Fatal infection of a novel canine/human reassortant H3N2 influenza A virus in the zoo-housed golden monkeys

Influenza A virus (IAV) is one of the most challenging pathogens that threaten human and animal health. In June 2022, seven golden monkeys ( Rhinopithecus roxellanaes ) developed flu-like symptoms in succession at a zoo in Jiangsu Province of China, two of which died of respiratory distress. All the swab samples from affected golden monkeys were tested positive for IAV. In the dead animals, the most notable involved organ is the lung, which manifested as emphysema and pulmonary parenchymatous carnification. Histopathological and immunostaining data supported a diagnosis of pulmonary infection with influenza virus. One strain of H3N2 virus, named A/golden monkey/Jiangsu/1/2022 (Gm-1), was isolated from the lungs of dead golden monkeys. Sequence and phylogenetic analysis revealed that its PB1 gene is most closely related to an influenza isolate obtained from human (A/Hong Kong/4801/2014), while the remaining 7 genes show 100% sequence identity with those of canine H3N2 virus (A/canine/Jiangsu/06/2010, JS06). Experimental infection of two rescued viruses (rGm-1 and rJS06) by reverse genetics in BALB/c mice revealed that the rGm-1 virus induced more persistent pathological damage in the lungs, and was less likely to be cleared, compared to the rJS06 virus. Further investigation indicated that human-origin PB1 could induce higher levels of proinflammatory cytokines than canine-origin PB1, which might be a contributing factor to pathobiological characteristics displayed by the rGm-1 virus. This study extends the host range of influenza viruses, and underscores the need for efficient biosecurity practices and enhanced surveillance efforts in the endangered species.