Morantel resistance in Trichostrongylus colubriformis

The occurrence of anthelmintic resistance in Trochostrongylus colubriformis and resistance to morantel are reported for the first time in New Zealand. In two controlled anthelmintic trials with experimentally infected sheep, morantel citrate at either 8.8 mg/kg or 10 mg/kg had no effect on worm burden. An efficacy of >99% was demonstrated for mebendazole at 12.5 mg/kg against this strain.     

Resistance to ivermectin in a field strain of Ostertagia spp. in goats

The occurrence of a field strain of Ostertagia spp. showing a resistance to ivermectin in Angora goats is reported. In a controlled anthelmintic trial using naturally-infected goats, ivermectin at a dose rate of 0.2 mg/kg demonstrated an efficacy of 87% against this strain.     

Resistance to ivermectin in a field strain of Ostertugia spp. in goats

The occurrence of a field strain of Ostertugia spp. showing a resistance to ivermectin in Angora goats is reported. In a controlled anthelmintic trial using naturallv-infected goats. ivermectin at a dose rate of 0.2 mg/ kg demonstrated an efficacy of 87% against this strain. (New Zealand Veterinary Journal 38,72–74, 1990)     

Selection for resistance to macrocyclic lactones by Haemonchus contortus in sheep.

An anthelmintic-sensitive Haemonchus contortus strain was selected for moxidectin and ivermectin resistance concurrently for 22 generations. Treatment with 0.002 mg moxidectin/kg BW or 0.02 mg ivermectin/kg BW produced >99% efficacy against the susceptible parent strain passaged for 22 generations without any anthelmintic exposure. However, to obtain similar efficacy the moxidectin-selected and the ivermectin-selected strains of H. contortus required 0.05 mg moxidectin/kg BW or 0.4 mg ivermectin/kg BW. These results indicate that development of resistance to one macrocyclic lactone, simultaneously results in resistance to another macrocyclic lactone. However, rates of resistance development differ between compounds and occurs more slowly with moxidectin than with ivermectin.     

Efficacy of oxfendazole against naturally acquired gastro-intestinal nematode infestations in buffaloes in Egypt

The benzimidazole anthelmintic, oxfendazole, was used as an oral suspension at 4.5 and 2.8 mg/kg to treat naturally infested indigenous buffaloes in Egypt. Worms of the genera Haemonchus, Cooperia, Trichostrongylus, Ostertagia, Chabertia and Oesophagostomum were identified in the animals prior to treatment. A 100% reduction in faecal egg counts was obtained at the 4.5 mg/kg level when compared to untreated control animals. Reductions in faecal egg counts greater than 90% were recorded at 2.8 mg/kg and these exceeded reductions obtained by drenching with the older benzimidazole anthelmintic, thiabendazole, at 67 and 111 mg/kg.     

Evaluation of Cymbopogon schoenanthus essential oil in lambs experimentally infected with Haemonchus contortus

Hematophagous gastrointestinal parasites cause significant economic losses in small ruminant grazing systems. The growing reports of multi-drug resistant parasites call for intensive research on alternative treatments for anthelmintics to help small ruminants cope with these parasites. Two-month-old lambs with mean body weight (BW) of 22.5 kg were experimentally infected with a multidrug-resistant Haemonchus contortus strain. Infected animals were dosed orally with Cymbopogon schoenanthus essential oil to evaluate its anthelmintic potential. Eighteen animals were allocated into three groups of six animals, and each received one of the following treatments: Group 1 - control (10 mL of water), Group 2 - C. schoenanthus essential oil (180 mg/kg BW); and Group 3 - C. schoenanthus essential oil (360 mg/kg BW). Animals received the oil once a day for 3 consecutive days. Lambs were evaluated clinically for blood biochemistry before, at 1, 5, 10, 15 and 20 days after treatment, and then were euthanized to assess the total worm burden. No statistically significant reduction in fecal egg count, packed cell volume or total worm count was observed after treatments. Also, no statistical difference among group means for blood levels of urea, creatinine, albumin, alkaline phosphatase, aspartate aminotransferase and gamma glutamyl transferase was found. Larval development assay (LDA) and egg hatch assay (EHA) were performed from feces of treated animals at 1, 5, 10 and 15 days after essential oil administration. An inhibition in LDA was observed 1 day after the 3-day treatment in larvae from feces of animals treated with 360 mg/kg essential oil. In conclusion, the essential oil at the doses of 180 mg/kg and 360 mg/kg was safe to sheep, but failed as an anthelmintic treatment when applied to young sheep artificially infected with a multidrug-resistant H. contortus strain.     

A strain of Haemonchus contortus resistant to thiophanate

The occurrence of a field strain of Haemonchus contortus resistant to thiophanate is reported for the first time in New Zealand. In a controlled anthelmintic trial with experimentally infected animals, thiophanate at 50-100 mg/kg had no appreciable effect on the Haemonchus burden. Albendazole reduced faecal strongylate egg counts by 95% in animals with naturally acquired 59 infections.     

EFFECTIVENESS OF BROAD SPECTRUM ANTHELMINTICS AGAINST SELECTED STRAINS OF TRICHOSTRONGYLUS COLUBRIFORMIS

SUMMARY A field population of Trichostrongylus colubriformis was divided into 4 lines for exposure to selection in the laboratory. The first line was selected with 50 mg/kg thiabendazole, the second with 4 mg/kg morantel tartrate, the third with 50 mg/kg thiabendazole followed by 4 mg/kg morantel tartrate and the fourth line was not selected for drug resistance. Following at least 9 generations of selection there was no difference in LD₅₀ or LD₉₅ between the unselected and single selected strains of worms. The strain selected by⁵⁰both thiabendazole and morantel tartrate had a significantly higher LD₅₀ against thiabendazole, morantel tartrate and levamisole than did the other three strains. The single selected strains had LD₉₅'s of 172, 21.5 and 2.3 mg/kg for thiabendazole, morantel tartrate and levamisole respectively, compared with corresponding values of 111, 17.3 and 2.4 in the unselected strain and 124, 15.5 and 3.0 in the double selected strain. The estimated efficiency of the recommended dose of each anthelmintic against the unselected field strain was:—thiabendazole (44 mg/kg) 50% efficient, morantel tartrate (8.8 mg/kg) 76% efficient and levamisole (7.0 mg/kg) 99.9% efficient.     

Multiple anthelmintic resistance in Trichostrongylus colubriformis

Following the failure of anthelmintic treatment to control an outbreak of trichostrongylosis in sheep, multiple resistance to levamisole and oxfendazole was confirmed in field strains of Trichostrongylus colubriformis at the CSIRO Pastoral Research Laboratory, Armidale. Resistance in Trichostrongylus spp to levamisole was also confirmed on an adjoining farm. From the results of an experiment where lambs were treated at the recommended dose rate with one or both anthelmintics, it was estimated that 32% of T. colubriformis were resistant to levamisole, 19% to oxfendazole, and 12% to both drugs. Simultaneous administration of levamisole and oxfendazole resulted in an additive anthelmintic effect. Naphthalophos (36.6 to 51.2 mg/kg) was 93% efficient against the multiple resistant strain. The similar histories of anthelmintic usage at the CSIRO Pastoral Research Laboratory and on the northern tablelands of New South Wales generally, suggest that multiple anthelmintic resistance in T. colubriformis may soon emerge as a problem on the northern tablelands.     

Results of diagnostic milk samples sent to the wallaceville animal health laboratory

The occurrence of a field strain of Haemonchus contortus resistant to thiophanate is reported for the first time in New Zealand. In a controlled anthelmintic trial with experimentally infected animals, thiophanate at 50–100 mg/kg had no appreciable effect on the Haemonchus burden. Albendazole reduced faecal strongylate egg counts by 95% in animals with naturally acquired infections.     

Ivermectin as a bird anthelmintic--trials with naturally infected domestic fowl

To evaluate the use of ivermectin as a bird anthelmintic, 29 White Leghorn hens naturally infected with Ascaridia spp., Heterakis spp. and Capillaria spp. were treated with 0.2, 2 or 6 mg/kg intramuscularly or 0.2 or 0.8 mg/kg orally. Faecal samples were collected before treatment and at autopsy, 2, 6, or 16 days after treatment, when the intestines were also examined for helminths. None of the treatments gave satisfactory anthelmintic results.     

Seasonal variation in anthelmintic response by cattle to dermally applied levamisole

Four experiments in 1978-79, and 2 in 1982 designed to define the optimum dose rate of dermally applied formulations of levamisole are described. These experiments showed that the absorption of levamisole with resultant blood levels and anthelmintic activity is strongly influenced by temperature. In warm to hot conditions percutaneous absorption is rapid and high blood levels with high anthelmintic activity against Haemonchus placei, Ostertagi sp, Trichostrongylus sp, Cooperia sp, Oesophagostomum radiatum, O. venulosum and Dictyocaulus viviparus result from dose rates of 10 mg/kg or more. In cold weather the high efficacy against H. placei, Cooperia sp, and Oesophagostomum sp is unchanged, but efficacy against Ostertagia sp, T. axei and D. viviparus decreases to the extent that a mean dose rate of 20 mg/kg (range 15 to 25 mg/kg) is necessary if the anthelmintic activity of dermally applied levamisole is to match that of either parenterally or orally administered material. These anthelmintic data are supported by the levamisole blood profile which in winter months, peaks at a figure of one quarter or less of that obtained from a similar dose rate in warm conditions. The implications of this variability in action are discussed.     

ANTHELMINTIC RESISTANCE IN TRICHOSTRONGYLUS COLUBRIFORMIS

Resistance to thiabendazole has been found in two strains of Trichostrongylus colubriformis from sheep. These strains occurred in flocks on research properties where the anthelmintic had been used at frequent intervals for experimental purposes for several years. The LD₅₀ values for the resistant strains were approximately 70 mg/kg and 125 mg/kg respectively, compared with an expected value from published reports of less than 10 mg/kg for susceptible strains. Apparent cross-resistance to the related benzimidazole compound parbendazole was observed at the normal therapeutic dose rate of 20 mg/kg in sheep. Both anthelmintics depressed egg-production in resistant female worms at normal therapeutic dose-rates. Both dl-tetramisole and pyrantel tartrate were effective against one of the benzimidazole-resistant strains of T. colubriformis, but the efficiency of the latter anthelmintic was less than that normally expected against benzimidazole-susceptible strains.     

Critical test evaluation of butamisole against gastrointestinal parasites of horses and ponies.

A critical test was performed to evaluate the anthelmintic properties of an injectable butamisole formulation and to compare the efficiency with that of a commercially available piperazine-thiabendazole anthelmintic. The test was done in 10 horses and 15 ponies with naturally acquired parasitic infections. Butamisole was administered at the dose level of 2.5 or 3.75 mg/kg of body weight by either subcutaneous or deep intramuscular injection. Given at the dose level of 2.5 mg/kg, butamisole was highly effective (99%) against Strongylus vulgaris and moderately effective (49%) against Parascaris equorum. At the 3.75 mg/kg dose rate, butamisole was highly effective against both S vulgaris (97%) and P equorum (94%). Butamisole had limited efficacy against other parasite species. Signs of toxicosis, long-term swelling of the injection sites, or tissue damage were not seen after injection.     

米尔贝肟片治疗犬弓蛔虫病与钩虫病的疗效观察

为了观察米尔贝肟片对犬弓蛔虫和钩虫驱虫效果,采用人工感染方式,对犬弓蛔虫和钩虫的动物模型进行疗效研究。结果表明,单次口服0.5 mg/kg米尔贝肟片对犬弓蛔虫和犬钩虫的虫卵减少率、驱虫有效率和治愈率均可达到100%。说明米尔贝肟片在治疗犬弓蛔虫和钩虫时具有剂量小、疗效高、作用快、副反应轻等特点,在临床治疗方面有十分广阔的应用前景。     

Anthelmintic efficacy of febantel combined with praziquantel against Ancylostoma tubaeforme, Toxocara cati, and Taenia taeniaeformis in cats

Forty cats, each harboring 2 or 3 parasitic infections (Ancylostoma tubaeforme, Toxocara cati, and/or Taenia taeniaeformis), were used to titrate the anthelmintic efficacy of a paste containing 3.4% febantel and 0.34% praziquantel. The cats were allotted into 4 groups (10 cats/group). For 3 consecutive days, the cats were given febantel/praziquantel at 5/0.5 mg/kg/day, 10/1 mg/kg/day, 15/1.5 mg/kg/day, or a blank paste vehicle (control) at 0.29 g/kg of body weight. The recommended dosage of 10 mg of febantel and 1 mg of praziquantel/kg cleared greater than or equal to 98% of the 3 helminth species.     

Protection developed against reinfection by Dictyocaulus viviparus following anthelmintic treatment of a one-day-old primary infection in cattle

Single doses of 7.5 mg/kg levamisole subcutaneously and 5 mg/kg oxfendazole per os and three daily doses of diethylcarbamazine intramuscularly were 86.9, 82.1 and 46.6 per cent efficient, respectively, against one-day-old Dictyocaulus viviparus. These three dosage regimes were also associated, respectively, with 92.5, 36.4 and 56.0 per cent protection against reinfection following anthelmintic treatment. It is suggested that the high degree of protection following the use of levamisole may be a consequence of rapid and effective anthelmintic activity combined with immunomodulating effects.     

The anthelmintic effect of aqueous methanol extract of Combretum molle (R. Br. x. G. Don) (Combretaceae) in lambs experimentally infected with Haemonchus contortus

The aqueous methanol extract from the stem-bark of Combretum molle was evaluated for anthelmintic activity in lambs infected with Haemonchus contortus using faecal egg count (FEC) reduction assay. The extract showed a dose-dependent reduction in FEC in infected animals. At doses of 500, 1000 and 2000 mg kg(-1), the extract caused FEC reduction of 63%, 69.25% and 96.23%, respectively. Similarly, the standard anthelmintic (albendazole) at a dose of 200 mg kg(-1) produced FEC reduction of 99.24%. FEC reduction produced by the extract at doses of 500 and 1000 mg kg(-1) is below the minimum standard of 90% FEC recommended by the World Association for the Advancement of Veterinary Parasitology (WAAVP). However, there was no significant (P>0.05) difference between the means of groups treated with 1000 mg kg(-1) and 2000 mg kg(-1) compared to that of albendazole. In this study, C. molle has shown a promising anthelmintic activity against experimental haemonchosis. Nonetheless, further studies to evaluate its detailed toxicity are required for the plant extract to be developed into a useful anthelmintic drug. There is also the need to evaluate other parts of the plant (root, leaves, fruits, etc.) for the same effect.     

Efficacy of oxfendazole against inhibited Ostertagia ostertagi in naturally infected cattle.

Oxfendazole was administered to pregnant cows at 2.5 and 5 mg/kg body weight to determine the anthelmintic efficacy against naturally acquired larvae which became inhibited at the early 4th stage. The experimental design included three groups of orally-treated cows, that is, 10 placebo treated control cows, 11 cows treated with 2.5 mg/kg of oxfendazole and 10 cows treated with 5.0 mg/kg of oxfendazole. Oxfendazole at 2.5 mg/kg body weight was 82 and 94% effective against EL-4 and adult O. ostertagi, respectively. At 5 mg/kg, Oxfendazole was 95 and 99% effective against EL-4 And adult O. ostertagi, respectively. The results suggested the use of a field dosage level of 5 mg/kg body weight oxfendazole where inhibited larvae may be encountered.     

Evaluation of the anthelmintic activity of Khaya senegalensis extract against gastrointestinal nematodes of sheep: in vitro and in vivo studies

The anthelmintic effect of Khaya senegalensis is described. In vitro and in vivo studies were conducted to determine possible direct anthelmintic effects of ethanolic and aqueous extracts of K. senegalensis towards different ovine gastrointestinal nematode. A larval development assay was used to investigate in vitro, the effect of aqueous and ethanolic extracts towards larvae of strongyles. The LC50 values of the effects of both the aqueous and ethanolic extracts were calculated. Another study was conducted in vivo to evaluate the therapeutic efficacy of the extracts administered orally at a dose rate of 125, 250 and 500 mg/kg of sheep harbouring naturally acquired infection of gastrointestinal nematodes. The presence of K. senegalensis extracts in the cultures decreased the viability of larvae. The LC50 of the aqueous extract (0.69 mg/ml) is not significantly different (P >0.05, t-test) from the ethanolic extract (0.51 mg/ml). The activity of the extract is concentration dependent in vivo. Sheep drenched with 500 mg/kg K. senegalensis ethanolic extract had a mean faecal egg count (FEC) reduction of 88.82%. The extract of K. senegalensis could find application in anthelmintic therapy in veterinary practice.