BVDV Flashcards
Classifications and diseases (3)
Pestiviruses: BVDV – cattle: BVD/mucosal disease
Flaviviridae family: BDV – sheep: border disease
Pestivirus genus: CSFV – pigs: classical swine fever
Two geneotypes
Two biotypes
Genotypes:
BVDV 1: classical form of disease
BVDV 2: severe acute BVD (haemorrhagic syndrome)
Biotypes:
non-cytopathic: BVD
noncytopathic followed by cytopathic: mucosal disease
BVDV
Herd level (7) Individuals (2)
Herd level:
- decreased fertility
- abortion
- congenital defects
- stunted calves
- immunosuppression
- (diarrhoea) – transient
- Transplacental transmission – PI which sheds virus
Individuals:
- mucosal disease MD
- persistently infected PI – sheds virus through every orifice/skin
BVD PI (3)
NCP affects when pregnant and crosses placenta and before immune system starts to work and thinks part of self – Persistently infected. The first third of gestation when calf is immunotolerant.
important reservoir of virus
Initial BVD infection (5)
Clinical presentation (4)
- high morbidity, low mortality
- mild fever, inappetance and mild diarrhoea
- reduced milk yield in dairy cows
- rapid recovery within a few days (2-3 days)
- production of virus neutralising antibodies so become immune
Clinical presentation
• reduced fertility, EED (early embryonic death), abortion
• persistently infected calves - excrete the virus & may develop Mucosal Disease
• birth of calves with congenital defects –cerebellar hyperplasia – ataxic, intension tremor, shaking, nystagmus
• rarely acute haemorrhagic enteritis ± death
Mucosal disease (4)
- acquirement (4)
- age
- outcome (3)
- infrequent consequence of BVDV infection : fatal disease (acute/chronic)
- develops only in PI animals [infected NCP BVDV in utero]
- requires presence of NCP and antigenically related CP virus
- Mechanisms - mutation of NCP virus in PI animal, or superinfection of PI animal by CP virus (encountered de novo in the environment)
- 6months-2 years
- invariably fatal
- acute cases die within 1 - 2 weeks
- chronic cases may live for 2 months or more
Mucosal Disease Epidemiology
3 different circumstances of infection
Non-immun pregnant cow:
- day 0- 120: abortion/ foetal stunting
- day 120-240: congenital defects/abortion/foetal stunting
- day 240-280: (calving) abortion/foetal stunting
- Immune pregnant cow or heifer (seropositive for BVDV having encountered the virus previously) (colostral antibody to BVDV) - Infection during pregnancy will not affect the foetus
- Persistently infected cow or heifer (specific immunotolerance to BVD virus) (no colostral antibody to BVDV) - Persistently infected (PI) calf (or abortion).
MD clinical findings
- subjective (7)
- objective (6)
Subjective:
• depression
• reduced appetite / anorexia
• salivation - wetting of hair around the mouth
• profuse, homogeneous, watery diarrhoea
• lacrimation ± crusting around the eyes
• mucopurulent nasal discharge ± crusting around the nose
• loss of body condition - can be severe if chronic
Objective:
• ulcers - all parts of the oropharynx and extending onto the muzzle
• dry, cracked and inflamed rhinarium
• oral pain - resent mouth being opened
• oral flare / flush - reddening of oral mucous membranes
• ulcers in the interdigital cleft
• ± dermatitis - scabs and skin crusts - heels, perineal region and between the hind legs
MD Dx (4)
- clinical signs
- serology – BVD antibody negative, BVD virus positive indicating persistent infection (theoretically test twice; reality don’t – welfare issue so euth.)
- virus isolation
- post mortem
MD DDx (8)
- Foot-and-Mouth Disease - notifiable
- Bluetongue - notifiable
- Bovine Viral Diarrhoea (BVD) / Mucosal Disease
- Malignant Catarrhal Fever
- Bovine Papular Stomatitis (BPS)
- Calf Diphtheria
- Actinobacillosis - Wooden Tongue
- Actinomycosis - Lumpy Jaw
MD Pathology (5)
- microvesicles in the stratified squamous epithelia causing ulcers
- lesions throughout the alimentary tract
- transverse arrangement of ulcers on the palate
- longitudinal oesophageal ulcers
- depletion of gut-associated lymphoid tissue (GALT) ± underlying lymph nodes
BVDV control
- Find PIs and remove:
Identify persistently infected animals (Ag +ve : AB –ve)
Establish exposure (Ag –ve : AB +ve) - Protect against infection (Vaccine, Isolation / biosecurity)
- Monitor disease status: Screen tests (blood / milk)
BVDV Testing
- types (4)
- issues with blood sampling (5)
- Bulk milk testing in dairy herds (ELISA and PCR; 300 cow limit?)
- Individual animal blood samples (Beef & dairy) (ELISA and PCR)
- Ear notch samples (calves) PCR
- Test bulls and herd replacements
Blood sampling:
• Not <1 mo age – do ear tages
• Screen tests – at least 5 from each management group (9-18mo – any colostrum AB should have weaned) look for antibody
• Remember colostral ab can confuse – so don’t do anything until 9 months
• Remember seroconversion may be occurring – animal AB positive it has seroconverted already (not common)
• Does not distinguish between current, historic or vaccine exposure (unless repeated screens are done)
