Relationship between viral shedding in the transmission of bovine viral diarrhea virus to naïve calves by direct and indirect exposure routes

Authors: Falkenberg, Shollie; Dassanayake, Rohana; Neill, John; Ridpath, Julia

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2018
Publication Date: 3/16/2018
Citation: Falkenberg, S.M., Dassanayake, R.P., Neill, J.D., Ridpath, J.F. 2018. Evaluation of bovine viral diarrhea virus transmission potential to naïve calves by direct and indirect exposure routes. Veterinary Microbiology. 217:144-148. https://doi.org/10.1016/j.vetmic.2018.03.012.
DOI: https://doi.org/10.1016/j.vetmic.2018.03.012

Interpretive Summary: It is thought that the primary reservoir for and source of bovine viral diarrhea virus (BVDV) are animals persistently infected (PI) with BVDV, with transiently (acutely) infected cattle considered a less important source. PI animals are generally more efficient transmitters of BVDV than transiently acutely infected animals because PI animals secrete much higher levels of virus for a much longer period of time. Exposure to one PI animal can result in multiple transient acute infections in a naïve group, and the impact of these resulting transient acute infections could further transmit the virus even after removal of PI animals. The goal of this study was to evaluate transmission by both direct and indirect contact to naïve calves using two different species of typical virulent BVDV isolates that have a history of minimal viral shedding. Calves were inoculated with either BVDV type 1 (TGAN) or BVDV type 2 (RS886) viruses to mimic a transient acute infection that would be observed in nature. Two days post-infection, naive calves were exposed to the inoculated calves either by direct or indirect contact over a two week period. BVDV was detected in all inoculated calves, but not from any of the direct or indirect calves. Further, the direct and indirect calves did not seroconvert to BVDV as observed in the inoculated calves. Data from this study would suggest that there is an infectious dose needed to facilitate transmission of BVDV isolates that have minimal shedding patterns.

Technical Abstract: Bovine viral diarrhea viruses (BVDV) can cause both acute and persistent infections in cattle. Exposure to BVDV persistently infected (PI) animal’s results in transmission of the virus to a naïve animal which causes a transient acute infection. While it is known that direct exposure to PI animals is a highly efficient means of transmission, less information is available regarding the potential for transmission from transiently acutely infected either by direct or indirect exposure to naïve animals. Therefore, the objective of this study was to evaluate the potential for transmission of the virus from calves acutely infected, with typical virulence field viruses know to have minimal shedding, to naïve contact animals either by direct or indirect exposure. To accomplish this objective, two BVDV isolates belonging to two species of BVDV, type 1 and type 2, were used to inoculate calves. Subsequently on day 2 post-infection, naïve calves were exposed to inoculated calves, either directly or indirectly, over a period of two weeks. All calves were evaluated for the presence of virus in blood samples and nasal swabs, pyrexia, lymphopenia and seroconversion. BVDV was isolated from inoculated calves but not from any of the direct and indirect contact animals or from control calves. Similarly, pyrexia and lymphopenia were observed in the inoculated calves, but not in contact and control calves. Only the inoculated calves seroconverted by day 38 of the study indicating that no transmission had occurred to the naïve contact calves. This data would suggest that cattle acutely infected with typical virulence field isolates appear to not be major vectors for transmission.