Innocuity testing of foot-and-mouth disease vaccines. I. Formaldehyde-inactivated alhydrogel vaccines

Confirmation of botulism diagnosis in Australian bird samples by ELISA and RT rtPCR

We developed a sandwich ELISA that detects Clostridium botulinum C and D toxins and reverse-transcription real-time PCRs (RT-rtPCRs) that detect botulinum C and D toxin genes, respectively, to replace the mouse bioassay. The toxin genes were closely associated with the toxin molecules and used as surrogates for the presence of toxin. Samples (638) from 103 clinical cases of birds (302) with suspected botulinum toxicity came from wild birds and poultry (9 cases). Samples tested included blood serum, other body fluids, various tissues, gut contents, maggots, water, and sediment. Botulism was diagnosed in 34 cases (all of which had positive samples in the ELISA, the C toxin gene RT-rtPCR, or both assays). Botulism was suspected in 16 cases (each of which had 1 positive sample either in the ELISA or the C toxin gene RT-rtPCR). In the remaining 53 cases, no samples were positive, but botulism could not be excluded in 32 of these cases, whereas there was no indication of botulism or another diagnosis in 21 cases. The D toxin gene was not detected in any of the clinical samples. No C or D toxin genes were detected in 71 pooled cloacal swabs from 213 healthy migratory birds. The use of an ELISA that detects botulinum C and D toxins in combination with a RT-rtPCR for the botulinum C toxin gene can help confirm the diagnosis of botulism in birds.

In vitro potency assays for nonreplicating veterinary vaccines: comparison to in vivo assays and considerations in assay development

Each finished batch or serial of veterinary vaccine must be potency tested to assure the quality of marketed product. The potency assay must be correlated to efficacy in the target species. Potency assays of nonreplicating vaccines have traditionally measured the immune response to the vaccine in host or laboratory animals by serology or protection from challenge. Such tests are expensive, time-consuming, and raise animal welfare concerns. As disease agent protective antigens are described, in vitro techniques for quantitating them can be applied to vaccine potency measurement. However, in many cases the immunological adjuvants critical to the efficacy of the biological interfere with in vitro antigen quantitation techniques. The development of techniques that remove or compensate for the effect of adjuvants on the assays, sham vaccines containing no antigen, reference preparations containing a proven protective immunogen dose, characterization of the immunological reactants, and appropriate design and data analysis have contributed to the development of rapid, reproducible, humane, and relatively inexpensive in vitro potency assays to be used in the evaluation of veterinary biologicals.

In vitro assessment of viral antigen content in inactivated aluminum hydroxide adjuvanted vaccines

Antigen capture enzyme immunoassays (ELISA) were developed to assess the antigenic content of inactivated aluminum hydroxide (AH) adjuvanted porcine parvovirus, pseudorabies, and infectious bovine rhinotracheitis vaccines. Reference preparations of these viruses were constructed as a basis for comparison. Because AH-associated ELISA interference was largely circumvented, the need for isotopic or complex antigen-adjuvant desorption methods was eliminated. A 4-parameter logistic model related optical density to vaccine dilution. High correlation coefficients (r) were routinely achieved with commercial monovalent and polyvalent vaccines, and reference preparations. The procedure quantified antigen in both aqueous and AH-associated phases. The method may be generally applicable as a partial substitute for in vivo vaccine potency testing by allowing in vitro estimation of inactivated viral antigenic content in AH adjuvanted vaccines.

Desorption of porcine parvovirus from aluminum hydroxide adjuvant with subsequent viral immunoassay or hemagglutination assay

Cell culture fluids containing porcine parvovirus were adjuvanted with varying concentrations of aluminum hydroxide gel. Adsorption of virus and total protein to adjuvant was proportional to adjuvant concentration. Desorption of virus and protein from the adjuvant in substantial, reproducible quantities was achieved by washing adjuvanted preparations with 1.2 M potassium phosphate, followed by dialysis and concentration of wash fluids. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of unadjuvanted viral fluids, supernatants of adjuvanted mixtures, and desorptive washings of the corresponding adjuvant pellets revealed no qualitative differences in protein banding patterns. Desorbed virus was quantitated by a hemagglutination assay, or by an enzyme-linked immunoassay employing a monoclonal anti-porcine parvovirus antibody. Virus desorption and subsequent assays permitted in vitro estimation of virus content in adjuvanted porcine parvovirus preparations. This approach may be useful in estimating the antigen content of inactivated aluminum hydroxide adjuvanted veterinary vaccines and reducing the extent of required in vivo testing.

Formaldehyde inactivation of foot-and-mouth disease virus. Conditions for the preparation of safe vaccine

The inactivation of foot-and-mouth disease virus by formaldehyde was studied under different conditions, both as free virus and (as in routine vaccine production) after adsorption of the virus to aluminium hydroxide gel (alhydrogel). In the latter case infectivity was monitored after elution of the virus from the gel by isopycnic ultracentrifugation of the virus-alhydrogel mixture in CsCl. By this method good virus recoveries were obtained. Adsorption of the virus to alhydrogel (without formaldehyde) did not reduce infectivity significantly. Both adsorbed and non-absorbed virus lost infectivity at a rate of about one log10 per day (at pH 8.5, 25 degrees C--no formaldehyde). Kinetics of formaldehyde inactivation of adsorbed and non-adsorbed virus were also identical, with a fast reduction in the initial phase (in case of O1 and A10-virus approximately one log10/hour). After this initial phase inactivation became linear and rather slow (for O1 and A10-virus 0.2 log10/hour). No "tailing-off" was observed. Under standard conditions (0.04 per cent formaldehyde, pH 8.5, 25 degrees C) CD-virus was inactivated approximately 1.5 times faster than O1 and A10-virus. At 4 degrees C the inactivation of the three strains continued at about one log10/day. Increased lactalbumin hydrolysate concentrations reduced the inactivation rate, especially at the formaldehyde concentration of 0.02 per cent, which was originally applied. Quaternary amines like Tris strongly inhibited formaldehyde activity. These findings might explain some data of others who observed "tailing off". Analysis of formaldehyde inactivated antigen by SDS-PAGE and electrofocusing showed that extensive cross-linking occurs especially of VP1, probably with other virus proteins but also with non-virus proteins from the medium. VP2 and VP3 are less affected. Cross-linking was enhanced when the virus had been adsorbed to alhydrogel during inactivation. Progressive cross-linking was observed during storage of the vaccine at 4 degrees C, which also indicated that inactivation continued at this temperature. These data show that formaldehyde inactivated adsorbate vaccines can be safe.