Gastrointestinal nematode diseases Flashcards
How do GINs cause disease?
- Disruption of digestion and absorption
- Dehydration
- Disruption of the luminal environment
- Haematophagous GINs (H. contortus)
- Immune system response in disease
Basic Trichostrongyle lifecycle
- Eggs in dung
- 1st stage larvae in dung
- 2nd stage larvae in dung
- 3rd stage L3 larvae are infective, they migrate to herbage and wait to be eaten by a sheep
- Larvae mature and develop into adult worms (L4) in the sheep, host stage 16-21 days to complete
Effect of temperature
- Survive better in high temp
- Susceptible to cold and desiccation
Effect of moisture
- L1 and L2 develop in the faecal pat
- L3 migrate by swimming in a water film
- No water - no migration
- Desiccation kills worm larvae
Impact of host immunity
- Immune response decreases no. of worms, decreases lifespan of worms, decreases worm fecundity
- Ewe immunity, sips around parturition (2 weeks before, until 6-8 weeks after)
- Lambs gradually develop immunity to worms
- Rams never develop as good immunity
Non-chemotherapeutic tools to control GINs
- Increasing sheep resistance to infection (nutrition, vaccination, breeding worm resistant sheep)
- Decreasing sheep exposure to infection (grazing management, grow fast and sell them, bioactive forages, nematophagous fungi)
- Decreasing the impact of infection on sheep (tolerance, breeding resilient sheep)
Uses of anthelmintics
- To treat clinical disease, production losses already occurred
- To treat subclinical disease, some production losses already
- To reduce pasture contamination
- Quarantine, to prevent the import of new species/strains
How to detect treatment failure
Drench test
Submit faecal samples from 6-10 treated animals to check FEC is 0
Levamisole (yellow) - 7-10 days after treatment
Benzimidazole (white) and ML (clear) - 10-14 days after treatment
Risk factors for developing anthelmintic resistance
- Frequent dosing, use of long acting products
- Lack of unexposed worms (the refugia population)
- Under dosing
- Treatment of ewes at lambing time
Effect of withholding feed before dosing
Withhold feed for up to 24hrs prior to dosing increases the conc of BZ and ML drenches by up to 40%
The SCOPS principles
- Make sure treatment given is fully effective
- Try to reduce reliance on anthelmintics using management options
- Avoid bringing in resistant worms and/or other parasites by using a quarantine routine
- Minimise the selection of worms that are resistant to anthelmintics when you treat sheep
Targeted treatment
- Use mob pooled FECs to determine whether or not worming is necessary
- 6-10 separate, fresh, samples collected randomly
- Treat different fields as different groups
- Can use prior to mating and prior to lambing to determine the need to treat the adults as well
Selective treatment of ewes
-Twin and triplet bearing ewes shed 70-90% more worm eggs around lambing than singles
- Ewe lambs shed more eggs than ewes
- Do not treat singles, or twins/triplets that are BCS 3.5 or above
Targeted selective treatment
80:20 rule
Use growth rates as an approximation of worm burden, treat any animal less than 0.66 of target growth rate
FAMACHA scores
Scoring for H. contortus
Compare colour of inside of eyelid to test for anaemia, treat paler animals
Nematodirus clinical signs
Profuse watery diarrhoea
Dehydration
Thirst
Tucked up appearance
Usually 6-12 wks old
PGE clinical signs
Appetite suppression
Weight loss
Poor growth rates
Diarrhoea
Dehydration
Poor skeletal development
‘Open’ fleece
Reduced resistance to other diseases
Hypoproteinaemia
Death
Anthelmintic agents currently used in the UK (7)
- Benzimidazoles
- Imidazothiazoles
- Macrocyclic lactones
- Amino-aceto nitriles
- Spiroindoles
- Closantel
- Nitroxynil
Benzimidazoles
Group 1 or white drenches
Short acting only
Not effective against whip worm
Widespread resistance among T. circumcincta populations
Albendazole can be teratogenic if given during pregnancy
Imidazothiazoles
Group 2 or yellow drenches
Drench or injectable
Short acting
Only levamisole is used in farm animals
Resistance is common but less widespread than benzimidazoles
Goats very susceptible to levamisole toxicity
Macrocyclic lactones
Group 3 or clear drenches
Drench or injectable (used for sheep scab)
Resistance is common but less widespread than benzimidazoles
Avermectins (e.g. ivermectin) most common, short acting
Moxidectin (a milbemycin) is more lipid soluble so greater persistence
Amino-aceto nitriles
Group 4 or orange drenches
Monepantel is the active ingredient
Primarily a quarantine drench or if triple resistance present
Spiroindoles
Group 5 or purple drenches
Derquantel is the active ingredient
Only available in combination with ML abamectin
Primarily a quarantine drench or if triple resistance present
