Effects of daily pyrantel tartrate on strongylid population dynamics and performance parameters of young horses repeatedly infected with cyathostomins and Strongylus vulgaris.

Strongylid infections are ubiquitous in grazing horse populations. Infections with cyathostomin (small strongyle) and strongylin (large strongyle) nematodes have long been associated with clinical disease in horses, but little is known about their subclinical impact. A masked, randomized, controlled study was conducted to evaluate the effects of daily administration of pyrantel tartrate on body condition scores, weight gain, fecal egg counts, and total worm counts of young horses repeatedly inoculated with strongylid larvae. Twenty eight immature horses were treated with larvicidal anthelmintic regimens and randomly allocated to two groups. Group 1 horses were given a pelleted placebo product once daily, and those in Group 2 received pyrantel tartrate once daily at ∼ 2.64 mg/kg body weight. On five days during each week, ∼ 5000 infective cyathostomin larvae were administered to each horse. In addition, horses received ∼ 25 infective Strongylus vulgaris larvae once weekly. Horses were maintained on pasture for 154 days and had ad libitum access to grass hay throughout. At approximate, 14-day intervals, body weights were measured, body condition scores were assigned, fecal samples were collected for egg counts, and blood samples were collected for measurement of S. vulgaris antibodies and various physiologic parameters. After 22 weeks at pasture and 14-17 days in confinement, horses were euthanatized and necropsied. Nematodes were recovered and counted from aliquots of organ contents, representative samples of large intestinal mucosa, and the root of the cranial mesenteric artery. Daily treatment with pyrantel tartrate at the recommended dosage significantly reduced numbers of adult cyathostomins in the gut lumen and early third-stage larvae in the cecal mucosa, increased the proportions of fourth-stage larvae in the gut contents, and was accompanied by significant improvements in body condition scores. Fecal egg counts of horses receiving daily pyrantel tartrate were significantly reduced, with percentages of efficacy ranging from 84.4% to 98.9%, but egg counts of both groups increased significantly over the course of the study. Treatment also significantly reduced the numbers of S. vulgaris larvae in the cranial mesenteric artery by 99.2%. Serum antibodies to S. vulgaris apparently persisted from pre-enrollment infections, but ELISA values gradually declined over the course of the study. This study has provided useful insights into the effects of daily pyrantel tartrate on the dynamics of cyathostomin infection, and into some subclinical effects of strongylid parasitism in horses.

Parasite field study in central Kentucky on thoroughbred foals (born in 2004) treated with pyrantel tartrate daily and other parasiticides periodically.

Foals (79), born in 2004 on three thoroughbred horse farms (C, M, and S) in central Kentucky, were fed pyrantel tartrate daily, beginning at about 3 months of age. In addition, other parasiticides [fenbendazole (FBZ), ivermectin (IVM) alone or with praziquantel (PRAZ), oxibendazole (OBZ), pyrantel pamoate (PRT), and moxidectin (MOX)] were given periodically. All treatments were administered by farm personnel. Over a 14-month period, from May 2004 to July 2005, collections (n=989) of feces were made from the foals for determination of presence of internal parasite eggs/oocysts by qualitative and/or quantitative methods. Conclusions on drug activity are based necessarily on considering the combined effect of pyrantel tartrate and the other compounds. For small strongyles, this was related to which specific additional compound was given. Based on the percentage of foals with strongyle-egg-positive feces and/or the level of eggs per gram of feces (EPG) counts for the foals after treatment, drug activity on small strongyles was highest to lowest for MOX, IVM and IVM/PRAZ, FBZ, OBZ, PRT, and FBZ (2x for 5 days). The macrocyclic lactones (MOX and IVM) were highly superior to the other compounds. Some of the strongyle counts were high (over 2,000), especially on one farm (S), during periods when foals received only pyrantel tartrate, but a few days after administration of therapeutic dose rates of the drugs IVM or MOX, they were negative or very low. Ascarid eggs were present in feces of three foals after treatment with a combination of IVM and PRAZ. The qualitative method was more efficient than the quantitative method in detection of ascarid and strongyle eggs in the feces. Prevalence of eggs of ascarids (Parascaris equorum) was low (0, 4, and 31%), of strongyles high (80, 100, and 100%), of Strongyloides westeri very low (only one infected foal), and oocysts of Eimeria leuckarti medium to high (36, 41, and 85%) for the three farms, C, M, and S, respectively. It is uncertain whether the low ascarid prevalence was from activity of pyrantel tartrate and/or the other drugs or to a limited source of infective eggs.

Cyathostomes in horses in Canada resistant to pyrantel salts and effectively removed by moxidectin.

Clinical trials using fecal egg count reduction tests and coproculture were conducted with yearlings and mares on a farm in 1997. Fecal samples were taken from each horse to estimate the number of strongyle eggs/g feces with Cornell-Wisconsin centrifugal flotation and Cornell-McMaster dilution techniques. Eleven of 15 yearlings, which had been on a daily feeding of grain with pyrantel tartrate for 66 d were found with strongyle eggs in feces. This was the first time the in-feed medication had been used on the farm. Nine yearlings were randomised into three groups; continuation of daily pyrantel tartrate or one treatment with pyrantel pamoate or moxidectin. Two of three yearlings given pyrantel tartrate or pamoate had no reduction in the eggs/g feces. These six yearlings were then given moxidectin and in all yearlings the eggs/g feces was reduced to zero. The 66 d of pyrantel tartrate use was an inadequate time for development of resistant cyathostomes and a hypothesis was the resistance was due to extensive use on the farm over many years of pyrantel pamoate at twice the label dose for control of tapeworms. That hypothesis was tested with 12 mares with strongyle eggs in the feces randomised into two treatment groups: pyrantel pamoate at label dose or moxidectin. Five of six mares given pyrantel had <80% reduction in egg/g feces. These mares were then given moxidectin and in all mares the eggs/g feces was reduced to zero. Only cyathostomes were found on culture and apparently there was side resistance among the pyrantel salts.

Pyrantel pamoate resistance in horses receiving daily administration of pyrantel tartrate.

CASE DESCRIPTIONS: 16 horses treated daily with pyrantel tartrate (2.64 mg/kg [1.2 mg/lb], PO) as part of a prophylactic anthelmintic program. CLINICAL FINDINGS: Fecal worm egg counts (FWECs) were obtained on all 16 horses. Mean FWEC was 478 eggs/g (epg; range, 0 to 4,075 epg). Three of the 16 horses were responsible for 85% of the total fecal egg output for the herd on the day of sampling. Six horses had FWECs < 200 epg. Three horses that had arrived within 4 months of the sampling date had FWECs < 100 epg. TREATMENT AND OUTCOME: An FWEC reduction test was initiated the day after FWECs were obtained; all horses with FWECs > 100 epg (9 horses) were treated with pyrantel pamoate (6.6 mg/kg [3 mg/lb], PO), and 14 days later, the FWEC was repeated. During the 14-day period, all horses received pyrantel tartrate (2.64 mg/kg, PO) daily. Fecal worm egg count reduction was calculated for each horse. Mean FWEC reduction for the group was 28.5% (range, increase of 21% in FWECs 14 days after treatment to a decrease of 100% in FWEC 14 days after treatment). CLINICAL RELEVANCE: Farms should be monitored for cyathostomes resistant to pyrantel pamoate prior to use of pyrantel tartrate. Fecal worm egg counts should be monitored routinely in horses before and after treatment to ensure efficacy of cyathostome control measures.

Effect of daily administration of pyrantel tartrate in preventing infection in horses experimentally challenged with Sarcocystis neurona.

OBJECTIVE: To determine whether daily administration of pyrantel tartrate can prevent infection in horses experimentally challenged with Sarcocystis neurona. ANIMALS: 24 mixed-breed specific-pathogen-free weanling horses, 10 adult horses, 1 opossum, and 6 mice. PROCEDURE: Sarcocystis neurona-naïve weanling horses were randomly allocated to 2 groups. Group A received pyrantel tartrate at the labeled dose, and group B received a nonmedicated pellet. Both groups were orally inoculated with 100 sporocysts/d for 28 days, 500 sporocysts/d for 28 days, and 1000 sporocysts/d for 56 days. Blood samples were collected weekly, and CSF was collected monthly. Ten seronegative adult horses were monitored as untreated, uninfected control animals. All serum and CSF samples were tested by use of western blot tests to detect antibodies against S. neurona. At the end of the study, the number of seropositive and CSF-positive horses in groups A and B were compared by use of the Fisher exact test. Time to seroconversion on the basis of treatment groups and sex of horses was compared in 2 univariable Cox proportional hazards models. RESULTS: After 134 days of sporocyst inoculation, no significant differences were found between groups A and B for results of western blot tests of serum or CSF There were no significant differences in number of days to seroconversion on the basis of treatment groups or sex of horses. The control horses remained seronegative. CONCLUSIONS AND CLINICAL RELEVANCE: Daily administration of pyrantel tartrate at the current labeled dose does not prevent S. neurona infection in horses.

Determination of the activity of pyrantel tartrate against Sarcocystis neurona in gamma-interferon gene knockout mice.

Equine protozoal myeloencephalitis (EPM) is the most important protozoal disease of horses in the United States. Some horse owners and equine clinicians believe that horses which are on daily pyrantel tartrate at 2.64mg/kg for helminth prophylaxis are less likely to develop EPM. The present study examined the efficacy of pyrantel tartrate in preventing clinical disease in gamma-interferon gene knockout (BALB/c-Ifng(tm1ts)) mice. No activity was seen against sporocyst-induced Sarcocystis neurona infections in mice treated prophylacticly with 4-5mg pyrantel tartrate per mouse per day in the drinking water.

Experimental cyathostome challenge of ponies maintained with or without benefit of daily pyrantel tartrate feed additive: comparison of parasite burdens, immunity and colonic pathology.

Eighteen mixed-breed, naturally infected ponies ranging in age from 1 to 16 yr and four cyathostome-naïve ponies reared and maintained under parasite-free conditions ranging in age from 1 to 4 yr were used in this study. Naturally-infected ponies were treated with 1 dose of ivermectin (IVM) at 200 micrograms kg-1, followed by a 5-day regimen of oxibendazole (OBZ) at 20 mg kg-1 to remove existing cyathostome burdens; cyathostome-naïve control ponies were treated with IVM alone. The naturally infected ponies were matched on age and gender, then randomly assigned to one of three treatment groups of six animals per group; the four cyathostome-naïve ponies constituted a fourth group. Following OBZ treatment, Group 1 ponies were treated with pyrantel tartrate (PT) in their pelleted ration; the remaining ponies received only the pelleted ration. Beginning on experiment Day 3, a daily challenge infection of 10(4) mixed cyathostome larvae was administered orally to ponies of Group 1, Group 2 and the cyathostome-naïve controls. Group 3 ponies served as unchallenged controls to determine residual parasite burdens following IVM/OBZ treatment. Necropsy examinations were performed on three Group 3 ponies on Day 1; the remainder of the necropsy examinations began on Day 41. Cyathostome burdens were evaluated by recovery of larvae and adults from the luminal contents, by digestions of the intestinal mucosa, and by mural transillumination of full-thickness intestinal sections. Differences in postchallenge clinical responses were also compared. Necropsy examinations included comparisons of grossly visible inflammation of the large bowel, weights of biopsy specimens from each region, and histologic evaluations of these biopsies. Parasite recoveries at necropsy indicated a strong protective effect derived from daily PT treatment. Mean weights of intestinal biopsies corresponded with worm burdens, but histological evaluation did not reveal architectural or cellular changes to account for the increase in weight; therefore, edema was suspected. A strong age-related resistance to challenge infection was apparent in both the PT-treated and control groups by virtue of the lower mean worm burdens found in older ponies compared to younger ponies of the same treatment group; however, daily PT treatment of older ponies reduced the variability of their worm burdens to a uniformly low level. Comparisons of luminal and mucosal parasite burdens of age stratified nontreated controls further suggest that the age related resistance, which is acquired, targets increasing numbers of parasite stages as this resistance matures. Further, there is no evidence for an immune mediated acquisition of hypobiotic L3.

Controlled efficacy study of the bioequivalence of Strongid C and generic pyrantel tartrate in horses.

The bioequivalence of Strongid C and generic pyrantel tartrate was determined in a controlled study using 30 horses with naturally acquired endoparasitic infections. Three horses were randomly allocated to each of ten replicates based on quantitative nematode and ascarid egg counts and fecal larvae culture results. Horses within each replicate were randomly assigned to one of three treatment groups. Horses in Treatment Group 1 received only oats; horses in Treatment Group 2 received generic pyrantel tartrate pellets (2.65 mg pyrantel tartrate kg-1) mixed with oats; horses in Treatment Group 3 were fed Strongid C pellets (2.65 mg pyrantel tartrate kg-1) mixed with oats. Horses were treated daily for a 30 day continuous treatment period. At the termination of the study the horses were necropsied and endoparasites recovered, identified, and enumerated. In all instances, no significant difference (P > 0.05) in mean numbers of parasites recovered existed between horses treated with generic pyrantel tartrate and Strongid C. Numbers of gastrointestinal parasites recovered from horses treated with generic pyrantel tartrate or Strongid C were shown to be significantly different (P < 0.05) from numbers of gastrointestinal parasites recovered from non-treated controls for the large strongyles (Strongylus vulgaris, S. edentatus, and Triodontophorus spp.), small strongyles (Cyathostomum spp., Cylicocyclus spp., and Cylicostephanus spp.) and fourth-stage Parascaris equorum. Numbers of adult P. equorum recovered from horses treated with Strongid C were also significantly different (P < 0.05) from those from non-treated controls. Numbers of adult P. equorum recovered from horses treated with generic pyrantel tartrate were not significantly different (P = 0.0761) from those from non-treated controls. The determination of bioequivalence was based upon the 95% confidence interval of the difference between the mean number of parasites recovered from horses treated with generic pyrantel tartrate and the mean number of parasites recovered from horses treated with Strongid C. For all instances in which the numbers of parasites recovered from horses treated with either Strongid C or generic pyrantel tartrate were significantly different from the numbers of parasites recovered from non-treated controls, bioequivalence was demonstrated.

Efficacy of pyrantel tartrate against experimental infections with Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis in goats.

The efficacy of pyrantel tartrate was evaluated in goats against induced infections with Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis. All the strains were of sheep origin and tested for susceptibility to pyrantel tartrate in sheep at the standard dose rate (20 mg kg-1) prior to the infection of goats. Fifteen French Alpine female goats were inoculated with the three nematode species. On Day 25 post-infection, goats were randomized into an untreated control group and two pyrantel treatment groups (20 mg kg-1 bodyweight once, and 40 mg kg-1 bodyweight as two doses 24 h apart). The goats were killed and processed for worm recovery 10 days after treatment. The two dose rates achieved high and similar levels of efficacy (> 96%) against Haemonchus contortus and Teladorsagia circumcincta. Against Trichostrongylus colubriformis, however, pyrantel tartrate was less effective at both dose rates as worm reductions ranged from 55 to 62%.

Comparison of daily and monthly pyrantel treatment in yearling thoroughbreds and the protective effect of strategic medication of mares on their foals.

Studies on a Thoroughbred breeding farm in Ohio were done to: (1) compare the effects of daily administration of pyrantel tartrate feed pellets with monthly administration of a pyrantel pamoate paste to yearling horses (21 January-3 September); (2) assess the effects of daily pyrantel tartrate given strategically in spring/summer to foaling mares (1 April-16 August) and given for a prolonged period to barren mares (21 January-3 September); (3) determine if strategic medication of foaling mares with daily pyrantel tartrate protected their foals until weaning. There were no differences in cyathostome egg counts, pasture larval counts, body condition scores, or body weights of yearlings treated with daily pyrantel tartrate or monthly pyrantel pamoate. Both treatments failed to maintain fecal egg counts of yearlings below 100 eggs per gram (epg), and mean counts exceeded 400 epg (pyrantel pamoate) and 700 epg (pyrantel tartrate) in August and September, resulting in a sharp, but moderate increase in pasture infectivity in October. By contrast, prolonged or strategic use of daily pyrantel tartrate in mature horses were each highly effective in reducing pasture contamination and infectivity with cyathostome eggs and larvae respectively. Strategic medication of foaling mares provided protection of their foals until weaning and first treatment of foals was delayed until after weaning when mean strongyle counts exceeded 100 epg. Treatment of weanlings with pyrantel pamoate had little effect on egg counts. A comparative anthelmintic study with ivermectin, oxibendazole, and pyrantel pamoate confirmed earlier studies showing reduced efficacy of anthelmintics in young horses.

Patent infections of Ascaris suum in pigs: effect of previous exposure to multiple, high doses of eggs and various treatment regimes.

Fifty-four crossbred, 4-week-old pigs divided into nine equal groups were used to test whether multiple inoculations with high numbers of A. suum eggs with or without anthelmintic would result in patent infections. All pigs exposed to multiple prechallenge inoculations of 500, 1000, 2000, 5000, 10,000 and 20,000 and challenged orally 2 weeks later with 10,000 eggs harboured adult worms. When prechallenge infections were removed by pyrantel tartrate treatment the animals were more susceptible to challenge than controls not previously exposed to infections. The same drug used from 2 days before until 10 days after the last prechallenge infection eliminated that effect. Pigs subjected to the same multiple egg dosing regimen but given feed containing fenbendazole immediately before, during and for 10 days after multiple dosing developed significantly more adult intestinal worms after challenge than any other group. These worms were, however, significantly shorter than those that developed in any group of pigs. Adult worms from all these groups produced eggs that after embryonation were infective to mice.

Concurrent infections with the ruminant nematodes Haemonchus contortus and Trichostrongylus colubriformis in jirds, Meriones unguiculatus, and use of this model for anthelmintic studies.

Haemonchus contortus- and Trichostrongylus colubriformis-infected jirds (Meriones unguiculatus) are useful for anthelmintic studies. With concurrent infections of these parasites established in the jird, questions of not only anthelmintic activity, but to some extent spectrum, could be assessed in a single model system. This report outlines a model using immunosuppressed (0.02% hydrocortisone in feed) jirds concurrently infected with H. contortus and T. colubriformis. Immunosuppressed jirds were inoculated with approximately 1,000 exsheathed infective larvae of each species, treated per os on day 10 postinoculation (PI), and killed on day 13 PI. Stomachs and small intestines were removed, opened longitudinally, incubated in distilled water at 37 C for 5 hr, fixed in formaldehyde solution, and stored for subsequent examination. Contents of both organs were examined using a stereomicroscope (15-45 x). Various standard anthelmintics were evaluated in the model; modern broad-spectrum ruminant anthelmintics (benzimidazoles, febantel, ivermectin, levamisole hydrochloride, and milbemycin D) are active uniformly and in most cases at doses comparable to those required for efficacy against these parasites in ruminants. This model, using worms of 2 genera living in distinct sites, allows preliminary evaluation of anthelmintic activity and spectrum for experimental compounds in a single cost- and resource-efficient experiment.

Acquired resistance to migrating larvae of Ascaris suum in young pigs by repeated drug-abbreviated infections.

Cross-bred 3- and 8-wk-old pigs were used to test whether drug-abbreviated infections with Ascaris suum can stimulate acquired resistance to challenge. During the immunization period, both age groups of animals were infected with increasing numbers of A. suum eggs (500, 1,000, 2,000, 5,000, 10,000, and 20,000) at 7-day intervals while the pigs were receiving pyrantel tartrate in the feed. Two days after the last infective dose, animals were placed on unmedicated feed for 8 days and then challenged with 10,000 eggs. All pigs were killed 7 days after challenge, and milk spots on the livers and larvae recovered from the lungs were counted. Larval recoveries from lungs of the immunized animals were significantly smaller than those from the unimmunized animals in both age groups, suggesting that the pigs were capable of acquiring strong resistance to parasitic infections. In immunized animals, challenge infection did not contribute significantly to milk spot formation. The number of milk spots was significantly greater in the older animals, indicating that milk spot formation may be age related.

Evaluation of pyrantel-tartrate abbreviated Ascaris suum infections for the development of resistance in young pigs against migrating larvae.

Crossbred young pigs were used to test whether abbreviated infections with eggs of Ascaris suum can stimulate the acquisition of resistance to challenge. Weanling pigs from an Ascaris-free colony were kept free of A. suum until they were divided into groups at the age of 7-8 weeks. The experimental animals received pyrantel tartrate during the period when they were being exposed to increasing numbers of infective A. suum eggs and challenged 10 days after the last infective dose. Liver milk-spot counts and larval recoveries from the lungs indicated that the strongest resistance was acquired by the animals that received the drug continuously for 6 weeks while being exposed to six weekly infective egg doses. The data do not suggest any drug-related suppression of the resistance response to A. suum infection.

Effect of fenbendazole and pyrantel tartrate on the induction of protective immunity in pigs naturally or experimentally infected with Ascaris suum.

An experiment was conducted with 96 weanling pigs (avg initial wt 18.5 kg) divided into six treatment with two replicates of eight pigs each. Pigs in Treatments 1, 2 and 3 were penned in outside pens with dirt lots that previously were contaminated with A. suum ova to induce a natural ascaris infection. Pigs in Treatments 4, 5 and 6 were penned in an open-front building with solid concrete floors and were experimentally infected with 2,000 embryonated A. suum. ova on d 1, 15 and 29 of the experiment. Pigs in Treatments 1 and 4 were medicated with fenbendazole (FBZ, 3 mg/[kg BW.d]) for three consecutive days during three consecutive time periods. Pigs in Treatments 2 and 5 were medicated with pyrantel tartrate (PT, 106 mg/kg feed) for 28 d. Pigs in Treatments 3 and 6 served as infected, unmedicated controls. All pigs were challenged with 100 A. suum eggs 7 d after termination of the final FBZ treatment. All pigs were killed 66 d after challenge and worms were recovered. Fenbendazole treatment resulted in greater (P less than .07) average daily gain than PT treatment in pigs penned outside. Among inside pigs, FBZ treatment resulted in better (P less than .02) feed utilization than in controls. The FBZ and PT treatments reduced (P less than .03) the total number of A. suum, the length and weight of female ascarids and the length of male ascarids compared with controls. A natural continual infection with A. suum was less effective than experimental infection in inducing protective immunity in pigs.

Capillária hepática: relato de caso na infância / Capillária hepática: report of a case in childhood

A infecçäo por Capilária hepática é rara em humanos sendo, a maioria dos casos, diagnosticados à autópsia. Os autores relatam um caso de diagnóstico histopatológico em um menino de 17 meses; apresentam sua evoluçäo clínico-laboratorial e destacam o sucesso obtido com a terapêutica empregada

Heligmosomoides polygyrus: time of anthelmintic treatment and infection parameters in mice exposed to increasing doses of larvae.

Mice were multiply infected with increasing doses of Heligmosomoides polygyrus larvae. On Day 9 or on Day 30 after the beginning of infections, an anthelmintic treatment was administered and its effect on reinfections and egg production was studied. The time of treatment was found to be an important factor, since early treatment produced marked resistance to subsequent infection, whereas a similar effect was not observed for the late treatment. Most immunity appeared after a lag time of about 3 weeks following treatment. Mice placed in direct contact with high doses of larvae had massive infections, and large quantities of worm eggs were recovered in the faeces. After larval doses were no longer given, there was a decrease of the worm burden in both treated and untreated animals. Studies of egg laying showed that the increased resistance induced by the treatment was also responsible for a reduced egg production. The relationship between fertility of H. polygyrus females and the size of young parasite populations was positive, but was negative for older populations. The slope of the regression line of this relationship was steeper in treated than in untreated mice. Egg production by a female worm was depressed to a certain extent by the resistance reactions of the host, but did not decrease below a threshold value of 100 eggs per female per day.

Studies on chemotherapy of parasitic helminths (XVIII). Mechanism of spastically paralyzing action of pyrantel in Angiostrongylus cantonensis.

Pyrantel tartrate caused spastic paralysis through stimulating nicotinic cholinoceptors in Angiostrongylus cantonensis.