11.3.2: Dealing with parasitic gastroenteritis (PGE) Flashcards
True/false: in pet ruminants such as camelids and goats, endoparasites tend to cause mild disease.
False
* In these ruminants endoparasites can often cause very severe disease. This is both because of the management of these animals by smallholders, and the inherently susceptible nature of the species to parasites.
* Camelids are inherently very susceptible as they are evolutionarily used to high altitudes and low stocking densities where there is minimal parasitic challenge.
After the first grazing season, cattle and sheep will develop immunity to most endoparasites. What are the exceptions to this?
- Fluke (sheep and cattle)
- Haemonchus (sheep)
- With lungworm (cattle) immunity in short-lived
True/false: internal parasites are considered a minor problem in most UK sheep systems.
False
Internal parasites are considered the most important production-limiting disease in the UK sheep system.
Which endoparasites cause PGE in cattle and sheep?
GI nematodes (roundworms)
* Trichostrongylus
* Teladorsagia
* Nematodirus battus
* Haemonchus
* Ostertagia ostertagi
* Cooperia oncophora
* (Trichostrongylus axei)
The life cycle of which parasite is shown here?
Nematodirus
Which presents more of a challenge: trickle, low level infectious challenge, or abrupt high infectious challenge? Why is this the case?
- Trickle, low level infectious challenge over time allows immunity to develop without clinical signs of disease
- Abrupt, high level infectious challenge encountered over a short period of time exceeds the threshold and causes clinical/subclinical disease
- Avoiding all challenge means the animals are naïve and susceptible to infection
True/false: a worm control programme should centre around total elimination of the given parasite.
False
Worm control programmes are about reducing worm burdens to levels that can be tolerated without causing disease.
This diagram shows some parasitic causes of diarrhoea in sheep. What cause(s) is represented by 1?
Coccidiosis and Cryptosporidium
This diagram shows some parasitic causes of diarrhoea in sheep. What cause(s) is represented by 2?
Nematodirus
This diagram shows some parasitic causes of diarrhoea in sheep. What cause(s) is represented by 3?
Teladorsagia and Trichostrongylus
What parasites can cause diarrhoea in sheep?
- Coccidiosis/cryptosporidium
- Nematodirus
- Teladorsagia and Trichostrongylus
Describe the life cycle of Nematodirus battus and relate this to climatic conditions
- Atypical trichostrongyle life cycle
- Preparasitic phase (L1-L3) occurs within egg shells
- Eggs shells are resistant to freezing and drought, viable up to 2 years on pasture
- Hatching is stimulated by cold period followed by a mean day/night temperature (~10C) but L3 are susceptible to climate and need to be ingested quickly
- This is the first species to peak on pasture in spring
Which stage of the Nematodirus life cycle causes pathology and how?
- Large number of larvae simultaneously burrowing into the gut cause pathology (this is the larvae not adult)
- Huge numbers of immature larvae attacking the gut wall causing dehydration and rapid death
True/false: N. battus can cause disease twice in the same year.
True
* Some eggs deposited in spring can hatch in the autumn of the same year, causing contamination of pasture at this time.
* This indicates that some populations of the parasite have evolved to hatch without needing a winter cold period to prime them (this is still uncommon.
What times of year do we see disease caused by N. battus ?
- Disease is seen in spring (April, May, then into June)
- Disease is also seen in autumn (September, October) when eggs deposited in spring hatch in the autumn of the same year
True/false: Nematodirus is transmitted from ewes to lambs each year.
False
* Nematodirus is transmitted from lamb crop to next lamb crop the following year
What constitutes a risk pasture for Nematodirus?
- Risk pasture = areas that lambs grazed the year before.
- Nematodirus can sometimes survive 2 years on pasture, but there is relatively low risk of this.
What will a warm spring mean for Nematodirus ?
- Warm spring = earlier peak in Nematodirus as eggs hatch when weather warms
True/false: egg counts are a good way to assess Nematodirus battus. Explain why/why not.
False
* Disease happens before the worms reach adulthood
* Often there are no eggs found during an outbreak of clinical disease
* Therefore, we cannot rely on egg count to guide the timing of treatment; need to consider history and risk factors, SCOPS parasite forecasts
How can we treat/control Nematodirus ?
- Nematodirus is still susceptible to almost all the anthelmintics
- Use benzimidazoles (white drench)
What parasite’s life cycle is shown here?
This is the life cycle of Teladorsagia and Trichostrongylus.
What are the main GI nematodes in lambs?
Teladorsagia and Trichostrongylus
When might we need to use routine worming for Teladorsagia and Trichostrongylus in adult sheep?
Around lambing (we see a periparturient relaxation in immunity)
We might also see disease in adult sheep with iceberg diseases.
This image highlights the risk periods for certain parasites - which ones?
Teladorsagia and trichostrongylus
What impact does temperature and weather have on Teladorsagia and Trichostrongylus?
- These parasites are very weather-dependent
- Temperature influences how quickly eggs develop
- Rainfall influences how well the larvae can infect sheep
- With warm, wet summers, it becomes hard to rule out disease at any time of year
True/false: we need to preventatively worm all adult sheep on at-risk pastures for Teladorsagia and Trichostrongylus.
False
We should not need to routinely worm adult sheep for these species (except around lambing time due to PPRI)
What are the clinical signs of Teladorsagia/Trichostrongylus infection?
- Scouring
- Weight loss
- Poor fleece quality
- Dullness
- Depression
- Dehydration
- Death
- Signs may also be subclinical: reduced DLWG, reduced FCR, reduced immunity to other infections
DLWG: daily live weight gain
FCR: feed conversion ratio
Why is there high infectivity in mid-summer for Teladorsagia/Trichostrongylus?
- Eggs are deposited by lambing ewes in early spring - these take 10-12 weeks to develop into L3
- Eggs are deposited by lambs in summer - these take 1-2 weeks to develop into L3
If ewes are not wormed for Teladorsagia/Trichostrongylus around lambing, they can suffer loss of immunity and therefore generate pasture contamination through parasite eggs. Which ewes will suffer the greatest loss in immunity and therefore generate the most pasture contamination?
- Ewes under low stress (e.g. adult ewes in good BCS carrying 1 lamb) do not lose much immunity
- Ewes under high stress (triplets, low BCS, young i.e. ewe lambs and shearlings) are under greatest stress and will generate most of the pasture contamination
Where is Haemonchus contortus found in the UK?
- Common in SE
- Creeping further N
Haemonchus contortus
What groups of anthelmintics are there?
- Group 1 - Benzimidazoles (BZ) - White
- Group 2 - Levamisoles (LZ) - Yellow
- Group 3 - Macrocyclic lactones (ML) - Clear
- Group 4 - ‘Zolvix’, monepantel - Orange
- Group 5 - ‘Startect’ dual active product containing derquantel and abamectin - Purple
What are our aims when designing a GI parasite management plan?
- Good productivity/profitability i.e. fast growth, high milk yield, high fertility
- Good immunity where possible rather than relying on treatment
- Sustainability - continued efficacy of anthelmintics and delaying the development of resistance to products
How can we reduce dependence on anthelmintics?
- Genetics: useful for breeding flocks
- Grazing management: reserve low-risk pasture for lambs, put older/ immune ewes onto higher risk pasture
- Bioactive forage (chicory) - may combat parasitism or simply improve nutrition - jury still out
When it is a good idea to to try and kill all the parasites in an animal? How would you go about this?
As a quarantine protocol (don’t want to bring resistant parasites onto farm) and in autumn (late/ end of grazing season) to get rid of any resistance that has built up over summer.
* Usually do this with a flukicide + macrocyclic lactone
Describe the resistance present to different groups of anthelmintics
What is a selection event and how is this relevant to parasite control?
- The more you treat with anthelmintics, the more selection events given to the parasite
- Only expose the minimum number of parasites to a selection event by targeting your treatment to only those animals that need it
- “In a flock there are 80% of the worms in 20% of the sheep”
What is an in-refugia population and why is this important?
- It is a good idea to maintain an in-refugia population of worms that is not exposed to treatment
- This population includes those free-living on pasture and adults/ immature worms in untreated sheep
- This population will dilute the eggs produced by anthelmintic resistant worms
- This is the reason that whole flock/ whole group treatments are discouraged
What effect does a “dose and move” strategy have on the livestock, the pasture and its parasite population?
What effect dose “dose, delay, move” strategy have on the pasture and its parasite population?
This strategy means we always end up with some susceptible worms on the new pasture.
(This is a good thing, think in refugia population).
What effect does a part flock treatment / targeted strategic treatment have on the pasture and its parasite population?
This strategy means we always end up with some susceptible worms on the new pasture.
(This is a good thing, think in refugia population).
How should we decide when the appropriate time to treat with an anthelmintic is?
- Use pooled (mob) FEC
- Use regular FEC to track the rise and predict when treatment is appropriate
- The only exception is N. battus - this causes prepatent disease i.e. lambs dying before egg count rises, so treat for this parasite based on risk rather than FEC.
How should we decide who the appropriate animals to be treated with an anthelmintic are?
Targeted selective treatment (“as little as possible, as much as necessary”
* Use DLWG to work out at any given age of lamb/ calf which are underperforming and would potentially benefit from treatment
What are the different effects of various worm egg counts and what do they represent?
FEC represent what the worms were doing ~3 weeks ago. Consider what the weather has been like since and if levels of infective larvae are likely to have risen during that time.
Describe the DLWG you would expect from lambs at each stage from spring to winter
How often should you monitor FEC and DLWG in order to assess if worming is needing?
Every 3-4 weeks
How can you assess if there is resistance to the worming product being used?
Faecal egg count reduction test OR drench testing
What principles of grazing management can you use to reduce worm burdens?
- Weaning: move lambs to low risk pasture/ less contaminated areas at weaning (e.g. silage aftermath)
- Co-grazing: reduce stocking density of host species.
- Nutrition: good nutrition will minimise adverse effects of parasitism.
- Grazing by cattle/ mature ewes will hoover up larvae
Describe how to carry out drench testing
Drench testing = post-dosing FEC
* FEC pre-dosing
* FEC sample 7-14 days later (7 days for Levamisoles, 14 days for macrocylic lactones or benzimidazole)
* Result is an indicator of anthelmintic efficiency
* Would expect a 95% reduction if all well
Describe how to carry out FERCT
- Individual samples pre and post drenching
- Choose lambs with a high starting FEC (>500 epg)
- Split into 3 groups and worm each with a different class (BZ, LV, ML)
- Resample same lambs in 7-14 days
- Less than 95% reduction in FEC = resistance
- Less than 50% reduction in FEC = obvious drench failure
What drives resistance? How do we prevent this?
- Buying in resistant worms
- Under-dosing individuals
- Over-treating the population
- Allowing resistant worms the chance to dominate
Prevent this with:
1. Quarantine treatment for purchased stock
2. Dose for the heaviest in the group and calibrate equipment.
3. Minimise number of treatments (base treatment decision on FEC, DLWG, TST)
4. Administer the correct (narrow spectrum) product correctly
5. Dilute any resistant worms (in refugia population)
6. Use non-chemical means of control (inc clean grazing)
What parasites cause PGE in cattle? Which cattle are affected?
Ostertagia ostertagi (abomasum)
Cooperia oncophera (small intestine)
Disease generally only seen in young cattle during their first grazing season.
1
2
3
4
How long does it take cattle to form immunity to parasites that cause PGE and what could affect this?
Cooperia oncophera - one full grazing season
Ostertagia ostertagi - up to two full grazing seasons
- If we use sustained boluses throughout the grazing season, we can leave the animals without any exposure and therefore immunity to the parasites
How does the immunity formed by spring vs autumn born sucklers differ and why is this?
- Spring born sucklers - will be on dams for spring and summer so not exposed to many parasites in their first season; they are naïve and more at risk in their second season
- Autumn born sucklers - will be at risk of and exposed to parasites in their first grazing season
Describe the trends shown here
Type 1 Ostertagiasis
Type 2 Ostertagiasis
How should you worm cattle who are likely to remain on the same pasture for Ostertagia ostertagi?
(Advisable to do FEC, look at DLWG data to make an informed decision)
If cattle remain on the same pasture:
Strategic treatment (limit contamination of pasture)
* Within 3 weeks (PPP) of turnout then minimise contamination up to mid-July
* Could use long acting injection or bolus formulation at turnout -> this means larger population of parasite exposed to this, risks leaving cattle naïve at next season (must justify this if you do it!)
* Could use ML with shorter persistence (3-6 weeks) then repeat at 6-8 weeks
Type 2 - worm at housing with ML to remove inhibited O. ostertagi
* This removes the risk of Type 2 Ostertagiasis
* This also means that cattle will not immediately contaminate pasture with worm eggs the following year at turnout
We should NOT worm adults at housing routinely (should be risk-based) however this is still done in practice.
Which anthelmintic is effective against hypobiosed Ostertagi?
Macrocyclic lactones
How to make a parasite control plan for a farm
- There is no specific blueprint - needs to be farm specific
- Take a detailed history of the flock and herd management practices
- Identify disease threats (list all major parasites and rank in order of priority and chronology)
- Consider different risk periods in the year, the farm system, and non-chemical methods of control
- e.g. Nematodirus - use forecasts to allow strategic prophylactic treatment based on predicted larval peak. FECs not usefu.
- e.g. Trichostrongylus and teladorsagia - regular routine FEC and DLWG monitoring; treatment only at threshold epg (TST) is most effective to prevent disease and minimise resistance
