Ovine GI nematodes continued Flashcards
(38 cards)
Ovine Hemonchus Pathogenesis
3 types
Hyperacute hemonchosis (up to 30K adults)
- sudden death due to severe hemorrhagic gastroenteritis
Acute hemonchosis (2K-20k)
- clinical signs two weeks post infection
- regenerative anemia followed several weeks later by non-regenerative anemia if not treated
Chronic hemonchosis (several hundred)
- Weight loss, weakness, inappetance
Clinical signs of hyper acute hemonchosis
Sudden death
Clinical signs of acute hemonchosis
anemia (pale mm) submandibular edema ascites dark faces (diarrhoea not usually a feature) drooping wool inappetance
Clinical signs of chronic hemonchosis
Weight loss
Weakness
Inappetance
How to diagnose hemonchosis
Clinical signs - Anemia (pale mm) - Both ewe and lambs affected - Lowland flocks (high stocking density) Fecal Egg Counts - Typical trichostrongyle egg - 1K-20K epg PM
Discuss pathological lesions in hemonchosis
Adult worms on mucosa, focal lesions where feeding (hemorrhagic)
Pale carcass/liver/gelatinous bone marrow
What is FAMACHA and what is it used for?
Assess clinical anemia
Used to decided which animals in flock to treat
Place in eye and assess anemia (PCV) based on colour of conjuctival membrane
Discuss the epidemiology of hemonchosis
Parasite best in warm climates (temp is key to egg development)
- high temp/humidity
Cant overwinter in UK, so survive by hypobiosis
Epidemiology varies on region
-Tropical w/o severe dry season
-Tropical w/ severe dry season
-Temperate
Discuss the epidemiology of hemonchosis: tropical w/o severe dry season
East Africa
- hypobiosis unimportant
- high parasite burdens all year round
- high fecundity
- often year round deworming
- # s of L3s on pasture depend on rainfall
Discuss the epidemiology of hemonchosis: tropical w/severe dry season
Australia/Brazil
- Dry season: L3s can’t survive on pasture
- High levels of hypobiosis during dry season
- Dz outbreak at start of wet season
- -> reactivate arrested L4s
- -> rapid increase in pasture L3s
Discuss the epidemiology of hemonchosis: temperate
UK
- Aided by arrested development in winter (L4)
- Peak of abundance late in the year
- Gradual build up of infective stages thru the summer
- Don’t survive overwinter (no overwintered larvae)
- Reactivate in spring (don’t know the signal) –> adults –> pasture contamination with eggs –> develop to L3s
- Lambs ingest L3s in summer
Nematodirus species in sheep
N. battus: Small Intestinal
- Specific syndrome in lambs,
N. ficollis + N. spathiger = contribute to PGE in mixed infections
Life cycle of N. battus
Atypical - free living stages are different.
L3 still infective form
Eggs laid –> L1 to L3 development in egg –> infective L3 hatches–> ingested
PPP = 2 weeks
Overwinters as L3 in egg on pasture
Hatching requirements: prolonged chill followed by mean day/night temp of 10C
–> Thus eggs passed during grazing season do not hatch that year
What is different or atypical in the life cycle of N. battus
Free living stage development all occur within the egg shell (thus egg is 2x larger than other trichostrongylus species)
Egg is not infective, L3 that hatches from it is. Overwinters as L3 in egg on pasture. Hatches in spring
Hatching requirements: prolonged chill followed by mean day/night temp of 10C
–> Thus eggs passed during grazing season do not hatch that year
Hatching requirement for N. battus
- Hatching requirements: prolonged chill followed by mean day/night temp of 10C
- -> Thus eggs passed during grazing season do not hatch that year
Host age resistance in N. battus
Lambs more than 3mo = non-permissive host
Ewes very resistant to infection (no periparturient rise)
Resistance is physiological and not immunological
Lambs dont graze a lot in early life, so only susceptible from 3wk to 3mo = very narrow window of infectivity
Epidemiology of N. battus
Ewes have little role (age resistant)
“Lamb to Lamb dz”
Large #s hatch in spring from eggs passed on to pasture from previous years lambs
L3s die off quickly in warmer conditions
- For dz to occur, emergence of L3s must coincide with presence of susceptible lambs (3wk-3mo)
Thus varies year to year on weather and lambing period = PREDICTABLE
use weather forecasts
Cattle are permissive host - could be source of infection to lambs (calves on pasture one year followed by lambs the next) - consider rotational grazing
High disease risk factors: N. battus
Lambing just before it temperature rises and is maintained
Low disease risk factors: N battus
1) mild spring = L3s hatch early +/- late lambing
2) late spring = L3s hatch late +/- early lambing
N. battus Pathogenesis
Pathology due to larval stages –> severe disruption of SI mucosa
Most damage 10-12d post infection (during L4 moult to adult) (PPP =14d)
Large #s synchronous L3s
Enteritis + villus atrophy
Clinical signs: N battus
- Rapid onset
- Profuse diarrhea
- Dehydration, congregate around water
- Lambs affected, ewes fine
Diagnosis: N battus
Control: N battus
FEC not reliable since clinical sings due to larvae
Grazing history
Clinical signs
PM
Avoid grazing on pasture used for lambs the previous year
Nematodirus eggs vs other Trichostrongylus eggs
Nematodirus:
large eggs with large blastomeres and prominent parallel sides
Trichostrongylus:
large eggs with large blastomeres, NO parallel sides
Other Nematodirus species
Develop to L3 in egg, but no hatching requirements
Mixed infections
Contribute to PGE
