January 2025

Should we still be worried about BVDV?

By Dr. Gregg A. Hanzlicek

Numerous field surveys and results from bovine submissions to the Kansas State Veterinary Diagnostic Laboratory (KSVDL) indicate that BVDV is relatively rare in our cattle populations. Due to the low prevalence, we often are asked if biosecurity, testing, and vaccination against BVDV is still warranted. The case below might help answer those questions.

The owner of herd of 200 registered adult beef cows routinely tested the herd for bovine leukosis and Johne’s disease. The herd was split into multiple pasture groups that included about 60 adults in each. Most of the pastures did not have exposure to neighboring herds.

A group of 12 weaned heifer calves were to be offered for sale and the owner submitted an ear notch from each for BVDV PCR testing. The owner did not believe that BVD exposure had occurred, but he wanted to make sure the sale-animals were completely healthy. Four of the calves were BVDV PCR positive, all with cycle time (Ct) values below 30.

Studies conducted by KSVDL suggest that animals with ear notch Ct values below 30 are very likely to be persistently infected with BVDV. The only way to definitively determine persistent infection status is by isolating each of the positive animals and re-testing in three or more weeks. If an animal is transiently infected (a non-PI), this recovery period should allow them to clear the BVDV virus from their system and the subsequent test result should be negative. (further discussion below)

Because of the high economic value of these calves, individual isolation and retesting at three weeks was completed. All four animals were PCR positive again with Ct values below 30. Their dams were BVDV negative.

This herd had not observed excessive health or reproductive issues, and it had been closed for several years before testing. Artificial insemination-only is practiced, and female replacements are selected from home-raised animals. The vaccination program included a twice-yearly administration of a killed product containing both BVDV type 1 and 2.

What could be the source of exposure?

Often in BVDV investigations, the source of the viral exposure is never determined. Is it possible that BVDV was brought in before closing this herd, and it has been circulating since that time? If this were true, and the virus followed the commonly published disease scenarios, we would expect some observable previous year’s negative health or reproductive effects. Could there have been exposure through fence-line contact? There was fence-line contact with a single neighbor’s herd during this past breeding season. The health status of the neighbor’s herd was unknown. Is it possible that exposure to wildlife could explain the exposure? There have been reports of BVDV PI whitetail deer fawns present in some locations. Although, the interaction dynamics between wildlife and domesticated livestock is not well understood, this may offer another exposure explanation.

Given the results of this workup, a recent herd BVDV exposure did occur from an unknow source. The important message is that this virus is still present in animal populations and prevention methods are still appropriate.

Best practices to prevent the introduction of BVDV into a herd are several. 1.) An appropriate vaccination program designed by the local veterinary practitioner is extremely important. Some modified live BVDV vaccines are labeled as protective against the formation of persistently infected calves, but this vaccine type is not appropriate for every herd. No killed vaccine products carry PI protection label. Vaccines are tools and none provide absolute protection, but the choice of killed vs. modified live and vaccine-administration timing are important considerations that should be guided by the local veterinarian. 2) Quarantining new additions from the rest of the herd for 30 days is also important. Isolating them to allow the “clearance” of any viral infections (not just BVDV) they may possess will reduce the probability of exposure to the resident herd. 3) If new additions are purchased from unknown sources, testing each purchased animal for BVDV at the beginning of the quarantine period is very important. The key to the success of this program is to use the test that performs the best for identifying BVDV carriers.

Carriers can be persistent carriers (PI animals) or transient carriers (TI animals). During the 30-day quarantine period the TI animals, if not presently exposed to PI animals, should clear the infection and become non-carriers. PI animals are different, they will never be non-carriers and must be found and either isolated from the rest of the herd or disposed of appropriately.

A blinded study completed at KSVDL compared all test-types available for identifying PI animals and the results clearly indicated that polymerase chain reaction (PCR) performs the best. The other tests, (IHC, antigen capture ELISA, and BVD snap test) were unable to correctly identify up to 3% of the PI animals. One PI can cause major reproductive and health issues in any herd.

BVDV is still present in U.S. cow-calf herds. Protection against BVDV infection through a multi-faceted program that is best designed by each producer’s local veterinarian.

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