Practice of helminth control

Question 1

If an animal exhibits clear clinical signs, but faecel exams are negative, why could this be?

Answer 1

• The infection could be pre patent
• Hypobiosis might occur
• Infection could be unisex

Question 2

What are immunological reasons why an animal’s parasite load might be undetectable?

Answer 2

-Serology isn’t reliable and Ab can be from past not present infections , presence of an Ag shows you the infection is current.

Question 3

What are the available helminth control options

Answer 3

• Vaccination
• Biological control
• Pasture management
• Anthelmintics

Question 4

What is the role of Duddingtonia flagrans?

Answer 4

• A biological anthelmintic
• Reduces number of infective larvae on pastures
• It is an aerobic fungus, broad spectrum, no withdrawal period, active against drug resistant worms.

(not commercialized because in can trap larvae in faeces which the animal then consumes. Also needs to be given everyday which isn’t practical)

Question 5

Describe vaccines against GI nematodes

Answer 5

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

(problem: parasite genome can be very large= makes it hard to isolate and utilise markers)

Question 6

Describe the use of chemotherapy drugs as anthalmintics

Answer 6

-Very high developmental costs
Mianstay of parasite control
-e.g. ivermectin (macrocyclic lactones or levisamole (imidazothiazoles)

Question 7

Describe anthelmintic resistance

Answer 7

• Resistance against benzimidazoles= widespread in sheep farms
• Also widespread resistance against levamisole/ macrocyclic lactonres
• Once established anthelmintic resistance doesn’t regress

Question 8

What tests can you use to detect AR?

Answer 8

• Faecal egg count reduction test (McMaster): 2 samples, one 7-10 days after treatment of the animal
• Larval hatch test: In vitro culture of eggs in presence of anthelmintic compounds

Question 9

What is the equation for McMaster egg counting?

Answer 9

Number of eggs/g faeces= (number of eggs counted x total volume (60))/ (volume of counted chamber (0.3) x weight of faeces (1))

Question 10

How can you control anthelmintic resistance?

Answer 10

• Change drug classes annually
• Farms with resistance to benzomidazoles shouldn’t use it for 5 years
• NO underdosing
• keep frequency as low as possible
• Don’t dose and move= risk selecting resistant strains

Question 11

Describe what is meant by Refugia?

Answer 11

• Strategy to handle aR
• Only treat animals with heavy parasite burden, assess using FAMACHA
• Maintains a parasite population that is sensitive to anthelmintic treatment

Question 12

Which species suffer more from AR?

Answer 12

Small ruminants (less common in cattle)