence that the occurrence of nervous symptoms and lesions in infected horses is associated with the presence of Trypanosoma equiperdum parasites in cerebro-spinal fluid. The suitability of cerebro-spinal fluid as an environment for the parasite and its relationship with nervous manifestations of the disease are discussed. Observations support the previously reported lesions of peripheral polyneuritis and suggest a possible correltation between the consitstent position of the nervous lesions and the drainage of cerebro-spinal fluid containing the parasite. Chemotherapy with an experimental drug MSbE was used with varying results in 4 horses at different stages of infection.