Recipient Organization
AUBURN UNIVERSITY
108 M. WHITE SMITH HALL
AUBURN,AL 36849
Performing Department
Animal Health Research
Non Technical Summary
Bovine viral diarrhea virus (BVDV) is an important respiratory and reproductive pathogen that affects cattle throughout the world. The virus can cause economic loss as part of the bovine respiratory disease complex as well as due to infertility, abortions or birth of BVDV infected calves. Additionally, the virus can persist in the herd through animals persistently infected (PI) with BVDV. In areas of the USA where BVDV is endemic, economic losses have been estimated to be between 361 million to 1.4 billion dollars. Thus, effective prevention and control of BVDV in the USA is important and involves good biosecurity practices, test and removal programs and an effective vaccination program. Cattle that are PI with BVDV continuously shed large amounts of virus and serve as the major mechanism to spread BVDV within and among cattle populations. Clinical signs of persistent infection may include poor performance and poor growth rates, increased morbidity in the form of respiratory and gastrointestinal disease, and mucosal disease. It is very important to note that not all PI cattle perish as young calves, and some survive well into adulthood. The individual animal prevalence of PI carriers in the cattle population is small, and has typically been observed in the range of 0.5 to 3.0%. In terms of herd prevalence, data are variable. In randomly selected beef herd, only 4% (3 of 76 herds) contained PI cattle. Since PI cattle are the major reservoir of BVDV in beef cattle herds, detecting these animals that comprise a small percentage of the cattle population is difficult. Numerous diagnostic tests are available and offered by state and private diagnostic laboratories; however, a thorough evaluation of the ability of different diagnostic laboratories to detect BVDV has not recently been performed. In addition, BVDV diagnostic assays have remained relatively unchanged for the past 10 years, and concern exists regarding the ability of commercially available assays for BVDV to detect novel BVDV strains. Thus, this project will provide Southeastern cattle producers with knowledge regarding optimal detection methods for BVDV to facilitate its removal from a herd. Elimination of BVDV carriers will result in reduction in economic losses due to BVDV and enabling better meat quality and production by the elimination of cattle infected with BVDV.
Animal Health Component
80%
Research Effort Categories
Basic
20%
Applied
80%
Developmental
0%
Goals / Objectives
The long-term goal of this research is to evaluate and improve diagnostic assays for bovine viral diarrhea virus. The proposed project has two specific objectives, including evaluation of theability of diagnostic laboratories to accurately identify BVDV PI cattle using a variety of specimens and test formats, and develop develop a new diagnostic assay based upon antibody titers present in cows carrying BVDV PI fetuses
Project Methods
The purpose of the firstresearch objective is to perform a BVDV proficiency test of diagnostic laboratories performing BVDV testing. This objective will involve diagnostic laboratories accredited by the American Association of Veterinary Laboratory Diagnosticians (AAVLD). This objective will have two sub-objectives. A survey instrument will be sent to AAVLD-accredited labs to obtain information on what diagnostic tests are performed, the number of accessions per year, and the number of positive BVDV tests per year. Secondly, samples will be collected from known BVDV PI cattle and known BVDV-free cattle, and these samples will be bar-coded such that each laboratory is blinded as to positive and negative. All laboratories will send the results to a third laboratory, where results will be compiled and analyzed. The percentage of samples correctly identified as positive [percentage correctly positive = true positives/(true positives + false negatives) x 100], the percentage of samples correctly identified as negative [percentage correctly negative = true negatives/(true negatives + false positives) x 100], positive predictive value [positive predictive value (PPV) = true positives/(true positives + false positives) x 100], and negative predictive value for detecting cattle infected with BVDV [negative predictive value (NPV) = true negatives/(true negatives + false negatives) x 100] will be calculated for each of the diagnostic tests that are offered by the AAVLD-accredited laboratories. The kappa value (k) will used to determine the level of agreement between any 2 laboratories for each diagnostic test. A negative k indicates that the agreement between laboratories is less than expected by random chance, a k of 0 indicates that the agreement is the same as chance, k ≤ 0.20 = poor agreement, 0.21 ≤ k ≤ 0.40 = fair agreement, 0.41 ≤ k ≤ 0.60 = moderate agreement, 0.61 ≤ k ≤ 0.80 = substantial agreement, k > 0.80 = good agreement, and k = 1 indicates perfect agreement. Chi-square statistical comparison will be performed to evaluate the number of samples from the typical and atypical PI animals identified positive by each prospective test.The purpose of the second research objective is to evaluate prenatal testing methods for BVDV persistent infection. Identification of pregnant cattle that are carrying a PI fetus prior to calving will greatly facilitate control of this costly viral infection. We hypothesize that pregnant cows carrying PI fetuses have continual elevations in BVDV-specific antibodies as the gestation progresses. The bovine fetal-placental unit is not a complete barrier, and research over the past few years have demonstrated communication between the maternal and fetal circulations via the placenta. As part of previous research within the Investigator's laboratory, serum samples are available from pregnant cows that have undergone BVDV experimental infections, and the laboratory has repeat samples during gestation from pregnant cows that delivered PI calves as well as those who have delivered normal calves. In addition, the viral strains that caused the fetal persistent infection are also available and sequenced. Using these strains and other BVDV reference strains, the investigators will evaluate serology as a prenatal detection method. Virus neutralization and p80 antibody assays will be performed with the ultimate goal of determining potential BVDV-specific antibody titer cut-off values for differentiating cows carrying PI fetuses from cows carrying normal fetuses.