Ancylostomatoidea Life-Cycle

Description

The life-cycle of the Ancylostomatoidea is similar to that of the Strongyloidea, involving a single (definitive) host and several environmental stages. Eggs are produced by adult hookworms in the small intestine of the definitive host (the dog or cat) and passed out in faeces, where they develop to the L3 larval stage within 2-10 days. The larvae are active in moist environments but are quickly killed by desiccation. Dogs and cats are exposed to L3 larvae present on contaminated food or environmental surfaces and the larvae may be ingested or they may penetrate the skin, the major difference between their life-cycle and that of the Strongyloidea.

Transcutaneous Entry

Larvae that enter the body transcutaneously migrate into the blood, travel to the lungs and trachea and move into the airways. The larvae are then coughed up and swallowed to complete the final stage of their development (to adults) in the small intestine. The adult hookworms use their large buccal cavities to embed their heads deep into the mucosal layer of the small intestine. Local cutaneous immunity develops quickly to hookworm larvae and, when the host reaches adulthood, the larvae are usually killed in the skin before they can reach the blood.

Oral Entry

Most ingested L3 larvae develop through the remaining stages (L4, L5 and adult) directly in the small intestine but, in the case of Ancylostoma caninum, a small proportion will migrate to distant tissues (mainly skeletal muscle and fat) via the blood and remain encysted as dormant larvae. When female dogs lactate, these somatic larvae reactivate and migrate to mammary glands where they may be transmitted to neonates for up to three weeks after parturition. It is also possible for somatic larvae to reactivate in heavily debilitated animals and return to the intestine.

Clinical Disease

For clinical disease caused by hookworms, see:

• Hookworm Dermatosis
• Ancylostoma caninum
• Uncinaria stenocephala
• Ancylostoma in myositis