title: Seasonal change in a balanced polymorphism in Haemonchus contortus populations.
mesh_terms: D000818:Animals; D010641:Phenotype; D011110:Polymorphism, Genetic; D012621:Seasons; D012756:Sheep; D012757:Sheep Diseases / Q000209:etiology*; D014251:Trichostrongyloidea; D014252:Trichostrongyloidiasis / Q000662:veterinary*