Serodiagnosis of a viral haemorrhagic septicaemia virus infection

Viral hemorrhagic septicemia virus glycoprotein production in tobacco

Viral hemorrhagic septicemia virus (VHSV) causes mortality in numerous marine and freshwater fish species resulting in heavy losses in fish farming. The glycoprotein gene of VHSV was fused with the cholera toxin B subunit (CTB) and expressed transiently in leaf tissues of Nicotiana benthamiana via the agroinfiltration method. The glycoprotein gene was divided into two parts to improve assembly of CTB fusion proteins (CTB-VHSV99-235 and CTB-VHSV258-417). Production of CTB fusion proteins was confirmed in the agroinfiltrated leaf tissue by western blot analysis. The plant-produced CTB fusion proteins showed biological activity to GM1-ganglioside, a receptor for biologically active CTB, on GM1-ELISA. The expression level of the CTB-VHSV fusion proteins was 0.86% (CTB-VHSV99-235) and 0.93% (CTB-VHSV258-417) of total proteins in agroinfiltrated leaf tissue, as determined by GM1-ELISA. These results suggest that Agrobacterium-mediated transient expression of CTB fusion antigens of VHSV is a rapid and convenient method and demonstrate the feasibility of using agroinfiltrated plant leaf tissues expressing CTB-fusion antigens as a plant-based vaccine to prevent VHSV infection.

Serology in Finfish for Diagnosis, Surveillance, and Research: A Systematic Review

Historically, serological tests for finfish diseases have been underused when compared with their use in terrestrial animal health. For years the nonspecific immune response in fish was judged to make serology unreliable and inferior to the direct measurement of agent analytes. We conducted a systematic review of peer-reviewed publications that reported on the development, validation, or application of serological tests for finfish diseases. A total of 168 articles met the screening criteria; most of them were focused on salmonid pathogens (e.g., Aeromonas spp. and viral hemorrhagic septicemia virus). Before the 1980s, most publications reported the use of agglutination tests, but our review indicates that enzyme-linked immunosorbent assay (ELISA) has more recently become the dominant serological test. The main application of serological tests has been in the assessment of vaccine efficacy, with few applications for surveillance or demonstration of freedom from disease, despite the advantages of serological tests over direct detection at the population level. Nonlethal sampling, low cost, and postinfection persistence of antibodies make serological assays the test of choice in surveillance, especially of valuable broodstock. However, their adoption has been constrained by poor characterization and validation. The number of publications in our review reporting diagnostic sensitivity and specificity of serological tests in finfish was small (n = 7). Foreseeing a wider use of serological tests in the future for diagnostic end purposes, we offer recommendations for mitigating deficiencies in the development and evaluation of serological tests, including optimization, control of nonspecific reactions, informed cutoff points, diagnostic accuracy, and serological baseline studies. Achieving these goals will facilitate greater international recognition of serological testing in programs supporting aquatic animal health. Received March 21, 2016; accepted September 24, 2016.