AN IN-VIVO DOSE-RESPONSE STUDY OF FENBENDAZOLE AGAINST OESOPHAGOSTOMUM-DENTATUM AND OESOPHAGOSTOMUM-QUADRISPINULATUM IN PIGS

A dose-response study using fenbendazole (FBZ) was carried out in pigs infected with O. dentatum and O. quadrispinulatum to determine the mi nimum effective dose rate of the drug. Thirty pigs were randomly divid ed into 6 groups of 5 pigs and infected with 5000 infective larvae eac h. The animals were re-infected 5 days before treatment (Day 30 after the first infection) with the same number of larvae, On Day 35 the pig s in groups 1-5 were treated with FBZ at the following dose rates: 2.5 mg kg(-1) (i.e. 50% of the registered dose level), 1.0 mg kg(-l) (20% ), 0.25 mg kg(-1) (5%), 0.1 mg kg(-1) (2%) and 0.05 mg kg(-1) (1%), re spectively. Pigs in group 6 served as non-treated controls. Seven days after treatment (Day 42 after infection) the pigs were slaughtered, w orms recovered from the large intestine and counted. The species and s ex of adult worms was determined, A high faecal egg count reduction (F ECR) after treatment was observed in groups 1, 2 and 3 (98%, 88% and 9 1%, respectively), while in groups 4 and 5 the egg counts were not aff ected by treatment. The mean worm count reduction was high in groups 1 , 2 and 3 (100%, 99.9% and 98.6%, respectively), but declined in group s 4 and 5 (77% and 40%, respectively). FBZ showed a high efficacy agai nst immature worms in groups 1 and 2, while in groups 3, 4 and 5 count s were not reduced. Species differentiation revealed a higher effect o f FBZ against O. dentatum than against O. quadrispinulatum. Sex differ entiation indicated a slightly higher (not significant) efficacy again st females than males in both species. This study demonstrated a high efficacy of FBZ against the nodular worms in pigs, even at 5% of the c urrently registered dose level. (C) 1997 Australian Society for Parasi tology. Published by Elsevier Science Ltd.