|CROSSLEY, B - University Of California|
|ADASKA, J - University Of California|
|CHAMPAGNE, J - University Of California|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/17/2017
Publication Date: N/A
Interpretive Summary: Vaccination is used as a method to prevent infections with BVDV, but while vaccination is a management tool to help control BVDV infections, it does not provide sterilizing immunity. Vaccine licensing studies are conducted in healthy animals and the responses when administered to unapparent animals that have a compromised health status could have unintended consequences. While not labeled for use in unhealthy animals, vaccines are used in the face of an outbreak as method of treatment for the herd to prevent spread of the disease and are administered to clinically sick animals. Diagnostic results from a field study suggest that BVDV vaccines used in clinically sick animals was re-isolated from tissues at necropsy. It appears that the BVDV vaccine virus can spread systemically when given to compromised animals. While the intent and the vaccine was administered to help prevent the spread of disease, administering vaccine to compromised animals may alter the transmission and replication of the vaccine virus leading to unintended spread of the virus.
Technical Abstract: Bovine viral diarrhea virus (BVDV) was detected during routine necropsy of calves, from a well vaccinated, large Jersey/Holstein dairy herd (n=10,000) in California, that succumbed to ill thrift. According to herd management, BVDV has not been considered a problem in the past. The herd had been extensively vaccinated with various brands of modified live vaccines, all of which included the BVDV1a Singer strain. Subsequent testing of ear notches, by antigen capture ELISA, detected 18 positive calves out of 771 tested (2.3%). All dams from positive calves tested negative for BVDV. Virus isolation was performed and both cytopathic and non-cytopathic viruses were detected based on growth patterns in culture. PCR amplification of RNA isolated from isolates followed by sequencing and phylogenetic analysis based on the 5’UTR region of BVDV revealed three different scenarios. Clean sequence matching BVDV1a-Singer, based on phylogenetic analysis, segregated to the BVDV1b subgenotype and mixed sequence results indicating more than one BVDV present. Necropsy of the calves revealed a systemic infection of BVDV as demonstrated by real-time PCR in brain, lung, kidney, spleen and liver tissues of all necropsied calves. Calves infected with the Singer strain showed a marginally higher virus concentration in the lung compared to calves infected with the field strain. Two of the calves infected with the Singer strain had never been vaccinated due to their young age, however vaccine strain virus could be propagated from spleen tissue. The systemic infection of calves with vaccine virus and the presumed transmission of vaccine virus from vaccinated calves to naïve calves were not observed in the efficacy and safety trials required for licensure of the vaccines used in this herd. However, licensure studies are performed using healthy animals in the absence of persistently infected pen mates. The findings suggest that producers cannot rely on vaccination alone to prevent persistent infections and that vaccination of persistently infected animals and/or vaccination herd mates in the face of exposure to persistently infected animals may impact on the transmission and replication of vaccine virus included in modified live vaccines.