Morphological characterization of the stage of arrested development of Haemonchus contortus in sheep

Abstract

During autumn and winter, early fourth-stage larvae of Haemonchus contortus were recovered from sheep autopsied at least 21 days postinfection. The development of these larvae was arrested at a precise stage. Comparison of these larvae with normally developing parasites indicated that development of the males was suspended at a stage equivalent to 3 to 4 days postinfection, with no differentiation of the genital primordium apparent. The females were arrested at a slightly later stage, with some sexual maturation evident. Conspicuous crystals were observed within the intestinal cells of the arrested larvae. These inclusions varied considerably in size and number; they disappeared as the larvae recommenced development, and passed the fourth molt in spring.