Standardization of the equine infectious anemia immunodiffusion test and its application to the control of the disease in the United States.

In 1972 the US Department of Agriculture (USDA) established requirements that horses which had immunodiffusion antibody against equine infectious anemia could not be transported interstate. Forty-two states had regulations requiring that horses have a negative equine infectious anemia immunodiffusion test before movement. In order to standardize immunodiffusion testing, it was stipulated in the 1972 regulations that tests must be performed in approved laboratories. The approved laboratories were required to have personnel trained in the immunodiffusion test procedure, to follow the standard protocol, to use licensed reagents, successfully complete proficiency tests, and to report results to federal or state animal health officials. The number of approved laboratories was 160 in June 1983. The number of immunodiffusion tests performed in the United States increased from 82,777 in 1972 to 793,536 in 1977, and has remained at about that level. The percentage of positive samples has decreased from 3.9 in 1972 to 0.6 in 1982. Due to the laboratory standardization program, the reproducibility of test results has been excellent.