Life Cycle

The life cycle of H. contortus can be divided into three stages: The dung stage, the pasture stage and the host stage. The life cycle begins with eggs the shedding of eggs by females within the abomasum. The eggs travel through the small and large intestines and are excreted along with feces. Within the feces, the eggs hatch and 1st stage larvae are released. The 1st stage larvae will feed on bacteria and other fecal detritus and molt to 2nd stage larvae after 2-4 days. The 2nd stage larvae also fed on bacteria and feces before molting to 3rd stage larvae after another 2-4 days. Third stage larvae possess a double layered sheath (cuticle) which renders them unable to feed, thus, these larvae are dependent upon energy stores acquired during the 1st and 2nd stages. The larvae then migrate out of the feces and into the environment. The larvae are very prone to desiccation and will burrow into the soil during the day. At night and during the morning, the larvae will migrate onto pasture grasses and are ingested by grazing animals. Following ingestion, the larvae will move to the abomasum of the infected animal. There they develop into L4-stage larvae and begin feeding on host blood using a specialized buccal lancet. This process forms a small hemorrhage facilitating attachment of larvae to the mucosa. After 7 days larvae emerge from the hemorrhage as adults that copulate and produce eggs exiting the host upon defecation.