The word ‘helminth’ is a general term meaning ‘worm’, but there are many different types of worms.
Prefixes are therefore used to designate types: platy-helminths for flat-worms and nemat-helminths for round-worms.
The emergent larvae undergo 4 metamorphoses (moults) before they mature as adult male or female worms.
Cestode eggs released from gravid segments embryonate to produce 6-hooked embryos (hexacanth oncospheres) which are ingested by intermediate hosts.
Adult flukes usually cause obstruction, inflammation and fibrosis in tubular organs, but the eggs of blood flukes can lodge in tissues causing extensive granulomatous reactions and hypertension.
Helminths form three main life-cycle stages: eggs, larvae and adults.
Clinical signs of infection vary considerably depending on the site and duration of infection.Worms develop slowly compared to other infectious pathogens so any resultant diseases are slow in onset and chronic in nature.