Bovine Viral Diarrhea is a significant disease in alpaca. Unlike many other virus species, the BVD virus can infect a fetus in utero by crossing the placental barrier. If that happens during early pregnancy, specifically in the first trimester, the virus establishes itself at a time when the fetus’ immune system is still immature and unable to mount an immune response. At the time of birth, the virus will be present in very high numbers in the blood and virtually every organ and tissue of the cria. Without the benefit of an immune response to fight the virus, the cria will harbor BVDV for the rest of its life and is, by definition, persistently infected (PI).
While the development of a PI cria is rare, it is possible for such cria to be born, and to grow up, uneventfully and unrecognizable by observation only. During its stay on the premises, however, it will shed BVDV virus through every bodily fluid, including urine, feces, nasal excretions, tear fluid, and saliva, thereby not only contaminating the environment but also potentially infecting every alpaca it gets commingled with.
This creates a significant risk for all other animals on the premises and, if traveling to a show, many other animals to become transiently infected (TI) with BVDV. While those animals generally recover, they can cause significant economic losses to the alpaca owner, mostly through infection of other animals, possibly with significant veterinary expenses and reduced fertility. Additionally, if alpacas are kept alongside cattle, the virus can very readily affect the cattle as well. PI animals are considered to be the single most important and effective transmission mode of BVDV.
It is the VDX policy that, in the event of a BVDV positive test result, the client will be notified as soon as possible. Since, generally, the diagnosis of BVDV PI means the animal will be culled, clients are strongly encouraged to conduct follow up testing to confirm the diagnosis. Neogen will conduct the follow up testing at no charge, requesting only that whole blood collected in a purple top tube is sent to the lab. Confirmatory testing is conducted, potentially involving a third-party laboratory, until an unambiguous confirmation has been achieved.
In general, the sample type submitted is a blood card, where a small amount of blood is soaked up by a barcoded filter card. If a sample is found positive, a second confirmatory test with whole blood in a purple top tube should be conducted 3 weeks after the first sample collection. If the animal is unable to clear the virus from the blood stream within that time frame it must be considered PI.
Serum samples are not a good sample type because there is the potential that maternal BVDV antibodies, passively transferred to the cria through the mother’s milk, will force the virus from the bloodstream into the tissues. This effect is transient since eventually, the maternal antibodies will fade away. If serum is collected during that time of transient passive protection, there will be no virus present and a false-negative diagnosis will be made. It is, therefore, important to make sure that whole blood is either immediately collected on a blood card or collected in a purple-top (EDTA) tube and submitted as is.
BVDV testing is conducted using the polymerase chain reaction method (real time PCR), which provides excellent sensitivity and specificity.
