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As of February 1, 2006 Edward J. Dubovi, PhD Director Virology Section, Diagnostic Laboratory, New York State College of Veterinary Medicine, Cornell University and the Alpaca Research Foundation (ARF) have confirmed 40 cases of persistently infected (PI) alpacas with Bovine Viral Diarrhea Virus (BVDV). Although BVDV was initially thought to pose minimal risk to llamas and alpacas, the confirmation of these cases has led to a reevaluation of that thought.
The principal cause of the spread of the disease lies with the persistently infected (PI) cria. The immune system of a fetus infected with the BVDV virus at a certain stage of gestation will not recognize the virus as an infectious agent. At birth, this cria may appear to be normal, but will be persistently infected, shedding vast quantities of BVDV for life, and infecting other animals. They may even become dams themselves and give birth to additional PI cria resulting in the further spread of the disease. While some of the confirmed cases of PI cria in North America have been characterized by low birth weight or, poor doing cria, it is important to realize that they may also appear to be perfectly normal. The PI cria spreads large amounts of BVDV in its saliva, nasal secretions, urine and feces contaminating everything it touches.
Transporting females with cria at their side to other farms for breeding is another way to spread the virus. It would be prudent for all of us to take some precautions and co-operation from all breeders is an important part of this process. Any pregnant females who may have been exposed to BVDV during their pregnancy should have their cria tested for BVDV immediately after birth. Therefore, if a PI cria is found on an individual farm that had outside breedings, there is a need to disclose this information to the owners of the dam of the possible exposure to the virus. This will enable breeders to take appropriate precautions to prevent the possible spread of the disease to their own herd. Those precautions should be testing the suspected female for the presence of BVDV antibodies. If the tests for antibody are negative, it is unlikely the dam is carrying a PI fetus, if the result is positive, isolating that female prior to the birth of the cria is a necessity. The dam and cria should be in quarantine at least 20 feet away from all other animals. Strict hygiene measures must be in place to ensure no contaminates escape the quarantined area. The cria must be tested for the presence of the live virus and blood should be drawn soon after birth.
Polymerase chain reaction (PCR) is the commonly used test for diagnosing active BVDV. The PCR test reacts with a specific segment of the viral genetic material. Since it is so sensitive, it is more prone to giving a false-positive reaction. However, diagnostic laboratories go to great lengths to control this problem; very rarely is a false diagnosis made. It is a very rapid test with results available within a day after the sample is processed. If the first blood test is positive for BVDV, this may only represent an acute infection. A second blood sample must be collected three weeks later and tested to confirm that an animal is indeed persistently infected. This second test is essential for the animal since it will be euthanized based on a second positive test. A PCR test needs to be done only once in an animals lifetime. Low birth weight cria, poor doing cria, very premature cria and alpacas with unexplained illness should be tested for BVDV.
BVD has a short-lived existence in the environment, about 10 days once the source of the infection is removed. Unfortunately, the PI cria will be euthanized, effectively removing the possibility of re-infection on an individual farm. While a PCR test will verify an active virus, Serum Neutralization will determine antibody levels to verify exposure to the virus. Having antibodies does not mean that the animal is unwell or contagious, it shows that the animal was exposed to the virus at some time in the past and mounted an immune response, this could be from a clinical infection (appeared unwell) or a sub clinical infection (never appeared unwell). By having antibodies the alpaca is now protected from any BVD infection in the future.
Other sources for BVDV information are as follows:
www.alpacaresearchfoundation.org
www.silvercloudalpacas.com
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