Exsheathment Phenomenon in the Infective-Stage Larvae of Haemonchus contortus

The nature of exsheathment of 3rd-stage larvae of Haemonchus contortus was investigated further using a new simplified technique for the study of cuticular ring formation. The presence of a second ring on the 2nd-stage larval cuticle, 8 to 9 µ from the anterior, is described. Exsheathing activity was observed to occur in 4 consecutive steps on isolated sheaths of H. contortus. Metabolic fluid and somatic extract of Ascaris suum and Caenorhabditis briggsae were investigated for their ability to stimulate exsheathment in H. contortus. Scanning electron microscopy revealed some aspects of the fine structure of cuticle. Exsheathing factor(s) was found to be thermostable, to require no metal ion activation, and to be active over a broad range of pH. Temperature appeared to be an important factor for the exsheathment activity.