Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine

First Advisor

George W. Beran


The United States (US) national pseudorabies (PR) eradication program started with 5,813 known infected herds in January 1989 and ended 1990 with 6,637, 42% of them under cleanup plans. In between, 4,683 new infected herds were identified and 3,410 herds were cleaned up. During 1989, 6.0% of the US breeding swine population was surveyed with 4.0% being found to be positive. The surveillance went down to 5.3% but the positive rate went up to 4.4% during 1990. Swine movements and area spread were the two major means for PR virus spread. Most states have either feeder pig monitoring or qualified negative herd programs or both, covering 19.2% of the US herds. Traceback herd tests from reactors at first point of concentration was the most efficient case finding method, while area testing was advantageously used only in Iowa. Predictions on years to find and cleanup all PR infected herds have been calculated. Seventeen states are concluded to be free of PR; another seventeen states may require a minimum of 1 to 3 years; and eight other states may require a minimum of 4 to 6 years to find and cleanup their infected herds. However, Florida, Georgia, Iowa, Michigan, and Pennsylvania need to put more effort in order to meet the goal of eradicating PRV by the year 2000;A factor analysis based on the 1990 quarterly reports was conducted to analyze and evaluate state PR eradication progress in 30 states reported PR infected herds. Four factors, "prevalence", "producer participation", "case finding", and "regulatory" actions were found to be important in the PR eradication program. The last 3 factors functioned in association, thus PR eradication program activities were merged into a single "program factor". A "PR eradication index" was then generated by integrating the "prevalence factor" with the "program factor". The statistical model was constructed, with higher factor or index scores indicating a greater likelihood of eradication. Evaluations of indices and factors indicated that states with high scores in the "prevalence factor" and the "program factor" will be more likely to eradicate PR. In contrast, states with low scores in these 2 factors will present a challenge to the national PR eradication effort. These factors and indices can be used to monitor the eradication program in the future and provide guidance for decision making.



Digital Repository @ Iowa State University,

Copyright Owner

Ping-Cheng Yang



Proquest ID


File Format


File Size

347 pages