Anthelmintic resistance of nematode parasites of small ruminants in eastern Ethiopia: Exploitation of refugia to restore anthelmintic efficacy

Faecal egg count reduction tests (FECRT) were conducted in May 2003 to determine the efficacy of anthelmintics used for treatment against nematode parasites in separately managed sheep and goat flocks at Alemaya University in eastern Ethiopia. These tests revealed high levels of anthelmintic resistance to albendazole, tetramisole, the combination of these two drugs, and to ivermectin in the goat flock (predominantly infected by Haemonchus contortus and Trichostrongylus spp.), whereas all drugs were highly efficacious in the sheep flock. A second FECRT confirmed these observations. Following this, a new management system was implemented on the goat flock for a period of 9 months (January-September 2004) in an attempt to restore the anthelmintic efficacy. This involved a combination of measures: eliminating the existing parasite infections in the goats, exclusion from the traditional goat pastures, and introducing communal grazing of the goats with the university sheep flock and livestock owned by neighbouring small-holder farmers. A second series of FECRTs (Tests 3 and 4) conducted 7 months after this change in management, showed high levels of efficacy to all three drugs (albendazole, tetramisole and ivermectin) in the goat flock. This is the first field study to demonstrate that anthelmintic efficacy in the control of nematode parasites of small ruminants can be restored by exploiting refugia.

Anthelmintic resistance on an organized sheep farm in India

Monitoring anthelmintic resistance in strongyle nematodes by the faecal egg count reduction test and a commercial larval development assay on an organized sheep farm in the semi-arid area of Rajasthan revealed the emergence of resistance to benzimidazoles and rafoxanide and a potential risk of the development of levamisole/tetramisole resistance. A benzimidazole/levamisole combination, avermectins and closantel were each found to be efficacious.

Comparative anthelmintic activity of strategic sustained low-level administration of albendazole in feed pellets compared to single doses of closantel and tetramisole against natural ovine parasitic gastroenteritis

The strategic use of single therapeutic doses of closantel, tetramisole or sustained low-level administration of albendazole in feed pellets in controlling naturally acquired parasitic gastroenteritis in sheep was investigated on a farm in semi-arid Rajasthan, India. A total of 303 5- to 6-month-old sheep were divided into three groups. Two groups were dosed with single therapeutic doses of closantel and tetramisole and the third group was given a low-level medication with albendazole through feed pellets for 30 days. Faecal egg counts revealed significantly lower counts (p<0.001) in the group treated with closantel compared to the other two groups. The faecal egg counts in the group receiving sustained low-level albendazole rose after withdrawal of the medication but remained significantly lower than those in the group treated with tetramisole up to 7 weeks after treatment (p<0.05). On the other hand, in the group treated with tetramisole, the mean faecal egg count rose from 3 weeks after treatment and remained continuously higher than those in any other group up to 12 weeks after treatment. The closantel-treated group gained more body weight but the first six-monthly greasy fleece yield was greater in the group treated with medicated pellets. During the first 3 months of the experiment, three animals in the group treated with tetramisole died of parasitic gastroenteritis. Following sustained low-level administration of albendazole in feed pellets, the plasma disposition curve of both the sulphoxide and sulphone metabolites reached its plateau level by day 5 and remained almost constant thereafter. The comparative cost-effectiveness of the three treatment regimes during the first 3 months of treatment was best for the group treated with closantel followed by the group treated with medicated feed pellets.

[Levamisole- and tetramisole-resistant gastrointestinal nematodes in sheep]

Two experiments were carried out with sheep naturally infected with gastrointestinal nematodes to evaluate efficacy of anthelmintics using in vivo faecal egg count reduction (FECR) test. In experiment 1 with 28 ewes, the following efficacy of anthelmintics given at recommended dose rates was observed: albendazole 99.4%, ivermectin 99.3% and levamisole 81.8%. In experiment 2 with 18 ewes, tetramisole exhibited 71.3% efficacy. Suspected resistance to imidothiazole anthelmintics was confirmed by in vitro larval development test (LDT)--minimal inhibition concentration (MIC) values were estimated at 2.0 micrograms/ml. Infective larvae L3 cultivated from eggs produced by the population of resistant helminths were identified as Ostertagia and Trichostrongylus spp.

[Udder compatibility of tetramisole and levamisole hydrochloride and suggestion for the prescription of their intramammary use in cattle against Prototheca zopfii]

Preparations with 4 percent Tetramisole or Levamisole hydrochloride were compatible in the mammary gland after application up to 40 ml/quarter (4 mg/kg body mass) for up to 6 milking times. 100 ml of the preparations were also clinically compatible in a single quarter (10 mg/kg body mass) on several days. After intramammary application of 30 ml/quarter (3 mg/kg body mass) Prototheca suppressing values in milk serum were evident for at least 6 hours. One application of 200 ml in one quarter has caused Prototheca suppressing values for 36 hours in milk serum up to dilution 1:4. Nilverm given to cattle in high dosage orally did not lead to Prototheca suppressing values in milk sera.

[Experimental Prototheca mastitis in cattle and therapy with tetramisole hydrochloride]

In one cow all 4 quarters were infected with 2 x 10(8) germs of Prototheca zopfii each. 2 quarters of it were treated over 6 subsequent milking times with 20 ml Tetramisole hydrochloride (4 mg/kg body mass) in each case. Clinical symptoms diminished within 3-24 hours after the first application in comparison with the control quarters distinctly. Macroscopic alterations in the treated quarters could be found for a short time only, whereas they were evident in the control quarters for up to 2 days. The milk cell counts were raised til the 5. day p.i. The number of Prototheca excreted by treated quarters in each ml initial milk was reduced to 38% and in each ml end milk to 67% in comparison with the 2 control quarters. A more potent reduction of Prototheca can be expected after the application of Levamisole hydrochloride. At the future therapy applications after every milking time for at least 3 days with 25-40 ml of the preparations in each quarter are recommended. A total dose per animal and application time of 150 ml preparations (6 g Levamisole hydrochloride = 15 mg/kg body mass) must not be exceeded. Before Levamisole hydrochloride may be used for patients, susceptibility tests are necessary of the strains of Prototheca zopfii present and additional investigations for the reliability of the results hitherto obtained in one experimental Prototheca mastitis only.

Controlled tests of activity of several antiparasitic compounds against natural infections of Haemonchus contortus and other helminths in lambs from a flock established in 1962

Antiparasitic activity of several compounds was evaluated over a long period (about 25 years) in the same flock of sheep. Haemonchus contortus was of special interest, including its relation to drug resistance, especially to thiabendazole and other benzimidazoles, in addition to phenothiazine. Eleven compounds were evaluated in 15 controlled tests, done between 1966 and 1989 in naturally infected lambs (n = 145) born and raised on the same pasture. Sheep were first placed on the pasture in 1962, and a few more were added thereafter. Internal parasites in these sheep were classified in 3 general categories: indeterminate exposure to parasiticides; H contortus, resistant to thiabendazole; and H contortus, resistant to phenothiazine. The parasitic infections probably became more homogeneous after several years because of few introductions of outside sheep after initial establishment of the flock. Activity against naturally acquired internal helminths was evaluated for cambendazole (CBZ: dosage, 20 mg/kg of body weight), fenbendazole (FBZ: 5 or 7.5 mg/kg), mebendazole (MBZ: 10 mg/kg); oxfendazole (OFZ: 3.5 or 10 mg/kg), oxibendazole (OBZ: 10 mg/kg); parbendazole (PBZ: 15 mg/kg), phenothiazine (PTZ: 550 mg/kg); pyrantel pamoate (PRT: 25 mg base/kg), tetramizole (TET: 15 mg/kg); thiabendazole (TBZ: 30 or 44 mg/kg), and trichlorfon (TCF: 100 mg/kg). Thiabendazole was used more often (9 tests) than the other compounds. Thiabendazole was more active against mature H contortus in later years than when first used in 1966, although it was never 100% effective. Efficacy against immature H contortus for TBZ did not exceed 86%. Activity against immature and mature stages of this parasite was good overall for the other benzimidazoles.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of Nippostrongylus brasiliensis in normal and SPF rats using tetramisole loaded into zeolite

Administration to rats of tetramisole loaded into zeolite was more successful in killing adults of Nippostrongylus brasiliensis than the administration of tetramisole alone. The most successful treatment occurred in SPF (Specific Pathogen Free) rats dosed with tetramisole loaded into zeolite and no worms were present in this group at autopsy eight days post-infection. It is concluded that the slow release of drug from the zeolite matrix improved its efficacy, especially in removing worms from low-grade infections.

Isothiourea derivatives of 6-phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole with broad-spectrum anthelmintic activity

A series of isothiourea derivatives of 6-phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (tetramisole) is described. The compounds are prepared by the S-alkylation of the thioureas that were obtained either by the reaction of an amine with 6-(3-isothiocyanatophenyl)-2,3,5,6-tetrahydroimidazo[2,1-b] thiazole or by the reaction of an isothiocyanate with 6-(3-aminophenyl)-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole. These derivatives have an improved spectrum of activity over tetramisole and are active against nematodes, cestodes, and trematodes. The structure-activity relationships are discussed.

Response of preadult Necator americanus to some known anthelmintics in hamsters

Hamsters infected with laboratory-adapted preadult Necator americanus were dosed with 6 reference anthelmintics. Their efficacy was measured in terms of percentage cure of infected animals as well as percentage worm reduction following treatment. Mebendazole and pyrantel were equally effective in this system. Other anthelmintics, including anti-hookworm compound, bephenium hydroxynaphthoate, were less effective. The comparative results revealed that the N. americanus model is sensitive and reliable for identifying and characterizing new anti-parasite preparations.

[Helminths in an Askaniia-Nova herd of eland and experiences in eradicating Strongylata infestation]

Parasitological complex studies of the available eland stock (60 individuals) were first carried out. As a result 100 % infection rate of the herd and the age dynamics of strongylatoses were revealed. The autopsy of animals have shown that five species of six species of nematodes and one species of cestodes are common parasites of ruminants of the Ukraine steppe zone and two species are specific parasites of eland. For sanitation of the herd an anthelminthic preparation produced in Hungary was used. The preparation decreased the initial infection rate to 7.3%.

Effect of anthelmintic treatment on the development of resistance in sheep vaccinated or experimentally infected with Dictyocaulus filaria

This investigation was undertaken to study the immune response of Iraqi sheep vaccinated with Dictyocaulus filaria larvae (Filiraq) and to determine the effect of tetramisole on the development of resistance to reinfection. The findings confirm the effectiveness of Filiraq in conferring protection against experimental infection with D filaria. However, the administration of anthelmintic four weeks after each vaccination interfered with the development of immunity. Termination of D filaria infection at 28 days by tetramisole treatment also prevented the immune response.

Clinical laboratory evaluations of seven heartworm infected beagles: during disease development and following treatment

Clinical laboratory evaluations were performed in 7 beagles for 12 months following experimental infection with Dirofilaria immitis and for 14 months following adulticide and microfilaricide treatment. Few abnormalities were detected. A mild basophilia and thrombocytopenia developed late during the year of infection and after arsenical treatment there were transient increases in eosinophils, SGPT, and SAP. Coagulation and blood gas studies were normal. The minimal changes were attributed to either: (1) the one year infection with 50 infective larvae was an insufficient insult or (2) an idiosyncrasy in the host-parasite relationship is required in order to produce marked alterations in clinical laboratory evaluations.

Studies on the effect of treatment with anthelmintics on weight gain in calves, naturally infected with gastrointestinal nematodes

To avoid disease outbreaks caused by gastro-intestinal nematodes different prophylactic measures are recommended. In this connection pasture hygienic achievements and anthelmintics are used. In practice it is often difficult to realize pasture hygienic steps as move the animals to parasite free areas and to avoid that they come back to the infected. In many cases the parasite control is limited to routine deworming. Our intention was to study if anthelmintic treatment without other measures had any effect on weight gain and number of eggs in faeces in calves naturally infected with Ostertagia ostertagi. The studies were done during two stable seasons 1975/76 and 1976/77 when the calves were treated two weeks after stabling, and during two grazing seasons 1976 and 1977 when the calves were treated 20 days or 15 and 20 days after turning out. In none of the trials any obvious influence on the weight gain and number of eggs was observed. The failing effect during the stable season might depend on the fact that the parasites to more than 90% were in inhibited L4-stage, and the failing effect during grazing, is surely an effect of reinfection when the calves remain on the infected pastures. As prophylactic measure anthelmintic treatment is of very little value if not the calves at the same time are protected against reinfection by moving to clean pastures.

[Evaluation of the long term effect of antirheumatic drugs with the survey rate method]

In the long term study of antirheumatic drugs, drop out of patients (for failure of effect or side effects) can analysed with "survey rate" methods. Survey rates become in drug tests "treatment continuation rates". With this method D-penicillamine and levamisole have been compared. Penicillamine has better "continuation rate" not because of better tolerance, but because of better long term effectiveness compared with levamisole.

Effect of anthelmintic treatment on the performance of Awassi sheep in Iraq

Studies are reported on the effect of anthelmintic treatment on the body weight gain and wool growth of ewes with subclinical helminth infections. The parasites involved were Fasciola gigantica and Ostertagia spp., together with some Haemonchus contortus, Trichostrongylus spp., and Dictyocaulus filaria. In 1 group, 5 sheep, which were treated twice with tetramisole at an interval of 4 weeks to remove gastro-intestinal nematodes and lungworms, showed an increase of 41% in weight gain and 3.2% in wool growth compared with an untreated group. Another group, which was treated with both tetramisole and rafoxanide to remove nematode and fluke infections, had a 143% increase in weight gain and 81% in wool growth compared with the control.

Effect of periodic deworming on nutritional status of ascaris-infested preschool children receiving supplementary food

The weight for age of 154 undernourished preschool children in an ascaris-infested community receiving supplementary food was monitored for a year. 74 children were given tetramisole every 4 months, while 80 controls were given placebo. The prevalence of ascaris (roundworm) infection and the severity of protein-energy malnutrition were the same in the two groups at the onset of the study. Stool-positive rates for ascariasis came down significantly in the experimental group during the year, but eradication of the worm was not possible owing to constant re-exposure. Nutritional status remained unaltered in the controls but improved strikingly in the treated children 8 and 12 months after the start of the study. Periodic deworming should form a part of the supplementary feeding programme if malnutrition is associated with ascariasis in the community.

Efficacy of tetramisole and dichloroxylenol against Syngamus trachea in pheasants and turkeys

Two water soluble products currently recommended for the treatment of syngamiasis were tested in pheasants and turkeys. Dichloroxylenol (Rotgape; Adams & Moulson), was found to have no efficacy. Although tetramisole (Game Bird Wormer; ICI) administered in drinking water had a moderate efficacy against three- and four-day-old larvae (47 to 71 per cent), its level of efficacy against infections associated with disease, those of seven days and older, was poor (5 to 29 per cent). It is concluded that neither product is likely to be of value in field outbreaks of syngamiasis.

On the possible anti-rheumatic effects (immuno-effector?)of imidazole derivatives (levamisole, clotrimazole, niridazole)

Some imidazole derivatives (levamisole, clotrimazole) have no significant effect on the rat adjuvant arthritis at dosages used in human therapy. If the effectiveness of these drugs in rheumatoid arthritis is confirmed by double blind studies, it would be necessary to find an explanation other than an immuno-effective action does not occur in some patients.

Partial inhibition of primary lung tumourigenesis by tetramisole

Continuous treatment of mice with tetramisole (TMS, approximately 8 mg/kg/day) resulted in a highly significant (p < 0.002) reduction in numbers of primary lung tumours forming in response to neonatal urethane injection. Kinetic study indicated the slopes of the oncogenesis response curves differed, but not significantly. Therefore inhibition of primary lung tumourigenesis was only partial, even though TMS was given during the early stages of tumour development, continuously, and at near maximum tolerable dosage.

[Effectiveness of Nilzan and Dovenix in the treatment of fascioliasis in cattle and sheep]

The authors tested the effectivity of the foreign preparations Nilzan (tetramisole ++ oxyclozanide) and Dovenix (nitroxynil) in the treatment of cattle and sheep naturally invaded by Fasciola hepatica. The effectiveness of the two preparations was evaluated on the basis of the results of coprological examination in the test and control animals prior to treatment and in two intervals after treatment. In slightly invaded cattle (the average egg number in 3 g of faeces in 28 test cows was 1.46 per animal) the last examination (4 weeks after treatment) showed 100-per-cent extenseffectiveness and intenseffectiveness of both preparations. When the test was finished in sheep (average number of eggs in 3 g of faeces in 45 test ewes--5.40 per animal) six weeks after treatment, the EE of Nilzan was 86.7% and IE 97.4%; in Dovenix EE was 93.4% and IE 99.0%. Both preparations were accepted well, without any side-effects or unfavourable phenomena related to their application.

Studies on the development and chemotherapy of larvae of Parascaris equorum (Nematoda: Ascaridoidea) in experimentally and naturally infected foals

Experimentally induced infections of Parascaris equorum in worm-free pony foals required 14 to 17 days for migration of the larvae through the liver and lungs, and 79 to 110 days to become gametogenically functional. Treatment of experimentally infected or naturally exposed foals during the parenteral phase of development, using levamisole at 8 mg/kg, a mixture of levamisole at 8 mg/kg plus piperazine at 88 mg base equivalent/kg, or dl-tetramisole at 10 mg/kg, was quite efficacious in (1) reducing the number of P. equorum larvae recovered from the small intestines of the foals at necropsy, or (2)delaying the appearance of ascarid eggs in the feces of treated foals beyond the time period observed for the untreated foals. Three formulations of dichlorvos at doses of 10, 20, 30, or 40 mg/kg, and 2 formulations of trichlorfon at 20 or 40 mg/kg, were not effective when treatment was given on or before the 14th day after infective eggs were administered. Treatment with a gel formulation of dichlorvos at 20 mg/kg 17 to 28 days after experimental infection was 100% effective in removing ascarid larvae from the small intestines of poly foals.

[The average degree of parasitosis, a criterion for evaluation of the geohelminthic contamination of a population, and for application of santiary measures]

The severity of ascaridiasis in a region depends first of all on the degree of pollution by ascaris ova of the environemtn and consquently on the per diem output of ascaris ova in the stools. Therefore, the importance of ascaridiasis as an endemic disease, depends of course upon the number of positive cases, their prevalence, but still more, it depends upon the intensity of the infection of the diseased population (global parasitic discharge). Practically, this concept of global parasitic discharge is expressed by the number of ascaris ova expelled per gram and per day by a sample of the considered population. The mean parasitic discharge is the quotient of the global parasitic discharge through the number of positive cases of the sample. An epidemiological survey and a mass chemotherapy test at La Réunion has showed us that the conept of global parasitic discharge is a more representative reliable and sensitive measuring method than prevalence, to evaluate the gravity of endemic ascaridiasis and its variations.

Effects of levamisole (NSC-177023) and tetramisole (NSC-102063) in experimental tumor systems

Levamisole and tetramisole had no antitumor effect against the following transplantable syngeneic murine tumors: L1210 leukemia, P388 leukemia, B16 melanoma, Madison 109 lung tumor, and Lewis lung carcinoma. In the Lewis lung carcinoma system there was no effect on primary tumor growth, metastasis, or survival. Tetramisole had a variable effect on the growth of rhabdomyosarcomas and the survival of BALB/c mice following intramuscular inoculation of Moloney sarcoma virus. In two experiments treatment with tetramisole either prior to or following inoculation of Moloney sarcoma virus increased the number of mice with tumor regression as opposed to progressive tumor growth, incrneased the number of long-term survivors, and prolonged the lifespan of mice that died of tumor. In two further tests neither levamisole nor tetramisole had an effect in this system. In mice immunosuppressed with cyclophosphamide prior to virus inoculation, there was not effect of treatment with levamisole or tetramisole.

An epizootic of cerebral nematodiasis in rabbits due to Ascaris columnarus

An epizootic of cerebral nematodiasis due to ascaris columnaris occurred in a commercial rabbitry, and 80 diseased rabbits died or were killed. The morbidity was high in groups of recently purchased rabbits and in the offspring of 12 breeder rabbits. The breeder rabbits which had been on the farm for more than a yr survived the outbreaks. Wild animals and birds had access to the facilities, but raccoons and skunks were never observed. A columnaris larvae were found on histopathologic examination. and live larvae were recovered from brains of 2 diseased rabbits.

Influence of anthelmintic treatment on the liveweight of outwintered ewe hoggs

Three systems of outwintering ewe hoggs are normally practised on Scottish hill farms. A series of field trials involving some 2000 different animals was conducted to determine the response in liveweight from anthelmintic treatment for roundworms. The results suggest that, under field conditions, a strategic dosing programme using a modern anthelmintic can prevent liveweight loss in ewe hoggs wintered either on the hill or "inbye". The best response may be expected from a two dose regime--one in early winter (mid October to mid November) and the other in winter (mid January to mid February). In away-wintered hoggs, the kinder climate, better pssture, and, in the vast majority of cases, less contaminated ground, appear to outweigh the advantages of dosing after the late autumn.