Porcine epidemic diarrhea virus introduction into the United States: Root cause investigation.

Porcine epidemic diarrhea (PED) was identified in the United States in the spring of 2013, and professionals from many parts of the U.S. swine industry responded rapidly to understand and control the newly emerging disease. In less than two months, the disease had spread to more than 200 herds in thirteen states. Experts from the US Department of Agriculture (USDA) engaged in laboratory diagnostics, analytic support, epidemiology expertise, and data management to facilitate the effort. By 2014, a great deal had been learned about the disease; however, the question of how it entered the United States remained unanswered. In 2014, USDA formed an investigative group to address the question and leverage current knowledge with resources and partnerships not readily available to non-federal investigators. The group formed collaborations with other government and non-government organizations and individuals, and followed many avenues of inquiry; ultimately arriving at a small number of scenarios that describe possible mechanisms for PED introduction. For a scenario to be plausible, it had to explain: contamination of a person or product in the source country, its transit and entry to the United States, rapid dispersal across a wide geographic area, and exposure/infection of pigs. It had to be compatible with findings of swine herd investigations and research studies. Potential products had to have been imported legally during the time prior to the beginning of the epidemic, or delivered to the United States through prohibited channels. Follow-up studies were initiated to gather more evidence for the most plausible scenarios. Of the scenarios, flexible intermediate bulk containers ("feed totes") used to transport bulk feed serving as fomites for movement of PED virus provided the simplest explanation for the accumulated findings of the investigation.

Historical, spatial, temporal, and time-space epidemiology of very virulent infectious bursal disease in California: a retrospective study 2008-2011.

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.