Bovine viral diarrhea is one of the most important diseases of cattle which are causing
continuous economic losses to the cattle industry primarily due to decreased reproductive
I performance. Without doubt, direct contact between BVDV persistently infected, and susceptible animals is the most important transmission route of virus. All control programs which are in use in many countries of the world, mainly depend upon the detection of PI animals, eliminating them and preventing their return into the herds. Therefore, in this study diagnostic suitability of ear notch biopsies and serum samples were compared for the detection of PI animals, as well as proficiency of various diagnostic approaches like VI, AC-ELISA, IHC and real time RT-PCR were evaluated using ear notch biopsies. A total of 468 samples were collected from 12 participating dairy cattle farms located at Prince Edward Island, Canada. The samples were divided into two groups on the basis of age, A " 6 months), and B (> 6 months).
PI calves remain immunotolerant to the infecting strain but if exposed to a heterogonous strain postnatally, they may develop low level of antibody. Accordingly, serum neutralization was applied for initial screening of samples for further testing. The samples of animals of group B, having SNT (:S 1 :64) were selected, while all samples of younger aged group A were processed without considering the serum neutralizing titres, because unlike older animals, P.1. animals below 6 months of age can have passive colostral antibodies in the course of persistency. Diagnostic suitability of ear notch biopsy and serum sample for confirmation of BVDV

A significant discrepancy was observed between ear notch biopsies (51198 positive) and
serum samples (71198 positive) during first round of testing by real time RT-PCR. However, on

follow up testing, 30 days post first round of testing, a complete agreement between ear notch
biopsies and serum samples was observed. On second round of testing, a total of 4 animals out of
197 (one positive animals died before re-sampling) were confirmed with PI, using both ear notch
biopsies and serum samples. The decrease in the positivity using RT-PCR on serum samples in
the second round of testing reflected the presence of 2 transiently infected animals. Ear notch
biopsy (EN) testing did not detect any transiently infected animal indicating the lack of
delectability of the virus in EN during transient infection under conditions of this study. After
follow up testing, 2 animals in each of group A and B were identified as PI. These findings have
led us to conclude, that either serum or ear notch biopsy can be used for the detection of
persistent infection. Of 468 collected and 197 tested samples, an overall 0.85% and 2.03%
prevalence of PI animals with BVDV was observed respectively. A complete agreement (P value=l) was observed when three diagnostic approaches (Real time RT- PCR, AC-ELISA, and IHC) were compared with standard of VI. A total of 197 ear notch biopsies (145 of group A and 52 of group B) were tested by the four diagnostic tests, four animals (2 from group A and 2 from group B) were found positive by all the tests applied. A complete agreement was observed between the first and the second round of testing. All four assays were found specific but real time RT-PCR was found to be more sensitive. Both, VI and IHC were found labour intensive, as diagnosis may take more than one week to be made. Further PI calves remain immunotolerant tothe infecting strain but if exposed to a heterogonous strain postnatally, they may develop low leved
ofantibody. Accordingly, serum neutralization was applied for initial screening of samples for further testing. The samples of animals of group B, having SNT (:S 1 :64) were selected, while all samples of younger aged group A were processed without considering the serum neutralizing titres, because
unlike older animals, P.1. animals below 6 months of age can have passive colostral antibodies in the course of persistency. Diagnostic suitability of ear notch biopsy and serum sample for confirmation of BVDV persistent animals were evaluated by real time RT-PCR. TaqMan probes and primers specific for BVDVI and BVDV2 were used. They were found specific and able to detect 10·s and 10-4 TCID50 units ofBVDVI and BVDV2, respectively.