Nematodes

• 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. 

• 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 

• 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 

• 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 

• 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 

• 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 

• thiabendazole 
• oxibendazole
• fenbendazole
• oxfendazole
• albendazole 
• broad spectrum
• arrested larvae in abosmasum +
• N. battus - variable 
• Teladorsagis circumcincta
• Haemonchus contortus
• Trichostrongylus spp.

• levamisole (imidothiazole)
• tetramisole (imidothiazole)
• pyrantel (tetrahydropyrimidine)
• morantel (tetrahydropyrimidine)
• broad spectrum 
• adult and larvae of N. battus ++
• arrested larvae in abomasum +
• Teladorsagia circumcincta
• Trichostrongylus spp.

• 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 ++

• 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 

• 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 

• 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 

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 

• 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

• 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 

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

• 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 

• 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

• 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 

• 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