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PARASITOLOGY - 2 > 6 – Sheep GI Nematodes and Resistance > Flashcards

6 – Sheep GI Nematodes and Resistance Flashcards

1
Q

GI Nematodes background

A
  • Younger animals
  • Pasture transmission
  • Clinical disease is common and widespread
    o Worse in GOATS
  • Anithelmintic resistance is a huge global problem
  • Multiple nematode species involved
    o *Haemonchus contortus is most IMPORTANT
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2
Q

What is the lifecycle of GI nematodes?

A
  • Adults in stomach
  • Eggs in feces: L1 to L2 to L3
  • Ingest L3
  • *H. contortus: L4 arrest (hypobiosis) late in grazing season
  • *N. battus: eggs do NOT hatch until L3 has developed
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3
Q

What are the clinical signs of GI nematodes in sheep?

A
  • Bottle jaw
  • Death
  • Anemia
  • Weight loss
  • Reduced production
  • Diarrhea
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4
Q

Epidemiology of Trichostrongyles in grazing sheep

A
  • Peri-parturient egg rise: around time that they lamb there is a drop in immunity
    o *production of more eggs and reactivate L4=increased pasture larval count (end of spring/summer)
  • Lambs in pasture in spring=increased eggs in feces of lambs!
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5
Q

What are the 2 main syndromes of GI nematodes diseases? (EXAMS)

A
  1. Parasitic gastroenteritis
  2. Haemonchosis
    *species ID is important
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6
Q

Parasitic gastroenteritis clinical signs

A
  • Reduced weight gain and diarrhea
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7
Q

Haemonchosis clincial signs

A
  • Acute anemia
  • Edema
  • Lethargy
  • Death
  • Ex. Haemonchus contortus (“barber’s pole worm”)
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8
Q

Haemonchus contortus (sheep)

A
  • Typical trichostrongylid life cycle
  • ABOMASUM
  • *most pathogenic species in sheep
  • World wide distribution
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9
Q

What are the main clinical signs, hyperacute Haemonchus contortus (especially in lambs less than 6 months old)?

A
  • Sudden death due to heamorrhagic anemia
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10
Q

What are the main clinical signs, acute Haemonchus contortus (especially in lambs less than 6 months old)?

A
  • Anemia
  • Bottle-jaw
  • Ascites
  • Dark feces
  • Anorexia
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11
Q

What are the main clinical signs, chronic Haemonchus contortus (especially in lambs less than 6 months old)?

A
  • Weight loss
  • Weakness
  • Anorexia
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12
Q

How do you do definitive diagnosis of Haemonchus contortus?

A
  • L3 at coproculture
  • PCR/Nemabiome
  • Adults at necropsy
  • Fluorescein-labeled peanut-agglutinin (specific)
  • *FEC can be low (PPP) or very high (1,00-20,000)
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13
Q

Famacha system

A
  • Different degrees of anemia
    o Compare to eye mucous membrane
  • *alternative to PCV in resource limited areas
  • Correlation with burden varies
  • If score 4-5=treat
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14
Q

Nematodirus battus in small intestine

A
  • Develop to L3 inside egg
  • Eggs overwinter on pasture
  • Hatching triggered by sudden rise in temperature in spring
  • Illness and death in lambs in PPP
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15
Q

Nematodirus battus characterisitcs

A
  • *larger eggs than other trichostrongyles
  • *cuticular expansion
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16
Q

Relevant abomasum species in sheep

A
  • *Haemonchus contortus
  • Teladorsagia circumcincta
  • Trichostrongylus axei
  • Sheep, cattle, horses
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17
Q

Relevant small intestine species in sheep

A
  • *Trichostrongylus colubriformis
  • Cooperia sp
  • Nematodirus sp.
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18
Q

Relevant large intestine species in sheep (‘recognize them’)

A
  • Oesophagostomum sp.
  • Chabertia ovina
  • Trichuris sp.
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19
Q

Chabertia ovina (‘large-mouthed bowel worm’)

A
  • Use big buccal capsule for ID
  • Not generally pathogenic but consider general treatment for GIN if lamb crop is whoing poor growth and diarrhea
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20
Q

Relevant species in Canadian sheep: general

A
  • Mixed infections! PGE
  • Distinguishable L3s (coproculture) OR adults
  • Pathogenicity varies with species
  • Egg production varies with species, environmental conditions and interactions between species, etc.
21
Q

Control of GI nematodes in sheep

A
  • Maximize overall helath
    o Good nutrition
    o Pasture management
  • Breed resistant hosts!
  • Vaccination: Barbevaxx
  • Chemical treatments: limited avabilability
  • Strategic treatments
  • *targeted selective treatments to SLOW DEVELOPMENT of DRUG RESISTANT
22
Q

What is a strategic treatment for GI nematodes in sheep?

A
  • Monitor egg count
  • ID species when possible
  • *no ‘one fits all’ solution!
23
Q

Chemical control of GI nematodes in sheep: examples

A
  • Macrocylic lactones: Ivermectin
  • Salicylanilides: closantel (targeted activity)
  • Benzimidazoles: used OFF LABEL
24
Q

Chemical control of GI nematodes in sheep: examples: important to consider

A
  • Resistance to a drug in a class may mean resistance to all durgs in same class
  • *multi drug resistance
  • Mechanisms of resistance still poorly know for many drugs!
25
Q

What is the definition of anthelmintic resistance?

A
  • Heritable reduction in efficacy of a drug against a particular species of parasite
  • When drug efficacy is less than 95%
  • *reports of H. contortus resistance to all classes of durgs
26
Q

What is Teladorsagia resistant to?

A
  • Ivermectin
27
Q

Tichostrongylus and resistance

A
  • Mostly susceptible
28
Q

How does anthelmintic resistance develop?

A
  • Established when population of worms is submitted to a treatment pressure
    o *selects individuals with the resistant genotype over time
29
Q

What is refugia?

A
  • Susceptible subset of population present on pasture
    o Not exposed to anthelmintic treatment
  • *will subsequently re-infect the flock
  • *parasites in untreated hosts and external environment (free-living stages)
30
Q

What if refugia population is composed by susceptible worms?

A
  • Dilute the concentration of resistant worms delivered on pasture after treatment
  • *large the population=less the selection pressure
    o Resistant nematodes breeding with susceptible nematodes will DILUTE proportion of resistant genes
31
Q

What are some factors determining the rate of resistance development?

A
  • Underdosing
  • Length of time used
  • Frequency of treatment
  • Pasture management: open/closed flocks
  • Size of in-refugia population
32
Q

For sheep in temperate climates, what are most parasites in?

A
  • Refugia due to HIGH survival on pasture
  • *if treated: overtime resistance will develop
33
Q

What happens when there are few parasites in refugia (very clean pastures, dry climates)

A
  • *resistance develops rapidly!
  • *treatment during spring in Canada:
    o Low refugia of H. contortus (most are inside host)
    o Treatment at this time may mean high selection pressure
34
Q

What happens when animals are treated and moved to a clean pasture?

A
  • *strong selection for resistance
  • *no refugia!
35
Q

What is recommended to avoid selecting for resistance?

A
  • Treat and move to contaminated pasture OR
  • Treat and leave on contaminated pasture
  • *dilute out the resistant
  • THEN MOVE TO A CLEAN PASTURE!
36
Q

AH resistance is suspected when there is a poor response to AH treatment

A
  • Only apparent if RESISTANT STRATINS MAKE UP A LARGE POPULATION
  • Resistance goes undetected in early phases
  • First sign is SHORTENING OF EGG REAPPEARANCE PERIOD
37
Q

Diagnosis of AH resistance

A
  • In vitro tests: low specificity, time consuming
  • Molecular markers of resistance: early stages
  • **FEC reduction tests is widely used
38
Q

FEC reduction test

A
  • Ideally combined with species ID method
    o Morphology, PCR, DNA sequencing
39
Q

When is FEC reduction test ideally done?

A
  • Individually for all animals in a herd
  • Horses: often done only on high shedders
  • Cattle/sheep: run on pooled fecal samples (20 animals)
  • *ideally use quantitative centrifugation Wisconsin technique
  • *TEST, TREAT, RE-TEST IN 14 DAYS
40
Q

How do you calculate drug efficacy?

A
  • % efficacy= (pre-treatment FEC – post treatment FEC) divided by pre-treatment FEC MULTIPLY by 100
  • *drug resistance when FEC reduction test is less than 95%
  • If doing groups, get the average
41
Q

What are the current recommendations to reduce AH resistance?

A
  • Quarantine and AH treatment of purchased livestock
  • Good nutrition and management
  • Make informed choices on drug use
  • Monitor resistance status
  • *minimize and strategize AH use
  • Targeted selective treatment
42
Q

Quarantine and AH treatment of purchased livestock

A
  • Treat all incoming animals with COMBO of drugs
  • Isolate them for few days
  • Test FEC prior to introduction to her
43
Q

Good nutrition and management to reduce AH resistance

A
  • Lower stocking densities
  • Avoid using same pasture in spring used in previous fall
  • Mix age groups and/or species (**BUT NOT SHEEP AND GOATS)
44
Q

Minimize and strategize AH use to reduce development of AH resistance

A
  • Treat specific groups instead of whole flock
  • Calculate dose based on individual animals OR heaviest in the group
45
Q

Targeted selective treatment to reduce development of AH resistance

A
  • Goals is to LEAVE LARGE REGUGIA
    o Untreated animals on pasture
  • Treat only those with high FEC, poor body condition and high Famacha scores
46
Q

Targeted selective treatment: FEC approaches

A
  1. Use absolute FEC: treat all animals with FEC above a threshold
  2. Use proportions of shedders
    *do NOT treat whole flock
47
Q

Use absolute FEC: treat all animals with FEC above a threshold (targeted selective treatment)

A
  • Animals with high FEC tend to stay high
  • High shedders are MAJOR SOURCE of pasture contamination
  • BUT
    o FEC depend on season, host species, climate, management
    o Pathogenesis depends on parasite species present
48
Q

Use proportions of shedders: for targeted selective treatment

A
  • Treat only top 20-30% of shedders
    o Producers with more risk tolerance
  • Don’t treat bottom 20-30% of shedders
    o More conservative: for producers less tolerant to risk

PARASITOLOGY - 2 (13 decks)

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