Research articleEfficacy of bovine viral diarrhea virus vaccination to prevent reproductive disease: A meta-analysis
Introduction
Bovine viral diarrhea virus (BVDV) is the prototype virus of the Pestivirus genus and a principal viral pathogen in both dairy and beef cattle populations. Viral infection leads to a wide array of clinical signs including diarrhea, thrombocytopenia and hemorrhagic diatheses, respiratory disease, and ulcerations of the gastrointestinal tract. However, the largest economic consequence of BVDV infection may be through reproductive losses [1]. Reproductive disease as a result of BVDV infection has been recognized from the time the virus was first reported [2] and remains a major concern on dairy farms, cow-calf ranches, and breeding stock operations. The consequence of BVDV infection on reproduction depends largely on the immune status of the dam and the stage of gestation at the time of infection. Exposure of naive cattle to the virus at or near the time of breeding can result in reduced pregnancy rates because of decreased conception rates and early embryonic death [3], [4]. Abortion is most common in the first trimester but may occur at any time during gestation, including the third trimester. Viral exposure of the fetus between 18 and 125 days of gestation may lead to immunotolerance and persistent infection. Persistently infected (PI) calves are often weak at birth but may be phenotypically normal and are important to the epidemiologic aspects of viral propagation as they consistently shed high levels of virus in the environment. Infection during crucial times of organogenesis may also result in congenital defects including cerebellar hypoplasia, microphthalmia, hydranencephaly, hypotrichosis, and brachygnathism.
Control of BVDV is currently exerted primarily through strict biosecurity, eradication efforts, vaccination, or a combination of these factors. One of the primary aims of BVDV vaccination is to prevent the creation of PI calves that act as reservoirs of the virus. Although this goal was recognized by the mid-1970s [5], [6], the efficacy of early vaccines to prevent fetal infection was often incomplete [7], [8]. Improper vaccine usage has also contributed to their limited efficacy [9], [10]. More recently, several BVDV vaccines have been licensed that carry fetal protection claims with at least 365 days duration of immunity. Despite this, accounts of fetal infection in calves born to vaccinated dams continue to be reported in the literature [11], [12], [13] leading some to question the efficacy of BVDV vaccination to prevent reproductive disease. Consequently, the objective of this study was to analyze the published data in regard to the efficacy of BVDV vaccination to decrease the risk of abortion, the probability of fetal infection, or to prevent a decrease in pregnancy risk.
Section snippets
Materials and methods
In May 2014, a search for articles was performed in four relevant scientific databases (PubMed, Web of Science, CAB Abstracts, and National Agricultural Library catalog) using the keywords “BVDV vaccine” or “BVDV” and “vaccine.” The search results were not restricted by limitations on language or year of publication. The reference lists of several review articles on BVDV and BVDV vaccination [1], [14], [15], [16], [17], [18], [19], [20], [21], [22] were examined for further pertinent studies.
Results
A combined total of 1164 reports were returned by the four databases. After removal of duplicate citations and studies irrelevant to this meta-analysis, a total of 46 studies in 41 reports were identified for meta-analysis. One study using a vaccine subsequently found to contain a BVDV contaminant and one vaccine safety study with no BVDV challenge were excluded from further analyses, leaving a total of 44 studies in 39 reports included in the final quantitative analyses (Appendix A).
Discussion and conclusions
This meta-analysis provides a quantitative measure of the efficacy of BVDV vaccination to prevent subsequent reproductive disease, namely fetal infection, abortion, and decreased pregnancy risk. Meta-analysis of the results of published trials indicates that the risk of fetal infection in vaccinated cattle is less than one-seventh the risk in unvaccinated controls. Fetal infection resulting in the birth of PI animals represents the most critical step in the control of BVDV on farms. The
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