Nematodes

Sheep PGE

  • diarrhoea/weight loss (clinical disease)
  • decreased productivity (sub-clinical disease)
  • seasonal appearance
  • hypoalbuminaemia 

Abomasum - Teladorsagia circumcinta (gastric glands), Haemonchus contortus (close apposition to gastric glands)

Small Intestine - Nematodirus spp. (mucosa)

Bovine PGE:

Abomasum - Ostertagia ostertagi, Haemonchus placei

Small Intestine - Nematodirus spp. 

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Sheep PGE - Life Cycle

  • all direct, non-migratory 
  • L3s in grass > swallowed > develop in digestive tract > emerge as L5s in lumen > females lay eggs, excreted in faeces > eggs hatch to L1s in pature and develop to infective L3s 
  • accumulation of arrested EL4s coincides with onset of cold autumn/winter conditions > maturation around parturition 
  • PPR sources 
    • maturation of larvae arrested due to host immunity
    • increased establishment of infections acquired from pastures and a reduced turnover of existing animal infections 
    • increased fecundity of existing adult worm populations 
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Teladorasgia circumcincta - brown stomach worm

  • eggs > L3 within 2 weeks 
  • exsheath in rumen, develop in abomasal glands, sexually mature on mucosal surface 
  • PPP = 3 weeks 
  • PPR most important source of contamination 
  • clean pasture - only infection source is PPR - Type 1 disease in lambs July onwards
  • contaminated pasture - PPR and overwintered L3s - Type 2 disease not common in sheep, bar yearlings (late winter)
  • Type I disease - morbidity high, mortality rare
  • Type II disease - prevalence low, mortality high 
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Haemonchus contortus - barbers pole worm

  • prolific egg layers, egg > L3 in 5 days 
  • ingestion and exsheathment in rumen, close apposition to gastric glands > piercing lancet obtains blood from mucosal vessels > move freedly on surface of mucosa as adults 
  • PPP = 2-3 weeks 
  • single annual cycle most common 
  • hyperacute - sheep die suddenly - haemorrhagic gastritis 
  • acute - anaemia, oedema, loss of condition, lethargy
  • chronic - progressive weight loss and weakness 
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Nematodirus battus - thread-necked worm

  • development of L3s takes place within the eggshell 
  • only one generation is possible each year 
  • L3s > muscosa SI  > moult L4 ~4days post infection > L5 moult and inhabit lumen 
  • PPP = 14-16 days 
  • egg with L3 can survive on pasture up to 2 years 
  • critical hatching requirements - all appear at once (May-June)
  • lamb-lamb disease 
  • yellowy-green diarrhoea
  • faecal egg counts of little value 
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Anthelmintic Resistance

  • use effective quarantine procedures 
  • use anthelmintics sparingly 
  • dose correctly 
  • if you can, avoid broad-spectrum anthelmintics
  • keep worms in refugia to 'dilute' resistant populus 
  • asses!
  • faecal egg count reduction test, if <95% = resistance
  • egg hatch assay (benzimidazoles), if hatch = resistance 
  • larval inhibition assay, if not inhibited = resistance 
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Group 1 Anthelmintics (Benzimidazoles)

  • thiabendazole 
  • oxibendazole
  • fenbendazole
  • oxfendazole
  • albendazole 
  • broad spectrum
  • arrested larvae in abosmasum +
  • N. battus - variable 
  • Teladorsagis circumcincta
  • Haemonchus contortus
  • Trichostrongylus spp.
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Group 2 - (Imidothiazoles/tetrahydropyrimidine)

  • levamisole (imidothiazole)
  • tetramisole (imidothiazole)
  • pyrantel (tetrahydropyrimidine)
  • morantel (tetrahydropyrimidine)
  • broad spectrum 
  • adult and larvae of N. battus ++
  • arrested larvae in abomasum +
  • Teladorsagia circumcincta
  • Trichostrongylus spp.
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Group 3 - Macrolytic lactones/milbemycins

  • avermectins - ivermectin, abamectin, doramectin
  • moxidectin (milbemycin)
  • broad spectrum 
  • avermectins - N. battus variable 
  • moxidectin - residual activity 5 weeks, no persistent activity N. battus
  • Teladorsagia circumcincta

Novel anthelmintics 

  • monepantel - resistant populations +
  • closantel - H. contortus ++
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Bovine PGE - Ostertagia ostertagi - brown stomach

  • direct life cycle 
  • L3s ingested > exsheath in rumen > develop abomasal glands > L5s emerge ~18 days post-infection > mature on mucosal surface
  • PPP = 3 weeks 
  • reduction in functional gastric gland mass, thickened hyperplastic gastric mucosa, raised nodule lesion - visible on central orifice 
  • Type 1 disease - calves grazed intensel, July - October > larvae ingested 3-4wks previously > morbidity high, mortality rare 
  • Type 2 disease - yearlings, late winter/early spring > prevalence low, mortality high > profuse watery diarrhoea 
  • Epidemiology similar to Teladorsagia 
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Ostertagia ostertagi - Treatment

  • Type 1
    • normal dosage rates
    • benzimidazoles/pro-benzimidazoles
    • levamisole
    • avermectins/milbemycins
    • developing larvae and adult stages 
  • Type 2
    • arrested larvae and developing adult stages 
    • modern benzimidazoles 
    • avermectins/milbemycins 
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Dictyocaulus viviparus - bovine lungworm

  • direct life cycle 
  • eggs with fully developed larvae hatch straight away > L1s migrate to trachea > swallowed and passed > L3 in 5 days > L3s intestinal mucosa, mesenteric lymoh nodes > L4s lymph/blood to lungs > capillaries and alveoli ~1 week post infection > final moult in bronchioles > young adults move up to bronchi and mature 
  • PPP = 3-4 weeks 
  • sources - overwintered L3s, carrier animals, fomites; Pilobilus fungus - migrate up stalks of fungi or inside seed capsule - projected up to 3m with fungi
  • high biotic potential - 1000s eggs a day, develop rapidly in warm weather, susceptible to dessication 
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Weather differences Dictyocaulus

dry weather

  • calves immune at end of summer from repeated low level infection - shown no sign of disease 

warm, wet weather

  • disease outbreak may occur
  • large groups of naive calves suddenly exposed to large numbers of L3s
  • disease July - September 
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Dictyocaulus viviparus - pathogenesis

  • Pre-patent phase (8-25 days) - larvae in alveoli (alveolitis), bronchiolitis as larvae move up bronchi, bronchitis towards end, immature worms in airways and cellular infiltration of epithelium
  • Patent phase (26 - 60 days) - parasitic bronchitis, 100s/1000s of adult worms in frothy white mucus in lumina of bronchi, red collapsed areas around infected bronchi, oedema and emphysema
  • Post-patent phase (61-90 days) - recovery phase - adult worms expelled, bronchi still inflamed, residual lesions may persist for weeks/months, proliferative lesions may occur (epithelialisation), proliferation of type II pneumocytes on alveoli, interstitial emphysema/pulmonary oedema - more susceptible to secondary bacterial infections
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Dictyocaulus viviparus - clinical signs

  • mild - intermittent coughs
  • moderately - frequent bouts of coughing at rest, increased resp rate - tachypnoea, increased depth/rate - hyperpnoea
  • severely - severe tachypnoea and dyspnoea, frequently adopt 'air-hunger' position of mouth breathing 
  • treatment - modern benzimidasoles, levamisole, ivermectins/milbemycin 
  • if disease is severe treatment with anthelmintics may exacerbate clinical signs - death possible (antibiotics/hydration)
  • control - lungworm vaccine, immunity only 3-9 months 
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Dictyocaulus filaria - sheep lungworms

  • PPP= 4-5 weeks 
  • small numbers of worms - lung lesions not common 
  • treatment - no vaccine 
  • anthelmintics - move to fresh pasture of infected flock 
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Angiostrongylus vasorum - french heartworms

  • pulmonary artery - circulatory system parasite 
  • indirect life cycle 
  • definitive host - dog/fox
  • intermediate host - snails and slugs 
  • adult worms in larger pulmonary vessels lay eggs > carried to capillaries and hatch > L1s break into alveoli, migrate to trachea > swallowed, excreted in faeces > further development in intermediate host > infective stage in 17 days > mollusc ingested by dog (or fox) > L3s travel to lymph nodes adjacent to alimentary tract > 2 moults > vascular site 
  • PPP = 7 weeks 
  • adult worms can live for >2 years 
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Angiostrongylus vasorum

  • chronic condition, adult worms in larger vessels and eggs/larvae in pulmonary arterioles and capillaries 
  • blockage - circulatory impediment, congestive cardiac failure 
  • mild exercise intolerance > coughing, dyspnoea severe respiratory distress
  • reduced blood-clotting capacity - slowly developing painless swellings - lower abdomen/intermandibular space
  • monthly doses moxidectin 
  • no control methods
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Oslerus osleri - dog lungworm

  • direct life cycle
  • eggs hatch in trachea > larvae coughed up and swallowed and passed > infection by ingestion > infected b itch licks pups and transfers newly hatched L1s present in sputum > 1st moult L2 in SI > L2 to lungs via lymphatics/vascular > L5 in alveoli and bronchi > adults to tracheal bifurcation 
  • PPP = 10-18 weeks 
  • embedded in fibrous nodules ~2 months - pinkish-grey granulomas 
  • many inapparent, may be respiratory distress and dry persistent cough especially post exercise, impaired appetite and emaciation
  • treatment - fenbendazole/albendazole at increased dose rate 
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Aelurostrongylus abstrusus - cat lungworm

  • indirect life cycle 
  • intermediate host - snails 
  • paratenic hosts - birds, rodents, reptiles
  • L1s passed in faeces > penetrate foot of snail - develop to L3s > birds/rodents may eat mollusc > cat infected by ingestion > L3s travel to lungs by lymphatic and bloodstream > adults located in alveolar ducts and terminal bronchioles
  • PPP = 4-6 weeks 
  • low pathogenicity, mild clinically, chronic mild cough 
  • if heavy - diarrhoea and weight loss 
  • treatment - fenbendazole - 50mg daily, 3 days 
  • control impractical
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