Anthelmintic resistance

Anthelmintic resistance: a population of worms which survive a correctly applied anthelmintic treatment

Roundworms are resistant to anthelmintics ———- sheep carry these resistant roundworms

Key points to remember:

• It is the worms that are resistant to the anthelmintic, NOT the sheep
• Resistance develops to the group, not the individual product

Resistant worms produce resistant offspring

• Leaving some sheep untreated can dilute worms which survived treatment as untreated sheep will be putting out susceptible worms too