Infectious disease control

Question 1

Clinical presentation of BVDv

Answer 1

○ Immune suppression
○ Reduced fertility
○ Abortion
○ Congenital defects in calves
○ Milk drop
○ Mucosal disease
○ Impacts on productivity

Question 2

Diagnosing BVDv on farm

Answer 2

Bulk milk test for virus (PCR)
§ ? PI in the milking herd

Bulk milk test for antibody
§ Cows exposed to BVDv
§ Vaccine immunity
§ Level grade LOW/MEDIUM/HIGH

Serology on youngstock
§ Spot check on sample (n=5, n=10?)
§ Aged 9-12 months
§ Each epidemiological group

Why just 5?
§ If PI present the seroprevalence will be greater than 50%
§ Looking to see if at least one of the animals has seroconverted
§ If all negative, what is the probability of BVD being present?
□ (1-prevalence)^5
□ 3.3%
□ 0.1% with 10 samples!!

Question 3

Control of BVDv

Answer 3

BVD circulating
§ Bulk milk virus PCR positive
§ Positive serology in youngstock (be aware multivalent pneumonia vaccines)

PI hunt and remove
§ Blood sample all cattle
§ Appropriate test for the age of the animal
§ Pooled samples

Tag and test
§ Identify PIs young and remove from herd

Vaccination

Question 4

Clinical presentation of IBR

Answer 4

○ Respiratory disease in all ages of stock
○ Infectious pustular vulvovaginitis
§ Venereal transmission
○ Reproductive effects
§ Infertility
§ Abortion
○ Milk drop
○ Deaths

Question 5

Identification and control of IBR

Answer 5

Bulk milk serology for antibody
○ Exposure to infection, could be latently infected
○ Vaccination

Youngstock serology testing
○ (Be aware multivalent pneumonia vaccines)

Control
○ Vaccination

Vaccine technology
○ DIVA/Marker vaccine available
○ Glycoprotein E (gE) deleted vaccine
§ Can still seroconvert to wildtype
§ Do not become latently infected

Interpretation
○ IBR serology +ve
§ Natural infection or vaccination
○ IBR gE serology +ve
§ Wild type infection only
○ IBR +ve, IBR gE -ve
§ Marker vaccinated

Question 6

Aetiology of Johne’s disease

Answer 6

Infection with Mycobacterium avium subsp. Paratuberculosis (MAP)

Infection early in life
○ Greatest in younger animals

Long incubation period
○ Disease manifest 5-7 years of age

Transmission
○ Faeco-oral
○ In milk and colostrum
○ In-utero

Question 7

Tests available for Johne’s

Answer 7

○ Faecal culture - gold standard but takes weeks, intermittent shedding throughout disease course
○ Faecal PCR
○ Bulk milk serology
○ Individual animal blood serology
○ Individual cow milk serology

Serological tests have low sensitivity but high specificity

Question 8

Johne’s serology frequency

Answer 8

Dairy farms
§ Individual cow milk serology quarterly
§ Cow assigned level of risk
□ Control measured applied

Beef farms
§ Individual cow blood serology usually annually
□ Time related to breeding season
§ Follow up faecal PCR

Question 9

Control of Johne’s

Answer 9

May not be economic to eradicate infected animals

Limit transmission opportunities

High risk cows - cull (after lactation)
§ Serology level
§ Repeated positive

Lower risk cows
§ Do not keep their calves as replacements

Reduce exposure of calves to infected cows
§ No feeding of milk/colostrum from risk cows
§ Keep risk cows out of calving areas
§ Cleanliness
§ Biosecurity