Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2001
Publication Date: 1/1/2003
Citation: Ridpath, J.E., Neill, J.D., Endsley, J., Roth, J.A. Effect of passive immunity on the development of a protective immune response against bovine viral diarrhea virus in calves. American Journal of Veterinary Research. 2003. v. 64. p. 65-69. Interpretive Summary: Infection with bovine viral diarrhea viruses (BVDV) are a source of major economic loss to U.S. cattle producers. Prevention of BVDV infection by vaccination has had limited success. This is largely due to the ability of BVDV populations to change and evade protection. However, some of the problem is that we have not designed vaccines that are optimized to provide eprotection. To do this, we need to know more about the mechanisms involved in vaccine protection. This research addresses a question that arises in designing optimized vaccination programs. It is very desirable to provide protection against BVDV infections in young calves. However, frequently young calves have some protection against viral infection (passive immunity) that they receive from their mothers via milk produced soon after birth (colostrum). There is a question whether passive immunity prevents vaccination from working properly. Protection against infection provided by yvaccination is usually measured by the presence of substances in the blood called serum antibodies. We demonstrated that calves exposed to virus when they had passive immunity developed protection from later infections. However, this protection could not be measured by serum antibody levels. These results suggest that vaccination of suckling calves can be effective and that lack of detectable serum antibodies does not necessarily reflect a lack of protection. This information will be used to design more effective vaccination programs and ways of evaluating these programs.
Technical Abstract: Bovine viral diarrhea virus (BVDV), a viral pathogen of cattle found worldwide, is associated with reproductive, respiratory, and enteric disease. It also suppresses the immune system. Vaccination of suckling calves against BVDV is desirable from both management and disease control standpoints. There is a question, however, whether vaccination is negated by the presence of maternal antibodies. In this study, calves were divided into 6 groups (3 animals per group). Groups A and D were fed colostrum with a >1/106 titer against BVDV and exposed to a highly virulent BVDV while passive antibodies (Ab) levels were high (1 month of age) and again when passive Ab levels had dropped to zero (7 to 9 months). Groups B and E were fed the same colostrum and were challenged with virus when passive Ab levels were at 0. Group C was fed milk replacer without Ab and was challenged with virus at 1 month. Group F was fed milk replacer without Ab and was challenged with virus at 7 to 9 months. All animals is groups B, C E, and F became clinically ill. Animals in groups A and D did not become clinically ill, even after the second challenge when serum Ab levels were zero. One explanation is that passive serum Ab reduced viral replication after the first challenge but allowed limited replication, which led to the development of a protective T lymphocyte response. These results suggest that vaccination is effective in the face of passive immunity and that lack of detectable serum Ab does not necessarily reflect a lack of protection.