Bovine Viral Diarrhea Virus or BVDV is
one of the most costly bovine diseases in the world. But the power to bring BVDV under control is within reach. The first step is to understand how BVDV
enters a herd and how the disease spreads. In this presentation we’ll
discuss the impact of BVDV on herd health and farm profits, how BVDV
enters a herd, the role of persistently infected animals in transmitting the
virus, and the control strategies needed to detect and eliminate persistently
infected animals. So what exactly is BVDV? It’s a member
of the Pestivirus genus and it’s a highly contagious virus that can infect
cattle of all ages in any herd size 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 or have
stillbirths. Infected animals frequently have diarrhea, bruises, or bleeding
lesions. Their blood may not clot effectively. Young calves that contract BVDV are often weak in unthrifty and may have difficulty standing and nursing.
BVDV also suppresses the immune system.
This makes infected animals susceptible 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 euro or 10 to 88 dollars per head.
Controlling BVDV is essential to herd health, productivity, and profit. The
trouble is, not all BVDV infections are alike. Persistent infections are much
more serious than transient infections. A transient infection is short-term. It
lasts only 10 to 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 run its course the animal
becomes immune to further BVDV infection.
A persistently infected animal or a 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. Let’s watch how BVDV enters a healthy herd and how
animals become persistently infected. A healthy herd becomes infected with BVDV
whenever a PI animal shown here in red 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 adjoining pens.
If infection enters from a transiently infected animal shown here in yellow it
spreads through the herd at a slower rate because the transiently infected
animal sheds a moderate amount of virus. But if 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 indicated here in green. 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 to 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 any other way. How can you know whether a calf is
persistently infected. Many PI calves appear weak and sickly. In addition many are
often stillborn, die 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 the herd or they grow to adulthood spreading infection. Or
they may be sold and spread infection to other farms and 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
protect your herd. Use diagnostic tests to detect BVDV
PIs and 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. First determine your herd
status. Second test all new introductions to the herd including newborn calves. And
third work with your veterinarian to design an efficient biosecurity and
vaccination program where regulations allow.
IDEXX offers an array of BVDV diagnostic solutions to help you screen
and remove PI animals from your herd. Speak with your IDEXX representative
for information about tests and eradication and control programs. you