Turkey Coronavirus: Current Knowledge, Critical Gaps, and Future Directions in Transmission Biology and Pathogenesis.

Turkey coronavirus (TCoV) is an enteric gammacoronavirus that has become a re-emerging pathogen of major economic importance in commercial turkey production. First identified in the 1970s, TCoV continues to circulate endemically and periodically resurges as a primary viral contributor to poult enteritis complex (PEC) and poult enteritis mortality syndrome (PEMS). The continuous need to understand TCoV is highlighted by its severe enterotropism, quick fecal-oral transmission and capacity to propagate covertly among older turkeys and spillover hosts like chickens. Despite more than fifty years of research, key aspects of TCoV pathogenesis and ecology remain unresolved, including receptor usage, host-range determinants, age-dependent susceptibility, environmental persistence and the evolutionary origins of its highly recombinant genome. These persistent gaps are mostly caused by TCoV's absence of a reliable in vitro culture system, which restricts the use of recent advances in virology, glycomics, whole genome sequencing, and reverse genetics techniques that have revolutionized research on other coronaviruses. With current technological advancements, and after nearly a decade-long gap in research publications, the field is now regaining momentum and is positioned to revisit fundamental questions that were previously inaccessible. The USPOULTRY Research Initiative recently designated TCoV as a top research priority because of its influence on flock performance, production costs and supply-chain stability. Hence, this review summarizes current knowledge on TCoV epidemiology, evolution, transmission biology, pathogenesis, diagnostics, industry impact and outlines the critical research gaps necessary to be addressed for the long-term sustainability of the turkey industry.