UNDERSTANDING CONGENITAL INFECTION

When BVD strikes fetal calves

Of all the viral diseases afflicting beef and dairy herds, Bovine Viral Diarrhea (BVD) is one of the costliest, with a wide range of financial consequences ensuing directly from fetal infection.^1,2

Calves born after fetal infection may be either persistently infected (PI) or congenitally infected (CI). Here’s how they differ.

Persistently Infected (PI) Calves: A major reservoir of BVDV

A PI calf results when a fetus survives a BVD virus (BVDV) infection occurring at approximately between 45 to 125 days of gestation.

PI calves are PI for life due to the timing of their infection. Because their immune systems were not developed enough to recognize BVDV as an infectious agent, PI animals “tolerate” the virus and develop no antibodies. Consequently, they become reservoirs for BVDV, which they continue to shed, unpredictably, throughout their lives. In fact, PI cattle
are considered to be the primary source of BVDV transmission.²

Congenitally Infected (CI) Calves

After approximately 125 days of gestation, a fetus becomes increasingly immunocompetent.¹ If infected with BVDV during this period, a fetus that survives is deemed CI. At birth, most CI calves appear clinically normal and have antibodies for BVDV.

Dynamics of BVDV infection during gestation

What may result when BVDV infection of the dam occurs...

Days following conception

PI and CI calves compromise herd health and productivity

CI calves: More numerous and costly than generally thought

Although PI calves have historically dominated “coverage” in the literature and discussion in the industry, a major study¹ involving 446 dairy calves shows that CI calves can represent serious health costs and performance problems for producers.

Muñoz-Zanzi CA, Hietala SK, Thurmond MC, Johnson WO. Quantification, risk factors, and health impact of natural
congenital infection with bovine viral diarrhea virus in dairy calves. Am. J. Vet. Res. 2003. 64(3): 358-365

Helping your clients control PI and CI calves

BVDV-control programs come in many forms, but one measure remains essential to all of them — vaccination. Minimizing the possible occurrence of CI and PI calves requires BVDV vaccines that offer the dam the longest protection possible during gestation.