Anthelmintic Resistance Flashcards
(27 cards)
What are the main NEMATODE causes of ovine PGE in Britain? (most common)
- H eamonchus contortus
- O stertagia [Teladorsagia] Circumcincta
- T richostrongylus Spp
- C ooperia spp
- Nematodirus Battus
Which species other than nematodes may cause ovine PGE in Britain? (less common)
- Nematodirus spp
- Oesophagostamum venulosum
- Chabertia ovina
- Bunostomum trigonocephalum
- Strongaloides papillosus
What are the main NEMATODE causes of bovine PGE in Britain?
Ostertagia ostertagi
Which species other than nematodes may cause bovine PGE in Britain? (less important)
- Cooperia spp
- Trichostrongylus spp
- Nematodirus helvetianus
> Lungworm also important (Dictyocaulus viviparous)
Give the main lungworm of cattle
Dictyocaulus viviparous
What are the most important horse worms?
Strongyles (redworms)
How are strongyles grouped?
Based on SIZE and LIFECYCLE > Migratory (Large) - S vulgaris, S edentates, S equinus > Non-migratory (Large) - Triodontophorus spp > Non-migratory (Small) - Cyathostomins (=trichonemes) [4 genera, 40+ spp] - Poteriostomum, oesophagodontus
Why are worm control STRATEGIES necessary?
- treatment fialures due to innapropriate product use and application
- resistance increasing
Why may worming treatments fail?
- Underdosing (estimating body weight, maintainence of equipment, poor technique, failing to follow manufacturers instructions)
- Incorrect drug for target worms
- Re-introducing animals to heavily contaminiated pasture
- Resistance
How is anthelmintic resistance spread through a population?
- Individual able to tolerate doses which are noramllyl lethal due to resistance alleles pre-existant in worm population
- this is heritable
- resistance develops slowly at first than more rapidly as allele frequency ^
What drench is most commonly resistant?
BZ (White)
Which broad spec anthelmintics have least resistance?
Aminoacetonitrite derivatives [4] and spiroindoles [5]
Which species has most reports of resistnace?
Sheep
Cows not so much
Which species are most resistant to ML?
Cooperia
What is the most likely cause of resistnece developing?
Underdosing pour on treatments
What drug most commonly shows resistance in horses?
Benzimidazole for cyathostomins (UK and wordwide)
Which horse worms are rarely seen nowadays?
Large strongyles
Why is the clinical onset of resistance an indicator of worse problems underlying the population of parasites?
Alleles are recessive so by the time a clinical problem is detected it is likely that resistnace genes are wide spread in the population
At what stage of allele frequency is there likely to be clinical failure of the anthelmintic?
allele freq 50% (resistant parasites >25%)
Give 2 in vivo tests that may measure resistence
DT (Drench test) or WT (Wormer test)
FECRT (Feacal Egg Count Reduction test)
Give 3 in vitro tests that may measure resistance
Lab-based larval development assays eg.
- LDT (larval development test)
- EHT (egg hatch test)
- LMIT (larval migration inhibition test)
Are in vivo or in vitro tests more common?
> In vivo
X in vitro = time and money X
Outline the drench test
- FEC 10 faecal samples post anthelmintic treatment
- time after treatment depends on drench used
> LV: 7d
> BZ: 10-14d
> ML: 14-16d - snapshot of how many worms have survived the treatment; no way of knowing whether initial worm numbers were high, with small amount of resistance or low, with high resistance
Outline the faecal egg count reduction test
- estimate efficacy by comparing FEC before and after, with UNTREATED controls
- resistnace indicated if FEC not reduced by >95%
- 5 animials per group
- all given different treatments
> allows you to prioritise use of specific successful treatment
> more expensive and time consuming
