VPA 211: General Veterinary Parasitology and Helminthology (3+1)

LIFE CYCLE PATTERN OF NEMATODE

Direct life cycle

• Eggs develop and hatch outside the host. The larvae live as a free living for some time and later become infective. The infective larvae enter the host by two ways.
  • In some species the infective stage enter into the host through mouth along with feed and water. Eg. Strongylidae and Trichostrongylidae.
  • But the hookworm larvae (infective stage) enter into the host by skin penetration. Eg. Ancylostomum and Bunostomum spp.
• The development of eggs occur in the environment but eggs do not hatch outside the host (i.e., in the environment). Host getting infection by ingestion of embryonated eggs. Eg. Ascarid.

Indirect life cycle

• Eggs hatch outside the host or ovoviviparous. The larvae are free living for some time. Then enter into the suitable I/H and become infective stage. Final host acquire infection by ingestion of infected I/H or infective stage injected by the I/H while feeding. Eg. Metastrongylidae and Habronema.
• Eggs do not hatch outside the host. They hatch only after ingestion by I/H. D/H acquire infection by ingestion of I/H. Eg. Spirocerca lupi
• Viviparous in which the adult female worm directly give birth to larvae, they enter into the blood circulation of the host. From the blood it is taken up by blood sucking I/H, within the I/H the larvae become infective. The infection of final host by biting of infected I/H (by inoculation). Eg. Setaria digitata.