Revision practice of helminth control

Question 1

What are the control goals of anti-helmintics?

Answer 1

What are the goals?

• Prevention from clinical disease
• Immunisation (protection from large parasite burdens in subsequent pasture challenges)
• Economic aspects (increase productivity)

Question 2

What are the available options for helminth control?

Answer 2

• Biological control
• Vaccines
• Anthelmintics
• Pasture-management

Question 3

Discuss bio-concept of worm control?

Answer 3

• Duddingtonia flagrans as a “biological Anthelmintic”
• It reduces the number of infective larvae on pastures to an economically acceptable level
• Aerobic fungus, not genetically manipulated
• Broad-spectrum
• No residues, no withdrawal period
• Active against drug resistance worms
• Novel model of action ( Green Label )

Question 4

Discuss vaccines against GI-nematodes?

Answer 4

• Antigenes –> native or recombinant/synthetic
• Targets include: intestinal protein, transporters, enzymes
• Can achieve a very high protection rate
• Problems in commercial large scale production

Question 5

Discuss chemotherapy in parasite control?

Answer 5

Question 6

Discuss anthelmintic resistance?

Answer 6

• Resistance against benzimidazoles in most sheep farms
• Widespread resistance against levamisole and macrocyclic lactones
• Established by selective pressure
• Normally AR does not regress once it is established

Question 7

How to diagnose anthelmintic resistance?

Answer 7

Fecal egg count reduction test (McMaster)

• 2 faecal samples: first before and the second 7-10 day after treatment of the same animal

Larval hatch test

• In vitro culture of eggs in the presence of anthelmintic compounds

Question 8

How to McMaster count eggs?

Answer 8

Question 9

Are we facing a resistance problem?

1st count: 43,000 epg

2nd count: 3,500 epg

Answer 9

Cutoff: 95%

Calculated treatment efficacy: 92%

Yes, there is evidence for AR

Question 10

How should anthelmintic resistance be handled?

Answer 10

• Change anthelmintic classes annualy (between benzimidazoles–levamisole–macrocycliclactones)
• Farms with resistance against benzimidazoles: do not use this anthelmintic class for 5 years
• Do not underdose
• Keep the frequency of treatment as low aspossible
• No “Dose-and-Move” –> risk of selection of resistant strains
• Check the status of resistance periodically
• Quarantine teatment (suspect: check resistance status)

Question 11

Addition strategies how to handle AR?

Answer 11

• Resistant sheep breeds
• Combination therapies (Triple-/quadruple combination products in Australia and NewZealand)
• Plants with anthelmintic activity Caution: Activity may be season dependent, feed uptake and conversion, toxicity
• Animal density –> alternative grazing systems
• Refugia
  
  • Only treat animals with heavy parasite burden or showing clinical signs (UseFAMACHA ® )
  • Maintain a parasite population which is sensitive to anthelmintic treatment