Duck viral infection escalated the incidence of avian pathogenic Escherichia coli in China.

Avian pathogenic Escherichia coli (APEC) causes high mortality in poultry flocks and often is complicated with viral infections, leading to large economic losses; however, little information is available on the epidemiological characteristics of this pathogen in ducks. Therefore, a systemic epidemiological investigation was performed on 325 duck farms from 13 provinces in China during the period of 1 April 2016 until 31 March 2018, covering 2 years. A total of 26 APEC strains were isolated from different farms in this study, and analysis showed that all of those isolates carried multiple virulence-associated genes and drug-resistance genes, which led to high pathogenicity (15/26), strong or moderate biofilm formation (24/26) and multidrug-resistant abilities (26/26). On the other hand, coinfection with APEC, H9 avian influenza virus (AIV) and Tembusu virus (TMUV) was very common on those farms (11/26), with APEC and TMUV sharing a similar morbidity peak (from May to September) and susceptibility (60% infections occurred in ducklings); thus, we speculated that the emerging TMUV infection escalated the APEC incidence in ducks. Finally, the data presented in this report enhance the current understanding of the epidemiology of APEC and different viral infections in ducks and provide additional insight into the critical factors that determine their pathogenicity. Meanwhile, the emergence of multidrug-resistant APEC strains and their coinfection with different viruses emphasize that preventive measures against such infections on poultry farms should be implemented immediately.