Effect of treatment with levamisole or fenbendazole on primary experimental Dictyocaulus viviparus infection and on resistance in calves

Based on faecal larval counts, respiratory rates and live-weight gains, the anthelmintics levamisole and fenbendazole were equally efficacious against primary infection with Dictyocaulus viviparus in calves. Calves that were treated with levamisole or fenbendazole resisted the live-weight depressing impact of reinfection. Treatment somewhat impaired resistance to establishment of the secondary challenge as determined at necropsy. However, compared with previously uninfected controls, the treated animals harboured significantly fewer D viviparus, showing that they still strongly resisted reinfecting worms becoming established. The animal responses measured did not demonstrate any difference between levamisole and fenbendazole in relation to efficacy or to effect on resistance.     

Efficacy of fenbendazole against adult Dictyocaulus viviparus in experimentally infected calves.

Fenbendazole, methyl-5(phenylthio)-2-benzimidazolecarbamate, a new broad-spectrum anthelmintic, was evaluated against the adult Dictyocaulus viviparus, lungworm of cattle, in artificially infected calves. At a dosage of 5 mg/kg of body weight, fenbendazole removed 100% of the worms if given as an oral suspension, and 99.7% of the worms if given as a feed additive.     

Observations on the epidemiology of Dictyocaulus viviparus in north west England

A five year ley pasture was used as a source of natural infection with Dictyocaulus viviparus for cattle in anthelmintic trials. Pasture larval counts, faecal larval counts of permanently grazing calves and lungworm burdens harboured by tracer calves were monitored in three grazing seasons to assess the pattern of infection. Carrier calves were introduced at the beginning of the grazing season in the first two years of the study but not in the third. In the fourth year the pasture was subdivided into two paddocks where overwintered infection with and without carrier infection were compared. A control paddock exposed to carrier infection but no overwintered infection was also monitored. Pasture larvae survived the winter but carrier infection appeared to make a larger contribution to pasture larval counts and the onset of parasitic bronchitis in susceptible calves. In the absence of grazing cattle at the end of the grazing season the concentration of D viviparus larvae on the herbage fell rapidly to undetectable levels. Discrepancies between contamination of herbage by infective D viviparus larvae and infectivity of pasture for susceptible cattle occurred in all years but were particularly marked on the third year when natural immunity appeared to influence the number of lungworms accumulating in tracer calves. Failure to recover lung worms from tracer calves cannot be regarded as an accurate indication of lungworm free pasture. In the first three years the proportion of the lungworm population which was inhibited in tracer calves was higher early and late in the grazing season and negligible in mid season. This suggests that a predisposition to inhibition in larvae which have overwintered on pasture may influence the time of onset of parasitic bronchitis in the next grazing season, but results from the fourth year did not support this hypothesis.     

Persistent anthelmintic activity of topically administered ivermectin in red deer (Cervus elaphus L.) against lungworms (Dictyocaulus viviparus)

A controlled trial was conducted to evaluate the persistent anthelmintic effect of ivermectin as a topical treatment at 500 microg/kg against induced infection with lungworm (Dictyocaulus viviparus) in red deer (Cervus elaphus). The results showed a highly significant (p <0.01) anthelmintic activity for at least 28 days against a newly acquired infection with Dictyocaulus viviparus (>99% efficacy).     

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.     

The efficacy of two isolates of the nematode-trapping fungus Duddingtonia flagrans against Dictyocaulus viviparus larvae in faeces.

A series of experiments was carried out to examine the effects of two different isolates of the nematode-trapping fungus Duddingtonia flagrans to reduce the number of free-living larvae of the bovine lungworm, Dictyocaulus viviparus. A laboratory dose-titration assay showed that isolates CI3 and Troll A of D. flagrans significantly reduced (P < 0.05 to P < 0.001) the number of infective D. viviparus larvae in cultures at dose-levels of 6250 and 12,500 chlamydospores/g of faeces. The larval reduction capacity was significantly higher for Troll A compared to CI3 when lungworm larvae were mixed in faecal cultures with eggs of Cooperia oncophora or Ostertagia ostertagi and treated with 6250 chlamydospores/g of faeces. Both fungal isolates showed a stronger effect on gastrointestinal larvae than on lungworm larvae. Two plot trials conducted in 1996 and 1997 involved deposition of artificial faecal pats containing free-living stages of D. viviparus and C. oncophora on grass plots. Herbage around the pats was collected at regular intervals and infective larvae recovered, counted and identified. These experiments showed that both D. flagrans isolates reduced the number of gastrointestinal as well as lungworm larvae in faecal pats. During both plot trials, the transmission of C. oncophora larvae, but not D. viviparus, from faecal pats to the surrounding herbage was clearly affected by climatic conditions. After collection of faecal pats from the grass plots one month after deposition, the wet and dry weight of pats as well as organic matter content were determined. No differences were found between the fungus-treated and non-treated control pats. This indicated that the rate of degradation of faeces was not affected by the addition of the fungus.     

Antibody responses to natural Dictyocaulus viviparus exposure in first year grazing cattle using vaccination or different kinds of anthelmintic treatment.

In two field trials vaccination or different anthelmintic treatments against Dictyocaulus viviparus infections were used in 6 groups of first year grazing cattle. The antibody response to lungworm infections was determined using an ELISA. Cattle treated once or repeatedly at long intervals with levamisole developed clinical signs of dictyocaulosis. The detection of anti-D. viviparus antibodies at the end of the grazing season confirmed that these anthelmintic treatments were not able to prevent lungworm infections. Cattle that received strategically administered treatments with ivermectin remained clinically healthy. These cattle were seronegative until the end of the trial which proved the efficacy of the strategic control. Cattle that received an intraruminal slow release bolus did not develop clinical disease. However one animal shed lungworm larvae and the herd became seropositive at the end of the grazing season indicating a history of infection. The serological examination of a cattle herd at the end of the grazing season is able to demonstrate a history of lungworm infections and to determine the efficacy of anthelmintic control measures.     

Efficacy trial of an irradiated cattle lungworm vaccine in red deer (Cervus elaphus)

Lungworm (Dictyocaulus sp.) is the parasite of most concern to the New Zealand deer industry. Although lungworm can be controlled by anthelmintics there is an increasing concern over excessive drenching programmes and reliance on chemicals for parasite control. A live irradiated larval vaccine developed for cattle has been available in Europe for the past 40 years but has never been evaluated in red deer in New Zealand. Four groups of red deer and two of cattle were hand reared from birth in parasite-free conditions. The cattle acted as a control group to ensure that the vaccine was still efficacious on arrival in New Zealand. Two groups of deer were vaccinated, and all four groups were challenged with either D. viviparus or deer origin Dictyocaulus, tentatively identified as D. eckerti. The vaccine provided excellent protection to cattle under New Zealand conditions, there was no larval output in the vaccinated cattle and no adults were found in their lungs at necropsy. In red deer, patency was delayed in the vaccinated groups regardless of challenge species and larval output was lower but was not prevented. Adult lungworms were found in the lungs of all deer at necropsy but fewer were recorded in the vaccinated deer. Although Huskvac provided a degree of protection for red deer it was not effective enough to recommend its use.     

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.     

The persistence of benzimidazole-resistant cyathostomes on horse farms in Ontario over 10 years and the effectiveness of ivermectin and moxidectin against these resistant strains

Three clinical trials with fecal egg count reduction tests and coproculture were conducted on 2 standardbred farms in Ontario. On Farm A, the treatment groups were mebendazole and ivermectin in trial 1, and fenbendazole and moxidectin in another. On Farm B, treatment groups were mebendazole and ivermectin. All horses treated with mebendazole or fenbendazole were subsequently treated with ivermectin or moxidectin. Strongyle eggs/g feces were estimated pre- and post-treatment using the Cornell-McMaster dilution and Cornell-Wisconsin centrifugal flotation techniques. After treatment, there was no change in the arithmetic mean eggs/g feces for horses given mebendazole, and a reduction of only 49.1% for those given fenbendazole. All horses receiving ivermectin or moxidectin had their egg counts reduced to 0. Only cyathostomes were found on culture. On both farms the benzimidazole resistant strains appeared to have persisted for at least 10 years. Development of and monitoring for anthelmintic resistance are briefly discussed.     

Effect of ivermectin and oxfendazole on shedding of larvae of the lungworm (Dictyocaulus viviparus) by red deer (Cervus elaphus)

Thirty eight newly weaned hinds were randomly allocated to one of two equal groups. One group received ivermectin, the other, oxfendazole at dose rates of 0.2 mg/kg and 4.5 mg/kg, respectively. All deer were drenched four times and were grazed on pasture. Both anthelmintics reduced D. viviparus faecal larval counts to low levels 20 days after dosing, but the mean larval output and the proportion of deer shedding D. viviparus larvae at 27 and 33 days after treatment, were significantly lower in the ivermectin treated group. There was no significant difference in weight gain between the two groups throughout the trial. This study suggests that ivermectin prevents reinfection with D. viviparus for approximately 14 days longer than oxfendazole.     

A Field Evaluation of Benzimidazole and Nonbenzimidazole Drugs in a Herd of Dairy Goats

A study was conducted to investigate the efficacy of six anthelmintics in a herd of dairy goats. Pretreatment larval cultures indicated that the goats were infected with Haemonchus contortus and Trichostrongylus colubriformis. Three separate treatment regimens were administered. In each trial, mature nonlactating goats were allocated into two treatment groups and a control group. Treatment groups received thiabendazole (TBZ) or levamisole (LEV), mebendazole (MBZ) or fenbendazole (FBZ), and morantel tartrate (MOR) or ivermectin (IVR). LEV, MOR, and IVR reduced fecal strongyle egg counts by 99% to 100% of pretreatment values. The benzimidazole (BZD) drugs changed pretreatment fecal egg counts by +2% to -32%. Results of posttreatment larval culture demonstrated the presence of H contortus larvae following the administration of BZD drugs.     

Comparative efficacies of ivermectin, febantel, fenbendazole, and mebendazole against helminth parasites of gray foxes

Anthelmintic efficacies of ivermectin, febantel, fenbendazole, and mebendazole were compared in 45 adult gray foxes (Urocyon cinereoargenteus) naturally infected with helminth parasites. Fecal specimens were examined one week before treatment and one week and 3 weeks after treatment with each anthelmintic, using a sucrose flotation technique. Compared with pretreatment, fewer foxes in all groups were infected with helminths one week and 3 weeks after treatment. Ivermectin, febantel, and fenbendazole more effectively eliminated helminths than did mebendazole. Parasites found were Ancylostoma sp, Capillaria aerophila, and Aelurostrongylus abstrusus and/or Filaroides osleri.     

Evaluation of anthelmintic activity in captive wild ruminants by fecal egg reduction tests and a larval development assay.

The effectiveness of anthelmintics was evaluated in four herds of captive ruminants, wapiti (Cervus elaphus), Armenian red sheep (Ovis orientalis), giraffe (Giraffa camelopardalis), and pronghorn (Antilocapra americana), by the use of fecal egg reduction tests (FERTs) and a commercial larval development assay (LDA) designed to evaluate susceptibility or resistance of nematodes to anthelmintics. Haemonchus sp. was the predominant nematode in the red sheep, giraffe, and pronghorn herds, whereas Ostertagia sp. and Trichostrongylus sp. were predominant in the wapiti. The LDA data indicated susceptibility by the worms to benzimidazoles except in the red sheep flock, which showed a high level of resistance. High levels of resistance to levamisole were seen in the worm populations from the wapiti and red sheep, moderate resistance in the pronghorn herd, and susceptibility in the giraffe herd. Worms were susceptible in all four herds to a combination of benzimidazole/levamisole. There was suspected avermectin resistance by Trichostrongylus sp. in the wapiti herd and by Haemonchus sp. in the giraffe. The FERTs agreed with the LDA in showing the Haemonchus in the giraffe was susceptible to fenbendazole and had suspected resistance to ivermectin, whereas Haemonchus in the red sheep and pronghorn were susceptible to ivermectin. There was correlation between the tests evaluating anthelmintics. The LDA is useful as a screening test in the selection of an anthelmintic for use in grazing ruminants, but the effectiveness of a drug in a host species may depend as much on the dose used, and the method of administration, as it does on the parasite's sensitivity to the anthelmintic.     

Dictyocaulus species: cross infection between cattle and red deer

Aim: To discover whether cross infection between red deer (Cervus elaphus) and cattle is possible with either a bovine isolate of the cattle lungworm, Dictyocaulus viviparus, or with a cervine isolate of the lungworm, Dictyocaulus eckerti which is thought to be maintained primarily in deer. Method: Twelve cattle and 12 red deer were reared parasite-free from birth. At 3-4 months of age, half of each species (n=6) were experimentally infected with D. viviparus and the other half with D. eckerti. The course of infection was monitored for 34 days, after which the animals were slaughtered and the lungs removed to assess levels of infection. Results: Faecal larval counts demonstrated that patent Dictyocaulus infections occurred in all groups. At necropsy, adult worms were found in the lungs in all groups except the cattle that were infected with D. eckerti. The largest numbers of adult worms were found in the red deer infected with D. eckerti. Conclusion: It was demonstrated that both cattle and red deer could be infected with either D. viviparus or D. eckerti. However, D. eckerti larvae that originated from deer established more successfully in deer and D. viviparus larvae that originated from cattle established more successfully in cattle.     

Benzimidazole resistance in equine cyathostomes in Slovakia

The present study included 19 stud farms, including 243 horses, that were investigated for the occurrence of anthelmintic resistant cyathostomes. The number of horses on the farms varied from nine to more than 100, and horses of all ages were included. A minimum of seven horses were used for faecal egg count reduction (FECR) tests. The anthelmintics included were: fenbendazole (paste formulation), ivermectin (paste formulation) and pyrantel (powder). Resistance to benzimidazoles was detected on 14 farms, with FECR values ranging from 65.1 to 86.3%. Larval cultures after fenbendazole treatment revealed exclusively cyathostome larvae. Ivermectin was tested on eight farms and proved to be effective on all. Pyrantel was tested on two farms and FECR test indicated high efficacy (92-97%). Egg hatch assay (EHA) results showed that mean concentrations of thiabendazole that inhibited hatching in 50% of the eggs (ED(50)) in resistant populations were over 0.1 microg ml(-1). The results of our study suggest widespread resistance to fenbendazole in equine cyathostomes in Slovakia, and possible strategies to delay anthelmintic resistance are discussed briefly.     

Dictyocaulus viviparus seroprevalence and epidemiology in Costa Rican dairy cattle

A cross-sectional serological survey of Dictyocaulus viviparus was carried out to determine the prevalence of lungworm infections in 28 dairy cattle farms distributed in five selected areas from Costa Rica. The influence of area, farm, host (breed, age and lactation number) and ecological factors (altitude and life zones) on the presence of lungworm infection was analyzed. A sub-sample of 924 sera collected between September 1998 and July 1999 was processed by ELISA (Ceditest). A total of 162 (17.5%) animals from 26 (93.0%) farms showed antibodies against D. viviparus. The overall seroprevalence detected among areas was Poás 25.0%, Cartago 24.3%, Tilarán 22.0%, Alfaro Ruiz 12.0% and San Carlos 12.1%. Using analysis of variance no significant influence of area and host factors on D. viviparus infections was determined, whereas the variable farm within area was highly significant (p<0.001). However, altitude and life zones showed significant association to seropositive animals, when a Chi-square test was applied. In altitudes of 1000-2000 m (p<0.001) and life zones of Lower Montane moist forest and Montane moist forest (p<0.001) D. viviparus infections in bovines were significantly higher. The results obtained in this study indicate a high D. viviparus seroprevalence in the analyzed farms and that the factors farm, altitude and life zones were significantly related to lungworm infections.     

Induction of protective immunity to Dictyocaulus viviparus in calves while under treatment with endectocides

Three groups of five parasite-naive calves were used. The treatments were: (a) Group 1 calves were weighed on Day 0 and injected with doramectin at 200 microg/kg. From Day 1 to 19 they were dosed orally with 2000 infective larvae of Dictyocaulus viviparus. On Day 28 they were again injected with doramectin, and infected with D. viviparus larvae from Days 33 to 41. They were then left untreated until Day 81 when they were infected with 20 infective larvae of D. viviparus per kg body weight. They were killed on Day 110 and lungworms were counted; (b) Group 2 calves were immunised with oral lungworm vaccine on Days 0 and 28, and infected and slaughtered as Group 1 on Days 81 and 110, respectively; (c) Group 3 calves acted as infection controls. Blood samples were taken at Days 0, 21, 49, 77 and 110 for antibody tests to D. viviparus. At autopsy there were no significant differences between the number of lungworms from Groups 1 and 2 (Means 17.4 and 31.3, respectively); Group 1 had significantly less value than Group 3 (Mean 228) (p < 0.05). Increased antibody titres to the larval sheath of the infective larvae were observed from Groups 1 and 2, showing that the larvae in Group 1 had penetrated the intestine before being killed by the circulating anthelmintic. This experiment shows that if calves are exposed to infective larvae while under systemic endectocide cover, an immune reaction is stimulated.     

A comparison of lungworm faecal larval counts and trichostrongyloid faecal egg counts between red deer (Cervus elaphus) and red deer x wapiti F1 hybrids

To determine if breed differences in susceptibility to trichostrongyloid and lungworm infection exist, two groups of weaner deer containing seven red deer and red deer x wapiti F1 hybrids were compared using faecal egg counts and faecal larval counts. All animals were run on the same pasture at the same time and treated with the same anthelmintics at the same time. Results indicated that there were significant differences between red deer and red deer x wapiti hybrids, with red deer having higher faecal lungworm counts and red deer x wapiti hybrids having significantly higher faecal egg counts. It is likely that these differences were due to breed. Differences in the efficacy of anthelmintic treatments were also noted between the two groups, with oral oxfendazole being less effective at reducing faecal lungworm counts in red deer X wapiti hybrids than red deer.     

Comparison of the persistent efficacy of the injectable and pour-on formulations of doramectin against artificially-induced infection with Dictyocaulus viviparus in cattle

The persistent efficacy of the injectable and topical formulations of doramectin was compared against experimental challenges with infective larvae of Dictyocaulus viviparus in two separate studies. Four groups of 10 randomly-assigned calves, negative for lungworm larvae by the Baermann technique, were used in each study. Calves were treated subcutaneously in the midline of the neck or poured down the midline of the back with saline (1 ml/50 kg. injection: 1 ml/10 kg. pour-on) on Day 0 or doramectin (200 microg/kg = 1 ml/50 kg. injection: 500 microg/kg = 1 ml/10 kg. pour-on) on Day 0, 7, or 14. Two additional calves from the same pool of animals were randomly assigned as larval-viability monitors and received no treatment. Calves were inoculated daily with a gavage of approximately 100 larvae of D. viviparus from days 35 to 49 for the injectable study and days 28 to 42 for the pour-on study. The two larval viability monitor calves received approximately 3000 infective larvae in the same manner on Day 49 or 42 for the injectable and pour-on studies, respectively. Equal numbers of calves from each treatment group as well as the larval viability monitor calves were necropsied on days 14 and 15 after the last lungworm inoculation to enumerate the worm burden. The worms recovered were quantified and identified. For each study, geometric mean worm recoveries for each treatment group were back transformed from the natural log-transformed data (worm count +1) and were used to estimate percentage reduction. Doramectin injectable solution was 100.0% efficacious against lungworms for up to 49 days and the pour-on formulation was 100.0%, 93.1% and 81.5% effective in reducing lungworm infection resulting from challenge infection for up to 28, 35, and 42 days post-treatment, respectively.