Avipoxvirus in blackcaps (Sylvia atricapilla)

From July to September 2005, 1075 wild birds of 37 species were mist-netted at a location in the north-eastern part of the Czech Republic. The birds were examined for the presence of avipoxvirus lesions. This was demonstrated by electron microscopy in skin lesions in nine of 244 blackcaps (Sylvia atricapilla) examined (4% prevalence). Blackcaps skin bioptates were processed using the ultrathin section method. In skin bioptates, avipoxviruses were demonstrated in intracytoplasmic inclusions where, in addition to mature viruses, lipids and filamentous structures concentrated into large circular formations were found. The so-called additional inclusions were also found. These did not contain any virus components, and they served as the precursor of A-type intracytoplasmic inclusions. Blackcap avipoxvirus was isolated by passage on the chorioallantoic membrane of 9-day-old chicken embryos. The virus was successfully adapted after 11 passages (each passage lasted 5 to 7 days), at which time a marked changes in the form of tiny nodules 2 to 3 mm in diameter were observed on the chorioallantoic membrane. Further identification of field isolates and of the cultured virus was carried out using polymerase chain reaction and sequencing. Sequences were compared with consensus sequences of both canarypoxviruses and fowlpoxviruses. Our sequence was found to be 98.8% identical to the canarypox consensus sequence, but only 63% identical to the fowlpox consensus sequence. Our avipoxvirus sequence was proven to be significantly more closely related to canarypoxviruses than to fowlpoxviruses also by phylogenetic analysis.