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

TL;DR

This study shows that a new vaccine for a fungal disease in horses is safe for young foals, with no serious side effects.

Contribution

The study provides first-time safety validation of the inactivated HCF ‘8ZH’ vaccine in foals.

Findings

No severe adverse reactions were observed in vaccinated foals.

Mild, transient injection-site swelling occurred in three foals but resolved spontaneously.

Biochemical and haematological parameters remained within normal limits, indicating vaccine safety.

Abstract

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.

To evaluate the biochemical, haematological and clinical safety of the inactivated HCF ‘8ZH’ vaccine in foals.

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.

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.

The inactivated HCF ‘8ZH’ vaccine demonstrated a favourable safety profile in foals. These results support its continued development for use in EEL prevention programs.

This study assessed the biochemical and haematological safety of the inactivated Histoplasma capsulatum var. farciminosum ‘8ZH’ vaccine in foals. No adverse clinical signs or significant changes in liver, kidney or acute‐phase protein markers were observed. The results support the vaccine's safety and suitability for further immunogenicity evaluation in equine epizootic lymphangitis control.

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