Development of a live monovalent vaccine candidate for bovine trichophytosis

Vaccination against bovine trichophytosis

Abstract

The purpose of this study was to isolate Trichophyton verrucosum from naturally infected calves, characterize it phenotypically, and evaluate a live monovalent vaccine candidate against bovine trichophytosis. The study was conducted in the Mycology laboratory of Vetinvest Innovative Enterprise LLP. A total of 100 calves from farms located in different regions of Kazakhstan were clinically examined for dermatophytosis. Skin and hair samples were collected from affected areas for isolation and characterization of T. verrucosum. In addition, haematological changes in calves, comparison of protective efficacy between field isolates and reference strain in rabbits, vaccine protective efficacy, therapeutic efficacy, and safety assessment in rabbits, and field evaluation of developed vaccine in naturally infected calves were also performed. Clinical examination revealed dermatophyte lesions in 45 calves, whereas laboratory confirmation revealed only 40 calves as dermatophyte positive, with the majority displaying mild localized lesions. The infected calves showed a significant increase in erythrocyte count, haemoglobin concentration, and haematocrit value, with reduced lymphocyte percentages. The vaccine formulation developed from field isolates of T. verrucosum showed 70% protective efficacy after experimental challenge at an immunizing dose of 20 million microconidia/cm3 with respect to the reference strain T. verrucosum F-02. Since the reference strain demonstrated 100% protective efficacy in rabbit model, it was selected for vaccine preparation. It provided complete protection in experimentally infected rabbits at a vaccine dose of 20.0 million microconidia/cm3, with detectable anti-Trichophyton IgG levels 10 days post vaccination, suggesting humoral immune response induction. Post-vaccination mild and short-lived local inflammatory reactions were observed in rabbits for three days. Field evaluation of the vaccine revealed clinical resolution of visible lesions in all vaccinated calves with mild local reactogenicity during the observation period. In conclusion, results demonstrated significantly favourable immune and clinical responses to T. verrucosum F-02-based live monovalent vaccine candidate with short-term tolerable safety profile under field conditions of the present study. However, the results should be cautiously interpreted and extrapolated because of small sample size and lack of confirmation of isolates at the molecular level.