PARASITOLOGY - Ovine Nematodes

Question 1

What is parasitic gastroenteritis (PGE)?

Answer 1

Parasitic gastroenteritis (PGE) is the condition caused by the co-infection of gastrointestinal nematodes which reside in the gastrointestinal tract of ruminant hosts

Question 2

What are the general clinical signs of parasitic gastroenteritis (PGE) in sheep?

Answer 2

Reduced feed intake
Poor growth rates
Scour
Dehydration
Death

Note the faecal staining

Question 3

What is the most significant consequence of subclinical gastroenteritis (PGE) in sheep?

Answer 3

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

Question 4

What are the most significant nematode species which cause parasitic gastroenteritis (PGE) in sheep?

Answer 4

Teladorsagia circumsincta
Trichystrongylus species
Haemonchus contortus
Nematodirus battus

Question 5

What is the signalement for clinical teladorsagia circumsincta?

Answer 5

Teladorsagia circumsincta typically causes clinical disease in grazing lambs

Question 6

Where is teladorsagia circumsincta found within the ovine gastrointestinal tract?

Answer 6

Teladorsagia circumsincta is found in the abomasum

Question 7

Describe the pathogenesis of teladorsagia circumsincta

Answer 7

Teladorsagia circumsincta has a very similar pathogenesis as ostertagia ostertagi in cattle

Question 8

What are the clinical signs of teladorsagia circumsincta?

Answer 8

Reduced feed intake
Poor growth rate
Scour

Question 9

Where are trichostongylus species found within the ovine gastrointestinal tract?

Answer 9

Trichostongylus species’ are found in the small intestine

Question 10

What are the clinical signs of trichostongylus species?

Answer 10

Reduced feed intake
Poor growth rate
Dark scour

Question 11

What is the signalement for clinical haemonchus contortus?

Answer 11

Haemonchus contortus can cause clinical disease in sheep of any age

Question 12

Where are haemonchus contortus found within the ovine gastrointestinal tract?

Answer 12

Haemonchus contortus are found within the abomasum

Question 13

What are the clinical signs of haemonchus contortus?

Answer 13

Reduced feed intake
Anaemia
Ill thrift
Submandibular oedema
Ascites

Question 14

What causes the anaemia, submandibular oedema and ascites associated with haemonchus contortus?

Answer 14

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

Question 15

Where are nematodirus battus found within the ovine gastrointestinal tract?

Answer 15

Nematodirus battus are found within the small intestine

Question 16

What are the clinical signs of nematodirus battus?

Answer 16

Reduced feed intake
Rapid weight loss
Ill thrift
Profuse watery scour
Dehydration
Abdominal pain
Sudden death

Question 17

What is the general pre-patent period for ovine gastrointestinal nematodes?

Answer 17

The general pre-patent period for ovine gastrointesinal nematodes is 16 - 21 days except nematodirus which is 14 days

Question 18

What is the minimum amount of time it takes for ovine gastrointestinal nematode eggs to develop from eggs to L3 in the environment?

Answer 18

Minimum 7 - 8 days

Question 19

How do environmental factors influence gastrointestinal nematode larval challenge on pasture?

Answer 19

The larval challenge of gastrointestinal nematodes from egg to L3 larvae on pasture depends on temperaure (warm is typically better, however T. circumcinta can survive at cooler temperatures and even survive freezing) 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 crust 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

Question 20

What are the ideal conditions for the development of ovine gastrointestinal nematodes in the environment?

Answer 20

Ideal temperatures of 18 - 26°C
Humidity/moisture

Question 21

Which ovine gastrointestinal nematodes undergo hypobiosis?

Answer 21

Teladorsagia circumsincta
Haemonchus contortus

Question 22

Which conditions stimulate larvae to enter hypobiosis?

Answer 22

Cold and drought as these conditions would be unfavourable for larval development in the environment

Question 23

What is the significance of hypobiosis in the epidemiology of parasitic gastroenteritis (PGE) in sheep?

Answer 23

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

Question 24

What are the features of ovine host immunity to gastrointestinal nematodes?

Answer 24

Decreased fecundity (decreased egg production)
Stunting nematode growth
Limits establishment of infective larvae in the gastrointestinal tract

Question 25

(T/F) Rams have decreased immunity to parasitic gastroenteritis (PGE)

Answer 25

TRUE.

Question 26

What are the main risk factors that contribute to the seasonality of parasitic gastroenteritis (PGE) in lambs?

Answer 26

Peri-parturient rise (PPR) Survival of infective larvae on pasture

Question 27

What is the peri-parturient rise (PPR)?

Answer 27

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)

Question 28

Describe the epidemiology of parasitic gastroenteritis (PGE) in sheep

Answer 28

The magnitude of larval challenge is determined by over-wintering larval mortality and the peri-parturient rise (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 the 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. Because of this, the risk of clinical PGE increases during summer/early autumn due to the increased larval challenge and infection pressure

Question 29

When is clinical parasitic gastroenteritis (PGE) most prevalent in sheep?

Answer 29

Clinical parasitic gastroenteritis (PGE) is most prevalent in sheep at the end of summer and start of autumn ## Footnote As the pasture larval contamination has had time to build up and increase infection pressures

Question 30

What are the unique features of the nematodirus battus lifecycle and epidemiology?

Answer 30

Nematodirus battus has a delayed lifecycle, where eggs are passed out in the faeces and the development to an infectious L3 occurs within the egg. These eggs and larvae are very resistant to dessication and thus can persist in the environment and cause infection to lambs in the subsequent lambing season. N. battus requires a cold period followed by a sharp temperature rise in order to hatch. Thus, the infective L3 larvae can hatch en masse in the early spring resulting in a sudden pasture contamination, and lambs will become infected by ingesting these larvae on pasture - which can result in severe clinical disease and even mortality. Be aware this can vary from year to year and farm to farm

Question 31

What is the seasonal occurence of the different ovine gastrointestinal nematodes?

Answer 31

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

Question 32

Which techniques can be used to monitor and diagnose parasitic gastroenteritis (PGE) in sheep?

Answer 32

Monitor daily liveweight gain Faecal egg counts FAMACHA Serum pepsinogen Post mortem (PM)

Question 33

What are the benefits and limitations of monitoring daily liveweight gain to monitor for parasitic gastroenteritis (PGE)?

Answer 33

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

Question 34

What is essential to allow for interpretation of faecal egg counts in sheep flocks?

Answer 34

Grazing history Anthelmintic history Clinical signs

Question 35

How many faecal samples should you collect to achieve representative faecal egg counts?

Answer 35

10 faecal samples

Question 36

How many faecal samples should you collect for representative faecal egg count reduction tests (FECRT)?

Answer 36

15 faecal samples

Question 37

Identify this genus of nematode eggs

Answer 37

Trichostrongylus eggs

Question 38

Identify this genus of nematode eggs (the large brown eggs)

Answer 38

Nematodirus eggs

Question 39

Why is it particularly important to be able to identify nematodirus eggs?

Answer 39

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

Question 40

Whata are the benefits of faecal egg counts for parasitic gastroenteritis (PGE)?

Answer 40

Cheap Easy Good indicator of pasture contamination FECRT used to demonstrate anthelmintic efficacy Can be used to determine pattern of infection on individual farms Nematodirus battus diagnosis

Question 41

What the limitations of faecal egg counts for parasitic gastroenteritis (PGE)?

Answer 41

Requires training Not representative of total worm burden Faecal egg count does not equate to clinical disease Can't be used as a threshold for treatment for individual animals *(however can be done at a group level)*

Question 42

Which nematode has a linear relationship between faecal egg counts and worm burden?

Answer 42

Haemonchus contortus

Question 43

Which post mortem features can be indicative of teladorsagia circumsincta?

Answer 43

Swirling abomasal contents Abomasal glandular hypertrophy Small brown worms

Question 44

Which post mortem features can be indicative of haemonchus contortus?

Answer 44

Pallor Ascites Swirling abomasal contents 'Barber pole' worms

Question 45

Which post mortem features can be indicative of nematodirus battus?

Answer 45

Small intestinal inflammation and mucosal thickening Thin white worms

Question 46

What is FAMACHA?

Answer 46

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

Question 47

What can be done to control the peri-parturient rise (PPR) of faecal egg count in ewes?

Answer 47

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)

Question 48

Which grazing management techniques can be useful to control the peri-parturient rise (PPR) of faecal egg count in ewes?

Answer 48

Mixed grazing Grazing on freshly sown grass pasture

Question 49

What are the advantages and disadvantages or treating pregnant ewes with long acting anthelmintics?

Answer 49

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

Question 50

What can be done to control gastrointestinal nematodes in lambs?

Answer 50

Grazing management Anthelmintic management Improve ewe nutrition Selective breeding for resistance and resilience

Question 51

Which grazing management techniques can be useful to control gastrointestinal nematodes in lambs?

Answer 51

Mixed grazing Grazing with dry adult ewes Grazing on freshly sown grass pasture

Question 52

What is resistance?

Answer 52

Resistance is the host's ability to limit the establishment, development, fecundity and longevity of parasite populations

Question 53

What is resilience?

Answer 53

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

Question 54

What are the limitations of selective breeding for resistance and resilience?

Answer 54

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

Question 55

What is the main risk of routine anthelmintic treatment of lambs?

Answer 55

Routine anthelmintic treatment of lambs promotes the development of anthelmintic resistance in gastrointestinal nematodes due to the excessive exposure to anthelmintics

Question 56

What is strategic anthelmintic treatment?

Answer 56

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 hence reduce the risk of parasitism

Question 57

What is the main risk of strategic anthelmintic treatment of lambs?

Answer 57

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

Question 58

What is the main risk of therapeutic anthelmintic treatment?

Answer 58

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

Question 59

What are targeted selective treatments (TST) with anthelmintics?

Answer 59

Targeted selective treatment (TST) is treatment of individual animals with anthelmintics when monitoring daily liveweight gain indicates subclinical infection and loss of performance

Question 60

What are the five groups of anthelmintics available for parasitic gastroenteritis (PGE) in sheep?

Answer 60

White drenches (Benzimidazoles) Yellow drenches (Levamisole) Clear drenches (Macrocyclic lactones) Orange drenches (Monepantel)(Amino-acetonitrile derivatives) Purple drenches (Derquantel and Abamectin)(Paraherquamide derivatives)

Question 61

Which anthelmintics are ineffective against hypobiotic larvae?

Answer 61

Fenbendazole Mebendazole Yellow drenches (Levamisole)

Question 62

Which anthelmintic drug has a low therapeutic index?

Answer 62

Closantel | Overdosing closantel can lead to blindness and death

Question 63

Which nematode does closantel treat?

Answer 63

Haemonchus contortus | Closantel can also be used for liver fluke

Question 64

What is pseudo-targeted treatment of nematodirus battus with benzimidazoles?

Answer 64

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

Question 65

What are the routes of administration available for anthelmintics in sheep?

Answer 65

Oral Injection Topical (pour-on)

Question 66

What should you make farmers aware of when oral drenching sheep?

Answer 66

It is important to carry out oral drenching correctly and the sheep are properly restrained to prevent underdosing the anthelmintic or causing damage to the sheep gullet *(oesophagus)* which can be fatal

Question 67

Why is injection not a commonly used route of administration for anthelmintics?

Answer 67

Injecting anthelmintics can risk damage to the carcass

Question 68

Why are pour-on anthelmintics not very effective in sheep?

Answer 68

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

Question 69

What are the risk factors for nematodirus battus?

Answer 69

Young, naive grazing lambs *(generally 6-12 weeks of age but may be younger if ewes are not milking well)* Pasture grazed by lambs last spring Later born lambs *(as they are naive and their grazing often coincides with peak larval hatch)* | SCOPS has a nematodirus forecast which can be used to monitor

Question 70

How do you manage nematodirus battus?

Answer 70

If possible, have at-risk lambs grazing on low risk pasture - i.e. hasn't been grazed by lambs in the previous spring. If you cannot avoid high risk pasture, treat the lambs with benzimidazoles when appropriate, and check it has been effective using a FECRT *(as there is beginning to be resistance to benzimidazoles by nematodirus)