Sheep Iceberg Diseases Flashcards
Lentivirus that causes wasting, respiratory and neurological signs
Maedi visna
Is the maedi visna incubation period long or short?
Long (months to years)
Transmission of maedi visna
Oronasal
(Colostrum/milk, fomites)
Treatment for maedi visna
None
Diagnosis of maedi visna
Serological (antibodies produced within weeks/months but wax and wane)
Control of maedi visna
Purchase from accredited flocks or isolate and test
Cull positives
Reduce stocking density
Prevent contact with neighbouring flocks
Handling a maedi visna infection if culling is not practical
Keep flock young
Split into old and young sheep (clean/dirty)
Cull thin/suspect cases
Run less intensive system to reduce spread
Retrovirus causing weight loss, respiratory signs and sudden death
Ovine pulmonary adenocarcinoma (OPA)/jaagsiekte
Transmission of OPA
Aerosol
(Milk/colostrum)
How long is the incubation period of OPA?
6 months to several years
Definitive diagnosis of OPA
Post mortem (well demarcated consolidation in lung)
Treatment of OPA
None
Control of OPA
Identify and cull infected sheep/offspring
Manage in single age groups
Reduce close contact (housing, troughs, hygiene, stocking density)
Snatch lambing (impractical)
Lymph node abscesses and weight loss caused by Corynebacterium pseudotuberculosis
Caseous lymphadenitis (CLA)
Where are caseous lymphadenitis lesions found?
Around head/neck
(Inguinal/scrotal region in tups)
Colour of pus in caseous lymphadenitis
Green
Diagnosis of caseous lymphadenitis
Bacteriology (drain abscess)
Serology (antibodies wax and wane, antibody does not always mean disease, repeat testing)
Control of CLA
Buying from trusted sources
Boundary biosecurity
Separate infected animals
Vaccine under special license
Which iceberg disease is zoonotic?
CLA
Are antibiotics effective against CLA?
No
Reduced fertility and weight loss caused by Mycobacterium avium spp. paratuberculosis
Ovine Johne’s disease (OJD)
What is the effect of ovine Johne’s disease on the gut?
Inflammation reduces metabolic efficiency
Does ovine Johne’s disease cause scour?
No
Are sheep susceptible to the cattle strain of Johne’s?
Yes
Are cattle susceptible to sheep strain of Johne’s?
No
Transmission of ovine Johne’s disease
Faeco-oral
(Milk/colostrum)
When are lambs infected with Johnes disease and when do they show clinical signs?
Infected early in life (3-4m)
Clinical signs in animals over 2-3 years
Diagnosis of OJD
Post mortem most effective
Serology (antibodies low until there is clinical disease)
Faecal PCR (bacteria doesn’t always cause disease)
Challenges with control of OJD
Low sensitivity of diagnostic tests
Inability to detect sub-clinical animals
Practicalities of testing entire flock
‘Snatch lambing’ not practical
Contact between sheep and cattle (co-grazing/slurry)
Control methods for ovine johne’s disease
Lamb high risk (old/thin) ewes away from the rest of the flock
Select replacements from younger ewes
Cull low BCS ewes
Maintain good hygiene and clean bedding
Pestivirus causing poor ewe fertility, ‘hairy shaker’/weak lambs and abortions
Borders disease
Pestivirus in cattle that is similar to borders disease
BVD
Transmission of borders disease
Respiratory secretions
Transplacental (dam to offspring or via semen of PI rams)
What happens if a sheep is infected with borders disease at <60 days of gestation?
Abortion or survival (Ag + and AB -)
What happens if a sheep is infected with borders disease at 60-85 days of gestation
Lamb can be antigen or antibody positive
What happens if a sheep is infected with borders disease at >85 days of gestation?
Lamb born normal (Ag - and AB +)
Diagnosis of Borders disease
Detection of antibody or antigen (PIs)
Is there a vaccine for borders disease?
No
