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Diagnosing Bovine Viral Diarrhea in Persistently Infected Animals

  Bovine Viral Diarrhea (or BVD) is a disease complex with many manifestations including subclinical infections, immunosuppression, repeat breeding problems, abortion and mummification, congenital defects, persistent infection (PI), and acute and chronic mucosal disease.  The PI animal results from a viral infection of the fetus during the first four months of gestation.  PI calves may be born prematurely, grow poorly, exhibit lethargy, have difficulty nursing, have reduced resistance to disease, or die at a young age.  Most PI calves will die within the first 18 to 24 months of life; however, PI calves may appear healthy and grow at a normal rate).

  PI cattle in herds or newly introduced to herds are the main source of BVD virus in cattle herds.  Accurate identification of these infected cattle is critical for eliminating infected animals from herds.  There are countries currently in the European Union that are attempting to eliminate or have already successfully eliminated BVD virus.

  Clinically apparent PI animals and PI calves with mucosal disease are not a diagnostic challenge, but accurate identification of clinically silent PI animals requires an accurate herd history and specialized diagnostic tests.  The current “gold standard” for demonstrating
BVD virus is virus isolation.  A high level of viremia is typical in most PI animals so virus is often easily isolated from serum or buffy coats from whole blood.  Virus can also be isolated from nearly every tissue in the body, but greatest results typically come from lymphoid organs (spleen, Peyer’s patches, mesenteric lymph nodes, and thymus).  This test can be time consuming and very expensive if many animals are to be tested.  In addition, circulating maternal antibodies to BVD virus can interfere with the virus isolation in very young calves.

  There are other molecular techniques available around the country and across the globe that can aid in the diagnosis of BVD.  One of these techniques is immunohistochemical detection of BVD viral antigen using frozen or fixed tissues.  Since most veterinarians submit fixed tissue, most immunohistochemistry has been developed for formalin-fixed tissues.  An antibody is applied to the surface of fixed tissue that is tagged with a signal.  This antibody is specific for BVD antigen and, if it finds its target, a chemical reaction takes place which amplifies the signal.  In PI animals, this technique can detect the virus is nearly any tissue examined.

  A second popular technique is Polymerase chain reaction (PCR).  This test is designed to be specific for a portion of the viral genetic material.  When the viral RNA is detected, the signal is amplified again so that the signal can be visualized.  This method is very sensitive and can detect extremely small amounts of BVD virus.  PCR can be used on pooled samples, such as bulk milk tank samples, thus screening large numbers of animals in lots of several animals and, if a positive signal is detected, the individual animals in that lot can be retested to determine which animal or animals are positive.

  In summary, there are many different tests available that can detect PI animals in a herd.  Blood, milk or tissues can be submitted for virus isolation, or can be sent to various diagnostic labs that routinely perform other molecular diagnostic techniques such as immunohistochemistry or PCR.  Virus isolation remains the gold standard for definitive diagnosis of BVD virus, but can become cost prohibitive if applied to large herds and can yield false results when testing very young calves that have circulation colostral antibodies.

  If you have questions regarding diagnosis of BVD please do not hesitate to call and we will discuss this with you further.

-by Lorrie Culver, Class of 2000

-edited by Brad Njaa, DVM, MVSc



ADDL-West Lafayette:
406 S. University
West Lafayette, IN 47907
Phone: 765-494-7440
Fax: 765-494-9181

11367 E. Purdue Farm Road
Dubois, IN 47527
Phone: (812) 678-3401
Fax: (812) 678-3412

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