Transmission studies on Trichinella species isolated from Crocodylus niloticus and efficacy of fenbendazole and levamisole against muscle L1 stages in Balb C mice

Forty-four Balb C mice, aged 18 weeks were infected with crocodile (Crocodylus niloticus)-derived Trichinella species. Of the infected mice, 32 were randomly divided into two groups each containing equal numbers of males and females; levamisole treated group and fenbendazole treated group. Each group was randomly subdivided into two subgroups as follows: levamisole group (subgroup 1: treated with levamisole on day 35 post infection, and subgroup 2: treated with levamisole on days 35 and 42 post infection) and fenbendazole group (subgroup 1: treated with fenbendazole on day 35 post infection and subgroup 2: treated with fenbendazole on days 35 and 42 post infection). The first subgroups treated on day 35 post infection were slaughtered on day 42 post infection and the second subgroups were treated on day 35 and day 42 post infection and slaughtered on day 49 post infection. Two female mice were infected a day after mating and were slaughtered together with the offspring on day 64 post-infection. Ten infected control mice were given 1 ml distilled water orally as placebo, and five of these were slaughtered on day 42 post infection. The results showed that the mean reproductive capacity index of this strain (RCI) in Balb C mice was 110. There was a significant reduction (P < 0.01) in larval counts in the single treatment groups (day 35) and in the double treatment groups (days 35 and 42) for both anthelmintics when compared the number of parasites in the control groups. After a single treatment, levamisole reduced the infection by 79.9% and fenbendazole by 76.7%. Following double treatments, levamisole reduced the infection by 95.5% and fenbendazole by 99.1%.There was evidence that the infected pregnant mice transmitted the parasite to their offspring. It is not certain whether the parasite was transmitted congenitally or transmammary Alternative ways of controlling the parasite in crocodile farms in Zimbabwe are discussed.     

Evidence for multiple anthelmintic resistance in sheep and goats reared under the same management in coastal Kenya

Four experiments, two with sheep and two with goats, were carried out to determine the efficacy of ivermectin, fenbendazole, levamisole, closantel and some of their combinations by faecal egg count reduction tests. In the first experiment, injectable ivermectin, oral ivermectin, fenbendazole and levamisole were tested in 6-month-old lambs, and their reduction percentages were 77%, 13%, 42% and 92%, respectively. In the second experiment, with yearling sheep, the reduction percentages were 35% for injectable ivermectin, 32% for fenbendazole, 99% for levamisole, 48% for closantel, 92% for injectable ivermectin combined with fenbendazole, 99% for injectable ivermectin combined with levamisole, and 100% for fenbendazole combined with levamisole. In the study with 18-month-old goats given the same dose rates as those recommended for sheep, the reduction percentages were 73% for injectable ivermectin, 25% for fenbendazole, and 78% for levamisole. Another group of 14-month-old goats was treated with dose rates 1.5 times those recommended for sheep and the reduction percentages were 93% for levamisole, 92% for injectable ivermectin, and 97% for a combination of levamisole and ivermectin. In all experiments with sheep and goats the gastrointestinal nematode parasites identified by larval cultures were Haemonchus contortus, Trichostrongylus spp. and Oesophagostomum spp. The gastrointestinal nematodes of both sheep and goats on this farm are resistant to ivermectin and fenbendazole, whereas levamisole is still effective in sheep, but not in goats. The results are discussed in relation to the farm as a source of breeding stock to smallholder farmers and its potential to spread anthelmintic resistance.     

Multiple anthelmintic resistance in Haemonchus contortus on a sheep farm in India

Multiple resistance to benzimidazoles (fenbendazole, albendazole and mebendazole) in a strain of Haemonchus contortus in sheep was detected on a farm where fenbendazole resistance had already been identified. Following a faecal egg count reduction test, this was confirmed by both critical and controlled anthelmintic tests. Different groups of sheep infected naturally or given an experimental infection with the fenbendazole-resistant strain were treated with the recommended doses of various anthelmintics. Compared to the control group, percentage reductions in faecal egg counts of sheep treated with fenbendazole, albendazole, mebendazole, levamisole and morantel varied between 56% and 81% and worm counts between 71% and 86%. The results indicate the presence of multiple anthelmintic resistance in this strain of H. contortus on this farm. Sheep treated with ivermectin and closantel showed 100% reductions in faecal egg and worm counts, suggesting high efficacy of these drugs against the population of H. contortus on this farm.     

Speed of actin of some anthelmintics against Dictyocaulus viviparus infection in cattle

In a study of the comparative speed of action of anthelmintics against Dictyocaulus viviparus infection in cattle levamisole reduced the lungworm burdens by 87 per cent within three hours of administration whereas fenbendazole and febantel required 36 hours to achieve 80 and 87 per cent reduction, respectively. The more rapid action of levamisole may be advantageous in the treatment of bovine parasitic bronchitis since it allows virtually immediate elimination of the majority of the lungworms and limits undesirable sequelae dependent on the continued presence of the parasite.     

Efficacy of repeated doses of levamisole, morantel, fenbendazole, and ivermectin against gastrointestinal nematodes in ewes

Levamisole, morantel, fenbendazole, or ivermectin was administered at 2-week intervals from May 1 through Sept 14, 1985, to breeding ewes (20 ewes/drug) infected with various gastrointestinal nematodes. All ewes had fewer gastrointestinal nematode eggs per gram of feces (epg) after 2 treatments, compared with pretreatment epg counts. Ewes administered ivermectin continued to have a low mean epg (0 to 3) throughout the study. The mean epg counts of ewes treated with levamisole increased from 3 to 483 during the study. This increase was similar to that of ewes treated with morantel (7 to 485 epg). The mean epg count of fenbendazole-treated ewes increased from 4 to 192 during the study. By the end of the study, the mean epg counts when expressed as a percentage of the pretreatment epg counts were 4% (ivermectin), 249% (fenbendazole), 627% (levamisole), and 630% (morantel). With the exception of the ivermectin-treated ewes, the epg count increased almost linearly in the ewes after the 2nd anthelmintic treatment. These data indicate that the gastrointestinal nematodes (including Haemonchus contortus) may have developed more resistance to levamisole and morantel than to fenbendazole. On the basis of the epg counts, resistance to ivermectin did not develop during the 4.5-month treatment period. The percentage of ewes shedding eggs after 2, 4, and 6 anthelmintic treatments was lowest for ewes treated with ivermectin (20%) and was similar (40%) for ewes treated with 1 of the other 3 anthelmintics. At the conclusion of the study, most of the ewes (90%) were shedding at least a small number of eggs, regardless of the anthelmintic treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficacies of fenbendazole and levamisole in the treatment of commercial turkeys for Ascaridia dissimilis infections

A field trial was conducted on a farm in Michigan with commercial turkeys naturally infected with Ascaridia dissimilis. The birds were treated at approximately 8 and 14 wk of age on a per-barn basis with fenbendazole (Safeguard) in the feed at 16 ppm for 6 d (1 barn), or with levamisole (Prohibit) in the water at 16 mg/kg of BW (2 barns). Six birds were obtained at random and sacrificed in each barn for worm burden determinations before treatments and again soon after treatments. Nematicidal efficacies for fenbendazole and levamisole were shown to be 99.3 to 99.9% and 54.6 to 85.8%, respectively. Despite the far greater reductions in worm burdens by fenbendazole as compared with levamisole, the burdens at the time of retreatment had equalized in all barns, illustrating the role of premunition regarding turkey ascaridiasis, and highlighting the overriding importance of reducing the challenge to provide long-term control of this parasitism.     

Naphthalophos combinations with benzimidazoles or levamisole as effective anthelmintics for sheep

Objective: To investigate the relative efficacy and safety of the anthelmintic naphthalophos in sheep, either given alone or in combination with benzimidazole (fenbendazole and albendazole) or levamisole anthelmintics.
Design: A parasitological study using faecal egg count reduction tests, a validating slaughter trial and field safety trials.
Procedure: Faecal egg count reduction tests were carried out on 13 farms. Naphthalophos and combinations of naphthalophos with levamisole and fenbendazole were included in the drench tests. On one property a controlled efficacy study was carried out to validate faecal egg count reduction test findings. In this trial, sheep were slaughtered 10 days after treatment and the remaining parasites recovered from the gastro-intestinal tract. Safety trials were carried out on eight farms where approximately 50 000 sheep were treated with naphthalophos and albendazole that were tank mixed in the backpack.
Results: The efficacy of naphthalophos alone in faecal egg count reduction tests ranged from 59 to 98% with one test showing 95% reduction. The efficacy of naphthalophos and levamisole ranged from 74 to 100%, with 5 farms showing 95% reduction. The efficacy of naphthalophos and fenbendazole ranged between 88 and 100% with 95% reduction achieved on 10 farms. The controlled efficacy study showed a good correlation between the faecal egg count reduction tests and numbers of parasites recovered, except for Nematodirus where the faecal egg count reduction tests overestimated efficacy. The mortality rate in the safety trials was 0.05%, with most fatalities occurring on one farm.
Conclusion: The combination of naphthalophos and fenbendazole was more effective than a combination of naphthalophos and levamisole, and will provide a sufficiently safe drench rotation option.     

Multiple anthelmintic resistance in a goat herd

Anthelmintic resistance was monitored over a 30 month period within a goat herd in eastern Virginia, USA. Resistance to ivermectin, levamisole and benzimidazole drugs was detected in Haemonchus contortus using the fecal egg count reduction test (FECRT). When levamisole use was discontinued for 1 year, susceptibility to levamisole appeared to return. Although a single treatment with fenbendazole was able to reduce fecal egg counts by only 50%, two doses administered in a 12 h interval increased efficacy to 92%, however, confidence intervals indicated that resistance was still present. When fecal egg counts were determined the following year after several treatment using this protocol, the efficacy of fenbendazole had fallen again to 57% reduction in fecal egg counts. The predominant genus present in cultured composite fecal samples was Haemonchus. Trichostrongylus, Cooperia and Teladorsagia were also present in smaller numbers.     

Anthelmintic evaluation of a thiabendazole-resistant strain of Ostertagia circumcincta recovered from sheep in England

A total of 35 worm-free lambs were infected with a strain of Ostertagia circumcincta isolated earlier from sheep in Cheshire, England, and found to be resistant to thiabendazole (TBZ). When patency was established the sheep were divided into groups of six, and dosed orally with either TBZ (44 mg kg-1, 88 mg kg-1), fenbendazole (FBZ; 5 mg kg-1) or levamisole (7.5 mg kg-1) or not treated. Three of the remaining five animals were dosed with FBZ at 10 mg kg-1. Egg hatch tests, post-dosing faecal egg counts and post-mortem worm counts confirmed resistance to TBZ, and a degree of side-resistance to FBZ was also revealed. Only levamisole gave the clearance expected of modern anthelmintics.     

Anthelmintic resistance in nematode parasites of sheep in Denmark with special emphasis on levamisole resistance in Ostertagia circumcincta.

This study was undertaken to elucidate the presence of anthelmintic resistance in nematode parasites of sheep in Denmark. Twenty two flocks of sheep were selected for Faecal Egg Count Reduction (FECR) tests, based on a prior history of either the same anthelmintic, or anthelmintic class having been used 3 times or more over the previous 5 years. Evidence of anthelmintic resistance was detected in 7 flocks. Two flocks showed FECR of 88% and 94% after treatment with thiabendazole, FECR of another 2 were 90% and 94% following treatment with fenbendazole. Three flocks showed FECR of 73%, 89% and 94%, respectively following the use of levamisole. Ostertagia circumcincta was isolated from 1 of the latter flocks and subjected to an in vivo controlled slaughter assay. Following treatment with levamisole at the recommended dose rate of 7.5 mg/kg, FECR was 44.5% and worm counts were reduced by 67.7%. These results were further substantiated by an in vitro egg hatch paralysis assay and by measuring pepsinogen levels in treated and non-treated lambs. This is the first instance of anthelmintic resistance in sheep nematodes in Scandinavia.     

Suspected resistance of Ostertagia ostertagi in cattle to levamisole

Observations on a beef cattle farm in Flanders led to the suspicion of resistance to levamisole in a strain of Ostertagia ostertagi. After treating a group of six animals with levamisole (5 mg kg-1 L.W., i.m.) the reduction in the number of trichostrongylid eggs per gram of faeces varied between 0 and 66.6%, whereas a similar group treated with fenbendazole (7.5 mg kg-1 L.W., p.o.) showed a reduction in worm burdens of 100%. Coproculture showed that the remaining eggs in the first treatment group were all Ostertagia sp. The suspected field strain was compared with a reference strain of O. ostertagi by means of the in vitro larval paralysis test. This test showed LC95 values of 9.12 micrograms ml-1 and of 99.04 micrograms ml-1 for the reference and the field strain respectively, which indicates a resistance factor for the latter of 10.9. These results were not unequivocally confirmed by the post mortem findings on a tracer calf necropsied 4 days after treatment with levamisole.     

MULTIPLE AND MULTIGENERIC ANTHELMINTIC RESISTANCE ON A SHEEP FARM IN KENYA

The anthelmintic efficacy of benzimidazoles (albendazole, fenbendazole and oxfendazole), levamisole, oral ivermectin and closantel was evaluated on a farm in Kenya using faecal egg count reduction test, larval cultures and a controlled slaughter trial. The results of this study indicated simultaneous resistance of Haemonchus contortus against benzimidazoles, levamisole and ivermectin, and of Trichostrongylus colubriformis and Oesophagostomum spp. against levamisole on the same farm. Ivermectin resistance developed to 47% within 15 months of first use. Closantel was effective against the benzimidazoles, levamisole and ivermectin resistant H. contortus.     

Primary anthelminthic screening on the L4 and L5 developmental stages of the lungworm, Dictyocaulus viviparus, in guinea pigs

The study was aimed at expanding the primary anthelmintic screening to cover a model of the group of pulmonary nematodes; in this particular case to introduce the lungworm, D. viviparus, in laboratory animals. A method of primary screening for the fourth and fifth larval states of D. viviparus in guinea-pigs was worked out after the selection of a suitable laboratory host. In the primary screening, three well-known anthelmintics of the benzimidazol series, including fenbendazole, mebendazole and levamisol, were tested by the method of controlled test. The anthelmintics were administered at the recommended doses of 7.5 and 10.0 mg per kg of live weight for two days in succession. The effectiveness of the control of the 4th and 5th larval states of D. viviparus was 93.4% in fenbendazole, 89.0% in mebendazole, and 89.9% in levamisol. It is confirmed by the results of the trials that guinea-pigs can be used for the testing model of the lungworm, D. viviparus, in anthelmintic screening.     

Comparison of the efficacy of dermal formulations of ivermectin and levamisole for the treatment and prevention of Dictyocaulus viviparus infection in cattle

Four groups of six parasite-naive calves were infected at seven day intervals with three doses of infective larvae of Dictyocaulus viviparus. Twenty-one days after the first dose three of the groups were treated either with an injectable formulation of ivermectin at a dose rate of 200 micrograms/kg bodyweight, or with pour-on preparations of levamisole at 10 mg/kg or ivermectin at 500 micrograms/kg. On day 28 two calves from each group were slaughtered and their burdens of lungworms counted. On day 35 the remaining calves were reinfected with D viviparus infective larvae at a rate of 80 L3/kg. The levamisole preparation was 94.6 per cent effective and both ivermectin preparations were 100 per cent effective against the initial infections. The ivermectin-treated calves were protected from the reinfection which subsequently became patent in the levamisole-treated and control calves.     

Further studies on anthelmintic resistance in sheep at an organised farm in arid region of Rajasthan

Faecal egg count reduction test (FECRT) and in vitro egg hatch assay (EHA) was performed on Indian Karakul (3/4 crosses of Karakul with Malpura, Marwari and Sonadi) transported from arid region campus, Bikaner, where resistance was reported in 1996. FECRT revealed that fenbendazole and levamisole were 100% effective in reducing the egg counts. LC50 value on EHA was 0.074 +/- 0.015 microg thiabendazole ml(-1). The faecal culture examination revealed the presence of Haemonchus contortus only. It was concluded that H. contortus was fully susceptible to both benzimidazole and levamisole.     

Anthelmintic resistance in nematode parasites of goats

Cases of anthelmintic resistance on 3 goat farms in Gippsland were investigated. On the first farm Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia (Teladorsagia) circumcincta were found to be resistant to fenbendazole, but the first 2 species were fully susceptible to levamisole. On the second farm a population of T. colubriformis, resistant to concurrent full doses of levamisole and a benzimidazole, was found to retain this resistance when transferred to sheep. On the third farm, heavy mortality due to Ostertagia and Trichostrongylus spp burdens was arrested only by the use of concurrent full doses of levamisole and oxfendazole; no single anthelmintic was found to be effective. A disturbing rise in the incidence of clinical helminthiosis, often accompanied by anthelmintic resistance, occurred on goat farms in Gippsland early in 1984.     

ANTHELMINTIC EFFICIENCY OF OXFENDAZOLE, FENBENDAZOLE AND LEVAMISOLE AGAINST NATURALLY ACQUIRED INFECTIONS OF OSTERTAGIA OSTERTAGI AND TRICHOSTRONGYLUS AXEI IN CATTLE

The anthelmintic efficiencies of oxfendazole, fenbendazole and levamisole, each at 4 dose rates spanning the manufacturers' recommended dosages were compared in beef cattle with naturally acquired infections of Ostertagia ostertagi and Trichostrongylus axei. In 8 of the 9 cases tested there was no significant increase in anthelmintic efficiency due to increased dose rates of any of the drugs. Percentage efficiencies and their standard errors, calculated from mean worm counts of pooled data for adult worms, developing 4th stage and early 4th stage larvae of O. ostertagi, were respectively, 86.9+/-4.2, 77.4+/-6.1, 74.5+/-7.3 for oxfendazole, 93.7+/-2.0. 80.7+/-6.8, 59.6+/-13.9 for fenbendazole and 69.7+/-6.9, 39.4+/-14.8, 31.2+/-22.6 for levamisole. Counts of O. ostertagi from cattle treated with oxfendazole and fenbendazole were not significantly different, but both were significantly lower than those from cattle given levamisole. Efficiency against T. axei exceeded 99% for all drugs. Practical implications for therapy and preventative control of ostertagiasis are discussed.     

The efficiency of levamisole, thiabendazole and fenbendazole against naturally acquired infections of Ostertagia ostertagi in cattle

In two experiments, conducted in cattle with naturally acquired infections of Ostertagia ostertagi, comparative assessments were made of the anthelmintic efficiency of levamisole, thiabendazole and fenbendazole, each at 1.0, 1.5 and 2.0 times the recommended dose rate. Variable efficiencies of 81 and 49 per cent for levamisole, 86 and 56 per cent for thiabendazole were obtained against adult O ostertagi. Neither drug showed substantial activity against early fourth stage larvae. Efficiency of fenbendazole against adult O ostertagi was consistently high; 85 and 89 per cent in the two experiments respectively. In the first experiment in which cattle were slaughtered two to three days after treatment, only 22 per cent of inhibited early fourth stage larvae were removed whereas in the second experiment when slaughter took place 10--11 days after treatment, this efficiency was 89 per cent. There was no increased effect of increased dose rates on treatments with thiabendazole or fenbendazole. The activity of levamisole against adult worms and inhibited larvae was increased at twice the recommended dose rate.     

Cell adherence to larvae of Dictyocaulus viviparus in vitro

Bovine eosinophils survived for up to 48 hours in vitro in a medium of undiluted bovine serum and became adherent to the surface of Dictyocaulus viviparus larvae earlier than other cells found in peripheral blood. Cell adherence was associated with a heat labile factor in normal bovine serum and a heat stable factor in hyperimmune serum. A factor associated with leucocytes in vitro appeared to cause larval immobility. Cells from calves treated with levamisole behaved identically to those from other sources. It is suggested that eosinophils are an important element in host defence against D viviparus infection.     

Anthelmintic resistance of nematodes in communally grazed goats in a semi-arid area of South Africa

A survey was conducted on the occurrence of anthelmintic resistance of nematodes in communally grazed goats in a semi-arid area in South Africa. In herds belonging to 10 small-holder goat farmers, the efficacies of fenbendazole, levamisole and rafoxanide were tested by faecal egg count reduction (FECR) tests. Efficacies of 80% were considered a threshold for anthelmintic resistance. The FECR tests showed that all drugs tested more than 80% effective in most instances, but there were notable exceptions. In 1 case, rafoxanide was only 31% effective and in another case fenbendazole was only 47% effective. The occurrence of anthelmintic resistance in this farming sector is of concern. Steps should be taken to prevent its further spread and to avoid the development of a situation as on numerous commercial sheep farms in South Africa where resistance is very common.