Efficacy of ivermectin versus dual infections of Haemonchus contortus and Heligmosomoides polygyrus in the mouse.

This report describes a novel assay for the detection of gastrointestinal anthelmintics using mice infected with Haemonchus contortus and adapted to the 1 animal/test group protocol. Mice infected with both H. contortus and Heligmosomoides polygyrus were fed ivermectin-medicated diets for 6 days. A dietary level of 0.09375 ppm was 98.1% effective against the 0- to 6-day-old abomasal stomach worm of sheep, whereas a level of 0.75 ppm reduced the 3- to 9-day-old H. polygyrus worm burden by 94.0%. H. contortus was approximately 8-fold more sensitive to ivermectin than was H. polygyrus in this model. The sensitivity of this assay rivals that of the gerbil-Trichostrongylus colubriformis model while utilizing a more economical host.

Evaluation of broad-spectrum anthelmintic activity in a novel assay against Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis in the gerbil Meriones unguiculatus.

The gerbil Meriones unguiculatus, infected with three species of nematodes, each located in a separate part of the gastrointestinal tract, provided a reliable laboratory assay for the evaluation of broad-spectrum anthelmintic activity. Gerbils harbouring 6-day-old infections of Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis were given selected broad-spectrum anthelmintics by gavage. Three benzimidazoles, thiabendazole, oxfendazole and albendazole, a tetrahydropyrimidine, morantel, an imidazothiazole, levamisole hydrochloride, a macrocyclic lactone, ivermectin and an experimental natural product, paraherquamide, were active against all three nematodes at various dosages. Trichostrongylus colubriformis was most sensitive to levamisole hydrochloride, morantel, thiabendazole and paraherquamide whereas ivermectin, oxfendazole and albendazole were more effective against H. contortus. All compounds were active against the caecal nematode T. sigmodontis although it was less sensitive than T. colubriformis. Haemonchus contortus was more sensitive than T. sigmodontis to all anthelmintics tested except thiabendazole.

The Hymenolepis diminuta-golden hamster (Mesocricetus auratus) model for the evaluation of gastrointestinal anticestode activity.

A novel laboratory anticestode assay was developed using Hymenolepis diminuta in the hamster. The commercial anticestode compounds, praziquantel, bunamidine, and niclosamide were active against patent infections of Hymenolepis diminuta in golden hamsters (Mesocricetus auratus) when given orally at 3.125, 100, and 200 mg/kg, respectively. The gastrointestinal nematode anthelmintics, cambendazole and mebendazole, were active at 50 mg/kg. Rafoxanide (fasciolicide) was active at 25 mg/kg, the lowest level tested. The coccidiostat, nicarbazin, was active at experimental levels (800 mg/kg and up). The anthelmintic-ectoparasiticide (endectocide), ivermectin, was inactive against the tapeworm at 0.5 mg/kg, as expected.

Efficacy of paraherquamide against immature Trichostrongylus colubriformis in the gerbil (Meriones unguiculatus).

Paraherquamide was 98 to 100 per cent effective against six-day-old Trichostrongylus colubriformis infections in gerbils when given as single oral doses of 1.56 mg kg-1 and above. Doses of 0.78 or 0.39 mg kg-1 were 96 and 66 per cent effective, respectively. A single oral dose of 200 mg kg-1 was well tolerated.

Use of parasite antigen detection to monitor the success of drug therapy in Dirofilaria immitis-infected dogs.

Recently the authors developed a monoclonal antibody-based enzyme immunoassay for circulating Dirofilaria immitis antigen and demonstrated its utility as a diagnostic tool for canine dirofilariasis. In the present study, serum parasite antigen measurements were used to monitor the success of thiacetarsamide therapy in 2 controlled trials that involved 24 naturally infected dogs. Parasite antigen levels correlated significantly with adult worm burdens in untreated control dogs. Antigen levels fell dramatically by 8 wk after treatment in successfully treated dogs and were undetectable 12 wk after treatment in dogs that were parasitologically cured. Microfilarial counts exhibited seasonal periodicity in both treated and control dogs and were not useful in monitoring the success of adulticide therapy. Parasite antigen detection is quite useful in monitoring the efficacy of adulticide therapy for dogs infected with D. immitis. This approach may lead to improved clinical use of thiacetarsamide, and it should facilitate evaluation of new drugs for this important infection.

Efficacy of ivermectin against third-stage Dirofilaria immitis larvae in ferrets and dogs.

Ivermectin prevented maturation of Dirofilaria immitis when given per os to ferrets at a dosage of 0 X 1 mg ivermectin per kg bodyweight two days after inoculation with third stage heartworm larvae. Similar results were found in dogs treated one day after infection at a dosage of 0 X 05 mg ivermectin per kg. No heartworm were found in the hearts and lungs of five treated dogs compared to an average of 11 worms per dog in five control animals.

Experimental Trichinella spiralis infection in the ferret, Mustela putorius furo.

Laboratory ferrets (Mustela putorius furo) were each inoculated with 500 larvae of a strain of Trichinella spiralis that had been passaged in mice for many generations. The recovery of adult worms from ferrets on Days 4 and 7 of infection represented a mean of 32% of the inoculum, with most of the worms being in the anterior three quarters of the small intestine. Larvae subsequently became encysted in the ferret musculature, with the diaphragm alone yielding as many as 5,750 larvae upon digestion. For comparative purposes, mice were each inoculated with 200 T. spiralis from the same batch of larvae. The recovery of adult worms from mice represented a mean of 54% of the inoculum. An abrupt decline in worm population, typical of infections in the mouse, was observed in both mouse and ferret hosts; in neither species had the decline begun on Day 7 of infection, but it had clearly begun by Day 11 and was essentially ended by Day 14.