Avian leukosis and reticuloendotheliosis viruses: biology, epidemiological risks, and the need for molecular surveillance in Kazakhstan

Background and Aim. Avian leukosis virus (ALV) and reticuloendotheliosis virus (REV) induce severeimmunosuppression and neoplastic processes, increasing susceptibility to concurrent infections and causing substantial hidden economic losses. Despite active viral circulation in neighboring countries (e.g., China, Russia), epidemiological data for Kazakhstan remain scarce. This review aims to synthesize current knowledge on retroviral biology, raise awareness of this hidden threat among veterinary professionals, and justify the need for systematic control at poultry facilities.Material and Methods. A comprehensive analysis of current scientific literature addressing the biology, classification, life cycle, and molecular mechanisms of retrovirus-host cell interactions was conducted. The role of exogenous and endogenous retroviruses in the development of infectiousand oncological diseases was examined. Additionally, available information on the epizootiological situation in countries bordering Kazakhstan was reviewed, alongside contemporary approaches to the diagnosis, therapy, and prevention of retroviral infections.Results. ALV and REV exhibit high genetic variability and establish persistent infections via host genome integration. These infections often progress subclinically: virus-induced lesions remain undetected, and secondary outbreaks are frequently misattributed to vaccine failure. The broad hostrange and active pathogen circulation in border regions pose a high risk of introduction into Kazakhstan,exacerbated by the current lack of systematic molecular epidemiology monitoring.Conclusion. Implementing continuous molecular-genetic monitoring of avian retroviruses in Kazakhstan is critical to ensure poultry biosecurity, mitigate economic losses, and develop effective disease control strategies.