Evaluating the Biochemical and Haematological Safety of the Histoplasma capsulatum var. farciminosum '8ZH' Vaccine in Foals.

BACKGROUND: Epizootic lymphangitis (EEL), caused by Histoplasma capsulatum var. farciminosum (HCF), is a neglected equine fungal disease lacking effective vaccines. The newly developed inactivated '8ZH' vaccine requires safety validation in the target species. OBJECTIVES: To evaluate the biochemical, haematological and clinical safety of the inactivated HCF '8ZH' vaccine in foals. METHODS: A controlled, single-blinded study was conducted on 30 clinically healthy foals (4-6 months), randomized into vaccinated (n = 15) and control (n = 15) groups. Vaccinated animals received a 5 mL intramuscular dose (10 mg antigen, MONTANIDE GEL 01 PR adjuvant) on Day 0 and a booster on Day 21. Clinical observations (temperature, appetite, behaviour, injection site) were recorded daily. Blood was collected at baseline and on Days 7, 14, 21, 35 and 42 for biochemical, haematological and acute-phase protein analysis. Data were analysed using repeated measures ANOVA. RESULTS: No severe or adverse reactions were observed. Mild, transient injection-site swelling (< 4 cm) occurred in three vaccinated foals and resolved spontaneously. All animals maintained normal temperature and appetite. AST showed a transient increase on Day 14 (p = 0.04); WBC also rose (p = 0.03), indicating a typical immune response. Other parameters, including ALT, GGT, creatinine, total bilirubin and acute-phase proteins (SAA, fibrinogen, haptoglobin), remained within physiological limits. No statistically significant long-term deviations or toxic effects were noted. CONCLUSIONS: The inactivated HCF '8ZH' vaccine demonstrated a favourable safety profile in foals. These results support its continued development for use in EEL prevention programs.