Please enable JavaScript.
Coggle requires JavaScript to display documents.
Ovine/bovine Johne's Disease (Flock/herd diagnosis (Serology (OJD:…
Ovine/bovine Johne's Disease
Clinical signs
"Tail mob", chronic wasting, soft faeces/diarrhoea, ventral oedema
Flock/herd diagnosis
Tests are poorly sensitive and specific, making diagnosis difficult prior to development of clinical disease
Faecal culture
Pooled (sheep) and individual (cattle). Faeces collected from 350 sheep and cultured in pools of 50. Most sensitive method, but SLOW (3 mth turnaround)
Faecal/ileocaecal smears
Detection of acid-fast bacilli. Low sensitivity, moderate specificity.
Serology
OJD: AGID, ELISA (500 sheep sampled), complement fixation test (CFT).
BJD: ELISA (210-300 cattle sampled).
Faecal PCR
Similar sensitivity to PFC, but much faster (much more expensive however)
Whole genome sequencing
Gold standard, but not common
Eradication
Eradication is not common and extremely difficult, so control is most common
Epidemiology
Shed in faeces and milk
Neonates infected, clinical disease develops years later (incubation period is 12 months to years)
Older animals relatively resistant to infection due to involution of ileal lymphoid tissue
Sheep typically show clinical disease at 3-4 yrs, cattle (dairy) at 3-7 yrs.
Pathogenesis
MAP phagocytosed by ileal Peyer's patches and a delayed hypersensitivity response ensues - granulomatous enteritis with lepromatous lesions along the intestine. This results in impaired nutrient absorption and chronic wasting.
Post-mortem findings
Thickening of ileocaecal/jejunal wall (lepromatous lesions) with transverse ridging of the mucosa, villous atrophy, ascites, subcutaneous oedema
Aetiology
Mycobacterium avium subsp. paratuberculosis
Potentially zoonotic (unknown association with Crohn's Disease)
Readily establishes in high rainfall zones - inclined to dark, moist and neutral pH conditions.
Persistence in soil for prolonged periods
Control
Aims to minimise spread
Combination of vaccination, regular testing, culling of identified cases/shedders, grazing management, farm biosecurity and abattoir monitoring
Vaccination
Doesn't entirely prevent, but reduces deaths and shedding
Single dose at 4-16 wks, or any age
Testing & culling
ID shedders/clinical cases using clinical signs, PFC, and abattoir monitoring. Cases should be culled ASAP.
Grazing management
Use rotational grazing, placing lambs on pastures that have been spelled for 4-6 wks (summer) or 6 mths in other seasons. Grazing prime lambs/steers on infected pastures can also reduce bacterial load.
Farm biosecurity
Stock should be sourced from an accredited sheepMAP flock, or recently tested for OJD.
Prevent movement of sheep between properties using quality fencing.
Request a signed National Sheep Health Statement prior to delivery of new stock.
Sound nutrition/drenching to decrease flock susceptibility to infection.
Comparison between sheep & cattle
Cattle
Scouring typical
Dairy cattle mainly at risk
Controlled using calf hygiene/testing
Lateral spread not confirmed
Sheep
Scouring not typical (if so, usually secondary to worms)
Risk is defined by geographic region
Controlled via vaccination
Lateral spread occurs
Market assurance programs
Sheep
SheepMAP
Voluntary
Allows promotion of low-risk status
Requires ongoing PFC +/- blood testing
Cattle
J-BAS (beef) & National Dairy BJD Assurance Score
May be required for interstate movement of stock → there are differing requirements between states
Used to assess JD risk when cattle are imported into WA/NT
Ongoing biosecurity plans and blood testing are required to maintain high assurance
DDx
Sheep: parasitism, caseous lymphadenitis, caprine arthritis-encephalitis, pneumonia, dental disease
Cattle: ostertagiosis (brown stomach worm), salmonellosis, Cu deficiency, chronic TRP, malnutrition, pyelonephritis, lymphosarcoma, amyloidosis