|
|
| (2 intermediate revisions by 2 users not shown) |
| Line 1: |
Line 1: |
| − | Caused by ''[[Dictyocaulus viviparus]]''
| + | #redirect[[Dictyocaulus viviparus]] |
| − | | |
| − | ==== Epidemiology of Parasitic Bronchitis ====
| |
| − | 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.
| |
| − | | |
| − | ''Disease is carried on from one year to the next by''
| |
| − | *Low numbers of L3 overwintering on pasture
| |
| − | *Carrier animals (30% yearlings and 5% cows in an endemic area)
| |
| − | | |
| − | ''Sequence of events that leads up to an outbreak of clinical disease is as follows''
| |
| − | *A few calves in a group pick up overwintered L3 from pasture after turnout, leading to patent infections
| |
| − | *L1 develop to L3 in dungpat
| |
| − | *Translation of L3 onto the pasture largely by fungus (''Pilobilus'' species)
| |
| − | *Remainder of calves infected. The infection may cycle 1, 2 or more times before sufficient L3 accumulate on pasture to cause disease (July – September)
| |
| − | *Large proportion of ingested larvae become inhibited in lungs of calves overwinter, leading to pasture contamination following spring turnout, i.e. “carrier animals”.
| |
| − | | |
| − | ''Immunity''
| |
| − | *Rapidly acquired following heavy exposure to infection (within a few weeks)
| |
| − | *Minimal age resistance (i.e. older stock susceptible if not previously exposed)
| |
| − | | |
| − | ==== Pathogenesis of Parasitic Bronchitis ====
| |
| − | '''Primary Infection'''
| |
| − | | |
| − | ''Penetration Phase (week 1)''
| |
| − | *Larvae migrate to the lungs; no clinical signs.
| |
| − | | |
| − | ''Prepatent Phase (weeks 1-3)''
| |
| − | *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)
| |
| − | | |
| − | ''Patent Phase (weeks 4-8)''
| |
| − | *Worms mature and become egg-producing. Main lesions are
| |
| − | **Bronchitis (due to adult worms)
| |
| − | **Parasitic pneumonia (due to aspiration of eggs and larvae → cellular infiltration of polymorphs, macrophages and “foreign body” giant cells)
| |
| − | | |
| − | ''Postpatent Phase (weeks 8-12)''
| |
| − | *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
| |
| − | | |
| − | '''Reinfection Syndrome'''
| |
| − | *Immune cattle only show clinical signs if exposed to a massive challenge
| |
| − | *Pathogenesis; large numbers of larvae reach bronchioles → killed by immune response
| |
| − | *Pathology; parasite granulomata (grey-green, 5mm diameter; macrophages, giant cells, eosinophils) and eosinophilic plugs in bronchioles
| |
| − | | |
| − | ==== Diagnosis of Parasitic Bronchitis (Calves) ====
| |
| − | *Seasonal incidence
| |
| − | *Previous grazing history
| |
| − | *Clinical signs
| |
| − | *Faecal examination for larvae
| |
| − | **Baerman technique; examine both healthy and sick cattle
| |
| − | **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
| |
| − |
| |
| − | '''NOTE''': All lungworm-positive faecal samples are potentially significant
| |
| − | | |
| − | *''Post mortem'' examination
| |
| − | **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
| |
| − | | |
| − | '''NOTE''': Only 200-300 worms are required to cause clinical disease c.f. >40,000 ''Ostertagia''
| |
| − | | |
| − | ==== Diagnosis of Parasitic Bronchitis (Adult Cattle) ====
| |
| − | *Seasonal incidence
| |
| − | *Previous grazing history
| |
| − | *Clinical signs
| |
| − | *Faecal examination
| |
| − | **Baerman technique; examine healthy and sick cattle, but often no larvae in faeces
| |
| − | *Blood and Milk examination (ELISA)
| |
| − | **Variable results (depending upon Ag used)
| |
| − | **Herd results better than individual results
| |
| − | *Grass examination for larvae around dung pats
| |
| − | *Response to anthelmintic treatment
| |
| − | | |
| − | ==== Control of Parasitic Bronchitis ====
| |
| − | '''Vaccination – “Huskvac” (Intervet, original vaccine = “Dictol”)'''
| |
| − | *First-season calves, >2months old, reared indoors
| |
| − | *Attenuated oral vaccine (each dose, 1,000 X-irradiated ''Dictyocaulus viviparus'' L3)
| |
| − | *Vaccinate 6 weeks and 2 weeks pre-turnout
| |
| − | | |
| − | '''NOTE''': '''Never''' mix vaccinated and non-vaccinated animals
| |
| − | *Result:
| |
| − | **Effective at preventing disease
| |
| − | **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
| |
| − | *Breakdown in protection can occur due to:
| |
| − | **Overwhelming challenge
| |
| − | **Improper storage or administration of vaccine
| |
| − | **Concurrent disease
| |
| − | **Mixing vaccinated and non-vaccinated calves
| |
| − | *Strategic anthelmintic programmes for preventing parasitic bronchitis:
| |
| − | **Ivermectin 3, 8 and 13 week post-turnout treatment
| |
| − | | |
| − | '''NOTE''': Residual activity of 28 days against lungworm
| |
| − | *No anthelmintic cover if challenge encountered either:
| |
| − | **early (0-3 weeks) or
| |
| − | **late (after 17 weeks) in grazing season.
| |
| − | | |
| − | ==Test yourself with the Cattle Nematode Flashcards==
| |
| − | | |
| − | [[Cattle_Nematode_Flashcards|Cattle_Nematode Flashcards]]
| |
| − | | |
| − | [[Category:Respiratory Diseases - Cattle]]
| |
| − | [[Category:To_Do_-_Clinical]]
| |