Ovine/bovine Johne's Disease (Flock/herd diagnosis (Serology (OJD:…
Ovine/bovine Johne's Disease
"Tail mob", chronic wasting, soft faeces/diarrhoea, ventral oedema
Tests are poorly sensitive and specific, making diagnosis difficult prior to development of clinical disease
Pooled (sheep) and individual (cattle). Faeces collected from 350 sheep and cultured in pools of 50. Most sensitive method, but SLOW (3 mth turnaround)
Detection of acid-fast bacilli. Low sensitivity, moderate specificity.
OJD: AGID, ELISA (500 sheep sampled), complement fixation test (CFT).
BJD: ELISA (210-300 cattle sampled).
Similar sensitivity to PFC, but much faster (much more expensive however)
Whole genome sequencing
Gold standard, but not common
Eradication is not common and extremely difficult, so control is most common
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.
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.
Thickening of ileocaecal/jejunal wall (lepromatous lesions) with transverse ridging of the mucosa, villous atrophy, ascites, subcutaneous oedema
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
Aims to minimise spread
Combination of vaccination, regular testing, culling of identified cases/shedders, grazing management, farm biosecurity and abattoir monitoring
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.
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.
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
Dairy cattle mainly at risk
Controlled using calf hygiene/testing
Lateral spread not confirmed
Scouring not typical (if so, usually secondary to worms)
Risk is defined by geographic region
Controlled via vaccination
Lateral spread occurs
Market assurance programs
Allows promotion of low-risk status
Requires ongoing PFC +/- blood testing
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
Sheep: parasitism, caseous lymphadenitis, caprine arthritis-encephalitis, pneumonia, dental disease
Cattle: ostertagiosis (brown stomach worm), salmonellosis, Cu deficiency, chronic TRP, malnutrition, pyelonephritis, lymphosarcoma, amyloidosis