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.

Pseudorabies (PRY), a disease primarily of swine, is present world-wide with a few exceptions. Economic losses from PRY infection can occur from mortality in preweaned pigs, abortions and other reproductive failures in sows, and reduced performance in market hogs.In a recent issue of the Journal, Ebel, Hornbaker, and Nelson (EHN) estimate welfare changes from PRY eradication in the United States. Their method builds on that of Lichtenberg, Parker, and Zilberman (LPZ). EHN correctly argue that LPZ omit part of producer surplus in calculating the welfare effects of a policy change. However, EHN incorrectly argue that LPZ's equations understate the producer surplus change from a downward supply shift.In this comment, we show that LPZ's equations actually overstate the producer surplus change and that EHN's correction of LPZ's equations compounds the overstatement. The error in ERN's equation for producer surplus change, combined with a miscalculation of that portion of producer surplus, results in a substantial overestimate of the economic benefits of the PRY program. We also discuss the implications of EHN basing the model on the prevalence rather than the incidence of disease and the need to discount the cost of the PRY program when comparing program cost to discounted program benefits. Measuring Change in Producer SurplusLPZ use first-order and market equilibrium conditions to solve for price and quantity changes among regionally disaggregated producers in a single market. From these price and quantity changes, LPZ measure producer surplus change as'Producer surplus change is illustrated in figure 1. The revenue change resulting from a downward shift in marginal cost (from MC to MC'), and the resulting market price decrease, is correctly measured as CDEFG -ABEFG. CDEFG -ABEFG corresponds to (P + dP)(Q + dQ) -PQ in (1), where dP is a negative change and dQ is a positive change. CDEFG -ABEFG simplifies to CD -AB. LPZ's measure of cost change is CDH -BCFHI. CDH -BCFHI corresponds to PdQ + dCfY . (Q + dQ) in (l), where dC is a negative change. The latter simplifies to D -BFI. Subtracting cost change from the revenue change gives LPZ's measure of producer surplus change, represented by CFI -A. EHN incorrectly refer to LPZ's measure of producer surplus change as F -A.EHN attempt to measure true producer surplus change (CF -A) as J In (1) and the equations that follow, dP refers to the price change resulting from a marginal cost shift. This is consistent with LPZ's notation. EHN use dP to denote vertical movement along the marginal cost curve when calculating its slope.

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