Resumen de Molecular, antigenic and pathological characterization of infectious bronchitis viruses isolated in spain
On the basis of the epidemiologic importance of IB in Spanish poultry industry, the clinical observations of frequent control failures of this disease, and the presence of IBV isolates which could not be serotyped by classical methods, new IBV variant isolates were suspected to be present in Spain in the last years. In a preliminary selection of the isolates to be investigated, based on partial sequence analyses, four Spanish IBV isolates were likely to be a distinct genotype. In order to determine whether these isolates formed a new serotype, in-depth molecular and antigenic studies were carried out in Study I. The four Spanish field isolates were demonstrated to form a new genotype together with Italy 02, an IBV sequence that had been released in GenBank database from a Russian laboratory. Serotyping further confirmed this group of viruses to be a new serotype. Thereby, it was considered interesting to better characterize IBV epidemiological situation in Spain, not only to determine epidemiologic significance of the new described serotype but also genetic and antigenic relationships among main IBV serotypes circulating in field. A large number of IB Spanish viruses, including viruses obtained in Spain over the last 14 years, were molecularly characterized in Study II. Genotyping based on the complete S1 gene sequence indicated that 4/91 serotype was the predominant serotype in Spain in the nineties, whereas Italy 02 was predominantly detected in the recent years. Detailed molecular studies identified apecific amino acids within S1 gene sequences of Italy 02 Spanish isolates and pointed out selection pressures. Furthermore, recombination analyses showed common recombination events among Spanish IBV isolates and pointed out isolates of the Italy 02 serotype to be more frequently involved in these events. More interestingly, recombination breakpoints were suggested to be associated with IG sequence motifs in the S1 gene of Italy 02 isolates. Finally, based on the increasing epidemiologic importance that this new serotype was acquiring all over Europe and particularly in Spain, in Study III pathological traits were investigated by infecting one-day old SPF chicks and adult SPF hens. Italy 02 tissue distribution and excretion patterns were investigated by RT-PCR and ISH. Nasal turbinates were pointed out as the primary replication site of IBV infection. RT-PCR results indicated that despite no renal disease was induced in adult hens it was likely that Italy 02 replicated in renal tissue of these birds, but probably at lesser extent than in young chickens. On the other hand, extensive and persistent replication was observed in rectum and cecal tonsil at both ages, which probably has important consequences in viral shedding and spreading patterns.
