engleski

Isolation and molecular biological investigations of avian poxviruses from chicken and turkey in Croatian flocks

Fowl pox is a common disease of chickens and turkeys with economic importance to the poultry industry. Disease prevention is achieved by vaccination with live fowl poxvirus (FPV) or pigeon poxvirus. In recent years, numerous outbreaks have been reported in vaccinated flocks, suggesting that these vaccines are often not effective. Several hypotheses on possible cause for re-emergence are discussed, beside possible alternation in the pathogenicity and virulence of recent isolates, speculation on the modification in the biological phenotype of FPV due to integration of Reticuloendotheliosis virus (REV) in their genome were published. Because REV has been associated with immunosuppresion, its presence in the genome of FPV seems to play an important role in the pathogenesis of fowl pox and prolongs persistence of FPV in the bird population. In 2002 several outbreaks of avian pox were observed in North Croatia. Four strains of avian pox viruses were isolated from cutaneous lesions by inoculation of embryonated chicken eggs on the chorioallantoic membranes (CAM). The resulting proliferative CAM lesions contained eosinophilic cytoplasmic inclusion bodies. One isolate originated from a meat turkey flock and 2 strains were isolated from layers. The 4th one originated from a small pigeon population located in the same area. The further identification and differentiation of the 4 various avian poxviruses were carried out by the use of a polymerase chain reaction (PCR) combined with restriction enzyme analysis (REA). Using one primer set, which framed a region within the fowlpox virus (FPV) 4b core protein gene, it was able to detect avian poxvirus specific DNA from all 4 tested isolates. PCR results revealed no recognizable differences in size of amplified fragments between the different avian poxviruses from chicken, turkey and pigeon. Restriction enzyme analysis of PCR products using NlaIII showed the same cleavage pattern for turkey and chicken isolates and a different one for the pigeon isolate. Further examinations were carried out to determine the possible integration of Reticuloendotheliosis virus (REV) in the genome of isolated avian poxviruses. For this purpose a multiplex polymerase chain reaction for direct detection of FPV and REV was carried out. The obtained results revealed that REV was present in chicken’ s and turkey’ s strains of poxviruses, while the pigeon isolate was negative. The pathogenicity of these four poxviruses from turkey, hens and pigeon was unusually high causing mortalities between 29% (turkey) and 10 % (pigeon). The source of REV contamination is not certain. It is not known whether the vaccine strain used in Croatia is contaminated or REV is from natural infection. The immunosuppression caused by REV is stressed to be responsible for high mortality seen in chickens and turkey flocks.

avian poxvirus ; chicken ; turkey

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