Prevalence and co-infection of infectious tumour viruses in chickens in Shandong Province, China

Between September 2023 and June 2025, a total of 454 samples from poultry farms across Shandong Province with clinically suspected avian tumorigenic diseases were subjected to laboratory testing. Using an integrated diagnostic approach combining gross and microscopic examination with molecular detection (qPCR and conventional PCR), cases were confirmed positive only when both tumour lesions and the corresponding oncogenic pathogen were identified. Overall, 90 samples were confirmed positive, yielding a detection rate of 19.8%. Among all tested samples, Marek's disease virus (MDV) was detected in 33.9%, avian leukosis virus (ALV) in 19.9%, and reticuloendotheliosis virus (REV) in 3.9%. Notably, co-infections involving two or more viruses were frequently observed: 33 of the 90 positive cases (36.7%) exhibited mixed infections. This study represents the first comprehensive investigation in Shandong Province to systematically characterize the epidemiology of avian infectious tumorigenic diseases by integrating multi-source clinical and laboratory data, including viral genotyping. It reveals a previously underappreciated epidemiological feature – a high co-infection rate of 36.7% among confirmed cases. Compared with prior regional studies, this work is distinguished by its larger sample size (n = 454), broader pathogen screening panel, and rigorous diagnostic criteria. Additionally, it delineates the genetic profiles of circulating oncogenic virus strains and identifies key epidemiological risk drivers, such as flock age, biosecurity level, and vaccination history, thereby providing evidence-based foundations for developing integrated prevention and control strategies to mitigate economic losses in the poultry industry.RESEARCH HIGHLIGHTS The co-infection rate of infectious tumour disease in chickens is 37% in China.The incidence rate is the highest in Dezhou City.