The effect of the hydrogen ionophore closantel upon the pharmacology and ultrastructure of the adult liver fluke Fasciola hepatica

The present study describes the effects of the H+ ionophore and anthelmintic closantel upon the in vitro motility and in vivo ultrastructure of the liver fluke, Fasciola hepatica. At a concentration of 50 micrograms/ml, closantel caused an initial stimulation, then suppression of activity, which was accompanied by an increase in muscle tone and led to a spastic paralysis within 2 h. The pattern of response was similar at lower concentrations, although the initial stimulation was not always evident, but the onset of paralysis could be reached more quickly. Scanning electron microscopy revealed gross surface damage from 24 h onwards in vivo, in the form of erosion of the anterior and posterior extremities of the fluke and large-scale sloughing of the tegument on both dorsal and ventral surfaces. Tegumental changes prior to sloughing included some swelling of the basal infolds and an apical accumulation of T1 secretory bodies. In the underlying tegumental cells there was reduced secretory activity and the mitochondria were consistently swollen and deformed. Reduced secretory activity was a feature of the gastrodermal cells as well; these cells were characterized by swollen, electron-lucent mitochondria, vesiculated GER cisternae and apical blebbing of packets of cytoplasm. The vitelline follicles became severely disrupted as a result of the breakdown of the nurse cell cytoplasm. The stem and intermediate type 1 (It1) cells rounded up and showed nuclear abnormalities. There did not appear to be a severe disruption of shell protein production in the intermediate vitelline cells, but there was a noticeable absence of glycogen in the mature vitelline cells. The effects of closantel are discussed in relation to its proposed mode of action as an uncoupler of oxidative phosphorylation.

The problem of escalating resistance of Haemonchus contortus to the modern anthelmintics in South Africa

During the past decade in South Africa there has been a continual increase in sheep of strains of gastrointestinal helminths resistant to the modern anthelmintics. Five strains of Haemonchus contortus are described in this paper. Despite the fact that 2 of the 5 strains were tested for susceptibility only to ivermectin, a total of 10 instances of resistance were found. Four of the 5 strains were resistant to ivermectin, 2 to closantel, 2 to rafoxanide and 2 to the benzimidazoles. One of these strains was concurrently resistant to 3 different anthelmintic groups, namely, the ivermectins, the benzimidazoles and the salicylanilides. Resistance to ivermectin developed in 2 strains of H. contortus after a history of only 3 treatments with this compound in one instance and 11 treatments in the other. In the latter case drenching with ivermectin was well interspersed with that of other anthelmintics. This rapid development of resistance suggests that there may be cross-resistance between ivermectin and another anthelmintic group. Two of the ivermectin resistant strains were recovered from separate properties in the south-western Cape Province, where Ostertagia circumcincta, which is usually the dominant parasite in this region, was virtually eliminated by the anthelmintic treatment. On each of these properties it was apparently replaced by a resistant strain of H. contortus. A serious threat to control is the dissemination of worm strains with multiple resistance to anthelmintics. The strain of H. contortus resistant to 3 anthelmintic groups has already been widely dispersed, as the farmer concerned suddenly decided to give up farming with sheep and to sell his flock.

Field trials with closantel and Haemonchus contortus in sheep in Papua New Guinea

Sheep treated once with closantel at 7.5 or 15.0 mg/kg and grazing with untreated sheep remained free of Haemonchus contortus for at least 4 to 5 weeks and 6 to 7 weeks respectively after treatment. When the whole flock was treated with 15.0 mg/kg, H. contortus began to become re-established 7 to 8 weeks later. Maximum benefit of the residual anthelmintic effect of closantel against H.contortus was obtained only when all sheep in the flock were treated; it took 10 weeks longer for H.contortus to form 50% of larval cultures when the whole flock was treated than when only a part of the flock was treated.

Resistance of field strains of Haemonchus contortus to ivermectin, closantel, rafoxanide and the benzimidazoles in South Africa

After a first description in 1975 of a strain of Haemonchus contortus resistant to the benzimidazole anthelmintics in South Africa, further strains of the same species developed resistance to rafoxanide and closantel, and a strain of Ostertagia species became resistant to the benzimidazoles. Recently five further strains of H contortus have been found which show resistance to these anthelmintics. Of these, four showed varying degrees of resistance to ivermectin and one was resistant to three anthelmintic groups. One of the strains became resistant to ivermectin very rapidly despite effective rotation of this anthelmintic with chemically unrelated anthelmintic compounds.

Flukicidal action of closantel against immature and mature Fasciola hepatica in experimentally infected rats and sheep

The relative importance of peak level- and residual level-related flukicidal activity of closantel against immature and mature Fasciola hepatica was evaluated in a comparative efficacy trial using two animal species with a different plasma elimination pattern, that is, the rat and the sheep with an elimination half-life of less than one week and of two to three weeks, respectively. The rats were dosed orally with closantel at 20 mg kg-1 at two, four, six, eight and 10 weeks; the sheep at 10 mg kg-1 at eight, 10 and 12 weeks after artificial infection. Necropsy was performed either one week after treatment or 12 weeks after infection. Efficacy rates and the length of the recovered flukes were evaluated. It was demonstrated that the flukicidal effect of closantel is directly related to its peak plasma levels and less to its residual plasma concentrations. In the rat, a high efficacy (P less than 0.001) could be demonstrated against immature stages of four weeks or older. The two-week immature stages were less markedly affected. No significant differences in efficacy and size of the flukes were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection. In the sheep, the efficacy against six-week and eight-week-old immature stages varied between 70.3 and 76.8 per cent and between 92.8 and 96.5 per cent, respectively. As in the rats, no marked differences in efficacy were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemotherapy of paramphistomosis in cattle

Controlled tests were used to assess the efficacy of anthelmintics against immature paramphistomes, predominantly Calicophoron calicophorum, in 127 calves which were exposed to contaminated pasture for 7 weeks, treated and slaughtered. When a combination product of oxyclozanide and levamisole was used, oxyclozanide at 18.7 mg/kg reduced parasite numbers in the small intestine, abomasum and rumen-reticulum by 61 to 96.1%, 50.0 to 92.6% and 56.5 to 98.1%, respectively. When 2 doses were given 3 days apart, oxyclozanide was 99.9%, 100% and 100% effective, respectively, in the above organs, and produced improvement in clinically affected calves. This treatment elicited transient diarrhoea. Hexachlorophene at 20 mg/kg as a single dose was 99.5%, 100% and 100% effective against the fluke in the small intestine, abomasum and rumen respectively but severe neurological signs were seen in some calves. Niclosamide at 160 mg/kg given as single or 2 doses 3 days apart was 91.1% and 92.6% effective, respectively, against the parasites in the small intestine. No toxicity was noted. Closantel, at 7.5 mg/kg was not effective. Oxyclozanide and niclosamide when given as a single treatment had varying activity. Two doses of oxyclozanide and a single dose of hexachlorophene gave consistent results. Further tests based on reduction of faecal egg counts, 10 to 14 days after treatment were conducted with oxyclozanide and hexachlorophene against mature paramphistomes in 207 cattle. Oxyclozanide as a single dose or 2 doses 3 days apart at 12.8 to 18.7 mg/kg was 93.6 to 97.5% effective in reducing egg counts. Hexachlorophene at 20 mg/kg was 83.0% effective.(ABSTRACT TRUNCATED AT 250 WORDS)

Schistosoma mansoni: salicylanilides as topical prophylactic against cercarial penetration of mice

Salicylanilide and 37 of its analogs were applied topically to mice as candidate chemoprophylactic agents against Schistosoma mansoni cercarial penetration. The compounds were solubilized in absolute methanol, dimethyl sulfoxide, or isopropanol at concentrations not exceeding 1.25% W/V. The tails of the mice of each experimental group were treated by immersion for 5 min in the test compound solution or in the vehicle. The treated tails of 5 mice from each group were washed for 30 min in flowing tap water 3-4 hr after compound application. Tails of all mice were then exposed to approximately 100 cercariae by tail immersion for 1 hr, 24 hr after treatment. The portal veins were perfused 49 days after exposure and worm burdens were determined. The protective capacity of each compound was calculated by comparing the reduction of the mean worm burdens of the compound treated mice to the worm burdens of those treated with only the vehicle and expressing the resulting value as percentage protection. Of the 38 compounds tested, 20 provided 98% or better protection if the treated tails were not washed before exposure to cercariae. Of these 20 active compounds, 16 provided 98% or better protection from infection by S. mansoni cercariae even after the mouse tails were subjected to the 30 min wash.

Control of helminthosis in lambs by strategic treatment with closantel and broad-spectrum anthelmintics

Treatment of ewes with broad-spectrum anthelmintic in August (pre-lambing) and early November, and of lambs in early November and early February, was effective in controlling infections with Trichostrongylus spp in lambs reared on contaminated pastures under set-stocked conditions. It was ineffective in controlling infections with Haemonchus contortus; 82% of lambs had to be withdrawn from the experiment because of severe haemonchosis. Treatment with closantel (7.5 mg/kg) at the same times was very effective against H. contortus but ineffective against Trichostrongylus spp; 25% of lambs had to be withdrawn because of severe trichostrongylosis. The same schedule using broad spectrum anthelmintic and closantel administered concurrently was effective against both parasites; no lambs had to be withdrawn and the bodyweight gain of lambs was higher than in lambs treated with broad-spectrum anthelmintic or closantel alone. The results provide a basis on which to develop a preventive anthelmintic treatment program to control haemonchosis and trichostrongylosis in sheep which will allow the current high frequency of treatment with broad-spectrum anthelmintics to be reduced. Such a program may retard selection for anthelmintic resistance in Trichostrongylus spp.

5-(Alkylsulfonyl)salicylanilides as potential dental antiplaque agents

A series of 22 5-(alkylsulfonyl)salicylanilides was synthesized and evaluated for in vitro antibacterial and antiplaque activity against Actinomyces viscosus and Streptococcus mutans, adherent microorganisms implicated in periodontal disease and dental caries. The minimum inhibitory concentrations of 25 salicylanilides (including 5-acyl-, 5-alkyl-, and 5-(alkylsulfonyl)-4'-bromo- and -4'-(trifluoromethyl)salicylanilides) were found to correlate (r = 0.94) with estimated log D values. Several salicylanilides, such as 5-(decylsulfonyl)- and 5-(dodecylsulfonyl)-4'-(trifluoromethyl)salicylanilides (15 and 19) were found to exhibit high levels of in vitro antibacterial and antiplaque activity against A. viscosus and S. mutans.

Activity of closantel against experimentally induced Fascioloides magna infection in sheep

The efficacy of closantel against experimentally induced Fascioloides magna infection in sheep was studied. In each of 3 experiments, closantel was administered 8 weeks after the sheep were given (oral inoculation) 100 metacercariae of F magna. In the 1st experiment, closantel was given orally to 5 groups of 6 sheep each at dosages of 0 (nontreated control), 5, 7.5, 10, and 15 mg/kg of body weight. In the 2nd and 3rd experiments, groups of 10 or 12 sheep were treated to confirm the efficacy of the previously determined optimal dosage of 15 mg/kg. An additional group of sheep (n = 10) was used in the 3rd experiment to evaluate the efficacy of closantel given IM at a dosage of 7.5 mg/kg. Closantel given orally at a dosage level of 15 mg/kg was highly effective (94.6% to 97.7%) in reducing F magna burdens. Also, pathologic scores associated with the F magna infection were reduced by 81.3% to 92.6% in sheep given this dosage of closantel. Efficacy of the IM administered dosage of 7.5 mg of drug/kg was equivalent to that of the 15 mg/kg oral dosage. Other than mild, transient lameness of the limbs which were injected with the drug (group 10), side effects were not observed.

Potentiation of fasciolicidal agents by benzoyl side chains. Synthesis of benzoylsalicylanilides

The synthesis and potent fasciolicidal activity of novel salicylanilides, with benzoyl substituents in the salicyl ring, is described. Several compounds surpassed the activity of commercially used flukicides against Fasciola hepatica infections in rats. Compounds 10, 11, and 15 were poorly active against the parasite in sheep and inactive in infected calves. It is concluded that the benzoyl substituents potentiate antiparasitic action by virtue of their electron-withdrawing properties rather than by advantageous protein binding at parasite receptor sites. Poor activity in sheep is ascribed to in vivo reduction of the carbonyl in the benzoyl group of the anilides.

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.

Inhibition of tumor promotion by a lecanoric acid analogue

3',5'-Dichloro-2,4'-dihydroxybenzanilide, an inhibitor of histidine decarboxylase, inhibited skin tumor promotion induced by 12-O-tetradecanoylphorbol-13-acetate in mice.

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 in the gastrointestinal tracts and the cranial mesenteric arteries. The results indicate a high antiparasitic activity of closantel against larval stages of Gasterophilus intestinalis and S. vulgaris, as well as against adult S. vulgaris, S. edentatus, Anoplocephala perfoliata and Triodontophorus spp., when used at doses of 20 or 40 mg kg-1.

Slight resistance to the residual effect of closantel in a field strain of Haemonchus contortus which showed an increased resistance after one selection in the laboratory

On the strength of a complaint of suspected resistance to closantel, a field strain of Haemonchus contortus was isolated from sheep on a farm near Pretoria and tested for resistance to the remedy, both without exposure to closantel in the laboratory (designated the "unselected" substrain of the parasite) and after a single selection with closantel (called the "selected" substrain). For comparative purpose a few sheep were treated with rafoxanide to ascertain whether the efficacy of this drug was unchanged. While the unselected substrain appeared to show only slight increased resistance to the residual effect of closantel drenched at a dosage rate of 5 mg/kg, there was a dramatic increase in resistance after one selection. The residual efficacy (determined by the modified NPM test of Groeneveld & Reinecke, 1969, as outlined by Reinecke, 1973), 13-14 days after treatment with closantel was reduced from the registered claim of the remedy in South Africa of greater than 80% effective in greater than 80% of the treated flock to "ineffective", or less than 50% effective in less than 50% of the treated flock. Furthermore, there also appeared to be a slight increase in the resistance of this substrain to rafoxanide, as its efficacy was reduced from 99-100% to about 92%. This sharp reduction in efficacy after a single selection with closantel seemed to indicate that the slight increase in resistance of the unselected substrain was probably due not to possible variation in the repeatability of the trail method but to repeated treatment with closantel on the farm.

Comparison of the activity of some fasciolicides against immature liver fluke in calves

The anthelmintic activities of nitroxynil, closantel and rafoxanide were tested in cattle against six- and eight-week-old infections of Fasciola hepatica. Administered by subcutaneous injection, nitroxynil and rafoxanide at dose rates of 10 and 3 mg/kg bodyweight respectively were 88.5 and 36.1 per cent effective in eliminating a six-week-old infection of F hepatica and 85.8 and 60.4 per cent effective against an eight-week-old infection. Closantel administered by intramuscular injection at a dose rate of 2.5 mg/kg bodyweight was 60.0 per cent effective against an eight-week-old F hepatica infection.

Anthelmintic activity of closantel against Ancylostoma caninum in dogs

The efficacy and minimum therapeutic dose of closantel, an injectable salicylanilide anthelmintic, was evaluated on adult Ancylostoma caninum. Doses of 7.5 and 10 mg/kg had a marked anthelmintic effect on adult stages, removing 99 and 98%, respectively. A second experiment tested the efficacy of closantel against hypobiotic larval stages of A. caninum. A dose of 20 mg/kg did not affect the abundance of arrested hookworm larvae or prevent their subsequent development, but it may have inhibited their full maturation as adult worms so that patent, intestinal infections did not occur. Small numbers of adults were recovered from treated dogs at 29, 43, and 57 days post-treatment, but no eggs were passed in their feces. These studies bear on the practical problem of control of hookworms in dogs.

Experimental allergic encephalomyelitis: suppression with SD-170, a new synthetic drug

SD-170 is a new drug synthesized by Umezawa and associates. The clinical, pathological, and immunologic effects of this drug on acute EAE were investigated. In guinea pigs immunized with 5 micrograms MBP in CFA, SD-170 diminished the clinical severity as well as delaying the onset of death in acute EAE. All clinical observations were supported by histologic findings. On the contrary in animals immunized with spinal cord homogenate SD-170 did not suppress acute EAE. In SD-170 treated animals there seemed to be a lowered cellular response to MBP by the lymphocyte proliferative response test; there also seemed to be a lowered humoral antibody response to MBP. We conclude that SD-170 is an immunosuppressive of acute EAE.

Prolonged anthelmintic effect of closantel and disophenol against a thiabendazole selected resistant strain of Haemonchus contortus in sheep

Two long-acting anthelmintics, closantel and disophenol, were tested by treatment 90, 60 and 30 days before challenge with a thiabendazole selected laboratory strain of Haemonchus contortus. The sheep were slaughtered 28 days after infection for total worm counts. A significant reduction in the number of adults remaining at autopsy was recorded after treatment with both anthelmintics 30 and 60 days before challenge but there was zero efficacy when the animals were treated 90 days before challenge. No significant difference was exhibited between the two compounds. Variability in response was recorded between animals on the 60 day period of treatment, which for disophenol may be dose related because animals receiving the lower volumes showed higher worm counts. For both anthelmintics a variability in the rate of metabolism may be responsible. The possibility offered by both anthelmintics for treating benzimidazole resistant strains of H contortus is discussed.

Pilot trials on the treatment of Dermatobia hominis infections in cattle with closantel

The therapeutic and prophylactic activities of closantel given to calves inoculated with larvae of Dermatobia hominis were studied. Calves (n = 9 principals, plus 3 nontreated controls) were given closantel at different dosages (8 to 12.5 mg/kg) and schedules of treatment. The largest dosage of closantel (12.5 mg/kg) had the most efficacious therapeutic activity (97.3%). Prophylactic activity was also seen in calves given the drug before they were experimentally inoculated.

A potent new salicylanilide effective against Fasciola hepatica

In sheep, 3-tert butyl 4'5 dicyano 6 methyl 2' bromo salicylanilide was found to be active against mature Fasciola hepatica down to 0.2 mg/kg but was toxic at 1.5 mg/kg.

Synthesis of 5-chloro-3'-nitro-4'-substituted salicylanilides, a new series of anthelmintic and antimicrobial agents

A number of 5-chloro-3'-nitro-4'-substituted salicylanilides (6--23) have been synthesized by treating 4',5-dichloro-3'-nitrosalicylanilide (5) with various sodium aryl oxides, alkoxides, or amines. These compounds have been tested against Hymenolepis nana infection in rats and have also been evaluated for their in vitro antimicrobial activity against various strains of bacteria and fungi. In the former test 17 was the most active cestodicidal agent showing activity at 30 mg/kg. In the antimicrobial screening, 22 inhibited the growth of all the bacteria and fungi used while 6 was active against the penicillin resistant Staphylococcus aureus at a minimum inhibitory concentration of 0.00609 microgram/mL.

In vitro antiplaque effects of antiseptic phenols

Several phenols known to be antiseptics were tested in vitro for their ability to adsorb to saliva-coated enamel and subsequently inhibit plaque formation. 3,5,4'-tribromosalicylanilide was found to be effective against growth and plaque formation of A viscosus, A naeslundii, S mutans and S sanguis. Dibromsalicil was effective against A viscosus. The other phenols (hexylresorcinol, thymol, phenylphenol and zinc phenolsulfonate) did not inhibit in vitro growth or plaque formation.

Enhancement of the antiplaque value of antibacterial agents by enamel conditioning methods: III. Animal results

A 1:1 water-paste slurry of a placebo and several experimental dentifrices was swabbed daily for six weeks on the teeth of albino rats, and the plaque collected on the teeth was measured in vivo first before the treatments began and one, two, three, and six weeks after. The results indicate that adding a suitable antimicrobial agent to a placebo dentifrice markedly reduced plaque accumulations on the teeth brushed with that product. When an enamel-conditioning vehicle was used instead of the placebo, the antiplaque effectiveness increased severalfold. It was concluded from the two first articles of this series 1,2 that adding antibacterial agents to enamel-conditioning systems resulted in the incorporation of the antimicrobial compound into enamel treated with these systems, and that enamel treated in such a fashion acquired marked antibacterial properties of its own. The data reported in this article support a third conclusion, namely, that the enamel-conditioning-antibacterial systems have a considerable antiplaque effect in laboratory rats.

Enhancement of the antiplaque value of antibacterial agents through enamel-conditioning methods: II. Acquisition of antiplaque properties by treated enamel

Enamel specimens treated with systems containing enamel conditioners and antibacterial agents have previously been shown to incorporate the latter into the enamel. It has now been demonstrated that enamel blocks treated with these systems become highly resistant to bacterial colonization, that this effect is rather long lasting, and that the treated specimens prevent acid formation when incubated with Streptococcus mutans in a sugar-containing medium.