Chicken infectious anemia virus (CIAV), Marek’s disease virus (MDV), reticuloendotheliosis virus (REV), and avian leukosis virus (ALV) are immunosuppressive pathogens of concern for poultry. To investigate the prevalence of immunosuppressive pathogens in diseased chickens and the interactions between different viral infections, 768 tissue samples collected from diseased chickens in Jiangsu Province, China were analyzed for CIAV, MDV, REV, and ALV using polymerase chain reaction. The detection rate of these four immunosuppressive pathogens was 55.99%, and the detection rates of CIAV, MDV, REV, and ALV were 29.95, 23.05, 9.90 and 23.44%, respectively. The detection rates of coinfection, dual infection, triple infection, and quadruple infection were 23.57, 17.45, 5.47 and 0.65%, respectively. The most common dual and triple infections were CIAV + ALV (detection rate: 5.08%) and CIAV + MDV + ALV (detection rate: 2.60%). The infection of chicken flocks with immunosuppressive pathogens in Jiangsu Province showed a decreasing trend from 2016 to 2022. There was a synergistic association between CIAV and REV or CIAV and ALV (P<0.01). Therefore, infections and co-infections with immunosuppressive pathogens are prevalent in chicken flocks in Jiangsu Province, China, and CIAV plays a critical role in co-infection, providing an important guide for the future control of these diseases.