Transiently Infected (TI) Naïve Antigen – Antibody - Transient infection (2weeks) Antigen + Immune Antibody + Antigen – 4-6 years BVDV Seroconversion Courtesy of Dr. John Pickering
BVDV Disease – Acute (TI) Incubation 5-7 days Viremia (virus in blood circulation) 4-5 d after infection (up to 15 d) Seroconversion 2-4 wk later Virus shedding For 1-2 weeks. Low concentrations compared to PI Diarrhea,slobbering, fever Ulcers - lips, gums, esophagus, etc. Immune suppression Fetal infections Most infections are not noticed - estimate 70-90% are subclinical but can be severe (death) if virulent strain Ref: Baker, Vet Cl. N. Am. 11:3, 1995
PI development Persistently Infected Carriers (PI’s) Infection BVD Virus 1 – 4 months gestation 93% of all PI’s produced this way PI’s produce PI’s 100% of the time Calf Courtesy of Dr. John Pickering
Persistent Infection PI Carriers If fetus becomes a PI and survives - will continuously shed millions of virus all its life from all its secretions - feces - urine - saliva - nasal - milk - semen - uterine secretions - aborted membranes, fluids, fetus - Across fences. Virus survives in environment up to 7 days If it’s a female and later gets pregnant then its offspring will be a PI and its offspring and so on and so on
Viral shedding rate RED DOT RED DOT = Normal Calf (non- PI) with a BVDV infection sheds 10,000 viral particles per day and recovers in 10–14 days. YELLOW DOTS YELLOW DOTS = PI calf sheds 10 million viral particles EVERY DAY (1000 x non-PI). Now you can understand how one calf that is persistently infected can affect so many other cattle..
What does it do? Effects on young stock (3-12 months of age) Unthrifty/Rough coats Diarrhea Coughing Ulcers in mouth (sometimes!!) Lameness Immunosuppression Often confused with parasitism High morbidity Low mortality
The classic BVD quiz Spot the PI among this group of heifers: Should instead be: Spot both BVD PI carriers
Diagnosis How do you find out if you have BVD? By blood or milk testing By skin testing Testing tissues of a dead animal.
PI Diagnosis Antigen Capture ELISA of Ear Notch or Serum identifies PI animals TI usually test – Calves must be 3 months old or precolostral to use serum Screening replacement heifers, bulls, stockers, purchased cows and show animals Screening prior to sale by seedstock producers Sick or dead calves-esp. BRD
Diagnosis in Live Animals Any positive test for PI in valuable animals can be confirmed by segregating the animal then retesting with serum ELISA or whole blood VI/PCR at least 3 weeks later to eliminate TIs and false positives. BVDV Serum Neutralization Test-detects and quantifies antibodies. Differentiation of titers due to vaccination or field virus exposure is difficult.
BVD Vaccination - Calves Vaccinate calves after 4 months of age Modified Live: 1 dose is protective; 2 doses best Killed: Two shots, weeks apart is required Best if done at least two weeks before stress (weaning/transport/commingling) 12 months protection against clinical disease
From the OSV: BVD-PI has significant impact on the health of Kentucky cattle herds. BVD including PI is reportable by labs, vets, owners, and others having knowledge. Both privately owned and university laboratories are currently reporting positive results
From the OSV: Interpretation of test results is currently being evaluated. It appears that the (AC) ELISA test provides a significant confidence level for identifying PI positive cattle. [Note from Arnold: The test kit used at the UKVDL requires two positive test results at minimum 3 weeks apart in order to call an animal “BVD-PI”; however, this may not be the case at other laboratories]
From the OSV: Actions by OSV upon receiving positive test results: Contact the owner/attending veterinarian regarding the current status and location of the animal. Provide an opportunity for the owner to understand the impact of the disease and the laws governing SV response.
Options for the Owner: Isolate and retest in 2-3 weeks to confirm the diagnosis. Transport to slaughter with OSV permit. Isolate either on owner’s farm or at permitted feedlot and feed to slaughter only. Euthanize and dispose of by an approved method. Test positive animal is not to be sold, given away, or transported without approval of the SV
Other Issues Under Consideration Official I.D. of tested animals recorded on laboratory accession sheet. Confirmed positive animal is officially ID’d and branded as positive. All movements of positive animal shall be documented by USDA Target education at the cow/calf level.