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April 2007 Issue

Bovine Viral Diarrhea Virus (BVD):
Establishing an Effective BVD Testing Strategy in Your Practice or Operation

BVD Impacts Producer Profitability, Animal Health
Bovine Viral Diarrhea Virus (BVD) is one of the most important pathogenic viruses in cattle, and has been called the root of many evils for the industry. In October and November 2006, veterinarians and feedyard operators from across the country gathered via a series of Beck Ag AgTelePanel conference calls to discuss how both groups can work together toward eliminating the virus with a solid BVD testing plan.

“We’ve not been able to control this disease with vaccinations alone,” stated Dr. Bob Larson of Kansas State University. “I think we have to look at testing and animal movement, and really get aggressive about controlling BVD. But we’re now getting the tools that we need to do that.”

Dr. Larson is very familiar with BVD issues in the cattle industry today. He serves as the Chairman of the BVD committee with the American Veterinary Consultants and also holds positions on the BVD ad hoc committee of the National Cattlemen’s Beef Association and the American Association of Bovine Practitioners. The awareness and concern over BVD has become such a priority that veterinary and livestock associations together are calling for a united front in eradicating BVD.

Despite nearly half a century of efforts to control BVD, Dr. Larson said it continues to be a major bovine health threat. “We’ve had good tools developed in terms of vaccinations for some time, yet we still have not beaten back the commonness of this disease.” But Dr. Larson contended the tide may be turning. “I think combining vaccination with other tools will allow producers and the industry to make some real headway.”

BVD Explained
Bovine viral diarrhea virus (BVD or BVDV) is a member virus of the genus Pestivirus within the family Flaviviridae. It is a single stranded enveloped RNA virus. The virus crosses the placenta in infected pregnant cows, causing reproductive losses due to abortions, stillborn calves or calves that die early in life. When cows become infected between days 30 and 150 of gestation, some calves survive, becoming immunotolerant to the virus. These persistently infected (PI) calves excrete large amounts of virus, infecting other animals in the herd. The carrier animals often die of mucosal disease in the first two years of life.

Persistently Infected (PI) Animals Are Biggest Threat
BVD poses unique challenges. “By far, the largest source of the virus and the biggest threat is in persistently infected animals,” says Dr. Larson. He explained, “…these are calves that were infected when they were still inside their mothers as fetuses. When they’re born they are persistently infected, meaning that they are infected for the rest of their life from that day onward with the virus.”

Here, Larson made an important distinction: “That persistently infected animal can only be infected while it is still a fetus. An animal that is positive, that is a PI animal at birth, will be a PI animal the rest of their life. Also, an animal that is not a PI at birth can never become a PI once it is born.”

PI calves shed tremendous quantities of the virus when they come into contact with other animals. Larson noted, “By far the greatest risk of the virus being spread is nose-to-nose contact between a PI animal and susceptible animals–that would be pen-mates and those right across the fence, around water troughs, etc. There are lots of opportunities to pass that virus across the fence in a feedlot situation.”

Persistently Infected Animals Affect Herd Health and Profitability
Not only does BVD challenge overall animal health and herd health, it impacts producer profitability. During the AgTelePanel conferences, veterinarians and feedyard operators agreed how important it is to eliminate PI calves from the herd.

Research supports the conference consensus. In a feedyard study led by Dr. Guy Loneragan, which compared non-BVD-exposed cattle to cattle with direct exposure, there were significant increases in morbidity and incidence of treatment for bovine respiratory tract disease (BRD) in cattle with direct exposure either in the pen or in the pen adjacent to a PI animal.

In another study, Dr. Bill Hessman, a Kansas practitioner, investigated how PI calves infect other cattle and the effect that has on health and performance in a herd. He found that the presence of BVD impacts cost of grain, feed conversion efficiency, weight gain and mortality causing a total cost of $30.78–$41.17 per head across the entire feedyard.

Individual Testing Is Key
Preventing exposure is one step in the process and PI calves cannot be eliminated without identifying them through a testing protocol.

Justin Nelson, a feedyard operator from Dimmit, Texas, says careful and aggressive BVD testing is important to his operation. “We test and get results back on a lot basis. We immediately pull out any animal that comes back hot and they go into an isolation pen. I’ve found at times, I’ll have a 20–60 percent death loss in those PI calves. Other times, I’ll raise them in an isolation pen with no problem whatsoever.” The point, he emphasized, is that those animals are isolated so they are unable to infect any other animals and impede overall performance of the herd.

Some feedyards have tried pooled testing where only a percentage of animals are tested for the presence of BVD. But Dr. Dan Stafford, consulting veterinarian from Shiner, Texas, said individual testing is far more advantageous. “Timeliness and accuracy are key here. You get results quicker when you are doing an individual test from the beginning.” He said early and correct identification of infected animals allows producers to eliminate the source of other infections from the herd. “You get results when problem calves are identified quickly.”

IDEXX HerdChek* BVD Antigen Test Kit offers fast, accurate results

The IDEXX HerdChek* BVD Antigen Test Kit is an enzyme-linked immunosorbent assay (ELISA) designed to detect BVDV antigen in serum and ear-notch tissue samples. Veterinarians and feedyard operators alike cite the effectiveness and ease of using the HerdChek* Test Kit in identifying BVD cases.

Justin Nelson reports the HerdChek* Test Kit works well in his operation. “It works with ease and speed of results. I incorporated testing into a processing protocol and it added no time to the overall process. It’s easy, simple and pretty straightforward. The only challenge is you have to find a way to identify each individual animal, which to me is a good thing. It forces me to do a good thing.”

“When we started using these tests, I was very skeptical on accuracy,” says Nelson. “And for a considerable amount of time, I would retest every positive, and I would also retest the animal that went through the chute in front of it and the animal that went through the chute behind it. And I’ll have to say that over the course of this year, and with several thousand head going through the chute, I have yet to have a positive result come back to me that was not confirmed on a retest–and a blind retest at that. I am very confident in the accuracy of the test.”

This type of precision and accuracy is no surprise to John Lawrence. He holds a senior R&D position with IDEXX Laboratories. He has developed over a dozen USDA-licensed veterinary diagnostic products. Lawrence explained that IDEXX HerdChek* Antigen Test Kits are USDA-licensed, meaning they are validated and approved through a rigorous process. “This product is produced through a licensed facility in a highly controlled manufacturing environment.” Lawrence continued, “Compared to other techniques that are out there, this is the only one that’s standardized and optimized for single animal testing. We’ve got some PCR tests that are being used out there that are not standardized or validated, so antigen ELISA really is the only proven method.”

In addition, Lawrence points out recent independent studies that showed effective results from the IDEXX HerdChek* Antigen Test Kits. “These studies showed that the antigen ELISA test is probably a better performer of any out there–most accurate, most reliable. In some cases, either on single animals or in pooling, the PCR is actually missing some true PI animals. So we feel pretty good about what we’ve done so far, and the comments are just great to hear.”

Ultimately, it comes down to performance. As one veterinarian noted, proper identification of infected animals greatly impacts the producer’s bottom line. Conference participants reported cattle perform much better when they don’t have to deal with daily contact of BVD virus. By identifying and removing infected animals, producers get better performance out of their animals.

Institut Pourquier in Montpellier, France, officially joined IDEXX Laboratories as a fully owned French subsidiary on March 6, 2007. Founded in 1870, the Institut Pourquier is a landmark institution in the development of human and production animal vaccines and diagnostic reagents. The Institut is known as one of the first developers of a lyophilized smallpox vaccine, contributing to the World Health Organization’s campaign to eradicate smallpox. In the 1980s, the Institut turned its focus exclusively on production animal diseases, and today has a worldwide-distributed portfolio of high quality products addressing more than 25 pathologies affecting bovines, small ruminants, equine, porcine and poultry. Among them, its diagnostic reagents for Paratuberculosis are now considered to be the reference tests by most European laboratories. With a state-of-the-art facility, high-level expertise, and a legacy of strong relationships throughout Europe, the Institut Pourquier is an exceptional complement to IDEXX’s global offerings, and a great benefit to our customers.

IDEXX and Institut Pourquier currently intend to continue providing and supporting their respective portfolios. Customers are advised to continue to contact their normal IDEXX or Institut Pourquier sales manager or distributor regarding IDEXX or Institut Pourquier products, respectively. For more information about Institut Pourquier visit http://www.institut-pourquier.fr.

Mixing samples for reliable test results

Mixing samples before plating is a very important step when running an ELISA test. Samples that are not mixed well will produce variable results.

Frozen samples can be thawed at room temperature or in a refrigerator. All thawed samples need to be thoroughly mixed prior to dilution to ensure that the proteins are dispersed throughout the sample. Mix by gentle vortexing or inverting at least five times. Frothing or over-mixing of samples will cause denaturation of serum proteins.

Prepared dilutions, especially the 1:500 in poultry kits, also require mixing with gentle vortexing or a pipette set at a volume of 100 µl or greater prior to plating. Mixing the diluted sample with a micropipette, such as the one utilized for transferring the 1 µl of sample, is not appropriate as the volume exchanged is not enough to thoroughly mix the sample.

When running the BVD test, after allowing the ear notch to soak in PBS, it is important to mix the tissue suspension again prior to running the ELISA.

Events around the world

• Belo Horizonte, Brazil—April 10–12, 2007
  AVESUI
• Berlin, Germany—April 12–14, 2007
  The 27th DVG Congress
• Verona, Italy—May 9–11, 2007
  Safe Pork 2007
• Nürnberg, Germany—May 17–20, 2007
  Bayerischer Tierärztetag
• Moscow, Russia—May 21–23, 2007
  VIV Russia

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