General life cycle of nematodes

General life cycle of nematodes:

• Nematodes are either oviparous, ovo-viviparous or viviparous/larviparous
• The basic life cycle is very simple:

• egg→L₁→L₂→L₃→L₄→Adult

·         The life cycle either direct or indirect (1 or 2 I/H)

·         with a moult between each larval stage, usually 4 moult/ecdyses take place but in some cases one moult may be omitted.

·         Periods between moults consist of 2 phases:

•  Active/feeding phase : The larvae feed and grow
•  Inactive/lethargic phase: structural changes take place for the preparation of next moult.

·         Generally after 2^nd moult the L₃ larvae become infective to the final host & cuticle is usually retained as protective sheath.

·         Migratory worm- in most cases the larvae travel through the host tissue & finally reach to the gut

·         Non migratory worm –little migratory occurs which is limited to the intestinal wall.

·         The migratory worms whose predilection site is gut follows 2 routes-

1. Blood stream (hepatic tracheal route)
2. Lymphatic stream (lymphatic tracheal route)