Features of the First Case of Foodborne Botulism Caused by Dual-Toxin Subtype A1(B5) in Spain.

The neurotoxin BoNT/B2 is the predominant subtype in foodborne and infant botulism cases in Spain. This study characterizes a novel case of foodborne botulism in Spain caused by a dual-toxin A1(B5) strain. A 64-year-old male presented with acute, progressive flaccid paralysis including diplopia, dysphagia, and respiratory failure. Although botulism was not initially suspected, the patient recovered with supportive care and without antitoxin administration. Genomic characterization confirmed the presence of both /A1 and silent /B5 genes. The /A1 gene was associated with an X+ neurotoxin gene cluster, while the silent /B5 gene was in an + cluster. Phylogenetic analysis of both /A1 and /B5 sequences showed 100% amino acid identity, respectively, to previously reported A1(B5) strains (e.g., CDC_69094, FE9504ACG). Multi-locus sequence typing (MLST) assigned the ST10, a genotype previously undetected in Spanish botulism cases, yet found in other European countries. This case highlights the importance of considering botulism in differential diagnosis due to its varied presentation and the significance of timely laboratory confirmation for effective management. The identification of this dual-toxin BoNT/A1(B5) X+/+ ST10 strain expands our understanding of epidemiology and genetic diversity in Spain.