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| − | | + | #redirect[[Dictyocaulus viviparus]] |
| − | Caused by [[Dictyocaulus|''Dictyocaulus viviparus'']]
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| − | ==== Epidemiology of Parasitic Bronchitis ====
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| − | Our knowledge of the epidemiology of disease is far from complete, i.e. there are still outbreaks of parasitic bronchitis that we are unable to explain.
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| − | ''Disease is carried on from one year to the next by''
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| − | *Low numbers of L3 overwintering on pasture
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| − | *Carrier animals (30% yearlings and 5% cows in an endemic area)
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| − | ''Sequence of events that leads up to an outbreak of clinical disease is as follows''
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| − | *A few calves in a group pick up overwintered L3 from pasture after turnout, leading to patent infections
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| − | *L1 develop to L3 in dungpat
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| − | *Translation of L3 onto the pasture largely by fungus (''Pilobilus'' species)
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| − | *Remainder of calves infected. The infection may cycle 1, 2 or more times before sufficient L3 accumulate on pasture to cause disease (July – September)
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| − | *Large proportion of ingested larvae become inhibited in lungs of calves overwinter, leading to pasture contamination following spring turnout, i.e. “carrier animals”.
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| − | ''Immunity''
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| − | *Rapidly acquired following heavy exposure to infection (within a few weeks)
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| − | *Minimal age resistance (i.e. older stock susceptible if not previously exposed)
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| − | ==== Pathogenesis of Parasitic Bronchitis ====
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| − | '''Primary Infection'''
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| − | ''Penetration Phase (week 1)''
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| − | *Larvae migrate to the lungs; no clinical signs.
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| − | ''Prepatent Phase (weeks 1-3)''
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| − | *Development and migration of larvae → bronchiolitis → eosinophilic exudate → blocks passage of air → alveolar collapse distal to blockage → clinical signs (tachypnoea, coughing depending on the number of worms)
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| − | ''Patent Phase (weeks 4-8)''
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| − | *Worms mature and become egg-producing. Main lesions are
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| − | **Bronchitis (due to adult worms)
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| − | **Parasitic pneumonia (due to aspiration of eggs and larvae → cellular infiltration of polymorphs, macrophages and “foreign body” giant cells)
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| − | ''Postpatent Phase (weeks 8-12)''
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| − | *Period at the end of disease when the majority of worms are expelled. In 25% of cases, clinical signs flare up as a result of alveolar epithelialisation, which may be accompanied by interstitial emphysema and pulmonary oedema, or secondary bacterial infection
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| − | '''Reinfection Syndrome'''
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| − | *Immune cattle only show clinical signs if exposed to a massive challenge
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| − | *Pathogenesis; large numbers of larvae reach bronchioles → killed by immune response
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| − | *Pathology; parasite granulomata (grey-green, 5mm diameter; macrophages, giant cells, eosinophils) and eosinophilic plugs in bronchioles
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| − | ==== Diagnosis of Parasitic Bronchitis (Calves) ====
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| − | *Seasonal incidence
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| − | *Previous grazing history
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| − | *Clinical signs
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| − | *Faecal examination for larvae
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| − | **Baerman technique; examine both healthy and sick cattle
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| − | **Carrier animals may be important in the epidemiology of disease, e.g. in an endemic area 30% yearlings and 5% cows harbour patent infections, as do vaccinated animals
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| − | '''NOTE''': All lungworm-positive faecal samples are potentially significant
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| − | *''Post mortem'' examination
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| − | **Recovery of worms from lungs; “Inderbitzen” or lung perfusion technique. Worms flushed out of lungs by pumping water through pulmonary arteries. Water and worms passed out of trachea collected over sieve
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| − | '''NOTE''': Only 200-300 worms are required to cause clinical disease c.f. >40,000 ''Ostertagia''
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| − | ==== Diagnosis of Parasitic Bronchitis (Adult Cattle) ====
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| − | *Seasonal incidence
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| − | *Previous grazing history
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| − | *Clinical signs
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| − | *Faecal examination
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| − | **Baerman technique; examine healthy and sick cattle, but often no larvae in faeces
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| − | *Blood and Milk examination (ELISA)
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| − | **Variable results (depending upon Ag used)
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| − | **Herd results better than individual results
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| − | *Grass examination for larvae around dung pats
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| − | *Response to anthelmintic treatment
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| − | ==== Control of Parasitic Bronchitis ====
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| − | '''Vaccination – “Huskvac” (Intervet, original vaccine = “Dictol”)'''
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| − | *First-season calves, >2months old, reared indoors
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| − | *Attenuated oral vaccine (each dose, 1,000 X-irradiated ''Dictyocaulus viviparus'' L3)
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| − | *Vaccinate 6 weeks and 2 weeks pre-turnout
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| − | '''NOTE''': '''Never''' mix vaccinated and non-vaccinated animals
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| − | *Result:
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| − | **Effective at preventing disease
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| − | **Not 100% effective at preventing infection, i.e. even vaccinated calves may pass a few larvae → boost immunity in vaccinated calves, but could cause disease in non-vaccinated animals
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| − | *Breakdown in protection can occur due to:
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| − | **Overwhelming challenge
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| − | **Improper storage or administration of vaccine
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| − | **Concurrent disease
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| − | **Mixing vaccinated and non-vaccinated calves
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| − | *Strategic anthelmintic programmes for preventing parasitic bronchitis:
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| − | **Ivermectin 3, 8 and 13 week post-turnout treatment
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| − | '''NOTE''': Residual activity of 28 days against lungworm
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| − | *No anthelmintic cover if challenge encountered either:
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| − | **early (0-3 weeks) or
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| − | **late (after 17 weeks) in grazing season.
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| − | [[Category:Cattle_Nematodes]]
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