BVD

Question 1

Diseases within Cattle Health Certification Standard System.

Answer 1

Significant endemic infectious diseases in the UK.
Farmers have the sole responsibility for the control of these.
BVD.
Johne’s.
Leptospirosis.
Bovine Herpes Virus 1 (BHV-1) / Infectious Bovine Rhinotracheitis (IBR).

Question 2

How can calves become infected with BVD?
What can BVD cause?

Answer 2

Infection in-utero.
Calves infected before developing a functional immune system will see the antigen as self.
Therefore will not mount an immune response to that virus.
- persistently infected (some appear normal).
Immunosuppression and congenital defects (shortened tail, additional ribs, cataracts, cerebellar hypoplasia), respiratory diseases.
Most of the time, does not cause diarrhoea.

Question 3

Hx questions in BVD case?

Answer 3

How many calves have been affected?
Is it only the calves out of the heifers?
Have any calves died?
Are the cases responding to Tx?
How do you feed colostrum?
Has the management / housing of the calves changed since last year?
What do you vaccinate against?

Question 4

Clinical signs associated with BVDV?

Answer 4

Abortion.
Poor pregnancy rates.
Calf pneumonia.
Calf D+.
Congenital abnormalities.
Immunosuppression.
Mucosal disease.
Stunted growth.

Question 5

1. BVDV family.
2. BVDV genus.
3. What other animals can BVDV affect?

Answer 5

1. Flaviviridae.
2. Pestivirus.
3. Sheep and pigs.

Question 6

1. BVDV genotypes.
2. BVDV biotypes.

Answer 6

1. BVDV 1 = classical form.
   BVDV 2 = severe acute BVD (haemorrhagic syndrome) (rare).
2. Non-cytopathic ~90%.
   - causes immunosuppression, persistent infection – these calves cannot recognise that the virus as foreign (antigen).
   Cytopathic ~10%.
   - either acquired from another animal or due to virus mutation.
   - damages cells.
   - animal will not mount an immune response as does not recognise the antigen as foreign.
   - get fatal mucosal disease.

Question 7

Clinical syndromes of BVDV?

Answer 7

Naive adult cattle:
- usually subclinical.
- systemic.
– mild pyrexia +/- D+.
– reduced milk yield.
- reproductive.
– poor fertility, early embryonic death and abortion.
– congenital defects –> when calf becomes infected around about the time it is able to mount an immune response as attacking tissues that are still developing.
– production of PI calves.
–> only ones that will get mucosal disease.
–> reservoir of infection in the population.
Naive calves:
- pyrexia +/- D+.
- immunosuppression.
– respiratory disease.
– calf D+.
– other infectious diseases.
- acute haemorrhagic enteritis + death (rare).
PI calves:
- poor growth rates.
- immunosuppression.
- mucosal disease – only when infected w/ cytopathic virus.

Question 8

Epidemiology of BVDV?

Answer 8

Transmission.
- faeco-oral.
- transplacental.
2 broad syndromes.
- acute infection followed by immunity.
- persistent infection +/- mucosal disease.

Question 9

A naive dam nfected during pregnancy.
Effects on the foetus.

Answer 9

0-1m pregnant = EED/LED.
1-4m pregnant = immunotolerance. PI calf. NCP virus produced.
4-9m pregnant = congenital abnormalities.
Abortion of the calf can occur at any stage.

Question 10

Mucosal disease process.

Answer 10

PI calves are immunotolerant to NCP virus.
- either mutation of virus to CP.
or
- superinfection with CP.
CP causes development of mucosal disease.
Usually in the first 2 years of life.
Some die v quickly.
Some have more chronic, protracted course of disease but ultimately die.

Question 11

Mucosal disease signs.

Answer 11

Mucosal ulceration:
- oropharynx – ulcers, hyperaemia, oral pain, ptyalism, reduced appetite / anorexia.
- muzzle – ulcers, dried cracked inflamed rhinarium.
- gut – ulcers, profuse, homogenous D+.
- feet – ulcers in interdigital cleft
Dermatitis - scabs and crusts, heels, perineal region and between the hind legs.
Eyes - lacrimation, epiphora +/- crusting.
Nose - mucopurulent discharge +/- crusting.
Rapid loss of condition.
Depression.
Ultimately death.

Question 12

Dx of mucosal disease.

Answer 12

Clinical signs.
PM exam.
- microvesicles causing ulcers, lesions throughout alimentary tract, transverse palatine ulcers, longitudinal oesophageal ulcers, depletion of gut-associated lymphoid tissue (GALT) +/- underlying LNs.
Lab testing.
- PCR looking for the virus.

Question 13

Differential diagnoses of mucosal disease.

Answer 13

FMD and differentials of FMD.
Bluetongue.
(Rinderpest).
Malignant catarrhal fever.
Bovine Papular Stomatitis.
BHV-1 (IBR).
Calf diphtheria.

Question 14

1. What if PI animals in herd?
2. When would a PI animal have antibody in its system?

Answer 14

1. Cull PI animals.
   Try to test other animas in herd.
   - antibodies and antigen testing on milk bulk tank with ELISA and PCR.
   – if found to be in herd, look for PI animals.
2. Antibodies derived from colostrum.
   So need to wait until animals are 3-6 months old or older before antibody screening when the antibodies will have waned.

Question 15

How to not produce PI animals.

Answer 15

Test animals for antigen and antibody.
Identify PI animals (antigen but no antibody) and cull.
Ensure all animals are vaccinated before they are pregnant.
Strict biosecurity.
Close monitoring of the herd.

Question 16

Monitoring of stock for BVDV.

Answer 16

Annual youngstock screen.
- 9-18m old animals, unvaccinated.
- separately managed groups.
Quarterly bulk milk PCR.
Establish status of purchased stock.
Possibly tag and test all calves born.