Sheep Iceberg Diseases

Question 1

Lentivirus that causes wasting, respiratory and neurological signs

Answer 1

Maedi visna

Question 2

Is the maedi visna incubation period long or short?

Answer 2

Long (months to years)

Question 3

Transmission of maedi visna

Answer 3

Oronasal
(Colostrum/milk, fomites)

Question 4

Treatment for maedi visna

Answer 4

None

Question 5

Diagnosis of maedi visna

Answer 5

Serological (antibodies produced within weeks/months but wax and wane)

Question 6

Control of maedi visna

Answer 6

Purchase from accredited flocks or isolate and test
Cull positives
Reduce stocking density
Prevent contact with neighbouring flocks

Question 7

Handling a maedi visna infection if culling is not practical

Answer 7

Keep flock young
Split into old and young sheep (clean/dirty)
Cull thin/suspect cases
Run less intensive system to reduce spread

Question 8

Retrovirus causing weight loss, respiratory signs and sudden death

Answer 8

Ovine pulmonary adenocarcinoma (OPA)/jaagsiekte

Question 9

Transmission of OPA

Answer 9

Aerosol
(Milk/colostrum)

Question 10

How long is the incubation period of OPA?

Answer 10

6 months to several years

Question 11

Definitive diagnosis of OPA

Answer 11

Post mortem (well demarcated consolidation in lung)

Question 12

Treatment of OPA

Answer 12

None

Question 13

Control of OPA

Answer 13

Identify and cull infected sheep/offspring
Manage in single age groups
Reduce close contact (housing, troughs, hygiene, stocking density)
Snatch lambing (impractical)

Question 14

Lymph node abscesses and weight loss caused by Corynebacterium pseudotuberculosis

Answer 14

Caseous lymphadenitis (CLA)

Question 15

Where are caseous lymphadenitis lesions found?

Answer 15

Around head/neck
(Inguinal/scrotal region in tups)

Question 16

Colour of pus in caseous lymphadenitis

Answer 16

Green

Question 17

Diagnosis of caseous lymphadenitis

Answer 17

Bacteriology (drain abscess)
Serology (antibodies wax and wane, antibody does not always mean disease, repeat testing)

Question 18

Control of CLA

Answer 18

Buying from trusted sources
Boundary biosecurity
Separate infected animals
Vaccine under special license

Question 19

Which iceberg disease is zoonotic?

Answer 19

CLA

Question 20

Are antibiotics effective against CLA?

Answer 20

No

Question 21

Reduced fertility and weight loss caused by Mycobacterium avium spp. paratuberculosis

Answer 21

Ovine Johne’s disease (OJD)

Question 22

What is the effect of ovine Johne’s disease on the gut?

Answer 22

Inflammation reduces metabolic efficiency

Question 23

Does ovine Johne’s disease cause scour?

Answer 23

No

Question 24

Are sheep susceptible to the cattle strain of Johne’s?

Answer 24

Yes

Question 25

Are cattle susceptible to sheep strain of Johne's?

Answer 25

No

Question 26

Transmission of ovine Johne's disease

Answer 26

Faeco-oral (Milk/colostrum)

Question 27

When are lambs infected with Johnes disease and when do they show clinical signs?

Answer 27

Infected early in life (3-4m) Clinical signs in animals over 2-3 years

Question 28

Diagnosis of OJD

Answer 28

Post mortem most effective Serology (antibodies low until there is clinical disease) Faecal PCR (bacteria doesn't always cause disease)

Question 29

Challenges with control of OJD

Answer 29

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)

Question 30

Control methods for ovine johne's disease

Answer 30

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

Question 31

Pestivirus causing poor ewe fertility, 'hairy shaker'/weak lambs and abortions

Answer 31

Borders disease

Question 32

Pestivirus in cattle that is similar to borders disease

Answer 32

BVD

Question 33

Transmission of borders disease

Answer 33

Respiratory secretions Transplacental (dam to offspring or via semen of PI rams)

Question 34

What happens if a sheep is infected with borders disease at <60 days of gestation?

Answer 34

Abortion or survival (Ag + and AB -)

Question 35

What happens if a sheep is infected with borders disease at 60-85 days of gestation

Answer 35

Lamb can be antigen or antibody positive

Question 36

What happens if a sheep is infected with borders disease at >85 days of gestation?

Answer 36

Lamb born normal (Ag - and AB +)

Question 37

Diagnosis of Borders disease

Answer 37

Detection of antibody or antigen (PIs)

Question 38

Is there a vaccine for borders disease?

Answer 38

No