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.

Determination of Poultry Feed-Through Insecticide Activity in an In Vivo Anticoccidial Assay

The ability of an in vivo anticoccidial assay to identify potential feed-through insecticides was demonstrated using first-instar Lucilia sericata on droppings from chicks fed medicated diets. Cyromazine, a commercially available feed-through insect growth regulator, ivermectin, diflubenzuron, fipronil, permethrin, and 2 experimental compounds were effective in varying degrees in killing L. sericata larvae. Eleven coccidiostats were effective against the protozoan parasites (Eimeria spp.) at commercially used levels, whereas they were ineffective against Lucilia larvae.

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.

Efficacy of ivermectin against Syphacia obvelata (Nematoda) in mice

Ivermectin was evaluated against natural and artificial pinworm (Syphacia) infections in mice. Ivermectin given in the diet for 6 days at 0.0005% was 99% effective against both immature and adult worms. A diet level of 0.0004% reduced immature and mature pinworm by 99 and 75%, respectively but 0.0001% was inactive. One oral dose of 2.0 mg/kg was 100 and 97% effective against gravid females and immature worms, respectively. A dose of 1.0 mg/kg was 96 and 66% effective against the same parasitic stages. A similar effect was observed against adult male worms where 94 and 86% were removed by one oral dose of ivermectin at 2.0 and 1.0 mg/kg, respectively.