Investigation of surveillance techniques to detect Bovine viral diarrhea virus in cattle
Bovine viral diarrhea viruses (BVDV) are important pathogens of cattle globally. Vaccination is often used to control BVDV, but complete control requires detection and elimination of cattle persistently infected (PI) with BVDV. These cattle are infected with BVDV during gestation, become immunotolerant to their strain of BVDV, and shed large amounts of BVDV throughout their lives. Infections of immunocompetent cattle are transient and produce a variety of clinical signs ranging from unapparent to fatal disease. Cattle PI with BVDV are the reservoir of most transient BVDV infections. Surveillance strategies and diagnostic assays have been developed to identify herds exposed to BVDV and individuals that are PI with BVDV. Many of these strategies and assays are costly and inconvenient for producers and are subsequently underused. New surveillance strategies that fit into common production schemes as well as accurate diagnostic assays based on easily-attainable samples are necessary to improve adoption of BVDV control. The research presented in this paper outlines opportunities to simplify BVDV sampling and detect immune evidence of BVDV infections in the form of nasal antibody specific to BVDV. Specifically, nasal swab samples were found to be as sensitive as the standard ear notch sample used in current antigen capture ELISAs. Alternative skin samples can also be used as accurate diagnostic samples in antigen capture ELISAs provided the kit used for diagnosis has been validated to use those samples. Before any surveillance program based on antibody responses to a pathogen can be implemented, the concentration and duration of passive antibodies to the pathogen must first be established. Research presented in this dissertation demonstrates that antibody of all isotypes can be measured in the secretions associated with the nasal and oral cavities. There is also strong evidence that passively acquired antibody is transferred transiently into mucosal secretions of the mouth and nose. Analysis of pathogen-specific data reveals that mucosal antibody profiles may prove to be a useful tool for detecting acquired immune responses in calves at a much younger age than is currently permitted by serum antibody analysis. A study designed to investigate the value of BVDV-specific nasal antibodies in calves showed calves with high levels of anti-BVDV nasal antibodies had decreased risk of respiratory disease compared to calves with low levels of anti-BVDV nasal antibodies. These nasal antibodies likely indicate development of a complete, mature immune response to BVDV because of the T-lymphocyte help and time required to produce nasal antibodies specific to BVDV. Overall, the research presented in this dissertation reveals opportunities to improve BVDV detection in the U.S., but more research is needed to validate these techniques and samples.