Bovine Viral Diarrhea Virus (BVDV)

Bovine viral diarrhea virus or BVDV is one of the most expensive bovine diseases in the world. But the power to control BVDV is within reach. The initial step is to understand how BVDV enters a herd and how the infection spreads.

BVDV is a member of the Pestivirus genus and it is a highly contagious virus that can infect cattle of all ages in any herd size and anywhere in the world. BVDV causes a variety of serious health problems. Cows and bulls are often infertile while infected and pregnant cows may abort their calves. Infected animals frequently have diarrhea, bruises, or bleeding lesions. Their blood may not clot effectively. Young calves that contract BVDV are often weak unthrifty and may have difficulty standing and nursing. BVDV also suppresses the immune system. This makes infected animals susceptible to other animals to other enteric and respiratory diseases such as scours and pneumonia. These illnesses often cause more losses than the BVDV infection itself. Infection weakens the herd and lowers performance and that lowers profits. The virus costs cattle and dairy farms alike anywhere from 7 to 63 euros or 10 to 88 dollars per head. Controlling BVDV is essential to herd health productivity and profit. The trouble is not all be BVDV infections are alike persistent infections are much more serious than transient infections. A transient infection is short-term, it lasts only 10-14 days. Yet can still affect overall herd health. The transiently infected animal is sick and less productive. It’s contagious during infection but usually recovers. After the infection has spread, the animal becomes immune to BVDV infection. A persistently infected animal or PI has a lifelong BVDV infection. The animal is always infected and always contagious. In fact, a PI animal sheds 1000 times more virus than a transiently infected animal. PI animals are the main source of BVDV transmission. They’re the reason the disease is so difficult to eradicate.

The entrance of BVDV in a healthy herd

A healthy herd becomes infected with BVDV whenever a PI enters the herd. The herd can also become infected when healthy animals have contact with sick animals. This can take place at the fence line or in joining pens. If the infection enters from a transiently infected animal, it spreads through the herd at a slower rate because the transiently infected animal sheds a moderate amount of virus. But if the infection starts from a persistently infected animal, it spreads through the herd quickly. This is because a PI animal sheds 1000 times more virus than a transiently infected one. All the newly infected animals except unborn calves acquire the transient form of BVDV infection. Once infected the animals become weak and unproductive. Other diseases like pneumonia begin to appear. Profits drop as animals become unproductive and expenses rise as animals contract other diseases and require treatment. When BVDV has run its course, most animals recover and develop immunity. But if pregnant cows are infected, they may soon give birth to persistently infected calves. Here’s what happens when a pregnant cow becomes infected with BVDV between 40 days and 120 days gestation. The virus crosses the placenta and infects the unborn calf. At this stage of development, the unborn calf cannot mount an immune response. So, it becomes infected but also tolerant of the virus. These calves are born persistently infected. They will always have BVDV and remain extremely contagious throughout their lives. All persistently infected animals are born with the infection. They cannot become persistently infected in any other way. Many PI calves appear weak and sickly. In addition, many are often stillborn died at a young age, or get mucosal disease. The mortality rate is high. When PI calves die, the farm loses the investment in those calves along with the future profits. Those animals might have produced but PI animals cannot be identified visually. In fact, and this is very important some PI calves appear as healthy as the healthiest animal in the herd. And because PI calves may look healthy. The infection often goes undetected. PI calves may be allowed to join in the herd or they grow to adulthood spreading infection or they may be sold and spread the infection to other farms feed Lots. And if a female PI calf lives to reproduce, her calves will be persistently infected.

The BVDV cycle can be stopped but only if PI animals are detected early and eliminated before they infect other animals.

Biosecurity measures like these can help can protect your herd:

• Use diagnostic tests to detect BVDV PI’s

• When you identify a PI animal, isolate it immediately

• Prohibit contact between PI animals and other animals, in fact, you should prevent the herd from having contact with animals that might carry infection.

• Follow this three-step strategy to control BVDV

1. Determine your herd status

2. Test all new introductions to the herd including newborn calves

3. Work with your veterinarian to design an efficient biosecurity and vaccination program where regulations allow.