Efficacy of ivermectin in a beef-based chewable formulation against Ancylostoma caninum and Uncinaria stenocephala in dogs

The effective dosage of a chewable formulation of ivermectin was determined in 35 young dogs with induced infections of Ancylostoma caninum and Uncinaria stenocephala. Dogs were inoculated with these parasites and held until the infections were patent. Within each of 7 replicates, dogs were allocated randomly to 1 of 5 treatment groups: vehicle control, or ivermectin at 6, 12, 18, or 24 micrograms/kg. Chewable treatments were tailored to body weight. Seven or 8 days after treatment, parasites were recovered using standard techniques. All 7 controls had adult A. caninum (geometric mean = 35.5) and U. stenocephala (geometric mean = 82.6). Against A. caninum, the efficacy of ivermectin was 52%, 98%, 95%, and 97% at 6, 12, 18, and 24 micrograms/kg, respectively. The statistical model that best described the dose response was linear to 12 micrograms/kg with a plateau thereafter. Using this model, the estimated reduction from the predicted control mean was 97.2%; the estimated dose to eliminate 90% of the worms (ED90) was 8.4 micrograms/kg, and the ED95 was 10.5 micrograms/kg. Against U. stenocephala, the dose response was linear in the range studied, with an ED90 of 20.8 micrograms/kg; it was estimated that 93.2% of the worms would be eliminated.

Hydatid disease in a horse

During routine necropsy of a 28-year-old horse with intestinal volvulus, numerous hydatid cysts were discovered in the liver. Viable protoscolices of Echinococcus granulosus were obtained from the cyst. As a 4-year-old, this horse had been imported from an area that is enzootic for equine hydatidosis.

Differences in lipid granulation as the basis for a morphologic differentiation between third-stage larvae of Uncinaria stenocephala and Ancylostoma caninum

Differences in the distribution of lipid granules between unstained third-stage larvae of Uncinaria stenocephala and Ancylostoma caninum cultured at 15 C was found to be an effective means for differentiating these 2 species of canine hookworms. In contrast, larvae cultured at 22 C were less easily differentiated based on the distribution of lipid granules. After culturing at 15 C, third-stage larvae of U. stenocephala were motile and exhibited 32 well-demarcated intestinal cells which contained intracellular lipid granules. Intestinal cells were easily visualized due to the absence of extraintestinal lipid granulation. Ancylostoma caninum third-stage larvae cultured under similar conditions were significantly less motile and contained extraintestinal accumulations of lipid granules which obscured intestinal cells. Both species exhibited an overall decrease in lipid granulation during a 14-day observation period following culture at 15 C. Morphologic differentiation of these 2 species after 14 days was based on the absence of intra- and extra-intestinal lipid in U. stenocephala and the presence of some lipid granules in both these locations in A. caninum. The first- and second-stage larvae of both species cultured at 15 C exhibited dense accumulations of extraintestinal lipid granules and were morphologically indistinguishable. This suggests that the observed difference in lipid granulation between the third-stage larvae of U. stenocephala and A. caninum cultured at 15 C is due to differences in lipid utilization during the third stage rather than differences in lipid synthesis by the first- and second-stage larvae and is related to the adaptation of these parasites to their respective climatic regions.

Fenbendazole treatment of pregnant bitches to reduce prenatal and lactogenic infections of Toxocara canis and Ancylostoma caninum in pups

A granulated formulation of fenbendazole was tested in a total of 23 treated and control, pregnant, parasite-free Beagle bitches experimentally infected with Toxocara canis and Ancylostoma caninum. The drug was administered to each treated bitch once daily in canned dog food at a dosage of 50 mg/kg body weight. Each of 2 treatment regimens tested was initiated on the 40th day of pregnancy. One regimen involved daily treatment continuing through the 14th postpartum day, and it resulted in 89% fewer ascarids and 99% fewer hookworms in pups born to medicated bitches, as compared with pups born to unmedicated controls. The other regimen of treatment, which was stopped on the day of parturition, was less effective in reducing ascarid and hookworm burdens (64% and 88% reductions, respectively). Three to 5 bitches from each of the treatment and control groups were allowed to whelp a 2nd litter without further treatment or further exposure to parasite infections. Hookworm burdens in 2nd-litter pups born of bitches that had initially received fenbendazole through the 14th postpartum day were significantly lower (P < 0.01; 85% reduction), when compared with the 2nd-litter control pups. All other parasite burdens were not significantly different. It was concluded that granulated fenbendazole is effective in reducing burdens of Ancylostoma caninum and Toxocara canis in newborn pups when the bitch is treated during the last third of pregnancy, especially when treatment (50 mg/kg/day) extends from the 40th day of pregnancy through the 14th postpartum day.

Activity of ivermectin against canine intestinal helminths

The anthelmintic activity of ivermectin was tested in 98 dogs against adult ascarids (Toxocara canis, Toxascaris leonina), hookworms (Ancylostoma caninum, A braziliense), and whipworms (Trichuris vulpis), and against experimentally induced infections (4th-stage larvae) of T canis and A caninum. Dosage levels tested were single subcutaneous injections of 50, 100, 200, or 400 micrograms/kg of body weight with appropriate vehicle-treated controls. A minimum of 4 (usually 5) dogs were tested with each parasite and dosage level. The lowest dosage level, 50 micrograms/kg, and all higher dosage levels expelled greater than 99% of the adult forms of both species of hookworms and intestinal larval forms of A caninum, as determined by worm counts at necropsy. A dosage level of 100 micrograms/kg was required to expel greater than 99% of whipworms and 200 micrograms/kg was necessary to expel adult (91%) and larval (97%) stages of T canis. Ivermectin was only marginally effective (34.2%, 46.2%, 69.2%, and 53.8%) against Toxascaris leonina at 50, 100, 200, and 400 micrograms/kg, respectively, and had no effect against occasional infections with the tapeworms, Dipylidium caninum (14 dogs) and Taenia spp (3 dogs).

Evaluation of granulated fenbendazole as a treatment for helminth infections in dogs

A granulated formulation of fenbendazole was tested in 95 dogs harbouring naturally occurring infections of Toxocara canis, Ancylostoma caninum, Trichuris vulpis, Dipylidium caninum, and Taenia spp and in 19 laboratory-reared Beagle pups experimentally infected with Toxascaris leonina. The drug was administered in moistened dry dog food or in canned dog food. In dosage titration and confirmational studies, using worm counts in naturally infected dogs, the drug was 98%-100% effective at a dosage of 50 mg/kg of body weight/day for 3 days against the commonly occurring nematodes of dogs (ascarids, hookworms, and whipworms) and against Taenia tapeworms. A dosage of 20 mg/kg for 5 days was equally effective against nematodes, but only 73% of the dogs were cleared of Taenia tapeworms. There was no activity at either dosage against Dipylidium tapeworms. Dosages of 100 or 150 mg/kg for a single treatment and 5 or 25 mg/kg daily for 3 days were unsatisfactory with respect to nematodes and tapeworms. Induced infections of T leonina were eliminated from all treated dogs at the dosage and dosing period tested (50 mg/kg/day for 3 days). Fourteen untreated controls expelled 13% of T leonina burdens. It was concluded that granulated fenbendazole is effective in dogs against natural infections of T canis, A caninum, T vulpis, Taenia spp, and experimentally induced infections of T leonina at a dosage of 50 mg/kg of body weight/day for 3 days.

Chronic respiratory disease in a horse infected with Dictyocaulus arnfieldi

A 6-year-old Thoroughbred gelding was examined because of respiratory disease that developed after it was placed on pasture occupied by a donkey. Clinical signs in the gelding included a harsh, dry paroxysmal cough and increased expiratory effort. Eosinophils were seen in smears of mucus aspirated from the trachea and the bronchi. Immature, 5th-stage Dictyocaulus arnfieldi was identified in the tracheal mucus. The cough and other clinical signs were not diminished by corticosteroid therapy or by the administration of bronchodilators. Treatment with 10-fold therapeutic dosages of thiabendazole (440 mg/kg) on each of 2 successive days resulted in permanent cessation of the clinical signs.

Anthelmintic activity of mebendazole against induced and naturally occurring helminth infections in cats

A formulation of mebendazole was used to determine the optimal dosage level against induced and/or naturally occurring infections of Toxocara cati, Ancylostoma tubaeforme, and Taenia taeniaeformis in cats. Amounts of 11 mg/kg of body weight/day or 22 mg/kg/day were given for 2, 3, or 4 days. Feces were collected for 7 days and were examined for expelled parasites. Cats were necropsied to recover retained parasites. A regimen of 22 mg/kg/day for 3 days was determined to be optimal with efficacies of 100%, 99%, and 50% against T cati, A tubaeforme, and Taenia taeniaeformis, respectively.

Evaluation of granulated fenbendazole (22.2%) against induced and naturally occurring helminth infections in cats

A granulated formulation of 22.2% fenbendazole was tested for anthelmintic activity against helminths in cats. The drug was administered in 20 g of canned food on each of 3 days at a dosage of 50 mg/kg of body weight/day. Of 31 young adult cats harboring naturally occurring infections of Toxocara cati, 16 were treated and 15 served as controls. There was 100% clearance of ascarids from all treated cats. Among controls, 18% of the ascarid burden was expelled naturally. Thirty additional cats were acclimated for 2 months prior to infecting them experimentally with Aelurostrongylus abstrusus, Taenia taeniaeformis, and Ancylosatoma tubaeforme. Treatment caused a transitory reduction in the number of lungworm larvae. Histopathologically, cells of developing eggs and of a majority of 1st-stage larvae in lungs of treated cats had evidence of marked degeneration and necrosis, whereas the same stage of larvae in lungs of control cats were normal. Although the number of lung lesions in treated cats was approximately half the number found in controls, there was no significant (P > 0.05) indication that this was due to treatment. Fenbendazole was effective against induced infections of A tubaeforme and Taen taeniaeformis. Greater than 99.9% of hookworms were expelled from 16 treated cats as compared with a 2% natural expulsion from 15 controls. Of 24 cats that developed patent infections of Taen taeniaeformis, 12 were treated and cleared of this parasite, whereas 9 of 12 controls continued to harbor 1 to 10 tapeworms at the time of necropsy. Fenbendazole at a dosage of 50 mg/kg/day x 3 days appeared to be an effective anthelmintic against the common ascarid, hookworm, and tapeworm of cats. Its activity against lungworms was inconclusive at the dosage used, but the data suggest the need for investigating its activity against this parasite at higher dosages, for longer periods of treatment, or both.

Use of fenbendazole suspension (10%) against experimental infections of Toxocara canis and Ancylostoma caninum in beagle pups

Eleven nematode-free Beagle pups were inoculated with Ancylostoma caninum and Toxocara canis; infection became patent 13 and 35 days later, respectively. Eight pups were treated with fenbendazole oral suspension (10%) at a dosage of 50 mg/kg of body weight/day for 3 days. The remaining three animals were unmedicated controls. The drug was effective in reducing both ascarid and hookworm burdens, and there was marked improvement in the clinical condition of treated pups as compared with unmedicated control pups. Natural expulsion of worms in control animals was 53% for ascarids and 2% for hookworms. Drug-related toxicosis was not observed in any of the medicated animals. It was concluded that fenbendazole oral suspension (10%) at the 50-mg/kg dosage is easily administered and is an effective drug for reducing nematode burdens in experimentally infected pups.

Comparative effects of uredofos, niclosamide, and bunamidine hydrochloride against tapeworm infections in dogs

A single dose of a new broad-spectrum anthelmintic, uredofos, was more effective than single doses of either bunamidine hydrochloride (HCI) or niclosamide in removing natural infections of Dipylidium coninum from pound dogs, as determined by necropsy examination for scolices. The efficacy of uredofos was equal to that of bunamidine HCI and exceeded that of niclosamide in removing Taenia spp from his host. All of 12 dogs harboring D caninum and all of 5 dogs harboring Taenia spp were completely cleared of tapeworm infection following treatment with uredofos at 50 mg/kg of body weight. Bunamidine HCl cleared 9 of 11 dogs (82%) of D caninum and 5 of 5 dogs of Taenia spp. Niclosamide had the least anticestodal activity of the 3 drugs; 2 or more scolices of D caninum were found at necropsy in each of 12 dogs treated with this drug. Four of 5 dogs were cleared of Taenia spp following niclosamide therapy. Untreated control dogs did not shed tapeworms of either species during a 3-day period of posttreatment fecal collections, but did have tapeworms at the time of necropsy.

Uredofos: anthelmintic activity against nematodes and cestodes in dogs with naturally occurring infections

A new broad-spectrum anthelmintic, uredofos, was tested in 146 dogs by single and multiple oral dosing. Single doses of 100 and 50 (but not 25) mg/kg were totally effective in removing Dipylidium caninum and Taenia spp from 46 dogs with infections of tapeworms. Among groups of 15 to 20 dogs, the average percentage efficacies against Toxocara canis for single soese of 100, 50, and 25 mg/kg were 98, 96, and 81%, respectively. The average percentage of efficacies against hookworm (Ancylostoma caninum) were greater than 96% in dogs treated with single doses of 100, 50, or 25 mg/kg and were 100% in the 35 dogs given 2 or 3 treatments (24-hour intervals) at dose levels of either 25 or 50 mg/kg. The whipworm, Trichuris vulpis, was not efficaciously eliminated by single doses of 25, 50, and 100 mg/kg (av percentage of efficacies of 30, 35, and 71%, respectively). Efficacy against T vulpis markedly improved when 2 doses were given at a 24-hour interval (av percentage of efficacies were 89% at dose level of 25 mg/kg and 99% at dose level of 50 mg/kg). At either dose (25 or 50 mg/kg), 3 daily treatments were no more efficacious against whipworms than were 2 doses. There was no evidence of drug toxicosis in any dogs tested. It was concluded that uredofos is highly effective against canine tapeworms, ascarids, and hookworms when given as a single dose of 50 mg/kg and against whipworm when given at dose level of 50 mg/kg/day for 2 days.