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Barcelona ASFV Variant Was Missing About 9,800 DNA Bases

Wild boar looking toward the camera in Dilek Peninsula National Park, Turkey
Research: Genetics & genomics, Disease, parasites & microbiology

Whole-genome sequencing of African swine fever virus (ASFV) from eight wild boar (Sus scrofa) in the Barcelona outbreak identified a genetically distinct genotype II variant with a large deletion in its genome. About 9,800 DNA bases were missing compared with the standard Georgia 2007/1 reference genome, removing 21 protein-coding sequences.

The outbreak began with two dead wild boar confirmed with African swine fever on 26 November 2025, Spain’s first confirmed cases in more than 30 years. Researchers sequenced virus from those two animals and six further positive wild boar detected through February 2026. All six later genomes retained the same deletion and were highly similar to the first two, showing that this unusual genomic feature remained stable during the early outbreak.

The deletion removed genes involved in host–virus interactions

Most of the missing coding sequences belonged to multigene families involved in interactions between ASFV and its host. A separate six-marker comparison also placed the Spanish virus in a newly defined genetic group, group 29. The biological effect of the large deletion is not yet known, however, and the study does not show that it changed the virus’s virulence.

Origin and biological effect remain unresolved

The Barcelona variant clustered genetically near some early genotype II viruses from the Caucasus, but the authors stress that this does not demonstrate a direct epidemiological link. Its precise origin remains unresolved. The isolated emergence near Barcelona and the lack of continuity with other affected regions are consistent with a possible long-distance introduction mediated by human activity, but they do not identify a source.

During follow-up, 44 of 137 PCR-positive wild boar tested also had ASFV-specific antibodies. The authors say this is compatible with a more prolonged infection course than is typical for highly virulent genotype II viruses. Whether the 9.8-kb deletion contributes to that pattern remains unknown and will require experimental testing.

Sources and image credit

  1. Gallardo, C., Marcet-Houben, M., Agüero, M., Nieto, R., Casado, N., Soler, A., Ruano, M. J., Villalba, R., Fernández-Pinero, J., Simón, A., Pérez, C., Gómez, C., García, C., Labrador, M., Argilaguet, J., Coronado, L., Majó, N., Aguilera-Sepulveda, P., Aldea, I., et al. (2026). Genetically distinct African swine fever virus genotype II variant in wild boar, Spain, 2025–2026. Emerging Infectious Diseases, 32(9), 1497–1501.Open-access primary research article originally published 19 August 2026. Whole-genome sequencing and molecular follow-up of eight ASFV-positive wild boar from the Barcelona outbreak identified a stable approximately 9.8-kb deletion removing 21 coding sequences and a new six-marker genetic group, group 29. The deletion persisted in six later genomes. The origin and biological effect of the deletion remain unresolved.

Image: Wild boar (Sus scrofa) in Dilek Peninsula–Büyük Menderes Delta National Park, Turkey, 8 June 2020. Photo: Esme Ilgın Uçar / Wikimedia Commons. CC BY-SA 4.0. Representative species image; not an animal from the Barcelona ASF outbreak. · CC BY-SA 4.0 · Source

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