Evolutionary dynamics of Bluetongue virus serotypes 3, 4 and 8 circulating in Italy, 2024-2025

Authors: PLEBANI, GLORIA - Università Degli Studi Di Teramo / University Of Teramo; PALOMBIERI, ANDREA - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; SGHAIER, SOUFIEN - Institut De La Recherche Vétérinaire De Tunisie / Veterinary Research Institute Of Tunis; GATTA, GARDENIA - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; HASSINE, THAMEUR BEN - The Directorate General Of Veterinary Services (DGSV); CURINI, VALENTINA - Università Degli Studi Di Teramo / University Of Teramo; CRESCI, MARTA - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; THABET, SARAH - Universite De La Manouba / University Of Manouba; PAROLINI, FRANCESCA - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; HAMMAMI, SALAH - Universite De La Manouba / University Of Manouba; ANCORA, MASSIMO - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; SPEDICATO, MASSIMO - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; DI SABATINO, DARIA - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; MARCACCI, MAURILIA - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst; Scroggs, Stacey; LORUSSO, ALESSIO - Istituto Zooprofilattico Sperimentale Dell'Abruzzo E Del Molise / Experimental Zooprofilattico Inst

Submitted to: Veterinaria Italiana
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2025
Publication Date: 12/31/2025
Citation: Plebani, G., Palombieri, A., Sghaier, S., Gatta, G., Hassine, T., Curini, V., Cresci, M., Thabet, S., Parolini, F., Hammami, S., Ancora, M., Spedicato, M., Di Sabatino, D., Marcacci, M., Scroggs, S.L., Lorusso, A. 2025. Evolutionary dynamics of Bluetongue virus serotypes 3, 4 and 8 circulating in Italy, 2024-2025. Veterinaria Italiana. https://doi.org/10.12834/vetit.3915.38031.1.
DOI: https://doi.org/10.12834/vetit.3915.38031.1

Interpretive Summary: Bluetongue virus (BTV) is a constant threat to ruminants in Europe due to repeated introductions and genome reassortment of co-circulating serotypes. In 2024-2025, Italy experiences a resurgence of BTV by three serotypes of BTV, BTV-3, BTV-4, and BTV-8. Whole genome sequencing revealed genetic reassortment of BTV-3 and BTV-4 indicating segment exchange between North African and European BTV lineages. BTV-8 populations remained constant with not evidence for reassortment, however, BTV-8 segments were found in BTV-3 and BTV-4 genomes suggesting stereotype-specific reassortment selection pressures. These findings highlight Italy as a key convergence point for BTV lineages in the Mediterranean basin and underscore the value of whole-genome surveillance for tracking viral introductions and reassortment dynamics.

Technical Abstract: Bluetongue virus (BTV) continues to pose a major threat to ruminant health in Europe, where repeated introductions, co-circulation of multiple serotypes and frequent reassortment shape its genomic diversity. During 2024–2025, Italy experienced a marked resurgence of bluetongue, driven mainly by BTV-3 and BTV-8. In this study, we performed whole-genome sequencing of BTV-3, BTV-4 and BTV-8 strains collected in Italy during 2024–2025 and integrated them with representative genomes from Italy and Tunisia generated over the previous decade. A total of 47 BTV whole-genome sequences were analyzed. Multiple reassortant genomic constellations were identified among BTV-3 and BTV-4 strains, reflecting extensive segment exchange between North African and European lineages. In contrast, all Italian BTV-8 genomes showed near-complete nucleotide identity with the contemporary BTV-8 FRA 2023 lineage, indicating nationwide circulation of a single strain. Despite its widespread diffusion, BTV-8 did not acquire heterologous genome segments, whereas its internal genes were frequently incorporated into BTV-3 and BTV-4 genomic backgrounds. These findings highlight Italy as a key convergence point for BTV lineages in the Mediterranean basin and underscore the value of whole-genome surveillance for tracking viral introductions and reassortment dynamics.