BVD Workshop Flashcards
What type of virus is BVD?
Pestivirus - single stranded positive RNA virus
What is the effect of BVD infection?
Abortion
Mucosal disease
Immunosuppression
Rarely diarrhoea
How does BVD infect an animal?
The virus first replicates in the naso-pharyngeal mucosa and, to high titres, in the tonsils. It then spreads to the regional lymph nodes followed by cell-associated (leukocyte) dissemination throughout the body. The highest levels of virus usually develop in the tonsils, thymus and ileum.
What are the biotypes of BVD?
Cytopathic
Non-cytopathic
Describe the effect of cytopathic BVD
Persistent infection => mucosal disease = acute D+ with ulcers in the mouth, pyrexia and nasal discharge
Describe the effect of non-cytopathic BVD in bulls
Infected semen -> transmit
Transient fever and slight D+
Describe the effect of non-cytopathic BVD in normal cattle
mild fever, transient leukopenia+/- D+
Describe the effect of non-cytopathic BVD in youngstock
profound leukopenia, increased disease susceptibility
Describe the effect of non-cytopathic BVD in pregnant females
Early pregnancy - abortion, congenital damage, PI calves
Mid gestation - congenital damage, foetal loss
Late gestation - no issues
What is the difference between cytopathic and non-cytopathic BVD biotypes?
Non-cytopathic - does not kill cells in culture, more common, leads to PI
Cytopathic - kills cells in culture, associated with mucosal disease in PI animals
Describe how animals with BVD persistent infection get mucosal disease
Mucosal disease occurs when PI animals become superinfected with a cytopathic (cp) strain of BVDV that is closely related to the ncp strain already present.
This cp strain arises due to mutation or genome rearrangement of the resident ncp-BVDV.
Describe the route of BVD infection leading to mucosal disease
The infection initially starts in lymphoid tissues such as: Tonsils, Lymph nodes (LN), Peyer’s patches (gut-associated lymphoid tissue), Lower intestinal lymph nodes (L. Intestinal LN)
The virus then spreads diffusely to the intestinal epithelium, causing extensive ulceration and necrosis.
Why do animals persistently infected with BVDV not respond to non-cytopathic BVD?
Immunotolerance:
If a foetus is infected in utero it recognizes ncp-BVDV as “self”.
As a result, the immune system does not attack the virus or produce antibodies against it.
This means the virus can persist indefinitely in the calf without triggering an immune response.
Viraemia and Virus shedding:
Because PIs never clear the virus, they constantly have viraemia (virus present in the blood).
They shed the virus continuously, infecting other animals in the herd.
No antibody production:
Since the immune system tolerates the virus, PIs never develop antibodies against BVDV, which is why serology (antibody testing) is ineffective for identifying PIs.
Instead, PCR or antigen testing is required to detect the virus.
What is the impact of being persistently infected with BVD?
Decreases daily liveweight game (DLWG)
Immunosuppression => increased risk of disease
What pathology can be seen here? (normal on left)
cerebellar hypoplasia
What congenital defects can be caused by BVD?
cerebellar hypoplasia
thymic hypoplasia
hypotrichosis
alopecia
curly hair coat
brachygnathism (dental malocclusion)
arthrogryposis (joint deformity)
skeletal defects
Give examples of tests for BVD
Biobest
APHA
Why is antibody testing useful in young stock herds?
BVD antibodies in mother => BVD antibodies in milk => BVD antibodies in calves => if no exposure to BVD, antibodies will have waned (‘turned off’) at ~8 months
Antibody testing will prove presence of BVD on farm if tested after 8mths as any antibodies present prove BVD infection
What does testing for BVD antigens show?
Circulating virus or persistent infection
What does it show if an animal is BVD antigen positive but antibody negative?
Persistent infection as immune system recognises BVD as ‘self’ so does not produce antibodies
OR new infection
Differentiate by looking at previous tests
What is the risk of BVD infection in adults?
No issue to the adults - immunocompetent, will be fine
Will produce PI calves
BVDV is closely related to what sheep disease?
Border disease
When youngstock screening how can you identify circulating virus?
All negative results indicates no circulating virus
2 positive results indicates the virus is circulating
