PARASITOLOGY - Ovine Nematodes Flashcards
What is parasitic gastroenteritis (PGE)?
Parasitic gastroenteritis (PGE) is the condition caused by the co-infection of gastrointestinal nematodes which reside in the gastrointestinal tract of ruminant hosts
What are the general clinical signs of parasitic gastroenteritis (PGE) in sheep?
Reduced feed intake
Poor growth rates
Scour
Dehydration
Death
What is the most significant consequence of subclinical gastroenteritis (PGE) in sheep?
Subclinical parasitic gastroenteritis (PGE) in sheep results in decreased growth rates, decreased daily liveweight gain and reduced feed conversion ratio mainly due to a reduction in feed intake. This all results in poor productivity
What are the most significant nematode species which cause parasitic gastroenteritis (PGE) in sheep?
Teladorsagia circumsincta
Trichystrongylus species
Haemonchus contortus
Nematodirus battus
What is the signalement for clinical teladorsagia circumsincta?
Teladorsagia circumsincta typically causes clinical disease in grazing lambs
Where is teladorsagia circumsincta found within the ovine gastrointestinal tract?
Teladorsagia circumsincta is found in the abomasum
Describe the pathogenesis of teladorsagia circumsincta
Teladorsagia circumsincta has a very similar pathogenesis as ostertagia ostertagi in cattle
What are the clinical signs of teladorsagia circumsincta?
Reduced feed intake
Poor growth rate
Scour
Where are trichostongylus species found within the ovine gastrointestinal tract?
Trichostongylus species’ are found in the small intestine
What are the clinical signs of trichostongylus species?
Reduced feed intake
Poor growth rate
Ill thrift
Dark scour
What is the signalement for clinical haemonchus contortus?
Haemonchus contortus can cause clinical disease in sheep of any age
Where are haemonchus contortus found within the ovine gastrointestinal tract?
Haemonchus contortus are found within the abomasum
What are the clinical signs of haemonchus contortus?
Reduced feed intake
Anaemia
Ill thrift
Submandibular oedema
Ascites
What causes the anaemia, submandibular oedema and ascites associated with haemonchus contortus?
Haemonchus contortus is a blood feeding parasite which feeds on blood in the abomasal mucosa, resulting in blood loss into the gastrointestinal tract, anaemia and hypoalbuminaemia which results in decreased oncotic pressure and oedema and ascites
Where are nematodirus battus found within the ovine gastrointestinal tract?
Nematodirus battus are found within the small intestine
What are the clinical signs of nematodirus battus?
Reduced feed intake
Rapid weight loss
Ill thrift
Profuse watery scour
Dehydration
Abdominal pain
What is the general pre-patent period for ovine gastrointestinal nematodes?
The general pre-patent period for ovine gastrointesinal nematodes is 16 - 21 days
What is the minimum amount of time it takes for ovine gastrointestinal nematode eggs to develop from eggs to L3 in the environment?
Minimum 7 - 8 days
How do environmental factors influence gastrointestinal nematode larval challenge on pasture?
The larval challenge of gastrointestinal nematodes from egg to L3 larvae on pasture depends on temperaure (warm is typically better) and moisture (rain), which is required for the dispersal of L3 larvae across the pasture, as if the weather is dry, the host faeces will dry up and form a curst which traps the larvae. Furthermore, any other factors which can disturb the faeces and distribute the larvae - such as harrowing - will increase the larval challenge on pasture
What are the ideal conditions for the development of ovine gastrointestinal nematodes in the environment?
Ideal temperatures of 18 - 26°C
Humidity/moisture
Which ovine gastrointestinal nematodes undergo hypobiosis?
Teladorsagia circumsincta
Haemonchus contortus
Which conditions stimulate larvae to enter hypobiosis?
Cold and drought as these conditions would be unfavourable for larval development in th environment
What is the significance of hypobiosis in the epidemiology of parasitic gastroenteritis (PGE) in sheep?
Hypobiosis is significant to the epidemiology of parasitic gastroenteritis (PGE), particularly in ewes where the larvae resume development at lambing time and contribute to the peri-parturient rise in faecal egg count
What are the features of ovine host immunity to gastrointestinal nematodes?
Decreased fecundity (decreased egg production)
Stunting nematode growth
Limits establishment of infective larvae in the gastrointestinal tract
(T/F) Rams have decreased immunity to parasitic gastroenteritis (PGE)
TRUE.
What are the main risk factors that contribute to the seasonality of parasitic gastroenteritis (PGE) in lambs?
Peri-parturient rise (PPR)
Survival of infective larvae on pasture
What is the peri-parturient rise (PPR)?
The peri-parturient rise (PPR) is the increase in ewe faecal egg count around the time of parturition. This is thought to be due to a combination of immune suppression and nutritional stress associated with gestation and lactation. The composition of worm fauna arising from the PPR is predominantely haemonchus contortus and teladorsagia circumsincta (due to hypobiosis)
Describe the epidemiology of parasitic gastroenteritis (PGE) in sheep
In spring lambing flocks, lambs begin to graze on pasture that has been grazed the previous year by sheep. The magnitude of larval challenge is determined by over-wintering larval mortality and the peri-parturient risk (PPR) seen in the ewes. Teladorsagia circumsinta and nematodirus battus survive well over winter, however trichostrongylus and haemonchus contortus less so. Although milk predominates in the diet of young lambs, they nibble at grass from a very young age and faecal egg counts have been observed in 4 week old lambs, suggesting that ingestion of larval stages can occur in their first 2 weeks of life (think about PPP). Worm eggs deposited by lambs on pasture augment those passed by the ewes during the periparturient rise. Lambs will not yet have developed immunity and thus the larval challenge will increase due to the increased worm burden and fecundity. Development of larvae is temperature dependent and given that the ambient temperatures increase steadily from spring to summer, eggs deposited earlier in thr season will take longer to hatch and develop than those deposited later. Consequently, there is a degree of synchrony in the presence of larvae on pasture. The first wave of pasture infectivity occurs in May/June and results from the peri-parturient rise (PPR), while a second wave occurs in late summer/autumn when larvae from eggs deposited by the lambs contaminate the pasture
When is clinical parasitic gastroenteritis (PGE) most prevalent in sheep?
Clinical parasitic gastroenteritis (PGE) is most prevalent in sheep at the end of summer and start of autumn
What is the seasonal occurence of the different ovine gastrointestinal nematodes?
Nematodirus battus is typically seen in the spring
Teladorsagia circumsincta is typically seen in the summer
Haemonchus contortus is typically seen late summer and/or autumn
Trichostrongylus is typically seen in late summer, autumn and/or early winter
Which techniques can be used to monitor and diagnose parasitic gastroenteritis (PGE) in sheep?
Monitor daily liveweight gain
Faecal egg counts
FAMACHA
Serum pepsinogen
Post mortem (PM)
What are the benefits and limitations of monitoring daily liveweight gain to monitor for parasitic gastroenteritis (PGE)?
Monitoring daily liveweight gain is a very sensitive and the most rapid test for parasitic gastroenteritis (PGE), however, it is not very specific as poor growth can be caused by multiple other factors
What is essential to allow for interpretation of faecal egg counts in sheep flocks?
Grazing history
Anthelmintic history
Clinical signs
How many faecal samples should you collect to achieve representative faecal egg counts?
10 faecal samples
How many faecal samples should you collect for representative faecal egg count reduction tests?
15 faecal samples
Identify this genus of nematode eggs
Trichostrongylus eggs
Identify this genus of nematode eggs (the large brown eggs)
Nematodirus eggs
Why is it particularly important to be able to identify nematodirus eggs?
It is particularly important to be able to identify nematodirus eggs, as if you identify these eggs in spring lambs in combination with clinical signs, this is clinically significant nematodirus
What the benefits of faecal egg counts for parasitic gastroenteritis (PGE)?
Cheap
Easy
Good indicator of pasture contamination
Can be used to demonstrate anthelmintic efficacy
Can be used to determine pattern of infection on individual farms
Faecal egg count reduction tests (FECRT)
Nematodirus battus diagnosis
What the limitations of faecal egg counts for parasitic gastroenteritis (PGE)?
Requires training
Not representative of total worm burden (except for haemonchus contortsus which has a linear relationship between faecal egg counts and worm burden)
Which post mortem features can be indicative of teladorsagia circumsincta?
Swirling abomasal contents
Abomasal glandular hypertrophy
Small brown worms
Which post mortem features can be indicative of haemonchus contortus?
Pallor
Ascites
Swirling abomasal contents
‘Barber pole’ worms
Which post mortem features can be indicative of nematodirus battus?
Small intestinal inflammation and mucosal thickening
Thin white worms
What is FAMACHA?
FAMACHA is a chart used to assess conjunctival colour as a means to determine the severity of anaemia and the requirement for treatment of haemonchus contortus
What can be done to control the peri-parturient rise (PPR) of faecal egg count in ewes?
Improve nutrition
Selective breeding for resistance and resilience
Grazing management
Anthelmintic management (targeted selective treatments based on BCS or number of foetuses can be useful)
Which grazing management techniques can be useful to control the peri-parturient rise (PPR) of faecal egg count in ewes?
Mixed grazing
Grazing on freshly sown grass pasture
What are the advantages and disadvantages or treating pregnant ewes with long acting anthelmintics?
Long acting treatment of ewes can reduce need to treat lambs, but can increase risk of anthelmintic resistance developing, due to a long tail off when the drug is at sub-therapeutic levels and sub-therapeutic transmission of drugs to lambs in the milk
What can be done to control gastrointestinal nematodes in lambs?
Grazing management
Anthelmintic management
Improve nutrition
Selective breeding for resistance and resilience
Which grazing management techniques can be useful to control gastrointestinal nematodes in lambs?
Mixed grazing
Grazing with dry adult ewes
Grazing on freshly sown grass pasture
What is resistance?
Resistance is the host’s ability to limit the establishment, development, fecundity and longevity of parasite populations
What is resilience?
Resilience is the host’s ability to perform adequately with parasitic challenge that would adversely affect non-resilient animals. Resilient hosts can harbour significant parasite burdens
What are the limitations of selective breeding for resistance and resilience?
Takes a long time
Labour intensive
Resistant animals often have decreased productivity
Resilient animals have a high worm burden and a high enough larval challenge will eventually result in clinical disease, even in resilient animals
What is the main risk of routine anthelmintic treatment of lambs?
Routine anthelmintic treatment of lambs promotes the development of anthelmintic resistance in gastrointestinal nematodes due to the excessive exposure to anthelmintics
What is strategic anthelmintic treatment?
Strategic anthelmintic treatment is the treatment of groups of animals during housing or early in the grazing season to limit pasture contamination with eggs and hance reduce the risk of parasitism
What is the main risk of strategic anthelmintic treatment of lambs?
Strategic treatment increases the pressure for development of anthelmintic resistance because there are low numbers of nematodes on pasture, so a low proportion of nematodes are left unexposed to anthelmintic (in refugia) to provide susceptible genes to dilute those of the resistant nematodes that survive treatment
What is the main risk of therapeutic anthelmintic treatment?
Therapeutic treatments allows significant losses in daily live weight gain to accumulate before treatment is given, resulting in decreased productivity. Furthermore, there is an increased risk of clinical parasitic gastroenteritis (PGE) which increases emergency call outs to farms
What are targeted selective treatments (TST) with anthelmintics?
Targeted selective treatment (TST) is treatment of individual animals with anthelmintics when monitoring daily liveweight gain indicates subclinical infection and loss of performance
What are the five groups of anthelmintics available for parasitic gastroenteritis (PGE) in sheep?
White drenches (Benzimidazoles)
Yellow drenches (Levamisole)
Clear drenches (Macrocyclic lactones)
Orange drenches (Amino-acetonitrile derivatives)
Purple drenches (Paraherquamide derivatives)
Which anthelmintics are ineffective against hypobiotic larvae?
Fenbendazole
Mebendazole
Yellow dreches (Levamisole)
Which anthelmintic drug has a low therapeutic index?
Closantel
Overdosing closantel can lead to blindness and death
Which nematode does closantel treat?
Haemonchus contortus
What is pseudo-targeted treatment of nematodirus battus with benzimidazoles?
Benzimidazoles are used for Nematodirus battus as a pseudo-targeted treatment due to resistance to this group of anthelmintics in other common sheep nematodes. There are growing pockets of the UK that have strains of nematodirus battus with resistance to benzimidazoles, but the majority of the country can still use these treatments effectively
What are the routes of administration available for anthelmintics in sheep?
Injection
Oral
Topical (pour-on)
Why is injection not a commonly used route of administration for anthelmintics?
Injecting anthelmintics can risk damage to the carcass
Why are pour-on anthelmintics not very effective in sheep?
Pour-on anthelmintics are not very effective in sheep as there is often poor absorption and underdosing due to the wool impairing contact of the drug to the skin
