Avipoxvirus in blackcaps (Sylvia atricapilla)
Résumé
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 presence of avipoxvirus lesions. A presence of avipoxviruses was demonstrated by electron microscopy in skin lesions in 9 blackcaps (Sylvia atricapilla) of 244 examined (prevalence 4 %). Blackcaps skin bioptates were processed using the ultrathin sections method. In skin bioptates, avipoxviruses were demonstrated in intracytoplasmic inclusions where, in addition to mature viruses, there were found lipids and filamentous structures concentrated into large circular formations. 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 passages on chorioallantoic membrane (CAM) of 9 day old chicken embryos. The virus was successfully adapted after 11 passages (each passage lasted 5–7 days), at which time a marked change in the form of tiny nodules 2–3 mm in diameter was produced on the CAM. Further identification of field isolates and of the cultured virus was carried out by the use of polymerase chain reaction (PCR) and sequencing. Sequences were compared to consensus sequences of both canarypox and fowlpox viruses. 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 canarypox viruses than to fowlopox viruses also by phylogenetic analysis.
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