Ovine Injectable Lyophilisate: Viability Windows and Aseptic Freeze-Drying

The ovine Toxoplasma gondii live attenuated vaccine is manufactured by blending harvested S48 tachyzoites with a sucrose-gelatine stabiliser and filling the resulting suspension into Type I glass vials before freeze-drying. Upstream antigen bulk is produced in stirred-tank bioreactors with a working volume of 50 L using Vero cell monolayers, and harvest viability is assessed by flow cytometry before aseptic clarification with a release threshold of 90%. Batch release testing is anchored to EudraLex Volume 4 Annex 1 for aseptic processing, EudraLex Volume 4 Annex 2 for biological active substances, Ph. Eur. 2.6.1 for sterility, Ph. Eur. 2.6.7 for mycoplasmas, Ph. Eur. 2.6.14 for bacterial endotoxins, and 21 CFR 610.12 for sterility in the United States. The reconstituted dose is targeted at 2.0 mL containing no less than 10^5.0 viable tachyzoites, while the pre-lyophilisation blend is prepared at an antigen-to-stabiliser ratio of 1:4 to 1:6; process development data show that increasing stabiliser content above 1:6 raises the glass transition temperature of the maximally freeze-concentrated phase and prolongs primary drying without improving viability retention. On production scale, freeze-drying is conducted in 12 m² shelf lyophilisers with a freezing ramp of 0.5°C/min to −45°C held for 180 min, followed by primary drying at −25°C and 80 µbar for 2,400 min, and secondary drying at +20°C and 50 µbar for 600 min; product temperature during primary drying must remain below the collapse temperature of −34°C to avoid microcollapse. Residual moisture is controlled below 1.5%, bacterial endotoxin release is held at ≤0.5 EU/mL, and container closure integrity is verified by dye ingress after capping. Terminal finished products include 10-dose, 20-dose, and 50-dose lyophilisate vials reconstituted with water for injection for intramuscular administration to breeding ewes before mating.

Inactivated Toxoplasma gondii tachyzoite antigen is processed into oil-adjuvanted injectable emulsions for booster vaccination programmes where live parasite use is restricted by farm-level biosecurity protocols or where import permits require non-viable antigen. The compliance framework for this route includes Ph. Eur. 2.6.1 for sterility, Ph. Eur. 2.6.14 for bacterial endotoxins, Ph. Eur. 2.6.7 for mycoplasma testing on the antigen bulk, and VICH GL18(R2) for residual solvents in the oil phase. Filling is conducted in a Grade A unidirectional airflow zone with a Grade B background maintained to ISO 14644-1 class 5. The aqueous antigen phase is introduced at 20–30% v/v of the final emulsion, with antigen concentration adjusted to 10^6–10^8 inactivated tachyzoites per 2.0 mL dose; this is emulsified into a double oil adjuvant using a rotor-stator homogeniser equipped with a 20 mm generator and an emulsion vessel jacketed at 15–20°C. Mixing is performed as a one-pass high-shear step at 10,000–15,000 rpm under vacuum to reduce entrapped air, and inline laser diffraction targets a droplet size of D50 0.8–1.2 µm; batches exceeding 1.5 µm D90 show accelerated creaming and are rejected. Terminal finished products are ready-to-use injectable emulsions filled into 50 mL Type II glass vials or HDPE bottles, and published field data for this specific inactivated toxoplasma configuration remains more limited than for the live ovine lyophilisate.

Oral Granule and Powder Processing Below the Viability Threshold

Freeze-dried antigen prepared with mannitol or trehalose matrices is dry-blended into oral granules and powders for investigational oral immunisation of small ruminants. Because live tachyzoites are sensitive to water activity above 0.4 and temperatures above 40°C, only inactivated antigen or lyoprotected viable formulations with enteric protection can be considered for this route, and published data for this specific configuration is limited. Compliance for non-sterile oral solids is anchored to Ph. Eur. 2.9.36 for powder flow, Ph. Eur. 2.9.37 for bulk and tapped density, Ph. Eur. 2.9.40 for uniformity of dosage units, and Ph. Eur. 5.1.4 for microbiological quality of non-sterile oral preparations. The antigen-loaded fraction is added at 0.1–0.5% w/w of the total granule mass, equivalent to 1 × 10^5–1 × 10^6 inactivated tachyzoites per 2 g oral dose; when live tachyzoites are lyoprotected, a 1:9 antigen-to-carrier ratio is used before dry granulation. Processing is carried out in a bin blender at 6–12 rpm for 15–20 min under ≤20% RH, followed by roller compaction at 30–60 kN and sieving to a 250–850 µm granule fraction; loss on drying is held at ≤2.0% before packaging. Sachets are filled under nitrogen flush and sealed with moisture barrier foil. Terminal finished products include single-dose oral powders, 2 g granules in stick packs, and oral premix fractions for reconstitution into drench solutions.

Tablet and capsule intermediates containing freeze-dried Toxoplasma gondii antigen require dry granulation because wet granulation would expose the antigen to water activity above 0.4 and drying temperatures above 40°C, accelerating antigenicity loss or reducing viability. The process is controlled under Ph. Eur. 2.9.40 for uniformity of dosage units, Ph. Eur. 2.9.3 for dissolution of tablets and capsules, Ph. Eur. 2.9.1 for disintegration, and Ph. Eur. 5.1.4 for microbiological quality of non-sterile oral dosage forms. Formulation ratios range from 5% w/w to 15% w/w lyoprotected antigen in a directly compressible matrix of microcrystalline cellulose and dicalcium phosphate, delivering 1 × 10^5–1 × 10^7 inactivated tachyzoites per 250 mg tablet or 350 mg capsule; the matrix is lubricated with 1% w/w magnesium stearate. Compression is performed on a rotary tablet press at 5–15 kN, with target hardness 30–70 N and disintegration time of ≤15 min; capsules are filled on an intermittent-motion capsule filler with nitrogen purge. Enteric coating is applied to 8–12% weight gain using Eudragit L 30 D-55 to prevent acid degradation in the gastric compartment. Terminal finished products include enteric-coated tablets, hypromellose capsules containing powder or granules, and compartmentalised capsule-in-capsule designs for delayed antigen release; published data for this specific configuration is limited, and no compendial monograph currently exists for oral toxoplasma vaccine tablets.

Are Bait Vaccines for Definitive Felid Hosts Feasible Under Feed Hygiene Rules?

Oral bait matrices containing live attenuated Toxoplasma gondii tachyzoites are investigated as a route to reduce oocyst shedding in cats, the definitive host of the parasite. Production scale for this investigational route remains limited to freeze-dried bait pellets prepared in veterinary biologics facilities rather than commercial feed mills, because feed hygiene regulations were not written for live parasitic antigens. The relevant regulatory framework includes EU Regulation 183/2005/EC for feed hygiene, EU Regulation 2019/4 for medicated feed intermediates, and Directive 2002/32/EC for undesirable substances in animal feed; in the United States, 21 CFR 558.3 defines medicated feed article requirements but live vaccine baits fall outside routine feed additive approvals. Antigen incorporation rates are set at 1 × 10^6–1 × 10^7 viable tachyzoites per 20 g bait, with freeze-dried antigen pellet comprising 2–5% w/w of the bait mass; a 1:1 blend of gelatin and fish meal is used as the bait matrix to maintain palatability while limiting thermal damage. Downstream processing uses cold extrusion or compression at ≤37°C, followed by vacuum drying to water activity aw <0.4 and packaging in metallised pouches with oxygen scavenger; bait hardness is controlled at 10–30 N to survive field distribution without fracturing. Terminal finished products include freeze-dried bait pellets, gelatin capsule baits, and coated granule baits for targeted delivery to free-roaming cat populations; published data for this specific configuration is limited to experimental field trials and no harmonised compendial specification currently exists.

When Oral Drench Solutions Require Nitrogen Sparging and Viscosity Control

Antigen suspensions for oral drench administration are prepared as low-viscosity aqueous buffers with stabilisers, used for experimental mucosal vaccination of lambs and goat kids where injection is impractical. The route is controlled under Ph. Eur. 2.6.1 for sterility, Ph. Eur. 2.6.14 for bacterial endotoxins, and Ph. Eur. 2.2.3 for pH measurement. The antigen concentrate is diluted at 1:20 to 1:50 with a 0.1 M glycine buffer containing 2% w/v sucrose and 0.5% w/v sodium carboxymethylcellulose, yielding 1 × 10^5 tachyzoites or antigen units per 10 mL oral dose; pH is adjusted to 6.8–7.4 and viscosity is maintained at 5–25 mPa·s to allow safe passage through drenching nozzles. Mixing is performed in a closed stainless steel vessel with a bottom-mounted magnetic stirrer at 100–150 rpm under nitrogen sparging at 0.1–0.2 L/min to minimise oxidative damage; the suspension is then passed through a 100 µm screen and filled into amber Type III glass bottles with child-resistant closures. Terminal finished products include 10 mL and 20 mL oral drench solutions, 100 mL multi-dose bottles, and veterinary oral syringes for neonatal lambs.