Practical Parasite Control in Farmed Animals Flashcards
At what age are internal parasites most important?
Internal parasites are the most important production limiting disease in UK sheep systems
In beef and dairy calves (<18 months old) they are important.
In adult dairy cows they are rarely important except occasionally lungworm and liver fluke
What are the most common parasites in farmed species?
- GI Nematodes (Trichostronyles, Nematodirus battus, Haemonchus, Teladorsagia, Ostertagia, Cooperia
- Trematodes (Fasciola hepatica and Oesophagostomum)
- Coccidia (sheep and cattle)
- Lungworms (Cattle and sheep)
- Ectoparasites (Lice and Mites) – important but covered else where in the course
- Tapeworms (sheep)
What are the most clinically important GI nematodes?
GI Nematodes: Trichostronyles, Nematodirus battus, Haemonchus, Teladorsagia, Ostertagia, Cooperia
Name 2 trematodes
Fasciola hepatica and Oesophagostomum
What does trickle exposure do and to which parasites?
Sheep and Cattle develop immunity with TRICKLE exposure over time to all the following parasites (Trichostrongyles, Nematodirus battus, Teladorsagia, Ostertagia, Cooperia, Coccidia, Lungworm)
Sheep and Cattle develop immunity with TRICKLE exposure over time to some parasites.
Which parasites do sheep and cattle NEVER develop immunity to?
They NEVER develop immunity to the following Fasciola hepatica or Haemonchus contortus
What is trickle challenge?
A trickle or low infectious challenge over time allows immunity to develop without clinical signs of disease
However, a high, abrupt infectious challenge encountered over a short period of time exceeds the ‘threshold’ and causes clinical/sub-clinical disease – and can result in clinical disease
Avoiding all challenge means animals are naïve and susceptible to infection. Important to remember this when you are devising a parasite control plan for a client
What is the cycle of nematadirus in terms of seasons?
All the eggs passed the previous year require a period of cold over the winter to prime them to hatch all together over a short period of time the following spring when weather conditions are consistently over 10oC. Causing a high seasonal peak of infectious larvae on pasture in spring to infect lambs when they start to graze. Exact date depends on how far north you are (late April in Cornwall, June in Scotland). A warm spring means an earlier peak. This is predicted by climate modelling
What is the clinical disease of neamtadirus caused by?
Clinical disease is caused by the huge numbers of immature larvae attacking the gut wall causing dehydration and rapid death. This happens before they reach adulthood so often NO EGGS FOUND on faecal egg count during an outbreak of clinical disease.
Why do we see outbreaks of nematodirus in autumn now?
Winter before temperatures warm up – allowing edges to hatch, however we do now see outbreaks of Nematodirus in autumn as well – where we are getting eggs released onto pasture this year, hatching that year and seeing disease in the autumn
Weather is important to enable hatching
What drug is nematodirus still susceptible to?
Nematodirus is still susceptible to almost all of the anthelmintics so we commonly use BZ wormers to treat them which are almost useless to treat other infestations. Rare cases of BZ resistance have now been reported in Nematodirus so BZ’s may also be of little use for Nematodirus either in the future
What is shown here and what is the likely cause?
Lambs suffering from nematodirus
Dirty back end, tucking in flanks – can be quite painful! Open fleece related to dehydration you will see with these lambs
Can also result in sudden death
What age of lambs is most susceptible to coccidiosis?
What is the difference between first born lambs and the youngest lambs?
Lambs on intensive systems are at greatest risk = early lambing systems with high levels of contamination in buildings and on dirty pasture around creep feeders or water troughs. Lambs 3-12 wks old most at risk. Disease in older lambs is rare as they become immune after exposure to low numbers of oocysts.
Typically lambs born in the first half of the lambing period are only exposed to a low level of oocyst challenge and develop immunity. However, these early lambs do multiply up the oocysts in the shed or field whilst they develop immunity and the later born, youngest lambs then encounter a high challenge of infectious oocysts and suffer with clinical disease (scouring, dehydration) before they develop immunity.
How many strains of coccidiosis are pathogenic to sheep?
What does this mean?
Only 2 of the 11 Eimeria species in sheep are pathogenic so a high oocyst count is not necessarily proof of coccidiosis
How can you tell the difference between coccidia and neamtodirus infection?
Coccidia vs Nematodirus – ask where were the lambs grazing the previous year,. If grazing on land used previously – may be Nematodirus. If early lambs not appearing to have clinical disease but later lambs do – coccidiosis. Might need to treat both if cannot differentiate
What are the 2 main GI nematodes in lambs?
Teladorsagia & Trichostrongylus
When do Teladorsagia & Trichostrongylus larvae hatch?
Infectious larvae can only hatch when conditions are warm and wet enough so ewes lambing in March-May contaminate the pasture with eggs which hatch in time to infect their lambs when they start grazing.
How can disease from Teladorsagia & Trichostrongylus present?
Disease presents as either clinical or sub-clinical depending on the dose of infectious larvae ingested:
Clinical = scouring, weight loss, poor fleece quality, dull depressed, dehydrated, death!
Sub-clinical = slower weight gain (Daily Live Weight Gain (DLWG)), reduced feed conversion efficiency and reduced immunity to other infections e.g. mastitis
When do the levels of Teladorsagia and Trichostrongylus drop off and what time of year is important?
Lambing period is the most important factor in worm control as it determines if the susceptible lamb crop will overlap with a pathogenic level of infectious larvae. Level drops off in colder months. At lambing time, hypobiotic larvae with lambing and levels stress at this time – reduction in immunity, so they go and shed more eggs that they would previously
What is the problem with immunity to ewes around lambing time?
Ewes under nutritional stress around lambing lose some of the immunity they have acquired to the parasite allowing hypobiosed EL4 larvae to develop to adults and also new infections to become patent.
What is the seasonal peri-parturient egg count like throughout lambing, peak lactation?
What does this mean for the lambs born?
- Ewes under nutritional stress around lambing lose some of the immunity they have acquired to the parasite allowing hypobiosed EL4 larvae to develop to adults and also new infections to become patent.
- As ewes pass peak lactation and the nutritional stress declines they recover their immunity and kill off the parasites so their FEC falls
- This seasonal (PeriParturient) egg count rise is crucial for the parasite as it contaminates the pasture for the lambs to become infected
- Ewes under low stress (e.g. adult ewes in good BCS carrying 1 lamb) do not loose much immunity but ewes under high stress (Triplets, Low BCS, young (ewe lambs & shearlings)) are under greatest stress and will generate most of the pasture contamination
What causes parasitic gastroenteritis in cattle?
Ostertagiosis & Cooperiosis
What causes parasitic gastroenteritis in sheep?
Strongylosis & Haemonchosis
What is type 1 parasitic gastroenteritis and what causes it to occur?
Wet summers cause eggs to hatch and infect stock early and cause disease in the same season – clinical signs of scour, weight loss, low DLWG, poor feed conversion efficiency…. Very Very Very common
What is type 2 parasitic gastroenteritis and what causes it to occur?
Dry summers cause eggs to remain unhatched until autumn wet conditions at which point the infectious larvae enter hypobiosis inside the stock rather than completing development to adulthood. All the larvae emerge from hypobiosis at the same time in the spring in the gut of the animal causing severe disease, dehydration and death (Ostertagia) and anaemia (Haemonchus) – type 2 is quite rare but need to understand the epidemiology
What is the difference in sheep with regards to haemonchus contortus and other strongyles?
sheep do not become resistant in the same way as they do to other strongyles
Different to the other strongyle roundworms of sheep – blood sucker similar to the adult Liver Fluke so causes anaemia, weakness, weight loss and sub-mandibular oedema in chronic cases. Fertility, fecundity, milk yield may all be affected by the infection in the same way as any other debilitating disease
What can you use to treat haemonchus contortus in sheep?
Can also use Closantel to treat Haemonchus infections as well as the other BZ, LV & ML groups
What are the different types of disease caused by fasciola hepatica?
Different types of disease: PerAcute, Acute and Sub-acute
What is the difference between peracute, acute, sub-acute and chronic infections with fasciola hepatica?
PerAcute – Chronic is just the question of dose. The higher the infectious dose of parasite the more severe the damage and the more severe the clinical signs.
PerAcute / Acute – sudden death – diagnosis by post mortem exam (PME)
Sub-acute - rapid deterioration, dull, depressed, sometimes anaemia ….dead – diagnosis by serology/biochem and PME
Chronic – weight loss, anaemia, poor productivity, sometimes submandibular oedema only die after a long slow decline – diagnosis by FEC, coproantigenELISA
What is the cycle for fasciola hepatica – liver fluke?
- Infected sheep drop fluke eggs onto pasture which then infect mud snails
- The parasite develops in the snail and emerges to contaminate the grazing pasture for the next sheep
- These first two stages can take 5 weeks to several months depending on the temperature and moisture.
- Once a sheep has ingested the parasite it migrates from the gut to the liver and completes its development. Migration through the liver destroys liver tissue due to the immune reaction to foreign protein. The more parasites the more damage and the worse the clinical signs
- In the bile ducts the adults suck blood and starts producing eggs that are passed in the faeces. This takes 10 – 12 weeks.
- Sheep and cattle never become immune to fluke unlike they do to the roundworms so ewes and cows are as suceptable as lambs
- But liver size means that for a given dose of fluke a smaller % of liver mass is affected in ewes and cows (bigger livers) compared with lambs
Once the sheep has ingested Fasciola hepatica, where does it migrate to and from?
What causes the immune reaction?
Once a sheep has ingested the parasite it migrates from the gut to the liver and completes its development. Migration through the liver destroys liver tissue due to the immune reaction to foreign protein. The more parasites the more damage and the worse the clinical signs
How can you use non-chemical control to control parasites?
Avoid the parasite with rotational grazing
Explain what each section of this graph means with regards to anthelmintic resistance
Doesn’t suddenly occur – a slow build up process
Have those genes occurring as a random mutation in parasite, then transfers resistance over time as they are selected for – things will increase selection pressure
In green zone – don’t notice too much difference in terms of anthelmintic effectiveness and no clinical difference
Over time – resistance builds up, go into orange area, where get greater level of resistance and starting to impact on efficacy of anthelmintics and may see subclinical disease –reduction in performance
Eventually selection pressures continue, go into red zone – resistance becomes obvious, greater than 50% resistance – notice clinically that seeing reduction in efficancy of anthelmintics and reports of drenches not working – end stage
Want to try and intervene at early on and idea is that we extend the life od the products and efficacy
How can you avoid parasite burden with rotational grazing?
Lambing field, highly contaminated – we can then use other grazing lands to try and avoid this contamination, so at 3-4 weeks before lambs graze, remove from contaminated field to pre-weaning and then do the same again to post-weaning field
So basically avoiding the contamination!
Depending on if the farm ahs appropriate fields for them to do this
Can also then: Rest lambing field or cut for hay or silage or put lambs back onto it after the hay or silage aftermath
