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Study Reports First Documented Avipoxvirus Infection in a Swift Species

Common swift in flight against a natural background
Research · Disease, parasites & microbiology

Avipoxvirus infection was documented in four juvenile Common Swifts (Apus apus) from three breeding sites in Lower Saxony, Germany, which the authors describe, to their knowledge, as the first documented cases in any swift species. The birds were about 30–35 days old when they arrived at a wildlife rescue centre in August 2024 with nodular, wart-like and crusted skin lesions on their wings.

The lesions were concentrated around the elbow, forearm and the skin between the outer primary flight feathers; the head, feet and mouth were unaffected. Histology — microscopic examination of the affected tissue — showed changes characteristic of avian pox. Electron microscopy directly revealed particles with the typical appearance of poxviruses, and PCR detected avipoxvirus DNA. A sequenced 176-base-pair fragment was identical to corresponding sequences from canarypox virus and shearwaterpox virus 2, but the authors could not determine the virus’s origin or transmission route.

Two swifts recovered as the skin lesions healed and were successfully released. In the other two, pox-related damage to the follicles — the tissue pockets from which the primary flight feathers grow — caused abnormal feather growth and loss. Because normal regrowth needed for flight could not be expected, those birds were euthanised.

The rescue centre had examined 920 Common Swifts between 2023 and 2025 and found comparable lesions only in these four birds. The authors therefore describe clinically apparent cases as apparently sporadic in the centre’s intake, while stressing that rescue-centre records cannot establish the true prevalence of avipoxvirus in wild swifts. Transmission from other wild birds through biting insects is considered possible but remains unconfirmed.

Sources and image credit

  1. Legler, M., Heenemann, K., & Gerhauser, I. (2026). Poxvirus Infections in Common Swifts (Apus apus). Veterinary Sciences, 13(8), 768.Primary open-access case report. Four juvenile Common Swifts from three Lower Saxony breeding sites had wing lesions supported as avipoxvirus infection by pathology, electron microscopy and molecular testing. Two recovered and were released; two were euthanised after damage to primary-flight-feather follicles made normal regrowth unlikely. The authors describe these as the first documented avipoxvirus infections in a swift species.

Image: Alexis Lours — wild Common Swift in flight, 18 July 2025. Source: Wikimedia Commons. CC BY 4.0. Representative healthy individual; not one of the birds in the German case report. · CC BY 4.0 · Source

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