RESUMO
In December of 2008 very virulent infectious bursal disease virus (vvIBDV) was identified in a commercial flock in northern California. Since then several other backyard and commercial facilities in California have had flocks affected by the same strain and other unique (previously unseen) strains of IBDV. Previous to this incident, very virulent infectious bursal disease (vvIBD) had never been identified in North America. Following the initial outbreak in 2008, California became the first state to undertake a voluntary surveillance effort to try to determine the geographical prevalence of vvIBD based on sequencing of a portion of the segment A region of the vvIBDV genome. To date we have complete geographical information on approximately 500 separate accessions representing approximately 1500 birds from over 200 commercial (-85% of the facilities) and backyard facilities (-15% of the facilities) throughout the state. Sequencing of targeted regions of both the segment A and segment B regions of the genome has revealed three distinct types of IBDV in California chickens. One type is genetically and in pathogenically consistent with vvIBDV. The second and third types only have a segment A region consistent with vvIBDV. Geographic information system mapping coupled with spatial-temporal cluster analysis identified significant spatial and time-space clustering; however, no temporal clustering was noted. The lack of temporal clustering coupled with negative vvIBDV results in tested avian wildlife implies that avian wildlife in California do not currently appear to play a significant role in vvIBDV transmission. In the voluntary surveillance that was done in the Central Valley of California, which has a high density of commercial poultry, no positive farms were found when 142 of 504 farms were sampled. Given this level of sampling, the confidence (probability) of detecting an affected commercial flock was calculated to be between 28% and 81% depending on whether one or five hypothetically affected farms were affected.
