Skip to content

Black-headed Gull Sample Yielded the Longest Known Calicivirus Genome

Black-headed gull in winter plumage flying over open water
Research: Genetics & genomics, Disease, parasites & microbiology

A faecal sample collected from a black-headed gull (Chroicocephalus ridibundus) in Hungary in 2018 yielded a taxonomically novel avian calicivirus genome. Caliciviruses are small RNA viruses found in a range of vertebrates, including birds. The genome report, published on 2 September 2026, described an 8,845-nucleotide sequence that the authors consider the longest calicivirus genome known to date. Recovering the viral genome shows that its genetic material was present in the faecal sample; the study did not investigate whether the gull was ill from the virus.

Long RNA structures made the genome unusual

The unusual length mainly came from long untranslated regions at both ends of the RNA genome. At the 5′ end, the researchers predicted a type IV internal ribosome entry site, or IRES — a structured RNA region that can help start protein production through a non-standard translation mechanism. Caliciviruses usually have short untranslated ends, but several avian lineages have much longer 5′ regions containing IRES structures. The Hungarian genome also carried an s2m-like motif in its 3′ untranslated region, a small conserved RNA structure found in several virus families.

Too divergent for any recognized genus

The major capsid protein VP1 was highly divergent from the recognized calicivirus genera, sharing less than 26% amino-acid identity with their members. Phylogenetic analyses placed the strain within a genetically diverse bird-origin calicivirus lineage that is not assigned to any accepted genus. The authors suggest that the Hungarian virus and a related gull calicivirus from New Zealand could represent founding members of a new genus, provisionally called “Birovirus”; this remains a taxonomic proposal rather than a formal genus assignment.

The researchers also screened ten additional gull faecal samples from Hungary with targeted RT-PCR, a method used here to look specifically for the virus’s RNA sequence, but none was positive for the novel calicivirus. The study therefore establishes a complete and unusually divergent genome from one black-headed gull sample, while the frequency of this lineage among gulls remains unresolved.

Sources and image credit

  1. Reuter, G., Balázs, B., Mátics, R., Boros, Á., & Pankovics, P. (2026). Novel avian calicivirus genome with type IV internal ribosomal entry site (IRES) in black-headed gull (Chroicocephalus ridibundus) in Hungary.Primary open-access genome report published 2 September 2026. A black-headed gull faecal specimen collected in Hungary in 2018 yielded an 8,845-nucleotide calicivirus genome, the longest known to the authors. It contained a predicted type IV IRES at the 5′ end and an s2m-like motif at the 3′ end; VP1 divergence placed the strain outside all recognized calicivirus genera. Ten additional gull faecal samples were negative by targeted RT-PCR.

Image: Black-headed gull at Klydesøen, Amager, Denmark, 4 March 2018. Photo: Donald Hobern / Wikimedia Commons / Flickr. CC BY 2.0. Representative species image; not the gull sampled in Hungary. · CC BY 2.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

Genetics & genomics

SPECIES IN THIS STORY

Species in this story

Black-headed Gull Chroicocephalus ridibundus Explore species

Independent research and conservation news archive

Did you find this information useful?

Wildlife Vagabond is independently built and maintained. Voluntary support helps cover source verification, hosting and continued work on research and conservation news.

Support Wildlife Vagabond

The news archive will remain freely available.