Iceberg diseases in sheep Flashcards

Question

OJD diagnosis

Answer 1

- Diagnosis can be by serology, but antibody levels often remain low until clinical disease, and antibodies can wax and wane - Faecal PCR – unclear how much bacteria correlates with disease - PME most definitive.

Answer 2

- Some sheep clear the infection and do not develop the dz - Exposed sheep can become lately infected (undetectable at this stage) -> Subclinical shedding of Johne's but no Ab yet -> exposure of Johne's to lambs from birth-6m/o - Infected sheep develop subclinical Johne's, then clinical shedding of Johne's bacteria into the environment -> clinical heavy shedding of Johne's and Ab detectable by ELISA -> exposure of Johne's to lambs from birth-6m/o

Answer 3

- Low sensitivity of diagnostic tests, so lots of false negatives - Inability to detect sub-clinical animals - Practicalities of testing entire flocks - 'Snatch lambing' and artificial rearing not practical - Contact between sheep and cattle (co-grazing/slurry spreading etc)

Answer 4

- Lamb old/thin/high risk ewes away from rest of the flock - Select replacements from younger ewes - Cull low BCS ewes - Maintain good hygiene and clean bedding - Vaccination - reduces shedding and clinical signs (not infection) -- Giudar vaccine reduces shedding by around 90% - can give to all replacements from 4 weeks of age

Answer 5

Cattle & sheep: - MAP - Causes production losses (fertility, growth, longevity) - Transmission mainly faeco-oral, but can be passed in milk/colostrum Cattle: - Scour - Some resistance to S strain - Individual animal testing feasible - No licensed vaccine in cattle: can use Guidar vaccine but it can interfere with TB testing Sheep: - No scour - Susceptible to both S and C strain - Vaccination and transmission management more cost-effective

Answer 6

= BDV - Caused by virus very similar to BVD in cattle (pestivirus) - Proportion of UK flocks infected estimated to be between 30-38% - Intensive flocks at increased risk - transmission in extensive flocks appears to be moderate (less likely to be close contact for spread) - Mainly infects sheep and goats, but can infect cattle - Cattle with BVD can also cause border dz in sheep, but this is not common

Answer 7

- hairy shaker lambs (congenital tremor, neuro signs, weak and odd crimped fleece) - poor ewe fertility - high levels of abortions - weak lambs - far fewer PI sheep survive compared to cattle (0.3-0.6%), so there's often more limited spread

Answer 8

- Transmission via respiratory secretions, transplacental, from dam to offspring during peri-parturient period, or via semen of PI rams

Answer 9

-> mounts an immune response and clears virus - sheep = Ag negative, Ab positive

Answer 10

- abortion, resorption, early embryonic death, mummification, barren ewes - foetus survival with virus in many organs (foetus may have clinical signs (HS) or be clinically healthy) - lamb = Ag positive, Ab negative (PI lamb) - BUT: colostral antibodies produced by the dam of a PI (as long as she isn't a PI herself) may interfere with serology in lambs <8w/o

Answer 11

- either like infection of a sheep <60d or >85d - lamb = Ag positive & Ab negative (PI) OR Ag negative & Ab positive

Answer 12

- lamb born normal, mounted immune response and eliminated virus - lamb = Ag negative, Ab positive

Answer 13

- PI hunt may not be practical (as you would with cattle) - BVD ‘Tag and Test’ not validated for border disease - Natural immunity through exposure of NON PREGNANT animals to PI (but transmission can be slow) - BVD vaccines? No published evidence of this - Don’t retain breeding females from lamb crops with affected cases/test all ewes be retained for breeding (antigen) - Optimise nutrition and parasite control - Extensive systems can limit potential for spread within in a flock, meaning that natural immunity though exposure of non-pregnant animals to a PI may be less reliable

Answer 14

Both: - Pestivirus - Creation of PI animals Border dz: - Time period for PI infection to develop is shorter (0-60 days). Sheep tend not to be housed during this time. - PI animals less likely to survive (0.3-0.6%) - Transmission through flocks often moderate - See poor ewe fertility, hairy shaker or weak lambs and high abortion rates - No vaccine BVD: - Time period for PI infection to develop is longer (45-145 days) - PI animals more likely to survive (0.5-2%) - Transmission through herds tends to be more rapid - Immune suppression, reproductive losses, congenital deformities (varied) - Vaccine There is some evidence that BDV and BVD can be transmitted between cattle and sheep. May become more important as BVD eradication schemes in cattle mean more herds are naïve.

Answer 15

Animal welfare - Weight loss - Respiratory insufficiency - Hairy shaker lambs - Lymph node abscesses Reproductive efficiency - BD may cause losses of up to 50% in naive flocks (2-8% in endemic flocks) - MV associated with a 9% reduction in conception rate Longevity - CLA causes 'thin ewe syndrome' and can cause mastitis = increased culling and reduced milk yield - MV associated with earlier culling Lamb health - BD is associated with increased levels of infectious dz in lambs and reduced growth rates (20%) - MV = 6-7% reduction in milk yield Decreased milk yield = poor lamb growth MV losses due to smaller/weaker lambs, lower weaning weights and higher culling rates

Answer 16

- Biosecurity – most risk from animal movement. - Testing/accreditation -- Premium Sheep and Goat Health Scheme - Screen cull ewes and fallen stock -- Cull ewes and fallen stock are those likely to be infected with iceberg diseases if they are present within the flock, so they are good ones to test -- BD exception here – screening lambs is more useful - Screen bought-in animals -- Ideally pre-purchase - (Quarantine) -- Keep purchased females separate from pregnant ones until after lambing (esp important for BDV but also enzootic abortion)