Chicken Infectious Anemia Virus Markedly Enhances the Pathogenicity of Infectious Bronchitis Virus–Infected Chickens

Chicken infectious anemia virus (CIAV) and infectious bronchitis virus (IBV) represent two of the most economically significant pathogens in the global poultry production. In recent years, coinfections involving CIAV and IBV have become increasingly prevalent in clinical scenarios across Southern China and globally. Nevertheless, the underlying synergistic pathogenic mechanisms remain largely elusive. This study establishes a coinfection model using specific pathogen-free (SPF) chickens infected with field-derived strains CIAV GDHY230813 and IBV CK/CK/GX/LA/071423 to systematically investigate pathogenic interactions. Our findings reveal a significant synergistic pathogenic effect through multiple experimental parameters between CIAV and IBV. Compared to the monoinfected controls, coinfected SPF chickens exhibited marked clinical deterioration: Survival rates decreased from 93.5% (CIAV) and 96% (IBV) to 76%, accompanied by profound growth retardation. In terms of viral transmission, coinfection markedly increased the viral shedding of both viruses through the respiratory and digestive tracts. At 14 days postinfection (dpi), the viral detection rates in both oropharyngeal and cloacal swabs soared to 100% in the coinfected group, up from 75% in the corresponding monoinfected groups. Moreover, coinfection facilitated the replication of IBV in the trachea, lungs, kidneys, and cecal tonsils. However, it did not lead to a significant change in the replication levels of CIAV. Pathological examinations revealed more severe lesions in the coinfected group, encompassing exacerbated atrophy of the thymus and bursa of Fabricius, splenomegaly, and heightened infiltration of inflammatory cells in various tissues. In summary, our findings suggest that coinfection with CIAV and IBV results in significant synergistic pathogenicity, worsening the severity of clinical disease and amplifying the potential for viral transmission. This study offers a vital theoretical foundation for comprehending the interactions between these two viruses and highlights the imperative of implementing integrated control strategies against both CIAV and IBV in chickens.