A Newcastle disease outbreak in backyard and free-range poultry in Slovenia

Žlabravec, Zoran (author), Slavec, Brigita (author), Dovč, Alenka (author), Hari, Aleksandra (author), Račnik, Joško (author), Maurer Wernig, Jedrt (author), Giussani, Edoardo (author), Palumbo, Elisa (author), Varotto, Maria (author), Monne, Isabella (author), Krapež, Uroš (author)

Newcastle disease (ND) is a highly contagious and economically important viral disease of poultry, caused by virulent strains of Orthoavulavirus javaense (OAVJ). In Slovenia, vaccination is mandatory in commercial poultry and selected avian species, whereas backyard and free-range flock remain largely unregulated. In January and February 2025, two unrelated backyard and free-range flock of laying hens experienced acute outbreaks with severe clinical signs, increased mortality and distinct gross necropsy findings (haemorrhages in the mucosa of the gastrointestinal tract, multifocal pale foci in the liver, atrophy to enlarged hyperaemic spleen, oophoritis and salpingitis). OAVJ was detected in cloacal, oropharyngeal, and brain samples from both outbreaks using real-time RT-qPCR. Analysis of complete fusion (F) gene revealed identical nucleotide sequences in both outbreaks, with the cleavage site motif, characteristic of velogenic strains (amino acid sequence 112RRQKR116 at the C-terminus of the F2 protein and F at residue 117, the N-terminus of the F1 protein). Further phylogenetic analysis of the F gene demonstrated that both viruses belong to class II, sub-genotype VII.1.1, showing 99.6–100% identity with strains recently detected in Poland. The hemagglutinin-neuraminidase (HN) glycoprotein comprised 571 amino acids, consistent with genotype VII viruses, with several amino acid substitutions previously associated with functional relevance. These results highlight that, despite the absence of ND in Slovenia for more than three decades, local poultry populations remain highly susceptible to the introduction of the virus, especially in backyard flocks where monitoring and disease control are difficult to implement. Although a virulent virus was confirmed in both outbreaks, no further spread to other poultry holdings was detected.

• Language: English
• Keywords: backyard poultry, free-range poultry, genotype VII.1.1, Newcastle disease, Orthoavulavirus javaense, Slovenia
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: VF - Veterinary Faculty
• Publication status: Published
• Publication version: Version of Record
• Publication date: 01.01.2026
• Year: 2026
• Number of pages: 8 str.
• Numbering: Vol. 13
• PID: 20.500.12556/RUL-185576
• UDC: 616:579:636.5:579.62
• ISSN on article: 2297-1769
• DOI: 10.3389/fvets.2026.1803248
• COBISS.SI-ID: 280943363
• Publication date in RUL: 14.08.2026

Record is a part of a journal

• Title: Frontiers in veterinary science
• Shortened title: Front. vet. sci.
• Publisher: Frontiers Media S.A.
• ISSN: 2297-1769
• COBISS.SI-ID: 3969402

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: dvoriščna perutnina, dvoriščna perutnina, prostorejska perutnina, genotip VII.1.1, atipična kokošja kuga, Newcastleska bolezen, Orthoavulavirus javaense, Slovenija

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P4-0092-2020
• Name: Zdravje živali, okolje in varna hrana

• Funder: EC - European Commission
• Project number: 101201937-EURL-AI-ND
• Name: Grant agreement no. 101201937-EURL-AI-ND