Blocking ELISA for distinguishing infectious bovine rhinotracheitis virus (IBRV)-infected animals from those vaccinated with a gene-deleted marker vaccine

Development of a blocking ELISA for detection of serum neutralizing antibodies against newly emerged duck Tembusu virus

Background

Since April 2010, domesticated ducks in China have been suffering from an emerging infectious disease characterized by retarded growth, high fever, loss of appetite, decline in egg production, and death. The causative agent was identified as a duck Tembusu virus (DTMUV), a member of the Ntaya virus (NTAV) group within the genus Flavivirus, family Flaviviridae. DTMUV is highly contagious and spreads rapidly in many species of ducks. More than 10 million shelducks have been infected and approximately 1 million died in 2010. The disease remains a constant threat to the duck industry; however, it is not known whether DTMUV can infect humans or other mammalians, despite the fact that the virus has spread widely in southeast China, one of the most densely populated areas in the world. The lack of reliable methods to detect the serum antibodies against DTMUV has limited our ability to conduct epidemiological investigations in various natural hosts and to evaluate the efficiency of vaccines to DTMUV.

Methodology/Principal Findings

A neutralizing monoclonal antibody (mAb) 1F5 binding specifically to the E protein was developed. Based on the mAb, a blocking enzyme-linked immunosorbent assay (ELISA) was developed for the detection of neutralizing antibodies against DTMUV. The average value of percent inhibition (PI) of 350 duck serum samples obtained from DTMUV-free farms was 1.0% ±5.8% (mean ± SD). The selected cut-off PI values for negative and positive sera were 12.6% (mean +2SD) and 18.4% (mean +3SD), respectively. When compared with a serum neutralizing antibody test (SNT) using chicken embryonated eggs, the rate of coincidence was 70.6% between the blocking ELISA and SNT, based on the titration of 20 duck DTMUV-positive serum samples.

Conclusions/Significance

The blocking ELISA based on a neutralizing mAb allowed rapid, sensitive, and specific detection of neutralization-related antibodies against DTMUV.

Advances in the development and evaluation of bovine herpesvirus 1 vaccines

This review deals with conventional and modern bovine herpesvirus 1 (BHV1) vaccines. Conventional vaccines are widely used to prevent clinical signs of infectious bovine rhinotracheitis. The use of conventional vaccines, however, does not appear to have resulted in reduction of the prevalence of infection. Novel BHV1 marker vaccines comprise either mutants with a deletion in one of the non-essential genes, or subunit vaccines that contain one or more glycoproteins. These marker vaccines can be used in conjunction with companion diagnostic tests to differentiate between infected and vaccinated cattle. Their efficacy has been evaluated in vaccination-challenge experiments, transmission experiments and in field trials. The results demonstrate that the marker vaccines can contribute to the eventual eradication of BHV1. However, there remains room for improvement of BHV1 marker vaccines.

Efficacy of a deletion mutant bovine herpesvirus-1 (BHV-1) vaccine that allows serologic differentiation of vaccinated from naturally infected animals

Fifteen bovine herpesvirus-1 (BHV-1)-negative calves were vaccinated intramuscularly with 10(7.4) plaque-forming units of a double-deletion BHV-1 mutant (IBRV(NG)dltkdlgIII), and 6 remained as nonvaccinated controls. Thirty days after vaccination, the animals were challenged by nasal instillation of 10(8.2) CCID50 of a virulent BHV-1 strain (Cooper). The vaccinated calves were protected against wildtype virus challenge as demonstrated by clinical evaluation. Most of the vaccinates developed only a mild rhinitis (lasting an average of 6.5 days) with almost no systemic symptoms, whereas the controls developed a serious illness characterized by rhinitis (mean = 11.5 days), conjunctivitis, hyperthermia, apathy, loss of appetite, and dyspnea. The vaccinates also shed significantly less virus and for a shorter period of time (mean = 5.5 days) than the controls (mean = 9 days). Thirty days after vaccination, the vaccinates were negative in an anti-gIII specific blocking enzyme-linked immunosorbent assay (ELISA), despite the fact that most of them had developed neutralizing antibodies (serum neutralization titers ranging from 1:2 to 1:16). Seroconversion to gIII was detected as early as 7 days postinfection (dpi). Fourteen days after the challenge, all the animals exposed to wildtype BHV-1 had developed anti-gIII antibodies and were positive in this differential serologic test. Six controls plus 8 vaccinates kept in isolation were still positive to gIII when tested at 75 dpi. The use of the IBRV(NG)dltkdlgIII strain in conjunction with an anti-gIII specific blocking ELISA kit represents a powerful tool for BHV-1 control/eradication programs.