Isolation and molecular characterization of a new Muscovy duck parvovirus from Muscovy ducks in the USA

Between 1997 and 1999 several cases of a new disease in Muscovy ducks were reported in Pennsylvania, USA. The cases were characterized by locomotor dysfunction, weakness, recumbency, 40 to 60% morbidity and 10 to 40% mortality. The most characteristic microscopic lesions were moderate to severe degenerative rhabodomyopathy. In order to characterize the aetiological agent, virus isolation was attempted from the spleen, liver, heart, skeletal muscle and intestine by inoculation of 14-day-old Muscovy duck embryos with tissue homogenates. Deaths occurred on the second egg passage and parvoviruses were isolated by serial passage of allantoic fluid from dead embryos and then in Muscovy duck embryo fibroblast (MDEF) cultures. Parvovirus particles were observed in allantoic fluids and supernatants of MDEF cultures by transmission electron microscopy. Two genomic fragments, comprising 1108 nucleotides of the right open reading frame that codes for the structural viral proteins 1, 2 and 3, were amplified by polymerase chain reaction from one of the isolates, Muscovy duck parvovirus (MDPV)/PSU-31010. Comparison of this fragment with available sequences of other MDPV and related goose parvovirus (GPV) isolates showed that it had only 84.5% sequence identity with other MDPV isolates and 84.6% identity with the GPV isolates. This region shares over 99% identity among previously sequenced MDPV isolates and 95% identity among the related GPV isolates. This suggests that MDPV/PSU-31010 is divergent from all other sequenced MDPV and GPV isolates, and may represent a new group of avian parvoviruses.