Effective Detection of Epidemiologically Significant Persistent Infections of Bovine Viral Diarrhea Virus

Abstract

Prior research has shown that virus cannot be isolated from the serum of some cattle which are persistently infected (PI) with bovine viral diarrhea virus (BVDV). However, the ability of these atypical PI animals to infect susceptible herdmates in a normal pasture environment remains to be determined. The accurate identification of PI cattle is a major factor in the control and prevention of BVDV. Furthermore, a lack of uniform standardization or validation of testing methods between diagnostic laboratories could compromise the ability to consistently and accurately diagnose PI cattle. The current level of agreement among laboratories and the accuracy of tests to identify animals PI with BVDV have not been fully evaluated. This research investigated the potential for an atypical PI animal to transmit BVDV to susceptible herdmates in a normal pasture setting. Groups of four naive calves were exposed to either a negative control (BVDV negative), a positive control (PI), or a test animal (PI that previously lacked easily isolated virus in serum by virus isolation). Blood was collected from each animal and tested by virus isolation and serum neutralization. Calves exposed to the negative control did not become viremic or seroconvert, but all calves exposed to either the positive control or the test animal became viremic and seroconverted to BVDV. The outcome of this study indicates that PI cattle that previously lacked easily isolated virus in serum by virus isolation are still capable of transmitting BVDV to susceptible herdmates. The diagnostic proficiency of various methods for detecting cattle PI with BVDV using intra- and inter-laboratory comparisons was also investigated. Blood and skin biopsies were collected from 2 BVDV negative animals, a PI animal, and a PI animal that previously lacked easily isolated virus in serum. Blind samples were submitted for detection of BVDV to 23 participating laboratories. The level of agreement between laboratories for each diagnostic test ranged from perfect to less than expected by random chance. The results from this research show that there is considerable variation among tests and laboratories and demonstrate the need for standardization of tests used to detect BVDV.