PREDICTING THE NUMBER OF HERDS INFECTED WITH PSEUDORABIES VIRUS IN THE UNITED-STATES

Epidemiologic modeling of the Likely herd-to-herd transmission of pseu dorabies virus (PRV) was developed to assess the progress and potentia l for the PRV-eradication program in the United States. The herd-to-he rd transmission of PRV over a 20-year period (1933 to 2012) in the Uni ted States was simulated under various scenarios, which included varia ble program-funding levels and variable prevalences. A transition mode l (Markov process model) was used to predict yearly changes in herd pr evalence of PRV infection. Five mutually exclusive states of nature fo r herds were assumed: uninfected and not vaccinated; uninfected and va ccinated; known to be infected and not vaccinated; known to be infecte d and vaccinated; and infected, but not known to be infected. Three pr evalences for states in the United States were assumed: higher prevale nce, moderate prevalence, and lower prevalence. Three funding levels w ere assumed: no eradication program, continued funding at the current level, and increased funding of 25%. Estimates made by an expert panel for determining probabilities in the state-transition matrices were u sed. A model also was developed, and was considered to be the most opt imistic scenario likely under increased funding of 25%. The most optim istic estimates of the probabilities that still lay within the range o f estimates made by the expert panel were used for this model. Only th e optimistic transmission matrices allowed for total eradication of PR V. Using the optimistic matrices, ail states in the United States of A merica had moved into the moderate- or low-level risk status by the ye ar 2000. The longest time taken to achieve eradication was for the sta te of Iowa, where eradication was not achieved until 2012.