S.D. Folz

Detecting in vitro anthelmintic effects with a micromotility meter.

An in vitro target parasite anthelmintic assay utilizing a micromotility meter has been developed and validated. Haemonchus contortus, an economically important ruminant helminth with worldwide distribution, was the parasite used in the model. Four commercially available ruminant anthelmintics (albendazole, ivermectin, levamisole hydrochloride and coumaphos) were initially evaluated at concentrations of 200, 150, 100 and 50 micrograms ml-1. All four significantly affected helminth motor activity and were active at 200 and 150 micrograms ml-1, and three of the four were active at 100 and 50 micrograms ml-1. An Upjohn compound (p-toluoyl chloride phenylhydrazone) was also assayed and was significantly active at all four levels. In a subsequent titration study, albendazole, levamisole hydrochloride, ivermectin and the hydrazone were significantly active at 100 and 10 micrograms ml-1; only levamisole hydrochloride and the hydrazone were active at 1.0 microgram ml-1. None of the drugs were active at 0.1 microgram ml-1. The data indicate that the in vitro H. contortus assay utilizing the micromotility meter is sensitive, accurate, rapid, repeatable, and inexpensive. With additional effort, this model can be extended to incorporate other target helminth parasites and stages of development. This in vitro assay system should be a valuable addition to the battery of tests used to identify anthelmintic candidates, monitor drug resistance, and define the kinetics and mode of action of drugs.

Anticoccidial evaluation of halofuginone, lasalocid, maduramicin, monensin and salinomycin

The activities of five anticoccidials were compared against Eimeria species in/of chickens, in controlled in vivo and in vitro laboratory studies. Two more recent and potent market entries (maduramicin and halofuginone) were compared with three older polyether antibiotic anticoccidials (monensin, lasalocid and salinomycin). Halofuginone, lasalocid, maduramicin, monensin and salinomycin were evaluated at 3, 125, 5, 120 and 66 ppm, respectively, of active drug in the diets. At these levels, all five drugs demonstrated significant activity against Eimeria tenella, E. maxima, E. necatrix, E. brunetti and E. acervulina (in vivo). Monensin was least effective against E. tenella, and one of the lesser efficacious drugs against E. necatrix, maduramicin, was least effective against E. maxima. In studies of single Eimeria species infections, comparable weight gains were noted for the drugs. In the mixed Eimeria species infections, however, birds treated with maduramicin had significantly higher weight gains than did birds medicated with monensin. Unlike in vivo potencies, titration in vitro indicated that monensin was most potent (active at 10(-6) mcg ml-1), and maduramicin and lasalocid least potent (inactive at less than or equal to 10(-3) mcg ml-1).

Clinical evaluation of amitraz as a treatment for canine demodicosis

A liquid concentrate formulation of amitraz was clinically evaluated in 1721 canines showing demodicosis, by 25 veterinary investigators. The therapy was applied topically at 14-day intervals, and at a concentration of 250 ppm active drug in water. The miticide was efficacious and safe; approximately 99% of the canines showing localized or generalized demodicosis became clinically normal, and the side-effects recorded were minimal and transient. Approximately 3/4 of the patients were pure-bred animals and the majority were less than 1 year old. The clinical data support the conclusion that amitraz (liquid concentrate) is efficacious and safe for treating canine demodicosis.

Development and validation of an in vitro Trichostrongylus colubriformis motility assay.

Abstract Development and validation of an in vitro Trichostrongylus colubriformis motility assay. International Journal for Parasitology 17 : 1441–1444. An in vitro Trichostrongylus colubriformis motility assay involving the use of a micromotility meter has been developed and validated. Four commercially available ruminant anthelmintics (albendazole, ivermectin, levamisole hydrochloride, and coumaphos) and an investigational hydrazone compound ( p -toluoyl chloride phenylhydrazone) were evaluated in this assay at four concentrations each. At 100 μg ml -1 , all five treatments significantly ( P ⩽ 0.05) reduced the motility of ensheathed L-3 T. colubriformis larvae, thereby indicating anthelmintic activity. At this concentration, coumaphos was significantly less active than any of the other four treatments. At 10 μg ml -1 albendazole, ivermectin, levamisole hydrochloride and the hydrazone compound were active, but coumaphos was not. At 1 μg ml -1 albendazole, ivermectin and levamisole hydrochloride remained significantly active, but neither coumaphos nor the hydrazone compound showed significant activity. At all three of the higher concentrations (1,10 and 100 μg ml -1 ), levamisole hydrochloride indicated greater activity than any of the other treatments. This difference was statistically significant at the 1 and 10 μg ml -1 concentrations. None of the five treatments showed significant activity at the lowest concentration (0.1 μg ml -1 ). The in vitro T. colubriformis motility assay proved to be sensitive, accurate, rapid, and repeatable. This assay system should be another valuable addition to the tests used to identify potential anthelmintics, monitor helminth resistance to drugs, and define the kinetics and mode of action of drugs.

Motility response of levamisole/benzimidazole-resistant Haemonchus controtus larvae

Electronic measurements of the motility of third stage larvae of a susceptible and a levamisole/benzimidazole-resistant strain of Haemonchus contortus were made after incubation in solutions of anthelmintics for 24 h. Results confirmed the resistance to benzimidazoles, but failed to show differences in response to levamisole. Visual observations of paralysis of first and third stage larvae in solutions of levamisole also failed to show significant differences between the two strains. The tests as conducted failed to demonstrate levamisole resistance, suggesting that nematode strains may vary in their mechanisms of resistance to levamisole.

Chemotherapeutic treatment of naturally acquired generalized demodicosis

Fifty-two dogs naturally parasitized with Demodex canis and having the generalized form of the disease were utilized to evaluate the efficacy and safety of single or multiple topical treatments with a liquid concentrate formulation of amitraz. Ten dogs (5 treated, 5 controls) were utilized to evaluate a single treatment. A single topical treatment with the miticide did not significantly reduce the incidence of dogs with mites, however, significant clinical improvement resulted. Side-effects were not observed after treatment. Forty-two dogs (26 treated, 16 controls) were utilized to evaluate multiple topical treatments with the liquid concentrate. A series of 3-6 treatments was applied topically at 14-day intervals. The dogs treated with the miticide received an average of 4.5 topical treatments. All (100%) of the dogs responded clinically, and the mean rate of improvement at four weeks post-treatment was 99.1%. Most dogs (96.2%) were cleared of mites after 3-6 treatments, and Mitaban did not cause any dermatologic, ocular, or other clinical side-effects. Multiple treatments with the liquid concentrate were highly efficacious and safe for treatment of generalized demodicosis. Control dogs did not improve clinically and retained mite populations.

ANTICOCCIDIAL ACTIVITY OF ALBORIXIN

Alborixin, a polyether antibiotic with ionophore properties, was evaluated to determine the effect of the drug on weight gain of chickens and to define the anticoccidial spectrum of activity. The 50-ppm concentration in the diet was identified as the maximum level that did not significantly reduce weight gain beyond that of monensin (standard drug); consequently, the drug was evaluated for anticoccidial activity at this dilution. At the 50-ppm level, alborixin demonstrated broad-spectrum anticoccidial activity; however, the drug lacked Eimeria necatrix efficacy. Monensin and maduramycin were significantly more efficacious than alborixin as a treatment for several species of Eimeria. Higher concentrations of alborixin (greater than 50 ppm) appear essential to achieve broad-spectrum and comparable anticoccidial activity, however, these levels substantially depressed weight gains. Alborixin is similar to many other polyethers in that weight gains are adversely affected at drug levels essential for solid broad-spectrum anticoccidial activity.

Evaluation of a topical treatment, alone and in combination with a detergent, for generalized demodicosis

Thirty dogs (20 treated, 10 controls) with naturally-acquired generalized demodicosis were utilized to evaluate the bio-activity and safety of a liquid concentrate formulation of amitraz, with or without the addition of a nonionic detergent. The detergent was added to the treatment mixture to enhance wetting and thereby reduce the number of treatments required to return diseased animals to a normal state. Three--six miticide treatments were topically applied to dogs at 14-day intervals, at a concentration of 250 parts per million active drug. The liquid concentrate with or without detergent, was equally effective and safe as a dermatotherapy for demodicosis; addition of the nonionic detergent grossly improved the wetting characteristics of the treatment mixture; however, it did not alter the biological activity or the safety of the therapy.

Anti-coccidial activity of 2-picoline, 6-amino-4-nitro-, 1-oxide.

An investigational drug (2-picoline, 6-amino-4-nitro-, 1-oxide) was evaluated to characterize the anti-coccidial spectrum of the compound. Two concentrations of the drug (125 and 250 ppm) were evaluated for bioactivity; weight gain, survival, dropping, and lesion scores were the response variables utilized to ascertain activity. The activities of the picoline derivative were compared with monensin, maduramicin, and a narasin/nicarbazin (1:1) combination. The investigational drug had significant activity against Eimeria tenella and Eimeria necatrix, and the 250-ppm level was significantly more active than 125 ppm. At 250 ppm, the E. tenella activity of the picoline derivative was comparable to both monensin (120 ppm) and the 50-ppm narasin/nicarbazin combination, significantly less effective than maduramicin (6 ppm), and significantly more efficacious than 30 ppm narasin/nicarbazin. At the same level (250 ppm), the picoline derivative had significantly less E. necatrix activity than monensin (120 ppm), maduramicin (6 ppm), and narasin/nicarbazin (50 ppm), and significantly greater activity than 30 ppm narasin/nicarbazin. At best, only extremely weak Eimeria acervulina, Eimeria brunetti, and Eimeria maxima activities were noted with the investigational drug; higher concentrations of the picoline derivative may achieve greater anti-coccidial activity against these species. The efficacy of narasin/nicarbazin compared favorably with monensin and maduramicin; the 50-ppm level of the combination appeared significantly more efficacious than 30-ppm.

Precluding coccidiosis with an anti-coprophagia drug.

Floor-pen studies were conducted to ascertain whether coccidiosis could be prevented by using a drug added to the litter to preclude coprophagia and ingestion of infective oocysts. An experimental drug (1-pyrrolidinebutyramide, 2-methyl-alpha,alpha-diphenyl) was added to litter contaminated with sporulated Eimeria tenella oocysts. Thereafter 7-day-old broiler chicks were reared on the litter for a nine-day period. Mortality, lesion scores and dropping scores were the criteria selected to determine efficacy. Treatment of the litter at the lowest level (2.3 g kg-1) did not reduce the incidence or severity of the disease, whereas treatment at two higher levels (11.5 and 23.0 g kg-1) significantly reduced both (incidence and severity). The highest level was the most efficacious; however, drug toxicity was also encountered at this level.