Avian circoviruses and hepadnaviruses identified in tissue samples of various waterfowl.

North America is home to over 40 species of migratory waterfowl. Utilizing tissue and cloacal-swab sampling from hunter-harvested carcasses in 2021-2023, we identified circular DNA viruses associated with 116 waterfowl samples from nine species (American wigeons, Mexican ducks, northern shovelers, northern pintails, canvasbacks, mallards, American black ducks, gadwalls, and green-winged teals). We determined the genome sequences of viruses in the families Circoviridae (n = 18) and Hepadnaviridae (n = 2) from the 13 virus-infected birds. The 18 circoviruses can be classified into four circovirus lineages: duck circovirus, wigfec circovirus 1, and two new lineages, marcaroli circovirus and spata circovirus. The new circovirus lineages identified are most closely related to waterfowl circoviruses based on the pairwise identities and phylogenetic analyses of full genomes, replication-associated protein, and capsid protein sequences. The two identified hepadnavirus genomes are part of the duck hepatitis B virus lineage sharing >89% identity with known ones.