title: Changes in the response of Haemonchus contortus eggs to the ovicidal activity of thiabendazole during the course of infection.
abstract: Hatching rates and susceptibility to thiabendazole were studied on Haemonchus contortus eggs collected after either a single, a challenge or a trickle infection of sheep with a non-resistant strain. Considerable changes were observed both in hatching rates and LC50 values for thiabendazole during the course of infection. Peaks in LC50 suggested that a susceptible strain can produce eggs at least tolerant and perhaps slightly resistant at some days pi even without any previous contact with anthelmintic. The peak obtained after a single infection was more transient than in the other cases thus suggesting that the immune response of the host may facilitate the selection of tolerant or resistant sub-populations of worms or of eggs. The inheritance of this feature was not clearly demonstrated. Nevertheless, the LC50 of a selected sub-population collected from an immune lamb and given to another lamb was higher and more constant than that of the original strain.
authors.affiliation: INRA, CR de Tours-Nouzilly, Station de Pathologie Aviaire et de Parasitologie, Unité d'Helminthologie, Monnaie, France.
authors.forename: D
authors.initials: D
authors.lastname: Kerbceuf
authors.forename: J
authors.initials: J
authors.lastname: Hubert
mesh_terms: D000818:Animals; D006188:Haemonchiasis / Q000188:drug therapy / Q000662:veterinary*; D007928:Lethal Dose 50; D010063:Ovum / Q000187:drug effects / Q000502:physiology*; D010270:Parasite Egg Count / Q000662:veterinary; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy* / Q000469:parasitology; D013827:Thiabendazole / Q000494:pharmacology*; D014252:Trichostrongyloidiasis / Q000662:veterinary*
chemical_list: D013827:Thiabendazole