|Briggs, Robert - Bob|
Submitted to: Canadian Journal of Veterinary Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/4/2005
Publication Date: 4/1/2006
Citation: Fulton, R.W., Johnson, B.J., Briggs, R.E., Ridpath, J.F., Saliki, J.T., Confer, A.W., Burge, L.J., Step, D.L., Walker, D.A., Payton, M.E. 2006. Challenge with bovine viral diarrhea virus by exposure to persistently infected calves: protection by vaccination and negative results of antigen testing in nonvaccinated acutely infected calves. Canadian Journal of Veterinary Research. 70(2):121-127. Interpretive Summary: Bovine viral diarrhea virus (BVDV) is an economically important pathogen of cattle worldwide. BVDV may cause both acute (transient infections that last 10 to 14 days) and persistent (life long infections in which the virus is continually replicated in and constantly shed by the host animal) infections. Most BVDV outbreaks can be traced to contact with a persistently infected animal. Requirements for the licensing of vaccines dictate that companies must show that use of the vaccine prevents infection following exposure to virus (challenge exposure). Historically the exposure required for licensing (challenge exposure) has been a one-time direct inoculation of the vaccinated animal with live virus. This type of challenge exposure does not mimic real life in that animals exposed to a persistently infected animal (PI) are "inoculated" not once, but around the clock, day in and day out for as long as they are in contact with the PI. This study demonstrates that it is possible to set up a reproducible model for testing vaccine effectiveness using continual contact with PI's rather than a one time inoculation as a challenge exposure. Such a model represents a more natural or "real life" measure of a vaccine's effectiveness. In addition this paper reports that diagnostic tests designed to detect PI's don't do a very good job of detecting acute infections.
Technical Abstract: Calves persistently infected (PI) with Bovine viral diarrhea virus (BVDV) represent an important source of infection for susceptible cattle. We evaluated vaccine efficacy using calves PI with noncytopathic BVDV2a for the challenge and compared tests to detect BVDV in acutely or transiently infected calves versus PI calves. Vaccination with 2 doses of modified live virus vaccine containing BVDV1a and BVDV2a protected the calves exposed to the PI calves: neither viremia nor nasal shedding occurred. An immunohistochemistry test on formalin-fixed ear notches and an antigen-capture enzyme-linked immunosorbent assay on fresh notches in phosphate-buffered saline did not detect BVDV antigen in any of the acutely or transiently infected calves, whereas both tests had positive results in all the PI calves.