FieldDxBVDV Persistently Infected Carrier Eradication ProgramClinical signs, differential diagnosis, treatment and prevention in cattle.
Overview
A calf persistently infected in utero with BVD virus sheds the virus for life and is the main source of new outbreaks in a herd. Bovine viral diarrhea virus (BVDV) infection of the fetus before its immune system recognizes the virus as foreign, creating lifelong immune tolerance to it.
Clinical signs
- May appear clinically normal or small and unthrifty.
- Act as a massive constant reservoir of virus, leading to mucosal disease in some carriers, or abortion and congenital defects in contact animals.
Predisposing factors
- Fetal infection with non-cytopathic (NCP) BVDV strain between 45 and 125 days of gestation, leading to immunotolerance.
- PI animals continuously shed massive quantities of virus.
Treatment
No treatment is available; all confirmed PI carrier animals must be strictly culled or sold directly for slaughter only to remove the herd reservoir.
Prevention
1. Test the herd using bulk tank milk PCR or individual PCR. 2. If bulk tank tests positive, test individual cows and calves. 3. If a calf is positive, test the dam. 4. If dam is positive, cull dam and calf. 5. If dam is negative (calf was transient/acute), return dam to breeding herd after weaning the calf. 6. Retest positives after 30 days to confirm PI vs. transient status.
Source
A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER (Passages 113-117 & Image 17).
MSD Veterinary Manual — Bovine Viral Diarrhea (accessed 2026-08-11)
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