Detection

Effective Bovine Viral Diarrhea Virus (BVDV) control on dairy farms is multifaceted and includes methods to accurately detect virus, remove BVDV persistently infected (PI) cattle, prevent virus introduction using comprehensive biosecurity plans, and optimize herd immunity through continuous vaccination against BVDV. The work in this thesis takes into consideration the above means to achieve effective BVDV control more specifically by attempting to: (1) determine the herd infection status by screening newborn calves for precolostral BVDV serum antibodies; (2) eradicate BVDV from a large commercial dairy herd through a combination of test and removal procedures and biosecurity measures; (3) characterize BVDV in PI calves from the Upper Midwestern United States by nucleic acid sequencing in order to more fully understand the changes that are occurring in the BVDV genome that may affect detection and elimination protocols, and; (4) implement a quantitative real-time RT-PCR (qRT-PCR) for quantification of BVDV RNA in a variety of clinical samples obtained from PI cattle. Chapter 2 of this thesis investigated a novel screening approach to detect BVDV by screening newborn calves for BVDV serum antibodies prior to colostrum feeding. Newborn calves that are seropositive for BVDV antibody prior to colostrum feeding indicate fetal infection during the last two trimesters of gestation. The number of newborn calves seropositive for BVDV serum antibodies at birth is estimated to be greater than the number of PI calves. Because the number of BVDV seropositive calves is greater than the number of BVDV PI calves fewer calves need to be tested by precolostral serum antibody screening to detect BVDV fetal infections and the probability of one or more PI cattle in the pregnant herd is likely. In addition to requiring fewer test animals, precolostral screening detects infections in lactating, non-lactating, and pregnant youngstock populations and is not confounded by vaccination. Chapter 3 of this thesis describes the elimination of BVDV PI animals in a large commercial dairy herd with a RT-PCR test. Previous testing in the study herd indicated that approximately 5% of the calves were born with BVDV precolostral serum antibodies. The birth of BVDV seropositive calves also roughly coincided with an increase in post-partum diseases that failed to respond to proven therapies. The herd owners elected to test all animals for BVDV PI with a serum BVDV RT-PCR test. Accurate detection of BVDV PI cattle is important in all herds, but less than perfect sensitivity and the potential of a false negative result are amplified in large herds with PI cattle. False negative test results would lead to the retention of one or more PI cattle and ultimately the continued persistence of BVDV within the herd. Serum samples from all cattle on the premises, and heifer calves born during the following 9 months, were tested for BVDV by RT-PCR and those determined to be BVDV PI on confirmatory tests were removed from the herd. Whether or not BVDV persisted in, or was eliminated from, this herd was determined by monitoring newborn calf precolostral serum antibodies for BVDV one year after the test and removal of all PI cattle. The objective of chapter 4 was to successfully sequence a portion of the viral RNA and compare the viral genome sequences of forty PI cattle detected on dairy farms in the Upper Midwestern United States. The 5' untranslated region (5'UTR) region of the BVDV genome contains conserved regions and is commonly used for PCR detection tests. This project described the use of primers targeting 5'UTR that produce a PCR product for nucleic acid sequence comparisons between vaccine and field strains and all