7 Things You Should Know About
Infection with BVD in the unprotected cow

 

Persistent Infection (PI)

Q: What is BVD?

A:" BVD is a common viral pathogen of cattle," says Dr. Glenn Rogers, a beef cattle specialist at North Carolina State University. "It can cause disease in a number of systems, probably the most important being reproductive. It's also involved with respiratory and digestive diseases. It's in the same class of viruses as hog cholera."

The proper abbreviation is actually BVDV, which stands for Bovine Viral Diarrhea Virus. Some of the common clinical signs you might be familiar with include fever, ulcers, depression, anorexia, diarrhea, excessive salivation and respiratory problems. However, it's such a complex virus that producers can easily fail to recognize its subtle ­ but costly -- symptoms.

Q: What are the symptoms?

A: "A family of several different strains of this virus is responsible for many different disease syndromes, some more evident than others," explains Dr. John Pollreisz, an Amarillo-based senior technical services veterinarian with Pfizer Animal Health. "Some syndromes are more economically devastating than others, but all are capable of causing economic losses to the cow-calf producer."

Certain birth defects may be an ominous indication that you've got BVD in your herd. Physical conditions like cloudy eyes, "dummy" calves that fail to nurse, uncoordinated calves that stand with front legs sprawled and have trouble walking, and "bulldog" calves with short noses and prominent foreheads, can all be caused by in utero exposure to BVD during the second trimester.

This complex viral disease causes other reproductive problems that hit a producer square in the pocketbook.

"The reproductive form of BVD is very relevant ­ and economically devastating -- to cow-calf producers," Pollreisz says. "That would include things like early embryonic death, which a producer will see as animals needing to be bred-back several times. Or, if they've pulled the bull out, they'll simply see open animals at preg-check time.

"BVD can cause sporadic abortion syndrome where, rather than invisible embryonic death, you'll actually see aborted fetuses if the coyotes don't get to them," he adds. "Typically, it is much more sporadic than something like IBR, where you'll see abortion "storms" or several at one time. BVD is usually more of an abortion here and there."

Obviously, that makes it very hard to identify the problem if you've got it. Other problems that stem from BVD infection include Mucosal Disease, a rapidly progressing and severe wasting disease. The animal will suffer ulcerations all the way through its digestive tract, from the mouth to the anus and all the way in-between.

"It can also cause a bleeding syndrome due to platelet deficiency," Pollreisz adds. "Cattle can either spontaneously bleed to death or they can bleed to death from something as mild as a 16-gauge needle injection site. Some animals can bleed to death just by seeping and seeping from those wounds over time."

Of course more invasive procedures, like castration or dehorning, could cause unstoppable bleeding as well. Pollreisz says both dairy and beef operations experience BVD-related hemorrhaging problems, particularly in lightweight calves.

Q: How do my calves get infected with BVD?

A:"The major problem with BVD is the way it affects the fetus, particularly during the first 120 days of pregnancy," explains Rogers. "There is a condition called persistent infection. It occurs when a heifer or cow is exposed to noncytopathic BVD in early pregnancy.

"During that stage, the fetus is not capable of mounting an immune response, so it doesn't develop any immunity," Rogers says. "When it's born, the fetus is persistently infected with the virus. If those animals born with a persistent infection come in contact with the cytopathic form of the virus, they may develop a clinical condition referred to as Mucosal Disease."

However, not all PI (persistently infected) animals develop Mucosal Disease, nor do they all die. In fact, the ones that don't die cause the most problems.

"Some will go ahead and grow, develop and reproduce themselves," says Rogers. "Then they are a constant source of the virus, shedding it and basically serving as the Typhoid Mary of the beef world. Unless you eliminate those animals from your herd, nothing you can do is going to totally solve the problem. You can't vaccinate your way through it because the vaccines are not totally protective, particularly with the fetus."

Acute BVD can be transmitted through inhalation or ingestion of infected saliva, nasal discharge, ocular discharge or feces. Rogers says any of these secretions can carry the virus and spread it. That's how stressed stocker cattle or fed cattle become infected.

Q: What is the difference between an acute infection and chronic?

A:"Persistent infection is like HIV. People understand that when you are infected with the HIV virus, you will always have it, much like these persistently infected calves," explains Pollreisz. "Acute infection occurs in a normal animal that has been exposed to BVD after 150 days of pregnancy ­ whether they're in the third trimester or after they've been born.

"They become infected with it, but are capable of ridding themselves of it. Acute in this case means the animal can become infected, but he can also get over the infection. Whereas persistent infection ­ probably a better term than chronic ­ means that he was born with it, he has it now and he will always have it," he adds.

There is no treatment for either an acute BVD infection or a persistent infection. However, you can provide some care with an acute case of BVD to support the animal's ability to recover. Electrolytes help with fluid loss from diarrhea and antibacterial agents help prevent secondary infections.

Q: How do I know if I have BVD and not some other disease?

A: One of the problems with BVD is the fact that it opens the door to other disease problems, like the Bovine Respiratory Disease (BRD) complex. That's why it's included in the routine vaccination schedules of stocker operators and feedyards. It's also why a BVD infection is difficult to identify apart from the resulting secondary infections.

"A significant factor in cow-calf operations, as well as any beef cattle operation, is just the immune-suppressive nature of the virus," Pollreisz explains. "Again, it's very similar to HIV in humans. It can devastate white blood cells, particularly those that are critical in directing the overall immune response ­ what we call 'helper' cells.

"The result is susceptibility to other infectious diseases. It's like people. They don't die from AIDS due to the HIV virus directly, they die from opportunistic infections that the HIV virus allows to get a foothold."

In a cattle population with BVD circulating through it, producers might see increased scours problems in calves and/or respiratory problems in both nursing and weaned calves.

"Frequently, we'll do diagnostics and come up with other viruses, like rotavirus or coronavirus in scours, or IBR and BRSV in respiratory disease," Pollreisz says. "We'll come up with bacterial problems like E. coli in scours or pasteurella in respiratory disease.

"If all we are doing is a culture, particularly of bacteria, in feces for scours or lungs from calves that died of respiratory disease, it's easy to overlook the true primary problem, which could be a BVD infection that made those animals more susceptible to other diseases."

He says producers have a misconception about the visibility of BVD incidence.

"BVD is reputed to be so severe in impact that when people don't see these dramatic syndromes and these very horrible diseases, they assume they don't have BVD," Pollreisz says. "Actually, the economic losses it causes are far more predominant in the subtle symptoms of reproductive failure and predisposition to other diseases than most people think. It is in the more subtle forms that the disease is most common."

He says he doesn't want to give folks the impression that any time they have a problem it's due to BVD. Rather, he's saying the fact is there's no one syndrome or clinical sign that can be used as a flag to identify BVD, which poses a tremendous difficulty both for producers and their veterinarians.

Q: If you suspect you have a BVD problem, then what?

A: First, contact your veterinarian to initiate the necessary diagnostics to confirm whether or not BVD exists within your herd.

"The key to what you're trying to do is to differentiate the acute from the persistently infected," says Pollreisz. "If that animal is acutely infected ... you don't have to cull that animal -- it will clear the infection." By the way, he believes that blood tests, as far as antibody titers, are overused and over-interpreted.

However, he fully supports the use of a BVD ELISA test (virus isolation from blood samples) to identify persistent infections, which is what you're really looking for. This test runs about $4 at the lab with a two- to three-week turnaround time and has a one-time accuracy rate of 80 percent to 90 percent, according to Pollreisz.

Of course, any animal found to be persistently infected should be culled from the herd. Producers should also make sure the pasture-mates to suspect animals are protected from infection through a sound prevention program. That includes an effective vaccination regime, common-sense animal husbandry practices and taking steps to prevent "buying" the disease.

"Certainly, anything you can do to prevent transmission of the virus from one animal to the next, like disinfecting oral dosing equipment between animals and other basic sanitation measures, would help," says Rogers. "Probably from a herd standpoint, the most important thing is to be careful with the purchase of bred heifers. That's usually the way it's brought onto the farm.

"The heifers appear normal and even if you tested them for persistent infection, they could be negative. But the fetus can be persistently infected and you won't know that until after they're born."

Rogers advises producers to purchase heifers from sources that have a good vaccination program, specifically a pre-breeding BVD immunization program. He also says breeders who have good culling practices tend to move poor-performing animals on more quickly and are less likely to have a PI animal on the place.

"Unfortunately, there are some PI animals that look completely normal and manage to produce calves," he explains. "Any time you have a PI animal that survives and stays in the breeding herd, her calf will always be a PI animal too ­ 100 percent of the time."

Other smart management strategies include avoiding the direct introduction of new animals into the herd and avoiding the mixing of sick animals with susceptible normal animals. Try to get scouring calves away from the rest of the herd and give new herd additions a 21- to 30-day quarantine period, during which they can be tested for persistent infection.

Q: How should I vaccinate against BVD?

A: As far as an effective vaccination schedule, Dr. Kenny Brock, professor at Auburn University's pathobiology department, has the following advice:

* Start vaccinating calves at 4 to 6 months of age, then again at weaning.

* Replacement heifers should have three doses of vaccine by the time they get to breeding age ­ once at 4 to 6 months, again at weaning and then 30 to 45 days prior to breeding. He includes both killed and modified live vaccines in this recommendation.

* Cows should be boostered at least annually.

* Stockers should ideally be vaccinated with two doses before they are shipped according to the above guidelines.

There are a couple of important things to remember about BVD vaccinations. Modified live vaccines cannot be used on pregnant animals and are also not recommended for use on calves nursing pregnant animals. This means you probably need to have a controlled breeding season.

Killed vaccines must be boostered within 28 days. The need for more frequent vaccination is dependent upon the level of challenge and frequency of exposure, says Pollreisz. Unfortunately, a recent nationwide survey showed that only 30 percent of producers adhered to the booster requirement, which means their vaccines likely produced less than the desired response.

There are pros and cons to each type of vaccine depending on the class of cattle you're vaccinating.

"Both killed and modified live vaccines can do an excellent job in protecting against clinical disease," says Pollreisz, whose company manufactures both kinds. "In that, I would include things like diarrhea, respiratory disease and prevention of abortion. That is actually how BVD vaccines are licensed in the United States today.

"In relation to preventing persistent infections, that's a whole different story. No vaccine today actually has a label that says it prevents persistent infection due to BVD," says Pollreisz. Some research has been done on modified live vaccines, which so far shows promising results.

You may have also heard about different types of BVD -- Type I and Type II. Is that important as far as choosing a vaccine? These are simply "two different branches of the same family," says Pollreisz. "As we talk about the two different types of BVD as it relates to vaccination, we have to look at the spectrum of protection a vaccine can provide ­ not only to Type I or Type II, but even to the different strain within each type."

Some vaccines may be more cross-protective against a broader array of different strains of BVD for a longer period of time than others. Your veterinarian or supplier should be able to provide that information to you. The bottom line?

"In reality, the best way for cow-calf producers to recognize whether they have a disease problem is to have a good record-keeping system in place and to set goals, such as percent calf crop or weaning weight," says Pollreisz. "Those types of things are critical.

"When they identify that they aren't meeting their goals, or their record keeping shows they've got health or production problems, then that's an indication to progress with diagnostics to identify exactly what problems they have, including BVD."*