Small Ruminants: Clinical Parasitology Flashcards
What is the definition of anthelmintic resistance?
When a drug (anthelmintic) has lower then 95% efficacy
Name the 5 species of nematodes that commonly infect sheep?
- Nematodirus battus
- Telodorsagia circumcincta
- Trichostrongylus spp
- Haemonchosis contorsus
- Dictylocaulus filaria
How do nematodes cause disease in sheep?
- Damage lining of guts
- Remove nutrients
- Remove blood (haemorrhage)
- Host immune response
What are the generic clinical signs of nematode disease in sheep?
- Reduced appetite
- Poor weight gain/weight loss
- Diarrhoea
- Anaemia
- Death
When do the following nematodes cause disease in sheep/lambs?:
1. Nematodirus battus
2. Telodorsagia circumcinta
3. Trichostrongylus spp
4. Haemonchus contortus
- Outbreaks of acute severe diarrhoea and death in lambs 6-12 weeks old
- Type 1- lambs first grazing, mid summer onwards, Type 2- yearlings winter months, emergence of hypobiotic larvae
- Black scour- lambs or replacments late summer/autumn
- Adults and lambs- mid spring to late autumn, non regen anaemia, sudden death
Describe the basic life cycle of nematode parasites in sheep
- L1 and L2 in faeces
- L3 infective stage ingested
- L4 and mature adults develop into adults
PPP- 16-21 days
Explain this Graph
- Jan- Mar: remaining over wintered pasture larvae slowly dying off
- Feb-May: increase shedding from ewes due to Peri-parturient rise
- April: lambs start grazing and has no immunity, buidling number on pastures
- Declines over winter as lambs gain immunity
Peak of infectivity over summer
Explain this Graph
- Jan- Mar: remaining over wintered pasture larvae slowly dying off
- Feb-May: increase shedding from ewes due to Peri-parturient rise
- April: lambs start grazing and has no immunity, buidling number on pastures
- Declines over winter as lambs gain immunity
Peak of infectivity over summer
When do the following species peak?:
1. Telodorsagia
2. Trichostrongylus
3. Haemonchus
- Early summer
- Late summer
- Mid spring to late autumn
Which species of nematodes in sheep hypobiose?
Telodorsagia
Haemonchus contortus
Trichostrongylus axei
Interupted development of L4 inside sheep
How does the epidemiology of nematodirus battus differ?
- Eggs shed by lambs one year and remain on pasture to infect next year (no hypobiosis)
- Hatching occurs after period of chill
- L3 hatch en masse in spring
Some now don’t require chill, cause clinical problems in autumn
- When should a lamb have developed immunity to nematodes by?
- What influences immunity to nematodes?
- Provided the lamb is exposed to nematodes: 5-6 months
- Influenced by:
* Nutrition
* Genetics
* Stage of parturition- PPR, 2-4w before lambing, 6-8 w after, less in singles, reduced by higher protein diet
Why is nematode control a balance?
It is not possible to eliminate infections, therefore control is a balance of suficent exposure to develop immunity, but not too much to cause disease
What are the 5 groups of anthelmintic drugs?
What colour drench are each?
1- Benzimidazoles- white drench
2- Levamisole- yellow drench
3- Macrocyclic lactones- clear drench
4- Amino-acetonitrile- orange drench
5- Spiroindoles- purple drench
Each anthelmintic has a different MOA. Match the following actions to the drugs:
* Block Cl- and GABA channel paralysis
* Nicotinic cholinergic paralysis
* ACH receptors, paralysis
* Tubulin binding, prevents uptake of glucose, ovicidal
* Ganglion blocking drugs, paralysis
3- MLs: block Cl- and GABA channels paralysis
5- spiroindoles: nicotinic cholinergic paraylsis
4 ADs: ACH receptors, paralysis
1 BZs- Tubulin binding, prevents uptake of glucose- ovicidal
2 LVs- Ganglion blocking drugs, paralysis
What are the special features of BZs?
- Broad spectrum round worms
- Tape worms
- Albendazole (also fluke)
- N battus
- Some hypobiosed larvae
- Most resistance
What are the special features of MLs?
- Round worms and mites
- Moxidectin- persistent activity against telodorsagia, all injectable forms active against mange mites
What are the key factors that influence the development of anthelmintic resistance?
- Treatment frequency
- Proportion of population exposed to treatment ‘in refugia’
- Under dosing
- Biosecurity (new strains introduced)
How can anthelmintic resitance be suspected and tested?
- Clinical signs- lambs growth rates reduced, diarrhoea, death
- Test- FEC reduction (FEC reduced to 0 after drug
- Drench test- post treatment FEC check
Describe how to do a drench and FECRT test
Drench test- FEC 7-14 days post treatment
FECRT
* 10 lambs
* Weigh and mark
* Pre- treatment FEC
* Accurate dose drug
* 7-14 days post treatment
* Calculate mean reduction in FEC >95%
What other tests can specialist labs do?
- Egg hatch assay
- Larval development test
- Larval migration test
- Adult motility
- Larval feeding inhibition assay
- BZ and LV
What are the SCOPS principles?
Sustainable control of parasites
- Always make sure treatment is fully effective
- Reduce dependence on anthelmintic using managment and monitoring
- Avoid bringing in resistant worms and/or other parasites by following a robust quarantine routine. Test for anthelmintic resistance
- Minimise the selection for worms that are resistant to anthelmintics when you treat sheep
How can you make sure treatment is fully effective?
- Avoid under-dosing- pick heaviest in group, weigh and dose to heaviest (if range then sub-group)
- Check dosing gun
- Test for resistance
- Choose correct product for task
How can we make sure the correct anthelmintic is used for the task?
- Broad spectrum for nematode parasites
- Use all 5 groups- rotate through
- Quarentine/biosecurity use new classes
- Avoid combination products
- Test for resistance
When should anthelmintics be used?
Adult sheep should have immunity by the time sheep are adult (not haemonchus)
* Treat at lambing time- reduce pasture contamination for lambs, leave portion untreated (only thin, triplets etc)
* Treat at tupping time- only thin, ideally FEC first
Vaccination programme at high risk period for Haemonchus barbervax
How can reliance on anthelmintics be reduced in grazing lambs?
- Rotational grazing practices (crops, cattle, adult sheep)
- Weaned lambs move to lower risk pastures
- Good plane of nutrition (protein)
- Manage concurrent disease (coccidiosis)
- Genetic selection (EBV for resistance)
- Vaccination- haemonchus barbervax
- Target use of anthelmintics to when actually required
- Monitoring treatments- FEC, forecasts
How and when should samples be taken for FEC?
- Sample groups of lambs every 2-4 weeks
- Fresh dung less than 1 hour
- Take at least 10 individual samples per group- 10% in larger groups
- Healthy sheep- access to pasture/feed
- Random samples
- Air expelled from bag and sample cool
- Interpret according to clinical signs for sheep
Not suitable for nematodirus monitoring
How and when should samples be taken for FEC?
- Sample groups of lambs every 2-4 weeks
- Fresh dung less than 1 hour
- Take at least 10 individual samples per group- 10% in larger groups
- Healthy sheep- access to pasture/feed
- Random samples
- Air expelled from bag and sample cool
- Interpret according to clinical signs for sheep- count depends on species
Not suitable for nematodirus monitoring
Why can live weight gain monitoring be useful for anthelmintic use?
If lambs are growing at required growth rates they do not need to be wormed
What is the FAMANCHA test used for?
Pallor or eye mucous membranes in sheep for haemonchosis
Describe high, medium and low pasture risk for spring and late june
Spring:
* High- ewes and lambs last year, nematodirus carried in previous spring, store lambs previous autumn
* Medium- grazed only by adult non-lactating sheep
* Low- crops, cattle or conservation
Late June
* High- ewes and lambs in spring
* Medium- adult, non lactating sheep in spring, cattle or conservation
* Low- cattle or conservation in first half of grazing season, forage or crops
How should bought in sheep be quarentined?
- Dose- monopantel (zolvix) and/or derquantel and abametcin
- Hold off pasture 24-48 hours for treatment to work
How is the risk of selection resistance reduced when treating sheep?
- Don’t treat and move- leave a couple of days
- Only treat thin, triplet bearing and young sheep at lambing
- Avoid long acting products if possible
What is ‘in refugia’
Why does it rapidly select for resistance?
When sheep are dosed with anthelmintics when the majority of the worm population is in the sheep
Autumn, winter, early spring
What are the 3 problems with cestode infections in sheep?
- Carcass condemnations at abattoir
- Echinococcus granulosus zoonosis
- Clinical signs in sheep ‘Gid’ cysts in the brain
For the following cestodes state the primary host, intermediate host and clinical significance:
1. Monezia expansa
2. Taenia hydatigena
3. Taenia ovis
4. Taenia multiceps
5. Echinococcus granulosus
How can tapeworms in dogs be controlled?
Praziquantel every 6 weeks
What affects epidemiology of fluke?
Rain-
* increases snail habitats,
* development of fluke eggs,
* miracidium finding snails
* dispercal of carcariae from snails
Temperature
* >10 for miracidia in egg
* >10 eggs to hach and for snails
What causes either acute or chronic fasciolosis in sheep?
Acute- large numbers of metacercariae on pasture in late summer (very wet summer)
Chronic- less numbers ingested over summer and autumn
Describe the life cycle of liver fluke?
- Metacercariae ingested
- Eggs shed
- 2-6 weeks eggs to miracidium
- Miracidium hatch to snail (in 24h)
- Miracidium to cercaria emerge to be metacercaria
What causes acute fluke disease and what does acute liver disease cause?
2-6 weeks after ingestion of very large numbers of metacercariae- Sep- Dec
* Severe haemorrhages- immature stage migration
* Sudden death
* Weakness
* Pale
* Dyspnoeic
When is chronic fluke disease caused?
What is the clinical presentation?
Late autumn/winter/spring- small numbers of metacercariae ingested
* Blood feeding adults in bile ducts-
* aemorrhagic anaemia,
* hypoalbuminaemia
* Hepatic fibrosis and cholongitis
* Anaemia, weight loss, submandibular oedema, hepatomegaly, secondary clostridial disease
How can fluke be diagnosed?
- History and clinical signs
- Parasite forecasts
- PM
- Abbattoir reports
- FEC- 12 weeks post infection
- Coproantigen ELISA similar time to FEC
- Serum ELISA antibody- 2-4 weeks post infection- usefult for naive animals
- Liver enzymes, haematology- not fluke specific
What are the 5 drugs currently available to treat fluke?
- Albendazole
- Oxyclozanide
- Nitroxynil
- Closantel
- Tricalbendazole
What is the optimum time for the following drugs for fluke treatment?
Albendazole
Oxyclozanide
Nitroxynil
Closantel
Triclabendazole
- Albendazole- spring/summer
- Oxyclozanide- spring/summer
- Nitroxynil- late autumn/winter
- Clostantel- autumn
- Triclabendazole- autumn- resistance
How can fluke be avoided?
Manage environment- assess snail habitats, fence
improve pasture- drain
Biosecurity- some farms free, risk resistance. Clostantel on arrival
How can fluke be monitored?
- Inform how well drug is working
- Guide to timing of doses- Abbatoir, serum Elisa, Coproantigen, FEC
- Forecasting
- PM sudden death
- Clinical signs
How should fluke be treated in an average rainfall year in known fluke area?
What should high risk farms/years additionally do?
- Autumn against immature stages- TCBZ
- Winter immature and adults- Clos/Nitrox
- Late spring remove all adults- Alben
Additionally dose in november (TCBZ), june (TCBZ)
How can drug resistance be prevented against fluke?
Rotational use of drugs- 3 classes
Only use TBCZ when necessary- autumn
Spring dose against adults- prevent egg output
Quarantine drenching
Closatnel/Nitroxynil
Test for resistance to TCB (increasing problem)
