Anthelmintic Resistance

Question 1

Most common gastrointestinal parasite of sheep in the UK

Answer 1

T. circumcincta (brown stomach worm)

Question 2

Most important gastrointestinal parasite of sheep worldwide

Answer 2

H. contortus (barber’s pole worm)

Question 3

Haemonchus lifecycle

Answer 3

L3 ingested by grazing ruminant
adult worms in abomasum
Eggs released in faeces
Molts to L3 on pasture

Question 4

Ways to measure resistance

Answer 4

Faecal egg count reduction test (FECRT)
FEC before and after treatment (efficacy <95% = resistance)

Laboratory bioassays
Expose parasites to different anthelmintics and measure response

Molecular tests

Question 5

Potential mechanisms of resistance

Answer 5

Reduced sensitivity to drug?
Change in target binding site

Reduced uptake?
Change in tegument/cuticle or amphid

Removal of drug?
Increased expression of ABC transporters (P-glycoproteins)

Question 6

Control of parasites (and resistance) in the meantime

Answer 6

Ideally, aim for a reduced reliance on anthelmintics

Question 7

Outline how to quarantine new sheep

Answer 7

1. Yard all new sheep for 24 - 48 hours
2. Treat with (4-AD and 5-SI)
3. Isolate on contaminated pasture (has been grazed
   by sheep this season) for 3 weeks

Question 8

Targeted Selective Treatment (TST)

Answer 8

Only a proportion of animals are treated
Animals performing as expected don’t require an anthelmintic

Question 9

How to measure performance in regards to targeted selective treatment

Answer 9

Famacha- selective treatment method for controlling the level of parasitic barber’s pole worm
BCS lumbar vertebrae
Growth rate

Question 10

Outline Famacha

Answer 10

It is a tool that matches the color of the eye mucous membranes of small ruminants with color chart showing 5 color categories that correspond to different levels of anemia. Category 1 represents “not anemic” with category 5 representing “severely anemic.”

Question 11

Refugia

Answer 11

free-living stages of parasite on pasture as either eggs or larvae, and parasites in untreated sheep, not exposed to anthelmintic

Question 12

Importance of maintaining the population ‘in refugia

Answer 12

Offers a means of maintaining genetic susceptibility

Question 13

Name some antihelmenthics

Answer 13

Monepantel ‘Zolvix’
Derquantel ‘Startect’
Moxidectin (3-ML)

Question 14

Fasciola hepatica also known as

Answer 14

Liver Fluke

Question 15

Fasciola hepatica treatment

Answer 15

Triclabendazole (TCBZ)