DIVA stands for Differentiating Infected from Vaccinated Animals. For Avian influenza, this can be achieved by using a vaccine based on a different strain (e.g. H5N2) than the current field strain (e.g. H5N1) and using a serological test that can differentiate between vaccine-induced antibodies (e.g. against N2) and antibodies against the field virus (N1).
DIVA means differentiating infected from vaccinated animals. These vaccines, also termed as marker vaccines, induce an immune response which is different from that induced by natural infection. Marker vaccines are based on deletions mutants of wild-type pathogens, subunit vaccines and inactivated whole virus vaccines. The DIVA immune response can be detected by companion diagnostic tests such as enzyme linked immunosorbent assays (ELISA).
DIVA vaccines were first used for the eradication of pseudorabies (Aujeszky disease) in pigs. Most of them are based on recombinant deletion mutants lack the gE envelope glycoprotein and thymidine kinase genes. The accompanying tests score pigs as seropositive for gE antibodies. DIVA vaccines against infectious bovine rhinotracheitis (IBR) of cattle, caused by the bovine herpesvirus 1 (BHV-1) work on a similar principle. Currently available foot-and-mouth disease (FMD) vaccines are prepared from purified and chemically inactivated whole virus particles. The non-structural proteins (NSP) were separated form virus particles. Serological assays detecting antibodies against NSP can therefore differentiate between infected and vaccinated animals. For classical swine fever (CSF) a baculovirus-expressed recombinant E2-subunit vaccine is on the market. Surface glycoprotein E2 is the most antigenic protein of CSF virus and elicits a neutralizing antibody response, which can protect pigs against CSF. For DIVA purposes ELISAs were developed which detect antibodies against the viral envelope glycoprotein Erns. In Italy an inactivated heterologous vaccine was used in order to control a low-pathogenic avian influenza infection (H7N1) in 1999/2000. This vaccine was based on the same hemagglutinin subtype (H7) as the wild-type virus but on a different neuraminidase (N3). The companion test, an indirect immunofluorescence assay, was detecting antibodies against N1.
The main advantage of DIVA vaccines and their companions test is the possibility to distinguish between infected and vaccinated animals. Therefore, special restrictions, which are necessary for infected animals, can be loosened for vaccinated animals. Depending on the kind of DIVA vaccine it is possible that the vaccines are not so effective like conventional vaccines (e.g. inactivated vaccines or subunit vaccines). Special DIVA tests have to be developed. Sometimes they are not so sensitive like conventional tests.
For classical swine fever chimeric pestiviruses were shown to be effective DIVA vaccines in animal experiments. They are based on bovine viral diarrhoea (BVD) or CSF viruses. Immunogenic proteins were exchanged with their equivalents from the respective other pestiviruses (CSFV, BVDV, BDV).
Emergency vaccination using DIVA vaccines could be one control tool for disease outbreaks in densely populated livestock areas. DIVA vaccination might limit the number of culled animals in the process of disease eradication, thereby enhancing public acceptance for disease control measures and limiting economic damage. In contrast to conventional vaccination DIVA vaccination should always be used as protective vaccination meaning that vaccinated animals are kept to the end of a normal production cycle and their meat eventually marketed.
Marker assays or companion tests allow the serological differentiation between vaccinated and infected animals. The differentiation of vaccinated and infected animals is based on the absence of one or more proteins in the vaccine that are present in the wild type microorganism. Marker assays detect antibodies against those proteins that are absent in the vaccine. Therefore, naturally infected animals can be detected in a vaccinated population.