578 Scientific Reports: Original Study JAVMA, Vol 228, No. 4, February 15, 2006 RUMINANTS B ovine viral diarrhea viruses are a diverse group of viruses that cause infections in domestic ruminants worldwide. 1 Bovine viral diarrhea viruses can be classi- fied by biotypes as cytopathic or noncytopathic on the basis of the presence or absence of observable cyto- pathic changes in infected cell cultures. 1 Additionally, BVDVs are diverse by their genotypic differences, which are also reflected by antigenic differences with the sub- types (BVDV1a, 1b, and 2a) found in the United States. 2-8 Bovine viral diarrhea virus infections cause clinically inapparent to severe disease involving 1 or more organ systems. 1 Historically, BVDV has been asso- ciated with gastrointestinal tract disease with high mor- tality rates. However, BVDV is presently associated with respiratory disease and fetal infections. The outcome of BVDV fetal infections in susceptible heifers and cows is dependent on the age of the fetus when exposed. Infection results in abortions, stillbirths, congenital malformations, and birth of PI calves. 1 Persistent infec- tion in a calf develops when a susceptible heifer or cow is exposed to noncytopathic BVDV during pregnancy at approximately 42 to 125 days of gestation. 9 Persistently infected calves are born alive, are immunotolerant to the initial virus infecting the fetus, and shed the virus for life. 1 However, PI calves are able to respond with an active humoral immune response (antibodies) to het- erologous BVDV, including naturally occurring strains or vaccine strains. 10 Thus, antibodies including mater- nally derived BVDV antibodies and those from vaccine- induced immunity may develop in PI calves. Persistently infected cattle are likely the most important reservoir or source of virus for susceptible cattle 1 ; 70% to 100% of susceptible nonvaccinated calves become infected after exposure to PI calves. 11 Bovine viral diarrhea virus and other viruses such as BHV-1, PI-3V, and BRSV contribute to BRD and bacterial pneumonia caused by Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma spp. 12,13 The role of BVDV in BRD is 2-fold: as a primary Evaluation of diagnostic tests used for detection of bovine viral diarrhea virus and prevalence of subtypes 1a, 1b, and 2a in persistently infected cattle entering a feedlot Robert W. Fulton, DVM, PhD; Bill Hessman, DVM; Bill J. Johnson, DVM; Julia F. Ridpath, PhD; Jeremiah T. Saliki, DVM, PhD; Lurinda J. Burge, MS; Dave Sjeklocha, DVM; Anthony W. Confer, DVM, PhD; Rebecca A. Funk; Mark E. Payton, PhD Objective—To evaluate diagnostic tests used for detec- tion of bovine viral diarrhea virus (BVDV) and determine the prevalence of BVDV subtypes 1a, 1b, and 2a in per- sistently infected (PI) cattle entering a feedlot. Design—Prospective study. Animals—21,743 calves. Procedures—Samples were obtained from calves ini- tially testing positive via antigen capture ELISA (ACE) performed on fresh skin (ear notch) specimens, and ACE was repeated. Additionally, immunohistochem- istry (IHC) was performed on skin specimens fixed in neutral-buffered 10% formalin, and reverse transcrip- tase PCR (RT-PCR) assay and virus isolation were per- formed on serum samples. Virus was subtyped via sequencing of the 5' untranslated region of the viral genome. Results—Initial ACE results were positive for BVDV in 88 calves. After subsequent testing, results of ACE, IHC, RT-PCR assay, and viral isolation were positive in 86 of 88 calves; results of all subsequent tests were negative in 2 calves. Those 2 calves had false-positive test results. On the basis of IHC results, 86 of 21,743 calves were PI with BVDV, resulting in a prevalence of 0.4%. Distribution of BVDV subtypes was BVDV1b (77.9%), BVDV1a (11.6%), and BVDV2a (10.5%). Conclusions and Clinical Relevance—Rapid tests such as ACE permit identification and segregation of PI cattle pending results of further tests, thus reducing their contact with the rest of the feedlot population. Although vaccines with BVDV1a and 2a components are given to cattle entering feedlots, these vaccines may not provide adequate protection against BVDV1b. (J Am Vet Med Assoc 2006;228:578–584) From the Department of Veterinary Pathobiology (Fulton, Johnson, Saliki, Burge, Confer, Funk) and Oklahoma Animal Disease Diagnostic Laboratory (Johnson, Saliki), Center for Veterinary Health Sciences, and the Department of Statistics (Payton), Oklahoma State University, Stillwater, OK 74078; Haskell County Animal Hospital, E Hwy 56, PO Box 876, Sublette, KS 67877 (Hessman, Sjeklocha); and USDA, Agricultural Research Service, National Animal Disease Center, Ames, IA 50010 (Ridpath). Supported by a grant from The Noble Foundation, Ardmore, Okla. The authors thank Diana Moffeit for manuscript preparation. Address correspondence to Dr. Fulton. BVDV Bovine viral diarrhea virus PI Persistently infected BHV-1 Bovine herpesvirus type 1 PI-3V Parainfluenza-3 virus BRSV Bovine respiratory syncytial virus BRD Bovine respiratory disease IHC Immunohistochemistry ACE Antigen capture ELISA RT Reverse transcription MDBK Madin Darby Bovine Kidney OD Optical density UTR Untranslated region