Treatment and prevention of equine parasitic disease

Question 1

Current anthelmintic resistance Cyathstomes to ivermectin, moxidectin, fenbendazole and pyrantel

Answer 1

Ivermectin: emerging

Moxidectin: emerging

Fenbendazole: widespread

Pyrantel: resistant/not too bad in UK

Question 2

Current anthelmintic resistance large strongyles to ivermectin, moxidectin, fenbendazole and pyrantel

Answer 2

Ivermectin: okay

Moxidectin: okay

Fenbendazole: okay

Pyrantel: okay

Question 3

Current anthelmintic resistance ascarids to ivermectin, moxidectin, fenbendazole and pyrantel

Answer 3

Ivermectin: widespread resistance

Moxidectin: widespread resistance

Fenbendazole: anecdotal

Pyrantel: few published cases (USA)

Question 4

Treatment of clinical cases

Answer 4

▪Treat animals with clinical signs of disease

Question 5

What would you use moxidectin for?

Answer 5

• larval cyathostominosis

Question 6

What would you use pyrantel for?

Answer 6

• colic due to high Parascaris burden

Question 7

What would you use praziquantel or double the standard dose of pyrantel for?

Answer 7

• recurrent colic and high ELISA for Anaplocephala

Question 8

Prevention of larval cyathastominosis

Answer 8

▪No control strategies is a bad idea -> clinical disease given our stock densities
▪Maintenance of parasite burdens low enough to mitigate clinical signs is the goal
– strategic use of anthelmintics
– pasture management

Question 9

Pasture management

Answer 9

▪Appropriate stocking
▪Faecal collection
– Minimum of twice weekly
– Larvae do not stay in faeces or recognise electric fencing
▪Dung heaps separate from grazing area ▪Pasture rotation
– Best to rest pastures in in hot dry condition as larvae overwinter in mild winters
– Hot dry condition more likely to kill off the parasites
▪Grazing with ruminants

Question 10

Creation of refugia

Answer 10

▪Treat those with high parasite burdens (if possible)
▪Minimize pasture contamination
▪Create a large percentage of parasites not exposed to anthelmintics
▪10-20% of horses produce 80% of the eggs

Question 11

Which horses to treat – recommendations

Answer 11

▪Must be a yard wide approach
▪Treat if faecal WEC > 250epg (Based on testing every 8-12 weeks
throughout the grazing season) with ivermectin or pyrantel
▪Perform a faecal egg count reduction test after 14 days to assess efficacy of treatment
▪Treat new arrivals at yard and hold away from turn out for a minimum of 3 days (or ideally until FWEC reduction) is assessed
▪For young horses WEC are required more frequently

Question 12

Low risk factors for parasitic infection

Answer 12

• Repeated negative WEC or Tapeworm Ab levels
• Cohort negative WEC or tapeworm Ab levels
• 5-15 years of age
• Faecal collection > twice per week
• Stable population/ low stocking density
• No youngstock
• No history of colic or parasitic disease
• Effective quarantine

Question 13

Moderate risk factors for parasitic infection

Answer 13

• Low/ moderate WEC or Tapeworm Ab levels
• Cohort low/ moderate WEC or tapeworm Ab levels
• > 15 years of age
• Sporadic faecal collection
• Medium stocking density
• Occasional movement

Question 14

High risk factors for parasitic infection

Answer 14

• High WEC/ tapeworm Ab levels
• Cohort high WEC/ tapeworm Ab levels
• < 5 years of age
• No faecal collection
• Transient population/ high stocking density
• Co grazing with youngstock
• History of colic / parasitic disease
• No quarantine
• Anthelmintic resistance as documented
  by FWECRT

Question 15

Tx of low risk horses

Answer 15

▪Low risk
– No Autumn treatment
– But do require regular FEC & tapeworm ELISA in spring & autumn

Question 16

Tx of moderate/high risk horses

Answer 16

• 1 dose of moxidectin (or ivermectin) in Autumn
  – trying to remove any early L3 larvae before they become hypobiotic
• debate re moxidectin vs ivermectin
  – moxidectin will kill all stages that aren’t hypo biotic but if used for prevention, will have nothing for tx or no protection for the tx of clinical cases
  – ivermectin just kills the majority of adults and can lead to the activation of hypo biotic larvae, so can sometimes made the dz process worse

Question 17

When should you do an ELISA test for tapeworm? When to treat it? What with?

Answer 17

▪Tapeworm ELISA in spring and Autumn and treat if high Ab titre with pyrantel/praziquantel

Question 18

What risk category are most horses in the UK?

Answer 18

• moderate or high risk