Nematodes of Sheep Flashcards
what are nematodes of the abomasum
Teladorsagia circumcincta
Haemonchus contortus
Trichostrongylus axei
what are nematodes of small intestine
Trichostrongylus vitrinus
Trichostrongylus colubriformis
Nematodirus battus
Nematodirus filicolis
Cooperia spp
Strongyloides papillosus
Bunostomum trigonocephalum
what are nematodes of large intestine
Esophagostomum venulosum
Trichuris ovis
Chabertia ovina
what are the nematodes of lungs
Dictyocaulus filarial
Muellerius capillaris
Protostrongylus rufescens
what are the most significant nematodes of sheep
Teladorsagia circumcincta:
- Formerly Ostertagia circumcincta the ‘brown stomach worm’
Haemonchus contortus:
- The ‘barber’s pole worm’
- Different clinical picture
Trichostrongylus vitrinus:
- ‘Black scour worm’
- Northern Britain
Trichostrongylus colubriformis:
- ‘Black scour worm’
- Southern Britain
Nematodirus battus:
- Has different epidemiology to other nematodes
what is the direct lifecycle of nematodes
Strongylid eggs (70–150 μm) usually hatch within 1–2 days
After hatching, larvae feed on bacteria and undergo two moults within feces to then develop to ensheathed third-stage larvae (L3s) in the environment (i.e., feces or soil)
The sheath (which represents the cuticular layer shed in the transition from the L2 to L3 stage) protects the L3 stage from environmental conditions but prevents it from feeding
Infection of the host occurs by ingestion of L3s
The infective L3 migrate onto pasture
During its passage through the abomasum, the L3 stage lose their protective sheath then transition to the L4 and pre-adult stages
what is the PPP for most nematodes
16-21 days
what are the ideal temperature for environmental stages
>5C, ideal 18-26C
what are the ideal humidity for environmental stages
min 50-60%
ideally >80%
what is hypobiosis
arrested development
unfavourable conditions for L3
how long do the parasites survive in the host
only a few months
few adults survive winter
unless hypobiosis
how long do the parasites survive on pasture
L3 are most resistant
- Temperature extremes and desiccation, for many species infective L3 can survive up for 10-12 weeks
- Some species they can survive for up to 12 months and not killed by frosts (T. circ)
Moisture
Temperature
- Increased survival under temperate conditions vs tropical
- Teladorsagia circumcincta can survive freezing
- Haemonchus contortus cannot survive freezing
describe the environmental survival of the unembryonated egg of Haemonchus contortus
high susceptibility to cold and desiccation
high mortality <10C
describe the environmental survival of the embryonated egg of Haemonchus contortus
susceptible to cold and desiccation
low hatching in absence of moisture and/or at <10C
describe the environmental survival of the pre infective larvae of Haemonchus contortus
high susceptibility to cold and desiccaiton
describe the environmental survival of the infective larvae of Haemonchus contortus
optimum survival under warm and moist conditions
poor survival in dry climates (warm or cool) and sub freezing winter
describe the environmental survival of the unembryonated egg of Trichostrongylus colubriformis
intermediate susceptibility to cold and desiccation
high mortality at <5
describe the environmental survival of the embryonated egg of Trichostrongylus colubriformis
intermediate susceptibility to cold
low susceptbility to desiccation
describe the environmental survival of the pre infective larvae of Trichostrongylus colubriformis
susceptible to cold and dessication
high mortality at <5C
describe the environmental survival of the infective larvae of Trichostrongylus colubriformis
optimum survival under warm or cool moist conditions
poor survival over sub freezing winters
describe the environmental survival of the unembryonated egg of Teladorsagia circumcincta
low susceptibility to cold
intermed to desiccation
high egg viability at 0-10C
describe the environmental survival of the embryonated egg of Teladorsagia circumcincta
low susceptibility to cold and desiccation
hatching at <5C
describe the environmental survival of the pre infective larvae of Teladorsagia circumcincta
intermed susceptibility to cold
susceptible to desiccation
describe the environmental survival of the infective larvae of Teladorsagia circumcincta
optimum surivival under cool moist conditions and sub freezing winters
poor survival under warm, dry conditions
what is the annual cycle of eggs on pasture
overall ‘normal’, unchecked/untreated pattern of ewe and lamb nematode egg production over the 12 month annual cycle
- At the start of the year there are some larvae that have survived the winter (dependent on weather and pasture management the previous year)
- These surviving larvae start to die off
- Ewes contaminate pasture during the peri-parturient rise (PPR) in egg output
- Then when lambs start eating grass from 4-5 weeks old they start to multiply the nematodes, because they are naive so high shedders, and contaminate pasture further
what is the annual cycle of ewe fecal egg output and larvae on pasture
PPR is when there is a rise in FEC in ewes around parturition, lasting from a couple of weeks before lambing to 6-8 weeks after lambing
Adult ewes have good immunity unless immune-suppressed
what is the periparturient rise (PPR)
Due to reduced immunity:
- Physiological associated with pregnancy?
- Re-distribution of nutrition of fetal develop and milk production
Results from:
- Renewed development of hypobiotic larvae into laying adults
- Increases susceptibility to further infection from pasture
- Increase in fecundity of adult female worms
what is the annual cycle of lamb and ewe fecal output and larvae on pasture
what does rate of contamination build up depend on in pasture (3)
- climatic conditions
- lamb anthelmintic treatments
- grazing management (pasture rotation)
when do hypobiotic larvae become an issue for
- store lambs
- breeding replacements
- pregnant ewes
what are the clinical signs of PGE
Reduced weight gain
Reduced feed intake (60-70% of reduced DLWG)
Poor body condition
Open fleece
Diarrhea (variable) — fecal staining
Dehydration
Death
what are the ddx for PGE
Coccidiosis (diarrhea/ill thrift)
Nematodirosis (diarrhea/ill thrift)
Selenium deficiency (ill thrift)
Cobalt deficiency (ill thrift)
Nutritional:
- Lush grass (diarrhea)
- Poor quality/quantity of feed (ill thrift)
- Ruminal acidosis (diarrhea +/- poor DLWG)
what are the causes of clinical signs in PGE
GIT inflammation due to immune response
Mucosal damage (short term +/- long term)
Due to larvae as well as adult nematodes
Anorexia
Malabsorption
what does the morbidity and mortality depend on with PGE
Species of GI nematode(s) (GIN)
Infective load
Host immunity
Mortality can be high if untreated
Subclinical effects on DLWG and feed conversion are significant
Distribution of infection
what groups are susceptible to PGE
Young, non-immune animals
Adult, immunocompromised animals
Those exposed to a high infection pressure from a heavily L3-contaminated environment
what do the early stages of PGE look like
Reduction in weight gain might be the only notable sign
60-70% of the reduction in growth rate in parasitized lambs can be attributed to reduced feed intake
Affected lambs develop low BCS, diarrhoea, an unkept ‘open’ fleece, dehydration and death
describe the clinical picture of Teladorsagia circumcincta
abomasum
anorexia
poor growth
scour
describe the clinical picture of Trichostrongylus spp
small intestine
anorexia
poor growth
scour
describe the clinical picture of haemonchus contortus
abomasum
anorexia
anemia
death
describe the clinical picture of nematodirus battus
small intestine
anorexia
severe scour/dehydration
death
when does Teladorsagia circumcincta PGE usually occur
summer and autumn
what does Trichostrongylus spp cause
dark scour
anorexia
poor skeletal growth
chronic ill thrift
protein leakage
electrolyte and mineral imbalances
when does Trichostrongylus spp PGE occur
autumn and winter
what is the lifecycle of nematodirus battus
Larvae develop in the egg (usually 8-9 months)
The majority of strains require a period of cold priming before they hatch
- Once period of warm (+ damp) after cold met —> mass hatch
Mass contamination of pasture in a very short period of time
If grazing lambs (over 5 weeks old) are present on pasture when this mass hatch occurs, it can result in mass infection and severe disease in those lambs
what does the acute onset of nematodirus battus look like
profuse watery scour
dehydration
dull
abdominal pain
rapid weight loss
death
poor mineral absorption – poor skeletal growth
when does nematodirosis occur
in spring (+ autumn)
how is nematodirus battus treated
all nematode anthelmintics
usually benzimidazoles
what is special about goats and nematodes
Develop no or minimal immunity
Multiply pasture contamination
High drug metabolism so need higher doses
Except Levamisole (high doses of levamisole are dangerous in goats and sheep)
Fast track development of anthelmintic resistance
- Due to the lack of immunity, which results in increased need for treatments and rapid metabolism of those treatments, goats are effective mediators for the rapid development of anthelmintic resistance in the nematodes that infect them
Many of the same species of nematode infect goats as shee
how are nematodes diagnosed (6)
- history and clinical signs
- fecal worm egg count (FWEC)
- PM
- pepsinogen
- species ID (PCR)
- FAMACHA (H. contortus)
how is fecal worm egg counts done
Modified McMaster technique
Dilute feces then multiply result
Give eggs per gram (epg)
Ideally 10 individual samples (15 for fecal egg count reduction test (FECRT)
Can be pooled (ask for them individually though)
Fresh samples
what egg is this
trichostrongylid
what species is this
trichostrongylus
what sp is this
coccidia
what species is this
nematodirus
what are the pros for using FWEC
Predict pasture contamination
Determine pattern of infection on individual farms
Encourage farmer/vet interaction
FECRT
Nematodirus battus diagnosis
what are the cons to using FWEC
Cannot speciate Trichostrongyle style eggs
FWEC not representative of burden (ex. H. contortus)
- These nematodes produce so many eggs that eggs from other nematodes become insignificant
Not related to lamb performance (resilience vs resistance)
- Some lambs will have high burdens and high FWEC but good growth rates (be resilient) and some lambs will have low burdens/FWEC but low growth rates (resistant – they are using nutritional reserves to attack the wo
how do intrepret FWEC
in conjuction with
CS
weather
grazing history
how do you diagnose nematodes on PM
- pallor
- ascites
- abomasum (swirling, H. contortus or T. circumcincta, glandular hypertrophy T. circumcincta)
- small intestine (catarrhal inflammation or mucosal thickening, N. battus worms)
- total worm counts
what are the uses of nematode pharmaceuticals
Treat disease
Metaphylactic treatment of others in a group
Prevent build up of pasture contamination
Promote good growth rates
what is the mechanism of action of benzimidazoles
binds β-tubulin
what are benzimidazoles active against
cestodes, nematodes +/- trematodes
what are examples of benzimidazoles
lbendazole (+ liver fluke)
Fenbendazole
Mebendazole
Triclabendazole (liver fluke not worms)
Febantel, netobimin and thiophanate — probenzimidazoles need liver activation
what is the mechanism of action of imidazothiazoles
spastic paresis (ganglion blocking)
what are imidazothiazoles active against
Active against nematodes (not inhibited larvae)
what are examples of imidazothiazoles
levamisole
what is the mechanism of action of MLs
flaccid paralysis (GABA chloride channels)
what are MLs active against
Active against nematodes and arthropods
what are examples of MLs
Avermectins (Ivermectin, doramectin, abamectin, eprinomectin)
milbemycins (moxidectin)
what does persistent activity of MLs depend on
relies on lipophilic characteristics so body fat presence
what is the mechanism of action of amino acetonitrile derivatives
spastic paralysis (acetylcholine receptors?)
what are examples of amino acetonitrile derivatives
monepantel
what are amino acetonitrile derivatives active against
nematodes
what is the menchanism of action of Spiroindoles
spastic paralysis (acetylcholine receptors)
what are examples of spiroindoles
derquantel
what are spiroindoles active against
nematodes
what are narrow spectrum anthelmintics
closantel and nitroxynil effective against H contortus only
BZ used for N battus
what are long acting anthelmintics
doramectin
moxidectin
what are anthelmintics use in lambs to control nematodes (5)
- regular routine treatments often every 3-4 weeks
- therapeutic treatments
- FWEC guided treatments
- reduce pasture contamination
- targeted treatments or targeted selective treatments
what are the problems with dose and move
promote resistance
what are the alternatives to dose and move
leave a proportion untreated (often 10%)
dose a few days before move (4-5 days if action is <3 days)
what are areas to target for prevention
eggs shedding from ewes in spring
and buildup in summer of pasture larvae
how do you prevent the ewe periparturient rise
- Nutrition
- Good immune response
- Selective breeding for resistance
- Low FWEC
- clean/safe grazing
- anthelmintics
- short acting
- long acting
how do you graze ewes in a clean/safe grazing pasture
Newly planted pasture/rotation with arable
Rotation with cattle
how can anthelmintics be used to prevent ewe peripartient rise
Repeated 3 weeks after lambing (but rarely are) as the PPR extends 6-8 weeks after lambing
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 moxidectin to lambs in milk
how do prevent lamb exposure to nematodes (5)
- newly planted pasture
- rotation with cattle or mixed grazing
- rotation with dry adult ewes (not rams)
- strategic treatments
- bioactive forages
how can a newly planted pasture reduce exposure to lambs
Reducing exposure to infectious larval stages of GI nematodes will maintain the best production and animal health levels, however this can be difficult to do in intensively farmed sheep flocks
Good as part of arable rotation
Providing clean pasture at 3 week intervals reduces re-infection rates, however this is not ideal for promoting good grass growth and utilization (paddock rotation for good grass use promotes the nematode cycle and is one of the major issues with this system)
how can roration with cattle or mixed grazing prevent lamb exposure
Many cattle and sheep farms
But, cattle are capable of multiplying up Haemonchus contortus and calves can cycle Nematodirus battus
Low contamination pasture can become contaminated very quickly, so must be used with care and not wasted
how does rotation with dry adult ewes reduce exposure of lambs
Only after weaning
Maintain/develop immunity
Don’t use rams!
how can strategic treatments reduce exposure to lambs
Strategic treatments can be used by treating lambs early, as they starting to shed eggs, to prevent pasture contamination
However, this increases the pressure for development of anthelmintic resistance because there are low numbers of nematodes on pasture, so a low proportion of nematodes not exposed to anthelmintic (in refugia) to provide susceptible genes to dilute those of the resistant nematodes that survive treatment
how can bioactive forages be used to reduce exposure to lambs
Bioactive forages, such as chicory have debatable effect on reducing GI nematode burdens in sheep
how can you reduce lamb susceptibility
nutrition
selective breeding
how can selective breeding reduce lamb susceptibility
Resistance
- Low burdens and egg output
- Low FWEC (normally carried out in the mid and late grazing season of their first year of life)
- These animals can have low growth rates when they are exposed to highly contaminated pasture, because they are using reserves to tackle the infection rather than grown
Resilience
- High growth rates despite GI nematodes
- Although this can be more difficult as there can be many factors influencing growth rates
IgA testing
- Useful immune responses but also good growth rates when exposed to nematodes. This test is carried out on saliva or blood, saliva is more user friendly for farmers, whereas blood is more reliable
how can quarantine reduce nematodes
avoid buying or moving resistant worms onto a farm
Effective treatment
Minimum of two anthelmintics active against all pathogenic gastrointestinal nematodes (from different anthelmintic groups
The use of multiple active ingredients reduces the number of surviving nematodes, as most will only be resistant to one active ingredient
Ideally these animals should have a FECRT carried out, or even just a post treatment text 10-14 days later
One after the other —> NEVER mix
Given 48 hours before turnout to ‘dirty’ pasture
Pasture that is likely to be contaminated with nematodes from sheep already on the farm, these will dilute any resistant nematodes in the new/returning stock
what are the lungworm species
Dictyocaulus filarial
Muellerius capillaris
Protostrongylus rufescens
what is the lifecycle of Muellerius capillaris
indirect lifecycle – molluscs
what are important cestodes
Hydatid disease (Echinococcus granulosus)
Cysticercus tenuiocollis (Taenia hydatigena)
Monezia spp.
Cysticercus ovis (Taenia ovis)
Coenurosis (Taenia multiceps)
what is the signficance of Coenurosis (Taenia multiceps)
dog definitive host
cysts in CNS
gid
what is the signifiance of Cysticercus ovis (Taenia ovis)
dog definitive host
cysts in liver, muscles
abattoir condemnations – sheep measles
what is the signifiance of Monezia spp.
sheep definitive host
minimal clinical effect
unless obstruction
what is the significance of Cysticercus tenuiocollis (Taenia hydatigena)
dog definitive host
cysts in liver, omentum, mesentery
what is the significance of Hydatid disease (Echinococcus granulosus)
dog definitive host
cysts in liver and lungs
zoonotic from dogs
how are cestodes controlled
worming dogs (praziquantel)
control dog movements
remove carcasses
dont feed raw sheep meat to dogs
