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Using a monoclonal antibody (MAb) specific for the H7 influenza surface glycoproteins, a serological enzyme-linked immunosorbent assay (ELISA) test has been developed. This MAb was made using the low-pathogenicity (LP) avian influenza (AI) strain (BS2676/99) isolated in Italy during a recent outbreak. The test is able to detect H7 antibodies in avian sera. The H7 ELISA has a 99% concordance of results with the classical hemagglutination inhibition (HI) test.

The Istituto Superiore di Sanità (ISS), the National Veterinary Services Laboratory in Italy, is in charge of assessing the quality, safety and efficacy of veterinary vaccines before and after licensing. To evaluate the relative potency of several vaccines against bovine respiratory syncytial virus (BRSV), infectious bovine rhinotracheitis virus (IBRV), bovine viral diarrhoea virus (BVDV) and parainfluenza-3 virus (PI3V), the serological responses in vaccinated calves were studied. Vaccination with any of the vaccines under study induced specific antibody titres against the different viral antigens. The differences of the mean antibody titres within and among the test group vaccines were statistically significant. The results confirm and support those obtained by other authors in similar studies, suggesting that serological responses in vaccinated calves can be used as a helpful means of assessing the relative potency of vaccines against viral respiratory diseases of cattle. The criteria allowing such an evaluation are discussed.

A tendency has emerged for some years to replace the challenge infection of cattle for the assessment of foot-and-mouth disease (FMD) vaccine potency. This can be actually evaluated by means of antibody assays on cattle sera, at about 3/4 weeks after the vaccination. Serological results can be worked out as single titres (to be compared with a pre-determined threshold level) or as mean antibody titres induced by different vaccine dilutions. However, the assessment of FMDV-specific antibody titres would not fully depict the extent and the efficacy of the immune response of cattle; moreover, the antibody response would not be proportional if potent vaccines are used (greater than or equal to 10-12 PD50). Thus, a particular approach is suggested for the serological procedures, which enable credible estimates of potent FMD vaccines to be formulated.

We have studied the ability of rabies virus ribonucleoprotein (RNP) to induce a protective immune response in animals against lethal challenge with rabies and rabies-related lyssa viruses. Liposomes containing either RNP or the glycoprotein (G protein) of a variant virus with multiple alterations in the G antigenic structure conferred no or poor protection, respectively, against lethal intracerebral challenge with rabies virus. By contrast, liposomes containing RNP and the variant G protein induced a good protective response, comparable to that achieved with inactivated virus vaccine against intracerebral challenge. Moreover, mice or raccoons immunized with RNP alone resisted lethal peripheral challenge with homologous or heterologous virus strains. These results indicate that the RNP of rabies virus plays a crucial role in induction of protective immunity.

Incubation of radiolabeled rabies virus with neutralizing monoclonal antibodies (MAbs) resulted in complete neutralization of the virus but only partial inhibition of virus binding to, and internalization by, BHK cells. Several of the neutralizing MAbs were capable of preventing infection after virus adsorption to cells; up to 30% of the bound virus was released when cells containing adsorbed virus were incubated with these MAbs at 4 degrees, indicating that the release of bound virus accounts only in part for the neutralization of adsorbed virus. To study the mechanism of neutralization of cell-bound virus, temperature shift experiments were carried out to follow the fate of neutralized cell-adsorbed virus at 37 degrees. Treatment of infected cells with each of the tested neutralizing MAbs had no effect on virus uptake at 37 degrees and the MAbs were endocytosed together with the virus; however, the ability of some of the MAbs to neutralize cell-adsorbed rabies virus correlated with the fusion inhibition activity of these MAbs. We hypothesize from these data that these MAbs neutralize rabies virus by inhibiting the intraendosomal acid-catalyzed fusion step that leads to virus uncoating.

Immunization experiments with vaccines prepared from the PM and ERA strains of rabies virus demonstrated that in mice, only ERA vaccine primes for an anamnestic response to the rabies-related strain Duvenhage (DUV6); in rabbits, both ERA and PM vaccines induced immunologic memory to DUV6 virus. In mice, ERA vaccine, but not an equal concentration of PM vaccine, conferred protection against a lethal challenge infection with DUV6 virus. This result indicated that the protective activity correlated with the vaccine's ability to induce immunologic memory. A vaccine prepared from a sequentially selected, neutralization-resistant, multiple-variant virus conferred protection against challenge with the parental strain, a result indicating that antigenic variation of the glycoprotein may not be the sole factor in determining the relative efficacy of rabies prophylaxis. We found no correlation between titers of neutralizing antibody and mortality rates in mice immunized with purified glycoprotein from these viruses.